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Connections of the parabrachial nucleus with the nucleus of the solitary tract and the medullary reticular formation in the rat
Abstract
We examined the subnuclear organization of projections to the parabrachial nucleus (PB) from the nucleus of the solitary tract (NTS), area postrema, and medullary reticular formation in the rat by using the anterograde and retrograde transport of wheat germ agglutinin‐horseradish peroxidase conjugate and anterograde tracing with Phaseolus vulgaris ‐leucoagglutinin. Different functional regions of the NTS/area postrema complex and medullary reticular formation were found to innervate largely nonoverlapping zones in the PB.
The general visceral part of the NTS , including the medial, parvicellular, intermediate, and commissural NTS subnuclei and the core of the area postrema, projects to restricted terminal zones in the inner portion of the external lateral PB, the central and dorsal lateral PB subnuclei, and the “waist” area. The dorsomedial NTS subnucleus and the rim of the area postrema specifically innervate the outer portion of the external lateral PB subnucleus. In addition, the medial NTS innervates the caudal lateral part of the external medial PB subnucleus.
The respiratory part of the NTS , comprising the ventrolateral, intermediate, and caudal commissural subnuclei, is reciprocally connected with the Kölliker‐Fuse nucleus, and with the far lateral parts of the dorsal and central lateral PB subnuclei. There is also a patchy projection to the caudal lateral part of the external medial PB subnucleus from the ventrolateral NTS.
The rostral, gustatory part of the NTS projects mainly to the caudal medial parts of the PB complex, including the “waist” area, as well as more rostrally to parts of the medial, external medial, ventral, and central lateral PB subnuclei.
The connections of different portions of the medullary reticular formation with the PB complex reflect the same patterns of organization, but are reciprocal. The periambiguus region is reciprocally connected with the same PB subnuclei as the ventrolateral NTS; the rostral ventrolateral reticular nucleus with the same PB subnuclei as both the ventrolateral (respiratory) and medial (general visceral) NTS; and the parvicellular reticular area , adjcent to the rostral NTS, and with parts of the central and ventral lateral and the medial PB subnuclei that also receive rostral (gustatory) NTS input. In addition, the rostral ventrolateral reticular nucleus and the parvicellular reticular formation have more extensive connections with parts of the rostal PB and the subjacent reticular formation that recieve little if any NTS input.
The PB contains a series of topographically complex terminal domains reflecting the functional organization of its afferent sources in the NTS and medullary reticular formation.
... The Kölliker-Fuse nucleus receives input from the pre-Bötzinger and Bötzinger complexes (Ezure et al., 2003;Tan et al., 2010;Yang and Feldman, 2018), and from several central chemoreceptor areas: the NTS (Loewy and Burton, 1978;Herbert et al., 1990;McGovern et al., 2015b), retrotrapezoid nucleus (Rosin et al., 2006;Bochorishvili et al., 2012;Silva et al., 2016b), and cerebellar fastigial nucleus (Fujita et al., 2020). In addition, the Kölliker-Fuse nucleus also receives input from the rVRG (Lipski et al., 1994;Yokota et al., 2016), cVRG (Holstege, 1989;Jones et al., 2016), periaqueductal gray (Trevizan-Baú et al., 2021b), spinal trigeminal nucleus (Panneton et al., 2006;Zhang et al., 2018), paratrigeminal nucleus (Saxon and Hopkins, 1998), pedunculopontine tegmental nucleus (PPTg) (Lima et al., 2019b), and vestibular nuclei (Shi et al., 2021). ...
... In addition to the extensive visceral inputs, the caudal NTS also receives central input, in particular from other regions of the NTS, lateral and paraventricular hypothalamus and central amygdala (Geerling et al., 2010;Ruyle et al., 2019;Gasparini et al., 2020), but also from the pre-Bötzinger complex (Tan et al., 2010;Koshiya et al., 2014;Yang and Feldman, 2018), Bötzinger complex Fedorko and Merrill, 1984;Livingston and Berger, 1989;Ezure et al., 2003), rVRG (Yamada et al., 1988;Ellenberger et al., 1990a;Zheng et al., 1998), Kölliker-Fuse nucleus (Fulwiler and Saper, 1984;Song et al., 2012a;Geerling et al., 2017), retrotrapezoid nucleus (Rosin et al., 2006;Bochorishvili et al., 2012), caudal raphe (Brust et al., 2014), bed nucleus of the stria terminalis (Gasparini et al., 2020), lateral and medial parabrachial nuclei (Saper and Loewy, 1980;Herbert et al., 1990;Bianchi et al., 1998), periaqueductal gray , spinal trigeminal nucleus (Panneton et al., 2006), paratrigeminal nucleus (Saxon and Hopkins, 1998;de Sousa Buck et al., 2001;McGovern et al., 2015b;Driessen et al., 2018), as well as from insular and infralimbic areas of the cerebral cortex (Gasparini et al., 2020; Figure 5C). Evidence for significant projections from the cerebellum to the NTS is currently lacking (Teune et al., 2000;Gasparini et al., 2020). ...
... As mentioned above, strong and direct projections from the NTS to the phrenic nucleus have been reported, while the NTS targets also the upper airway motor nuclei (Loewy and Burton, 1978;Norgren, 1978;Beckstead et al., 1980;Núñez-Abades et al., 1990;Hayakawa et al., 2000;Kawai, 2018;Guo et al., 2020). Other target areas are the pre-Bötzinger complex (Yang et al., 2020), Bötzinger complex (Gang et al., 1995), PiCo , lateral parafacial nucleus (Biancardi et al., 2021), cVRG (Loewy and Burton, 1978;Beckstead et al., 1980;Gerrits and Holstege, 1996), retrotrapezoid nucleus (Rosin et al., 2006;Lima et al., 2019b), locus coeruleus (McGovern et al., 2015b;Kawai, 2018), dorsal raphe (Peyron et al., 2018), lateral, paraventricular and dorsomedial hypothalamus (King et al., 2012;McGovern et al., 2015b;Kawai, 2018), bed nucleus of the stria terminalis and central amygdala (Shin et al., 2008;Bienkowski and Rinaman, 2013;McGovern et al., 2015b;Ni et al., 2016;Kawai, 2018), lateral and medial parabrachial nuclei (Loewy and Burton, 1978;Beckstead et al., 1980;Herbert et al., 1990;McGovern et al., 2015b;Hashimoto et al., 2018;Kawai, 2018;Yu et al., 2022), periaqueductal gray (Herbert and Saper, 1992;Kawai, 2018), spinal trigeminal nucleus (Loewy and Burton, 1978;McGovern et al., 2015b), pedunculopontine tegmental nucleus (PPTg) (Steininger et al., 1992), cerebellum (Batini et al., 1978;Somana and Walberg, 1979b;Saigal et al., 1980b;Fu et al., 2011), and inferior olive (Loewy and Burton, 1978;McGovern et al., 2015b; Figure 5C). ...
Respiration is a brain function on which our lives essentially depend. Control of respiration ensures that the frequency and depth of breathing adapt continuously to metabolic needs. In addition, the respiratory control network of the brain has to organize muscular synergies that integrate ventilation with posture and body movement. Finally, respiration is coupled to cardiovascular function and emotion. Here, we argue that the brain can handle this all by integrating a brainstem central pattern generator circuit in a larger network that also comprises the cerebellum. Although currently not generally recognized as a respiratory control center, the cerebellum is well known for its coordinating and modulating role in motor behavior, as well as for its role in the autonomic nervous system. In this review, we discuss the role of brain regions involved in the control of respiration, and their anatomical and functional interactions. We discuss how sensory feedback can result in adaptation of respiration, and how these mechanisms can be compromised by various neurological and psychological disorders. Finally, we demonstrate how the respiratory pattern generators are part of a larger and integrated network of respiratory brain regions.
... These receptors appear to be connected to small-diameter fibers, mostly unmyelinated vagal fibers that respond to the presence of hypertonic NaCl with a mean latency of around 10-20 s [39][40][41][42]. The first relay of visceral-vagal information from post-oral segments of the digestive system takes place in caudal segments of the nucleus of the solitary tract (NST), from which it is remitted to other brain structures [27,45,46]. Na absorption into the circulatory system largely takes place in the distal small bowel and the colon [47][48][49]. ...
... The CVO AP is located ventromedial to the fourth ventricle [46,68,69], but its involvement in salt intake is less well understood than that of SFO [58]. The activation of c-Fos in the AP after hypertonic saline injections but not in an Na-deprived state [70] suggests that it forms part of NaCl intake-inhibiting circuits [8]. ...
... The NST constitutes the first central relay of both gustatory information from the oral cavity and visceral information from the digestive system. The cNST receives visceralvagal information originating in post-oral segments of the digestive system as well as information from the AP [27,45,46]. The cNST contains neurons sensitive to aldosterone, a lipophilic hormone that crosses the blood-brain barrier. ...
Body sodium (Na) levels must be maintained within a narrow range for the correct functioning of the organism (Na homeostasis). Na disorders include not only elevated levels of this so-lute (hypernatremia), as in diabetes insipidus, but also reduced levels (hyponatremia), as in cerebral salt wasting syndrome. The balance in body Na levels therefore requires a delicate equilibrium to be maintained between the ingestion and excretion of Na. Salt (NaCl) intake is processed by receptors in the tongue and digestive system, which transmit the information to the nucleus of the solitary tract via a neural pathway (chorda tympani/vagus nerves) and to circumventricular organs, including the subfornical organ and area postrema, via a humoral pathway (blood/cerebrospinal fluid). Circuits are formed that stimulate or inhibit homeostatic Na intake involving participation of the parabrachial nucleus, pre-locus coeruleus, medial tuberomammillary nuclei, median eminence, par-aventricular and supraoptic nuclei, and other structures with reward properties such as the bed nucleus of the stria terminalis, central amygdala, and ventral tegmental area. Finally, the kidney uses neural signals (e.g., renal sympathetic nerves) and vascular (e.g., renal perfusion pressure) and humoral (e.g., renin-angiotensin-aldosterone system, cardiac natriuretic peptides, antidiuretic hormone , and oxytocin) factors to promote Na excretion or retention and thereby maintain extracellular fluid volume. All these intake and excretion processes are modulated by chemical messengers, many of which (e.g., aldosterone, angiotensin II, and oxytocin) have effects that are coordinated at peripheral and central level to ensure Na homeostasis.
... The PB is a multisensory integrating region primarily composed of glutamate neurons that have been shown to regulate a variety of behavioral responses associated with maintaining homeostasis including danger and distress (Chiang et al. 2019;Jaramillo et al. 2021;Palmiter 2018). For instance, the LPB is conceptualized as a major relay for viscerosensory and nociceptive signals to the forebrain and brainstem (Saper and Loewy 1980;Herbert et al. 1990;Moga et al. 1990;Palmiter 2018) where some of these projections have been shown to modulate arousal and behavioral responses to aversive conditions (Chiang et al. 2019;Jaramillo et al. 2021;Palmiter 2018). Afferent inputs to the LPB include catecholamine neurons in the NTS and VLM in addition to forebrain regions densely innervated by PB neurons (Tokita et al. 2009;Moga et al. 1990). ...
... The large number of neurons in the LPB compared to the rest of the brainstem is also consistent with our quantitative analysis of retrograde labeling in the brain following injections of CTB restricted to the aPVT and pPVT (Li and Kirouac 2012). It is generally understood that the PB relays brainstem and spinal cord viscerosensory, somato-sensory and taste-related signals to widespread regions of the forebrain (Chiang et al. 2019;Palmiter 2018;Herbert et al. 1990;Saper and Loewy 1980) including the PVT (Li and Kirouac 2012;Krout and Loewy 2000a). Mapping of brain-wide sources of neurons that make synapses on PB-PVT projecting neurons in the TRIO experiments revealed that the largest source of input cells is from neurons that are scattered in the brainstem RF. ...
... Furthermore, dendrites of LPB neurons extend outside subnuclear boundaries making the relevance of these anatomical distinctions debatable (Sarhan et al. 2005;Jasmin et al. 1997). However, it is clear that CTB neurons were located in the general region of the LPB that contains the external, ventral and dorsal lateral subnuclei presumed to receive afferents from general viscerosensory integration regions of the NTS (Chiang et al. 2019;Saper and Loewy 1980;Herbert et al. 1990) and nociceptive signals from the Gauriau and Bernard 2002;Deng et al. 2020). Since most of the PVT projecting neurons were localized in the LPB, we will refer to PB neurons that project to the PVT as LPB-PVT projecting neurons for the remainder of the discussion with the caveat that some neurons in the MPB contribute to this projection. ...
The paraventricular nucleus of the thalamus (PVT) projects to areas of the forebrain involved in regulating behavior. Homeostatic challenges and salient cues activate the PVT and evidence shows that the PVT regulates appetitive and aversive responses. The brainstem is a source of afferents to the PVT and the present study was done to determine if the lateral parabrachial nucleus (LPB) is a relay for inputs to the PVT. Retrograde tracing experiments with cholera toxin B (CTB) demonstrate that the LPB contains more PVT projecting neurons than other regions of the brainstem including the catecholamine cell groups. The hypothesis that the LPB is a relay for signals to the PVT was assessed using an intersectional monosynaptic rabies tracing approach. Sources of inputs to LPB included the reticular formation; periaqueductal gray (PAG); nucleus cuneiformis; and superior and inferior colliculi. Distinctive clusters of input cells to LPB-PVT projecting neurons were also found in the dorsolateral bed nucleus of the stria terminalis (BSTDL) and the lateral central nucleus of the amygdala (CeL). Anterograde viral tracing demonstrates that LPB-PVT neurons densely innervate all regions of the PVT in addition to providing collateral innervation to the preoptic area, lateral hypothalamus, zona incerta and PAG but not the BSTDL and CeL. The paper discusses the anatomical evidence that suggests that the PVT is part of a network of interconnected neurons involved in arousal, homeostasis, and the regulation of behavioral states with forebrain regions potentially providing descending modulation or gating of signals relayed from the LPB to the PVT.
... In contrast, the parabrachial nucleus (PB) located around the superior cerebellar peduncle was consistently found to contain labeled neurons with the lateral aspect of this nucleus (LPB) containing by far the most PVT projecting neurons in the lower brainstem (Li and Kirouac 2012;Kirouac et al. 2006;Li et al. 2014;Krout et al. 2002;Krout and Loewy 2000a). The LPB is densely innervated by catecholaminegic neurons in the NTS and VLM and is considered a major relay center of viscerosensory and nociceptive signals to the forebrain (Saper and Loewy 1980;Herbert et al. 1990;Moga et al. 1990;Palmiter 2018). ...
... The relatively large number of neurons in the LPB compared to the rest of the brainstem is also consistent with our quantitative analysis of retrograde labeling in the brain following small restricted injections of CTB in the aPVT and pPVT (Li and Kirouac 2012). It is generally understood that the PB relays brainstem and spinal cord viscerosensory, somatosensory and taste related signals to widespread regions of the forebrain (Chiang et al. 2019;Palmiter 2018;Herbert et al. 1990;Saper and Loewy 1980) including the PVT (Li and Kirouac 2012;Krout and Loewy 2000a). Mapping of brain-wide sources of neurons that make synapses on PB-PVT projecting neurons in the TRIO experiments revealed that the largest source of input cells is from neurons that are scattered in the brainstem reticular formation. ...
... The fact that the dendrites of LPB neurons extend outside subnuclear boundaries further makes the functional relevance of these anatomical demarcations debatable (Sarhan et al. 2005;Jasmin et al. 1997). However, it is clear that CTB neurons were located in the general region of the LPB that contains the external, ventral and dorsal lateral subnuclei that receive afferents from general viscerosensory integration regions of the NTS (Chiang et al. 2019;Saper and Loewy 1980;Herbert et al. 1990) and nociceptive signals from the brainstem and spinal cord (Chiang et al. 2019;Jaramillo et al. 2021;Han et al. 2015;Gauriau and Bernard 2002;Deng et al. 2020). It is also apparent that most of the PVT projecting neurons are localized in the LPB, and for this reason, we will refer to them as LPB-PVT neurons with the caveat that some neurons in the MPB contribute to this projection. ...
The paraventricular nucleus of the thalamus (PVT) projects to areas of the forebrain involved in behavior. Homeostatic challenges and salient cues activate the PVT and evidence shows that the PVT regulates appetitive and aversive responses. The brainstem is a source of afferents to the PVT and the present study was done to determine if the lateral parabrachial nucleus (LPB) is a relay for inputs to the PVT. Retrograde tracing experiments with cholera toxin B (CTB) demonstrate that the LPB contains more PVT projecting neurons than other regions of the brainstem including the catecholamine cell groups. The hypothesis that the LPB is a relay for brainstem signals to the PVT was assessed using an intersectional monosynaptic rabies tracing approach. Sources of inputs included the reticular formation, periaqueductal gray (PAG), nucleus cuneiformis, superior and inferior colliculi, and the LPB. Distinctive clusters of input cells to LPB-PVT projecting neurons were also found in the dorsolateral bed nucleus of the stria terminalis (BSTDL) and the lateral central nucleus of the amygdala (CeL). Anterograde viral tracing demonstrates that LPB-PVT neurons densely innervate all of the PVT in addition to providing collateral innervation to the preoptic area, lateral hypothalamus, zona incerta and PAG but not the BSTDL and CeL. The paper discusses the anatomical evidence that suggests that the PVT is part of a network of interconnected neurons involved in arousal, homeostasis, and the regulation of behavioral states with forebrain regions potentially providing descending modulation or gating of signals relayed from the LPB to the PVT.
... In light of previous studies, which showed that activation of neurons in the NTS contributes to the impairment of cold-evoked BAT thermogenesis in HFD fed rats (Madden and Morrison, 2016;Mohammed et al., 2018;Conceicao et al., 2021), that NTS neurons project to the LPB (Herbert et al., 1990;Conceicao et al., 2021), and that inhibition of LPB neurons (which are more active in HFD rats compared to chow-fed rats during cold exposure, Fig. 1) rescues cold-evoked BAT thermogenesis in HFD-fed rats (Fig. 2), we sought to assess whether activation of an NTS-LPB pathway inhibits BAT SNA and BAT thermogenesis (Figs. 3 and 4). ...
... Neurons expressing both GFP and mCherry were found exclusively in the NTS (Fig. 3B), predominantly in the rostral and medial portions of the NTS, with rare double-labelled neurons in the cNTS (Fig. 3C), and in the LPB (Fig. 3D), predominantly in the LPBc and LPBd, with a few neurons in the LPBel.The most plausible explanation for the finding of double-labelled neurons in the LPB is related to the nature of AAVs, which can, in general, be retrogradely transported (Haggerty et al., 2020). Since the NTS and the LPB have reciprocal neuronal connections (Herbert, Moga and Saper, 1990;Conceicao et al., 2021;Yang et al., 2020), we speculate that, when the AAV-DIO-hM3D(Gq) was injected into the NTS, neuronal terminals from LPB neurons expressing the AAVrg-Cre were infected by the cre-dependent vector. Therefore, these neurons would also express the cre-dependent virus and its reporter mCherry in their somas (Haggerty et al., 2020), as was the case in the present study. ...
Oxidation of fat by brown adipose tissue (BAT) contributes to energy balance and heat production. During cold exposure, BAT thermogenesis produces heat to warm the body. Obese subjects and rodents, however, show impaired BAT thermogenesis to the cold. Our previous studies suggest that vagal afferents synapsing in the nucleus tractus solitarius (NTS), tonically inhibits BAT thermogenesis to the cold in obese rats. NTS neurons send projections to the dorsal aspect of the lateral parabrachial nucleus (LPBd), which is a major integrative center that receives warm afferent inputs from the periphery and promotes the inhibition of BAT thermogenesis. This study investigated the contribution of LPBd neurons in the impairment of BAT thermogenesis in rats fed a high-fat diet (HFD). By using a targeted dual viral vector approach, we found that chemogenetic activation of an NTS-LPB pathway inhibited BAT thermogenesis to the cold. We also found that the number of Fos-labelled neurons in the LPBd was higher in rats fed a HFD than in chow diet-fed rats after exposure to a cold ambient temperature. Nanoinjections of a GABAA receptor agonist into the LPBd area rescued BAT thermogenesis to the cold in HFD rats. These data reveal the LPBd as a critical brain area that tonically suppresses energy expenditure in obesity during skin cooling. These findings reveal novel effects of high-fat diets in the brain and in the control energy metabolism and can contribute to the development of therapeutic approaches to regulate fat metabolism.
... The PBN, also located within the hindbrain, is involved in sodium-appetite regulation and receives input from the NTS [77] and AP [48]. Single-unit recordings from the PBN of sodium-deprived rats exhibit diminished neural responses to NaCl applied to the tongue [78], similar to other gustatory regions (e.g., NTS), suggesting that the PBN is involved in gustatory-mediated regulation of sodium appetite. ...
... Projections from the NTS to the PBN are also important for integrating signals pertaining to blood pressure and volume, fluid, and electrolyte homeostasis. The PBN integrates these inputs and transmits information throughout the brain to mediate neuroendocrine and autonomic activity to restore homeostasis [51, 77,[207][208][209][210]. The LC, adjacent to the PBN, has also been implicated in blood-pressure control. ...
Sodium (Na+) is crucial for numerous homeostatic processes in the body and, consequentially, its levels are tightly regulated by multiple organ systems. Sodium is acquired from the diet, commonly in the form of NaCl (table salt), and substances that contain sodium taste salty and are innately palatable at concentrations that are advantageous to physiological homeostasis. The importance of sodium homeostasis is reflected by sodium appetite, an “all-hands-on-deck” response involving the brain, multiple peripheral organ systems, and endocrine factors, to increase sodium intake and replenish sodium levels in times of depletion. Visceral sensory information and endocrine signals are integrated by the brain to regulate sodium intake. Dysregulation of the systems involved can lead to sodium overconsumption, which numerous studies have considered causal for the development of diseases, such as hypertension. The purpose here is to consider the inverse—how disease impacts sodium intake, with a focus on stress-related and cardiometabolic diseases. Our proposition is that such diseases contribute to an increase in sodium intake, potentially eliciting a vicious cycle toward disease exacerbation. First, we describe the mechanism(s) that regulate each of these processes independently. Then, we highlight the points of overlap and integration of these processes. We propose that the analogous neural circuitry involved in regulating sodium intake and blood pressure, at least in part, underlies the reciprocal relationship between neural control of these functions. Finally, we conclude with a discussion on how stress-related and cardiometabolic diseases influence these circuitries to alter the consumption of sodium.
... The PB receives many projections from the medulla, including the reticular formation, spinal trigeminal nucleus, and NTS (Norgren and Leonard, 1971;Herbert et al., 1990;Feil and Herbert, 1995;Tokita et al., 2009). CTb injections into the lateral PB strongly label these regions, and conditional rabies virus tracing labeled many neurons in these hindbrain regions, suggesting direct projections to the PB Calca/CGRP neurons. ...
The parabrachial nucleus (PB), located in the dorsolateral pons, contains primarily glutamatergic neurons which regulate responses to a variety of interoceptive and cutaneous sensory signals. The lateral PB subpopulation expressing the Calca gene which produces the neuropeptide calcitonin gene-related peptide (CGRP) relays signals related to threatening stimuli such as hypercarbia, pain, and nausea, yet the afferents to these neurons are only partially understood. We mapped the afferent projections to the lateral part of the PB in mice using conventional cholera toxin B subunit (CTb) retrograde tracing, and then used conditional rabies virus retrograde tracing to map monosynaptic inputs specifically targeting the PBCalca/CGRP neurons. Using vesicular GABA (vGAT) and glutamate (vGLUT2) transporter reporter mice, we found that lateral PB neurons receive GABAergic afferents from regions such as the lateral part of the central nucleus of the amygdala, lateral dorsal subnucleus of the bed nucleus of the stria terminalis, substantia innominata, and the ventrolateral periaqueductal gray. Additionally, they receive glutamatergic afferents from the infralimbic and insular cortex, paraventricular nucleus, parasubthalamic nucleus, trigeminal complex, medullary reticular nucleus, and nucleus of the solitary tract. Using anterograde tracing and confocal microscopy, we then identified close axonal appositions between these afferents and PBCalca/CGRP neurons. Finally, we used channelrhodopsin-assisted circuit mapping to test whether some of these inputs directly synapse upon the PBCalca/CGRP neurons. These findings provide a comprehensive neuroanatomical framework for understanding the afferent projections regulating the PBCalca/CGRP neurons.
... The parabrachial nucleus (PBN), a pivotal brain region that is closely associated with arousal (Kaur et al., 2013), possesses a vast network of glutamatergic neurons that project to multiple arousalenhancing areas in the brain. These areas include the basal forebrain, lateral hypothalamus, thalamus, amygdala complex, and cortex (Saper and Loewy, 1980;Saper, 1982;Fulwiler and Saper, 1984;Herbert et al., 1990), which are all well-documented players in the process of general anesthesia . Chemogenetic activation of the parabrachial nucleus glutamatergic neurons had a significant effect on sevoflurane anesthesia, increasing the ED50 for LORR, prolonging induction time, and reducing emergence time. ...
For over 170 years, general anesthesia has played a crucial role in clinical practice, yet a comprehensive understanding of the neural mechanisms underlying the induction of unconsciousness by general anesthetics remains elusive. Ongoing research into these mechanisms primarily centers around the brain nuclei and neural circuits associated with sleep-wake. In this context, two sophisticated methodologies, optogenetics and chemogenetics, have emerged as vital tools for recording and modulating the activity of specific neuronal populations or circuits within distinct brain regions. Recent advancements have successfully employed these techniques to investigate the impact of general anesthesia on various brain nuclei and neural pathways. This paper provides an in-depth examination of the use of optogenetic and chemogenetic methodologies in studying the effects of general anesthesia on specific brain nuclei and pathways. Additionally, it discusses in depth the advantages and limitations of these two methodologies, as well as the issues that must be considered for scientific research applications. By shedding light on these facets, this paper serves as a valuable reference for furthering the accurate exploration of the neural mechanisms underlying general anesthesia. It aids researchers and clinicians in effectively evaluating the applicability of these techniques in advancing scientific research and clinical practice.
... Nevertheless, remarkable are the efferent bilateral connections to the medullary region, especially to the rostroventrolateral medulla, the caudal half of the NTS and the dorsal motor nucleus of the vagus [28,[40][41][42]. They also show that the innervation is completely noradrenergic and that more than half of the neurones in area A5 project ipsilaterally to both nuclei, but in some cases, the projection could be bilateral. ...
Area A5 is a noradrenergic cell group in the brain stem characterised by its important role in triggering sympathetic activity, exerting a profound influence on the sympathetic outflow, which is instrumental in the modulation of cardiovascular functions, stress responses and various other physiological processes that are crucial for adaptation and survival mechanisms. Understanding the role of area A5, therefore, not only provides insights into the basic functioning of the sympathetic nervous system but also sheds light on the neuronal basis of a number of autonomic responses. In this review, we look deeper into the specifics of area A5, exploring its anatomical connections, its neurochemical properties and the mechanisms by which it influences sympathetic nervous system activity and cardiorespiratory regulation and, thus, contributes to the overall dynamics of the autonomic function in regulating body homeostasis.
... However, this pontine nucleus, which is an intermediate station in the taste pathways of many mammalian species [23], does not seem to be involved in taste in primates, including humans [42], in that the NST projections bypass the PBN and directly project to the VPMpc [43,44]. In subprimate species, the caudal and ventral portions of the medial PBN (waist area) receive afferents from the rostral and, to a lesser extent, the caudal NST [45]. The rostral NST-PBN projections are mostly ipsilateral, although, in rats and mice, the caudal NST-PBN afferents are also found to terminate in the contralateral PBN [46,47]; in addition, after unilateral injection of a retrograde tracer in the PBN, a small number of retrogradely labeled neurons were found in contralateral PBN in mouse [47]. ...
The present study was designed to establish the contribution of the corpus callosum (CC) to the cortical representation of unilateral taste stimuli in the human primary gustatory area (GI). Unilateral taste stimulation of the tongue was applied to eight patients with partial or total callosal resection by placing a small cotton pad soaked in a salty solution on either side of the tongue. Functional images were acquired with a 1.5 Tesla machine. Diffusion tensor imaging and tractography were also performed. Unilateral taste stimuli evoked bilateral activation of the GI area in all patients, including those with total resection of the CC, with a prevalence in the ipsilateral hemisphere to the stimulated tongue side. Bilateral activation was also observed in the primary somatic sensory cortex (SI) in most patients, which was more intense in the contralateral SI. This report confirms previous functional studies carried out in control subjects and neuropsychological findings in callosotomized patients, showing that gustatory pathways from tongue to cortex are bilaterally distributed, with an ipsilateral predominance. It has been shown that the CC does play a role, although not an exclusive one, in the bilateral symmetrical representation of gustatory sensitivity in the GI area, at least for afferents from one side of the tongue.
... Cardiovagal control in the brainstem includes both efferent and afferent feedback loops and involves the nucleus tractus solitarii (NTS), found in the dorsal medulla, as the primary target for vagal afference. The largest single projection from the NTS is to the parabrachial nucleus (PBN), located in the pons [1,2]. Additionally, the NTS sends a major projection to the periaqueductal gray matter (PAG) [3]. ...
Background
The autonomic response to transcutaneous auricular vagus nerve stimulation (taVNS) has been linked to the engagement of brainstem circuitry modulating autonomic outflow. However, the physiological mechanisms supporting such efferent vagal responses are not well understood, particularly in humans.
Hypothesis
We present a paradigm for estimating directional brain-heart interactions in response to taVNS. We propose that our approach is able to identify causal links between the activity of brainstem nuclei involved in autonomic control and cardiovagal outflow.
Methods
We adopt an approach based on a recent reformulation of Granger causality that includes permutation-based, nonparametric statistics. The method is applied to ultrahigh field (7T) functional magnetic resonance imaging (fMRI) data collected on healthy subjects during taVNS.
Results
Our framework identified taVNS-evoked functional brainstem responses with superior sensitivity compared to prior conventional approaches, confirming causal links between taVNS stimulation and fMRI response in the nucleus tractus solitarii (NTS). Furthermore, our causal approach elucidated potential mechanisms by which information is relayed between brainstem nuclei and cardiovagal, i.e., high-frequency heart rate variability, in response to taVNS. Our findings revealed that key brainstem nuclei, known from animal models to be involved in cardiovascular control, exert a causal influence on taVNS-induced cardiovagal outflow in humans.
Conclusion
Our causal approach allowed us to noninvasively evaluate directional interactions between fMRI BOLD signals from brainstem nuclei and cardiovagal outflow.
... In addition, different subpopulations of neurons in PVH control distinguishing aspects of energy balance. For example, MC4R neurons in PVH modulate the satiety by projecting to the hindbrain (18,19). Neuronal nitric oxide synthase 1 (Nos1) neurons in PVH control both feeding behavior and energy expenditure (20). ...
Background
Dysregulation of feeding behavior leads to a variety of pathological manifestations ranging from obesity to anorexia. The foraging behavior of animals affected by food deficiency is not fully understood.
Methods
Home-Cage system was used to monitor the behaviors. Immunohistochemical staining was used to monitor the trend of neuronal activity. Chemogenetic approach was used to modify neuronal activity.
Results
We described here a unique mouse model of foraging behavior and unveiled that food deprivation significantly increases the general activities of mice with a daily rhythmic pattern, particularly foraging behavior. The increased foraging behavior is potentiated by food cues (mouthfeel, odor, size, and shape) and energy deficit, rather than macronutrient protein, carbohydrate, and fat. Notably, energy deficiency increases nocturnal neuronal activity in paraventricular hypothalamic nucleus (PVH), accompanying a similar change in rhythmic foraging behavior. Activating neuronal activity in PVH enhances the amplitude of foraging behavior in mice. Conversely, inactivating neuronal activity in PVH decreases the amplitude of foraging behavior and impairs the rhythm of foraging behavior.
Discussion
These results illustrate that energy status and food cues regulate the rhythmic foraging behavior via PVH neuronal activity. Understanding foraging behavior provides insights into the underlying mechanism of eating-related disorders.
... Because gustatory and visceral afferent information appear to converge in the pontine PBN (Cechetto & Saper, 1987;Herbert, Moga, & Saper, 1990;Saper & Lowey, 1980; for a review, see Norgren, 1995), it is not surprising to find that this structure is involved with CTA learning. It was, however, unexpected when Reilly, Grigson, and Norgren (1993) found that PBN lesions also prevented the acquisition of a conditioned odor aversion (COA). ...
Rats with bilateral ibotenic acid lesions of the gustatory zone of the parabrachial nuclei (PBN) failed to acquire a conditioned taste aversion (CTA) in Experiment 1. They also failed to acquire a conditioned odor aversion (COA) when the olfactory cue was presented on an odor disk in Experiment 2 or when it was presented in water in Experiment 3. The failure to acquire the COA was not due to an inability to detect or use olfactory stimuli because the lesioned rats displayed neophobia to a novel odor in Experiment 3 and used an olfactory cue to predict the availability of an aversive capsaicin solution in Experiment 4. Together, the results demonstrate that, as with CTA learning, PBN cell bodies are essential for the establishment of a specific association between an olfactory conditioned stimulus and a lithium chloride unconditioned stimulus.
... Most AP neurons project to the lateral PBN (Shapiro & Miselis, 1985), and the lesions in the present experiments were centered more medially. Nevertheless, some electrophysiological and anatomical evidence indicates that in the medial PBN exists a small area in which gustatory and visceral projections from the NST may converge (Herbert et al., 1990;Hermann & Rogers, 1985). In addition to possibly reducing the aversive consequences of LiCl, the PBN lesions may reduce the animal's ability to perceive taste stimuli. ...
Intake and taste reactivity tests were used to determine the effects of bilateral lesions of the gustatory portions of the nucleus of the solitary tract (NST), the parabrachial nucleus (PBN), and the ventral posteromedial nucleus of the thalamus (VPMpc) on several complex ingestive behaviors. In the 1st experiment, lesions of the PBN and the NST blocked, and VPMpc lesions impaired, the behavioral expression of salt appetite. In the 2nd experiment, alanine was paired with injections of LiCl. Control rats as well as rats with NST and VPMpc lesions acquired the taste aversion, but rats with PBN lesions did not. In the 3rd experiment, all animals increased their food intake after injections of 2 U/kg insulin and 250 mg/kg 2-deoxy-D-glucose, and their food intake was suppressed after nutritive stomach loads.
... The parabrachial nucleus (PB) is a region of the brainstem that links sensory information to a wide variety of brain regions (Cechetto et al., 1985;Herbert et al., 1990;Saper & Loewy, 1980). Glutamatergic neurons in this region belong to two mutually exclusive macropopulations defined by the transcription factors Atoh1 and Lmx1b (Karthik et al., 2022). ...
In the brain, connectivity determines function. Neurons in the parabrachial nucleus (PB) relay diverse information to widespread brain regions, but the connections and functions of PB neurons that express Nps (neuropeptide S) remain mysterious. Here, we use Cre-dependent anterograde tracing and whole-brain analysis to map their output connections. While many other PB neurons project ascending axons through the central tegmental tract, NPS axons reach the forebrain via distinct periventricular and ventral pathways. Along the periventricular pathway, NPS axons target the tectal longitudinal column and periaqueductal gray then continue rostrally to target the paraventricular nucleus of the thalamus. Along the ventral pathway, NPS axons blanket much of the hypothalamus but avoid the ventromedial and mammillary nuclei. They also project prominently to the ventral bed nucleus of the stria terminalis, A13 cell group, and magnocellular subparafasciular nucleus. In the hindbrain, NPS axons have fewer descending projections, targeting primarily the superior salivatory nucleus, nucleus of the lateral lemniscus, and periolivary region. Combined with what is known about NPS and its receptor, the output pattern of Nps -expressing neurons in the PB region predicts a role in threat response and circadian behavior.
... NTS neurons receive direct projections from medullary and dorsal horn neurons and solitary tract afferents, and this overlap has been postulated to aid integration of somatosensory and interoceptive stimuli (Menétrey and Basbaum, 1987;Appleyard et al., 2007;Holt et al., 2019;Holt, 2022). Projections from the cNTS, including A2 neurons, preferentially target the lateral regions of the parabrachial nucleus (Herbert et al., 1990), a hub for processing aversive stimuli (Palmiter, 2018;Uddin et al., 2018;Bowen et al., 2020;Raver et al., 2020). PB-projecting NTS neurons are activated by noxious peripheral stimuli, and this activation is enhanced in a mouse model of trigeminal neuropathic pain (Okada et al., 2019). ...
The parabrachial complex (PB) is critically involved in aversive processes, and chronic pain is associated with amplified activity of PB neurons in rodent models of neuropathic pain. Here, we demonstrate that catecholaminergic input from the caudal nucleus of the solitary tract (cNTS cat ), a stress responsive region that integrates interoceptive and exteroceptive signals, causes amplification of PB activity and their sensory afferents. We used a virally mediated expression of a norepinephrine (NE) sensor, NE2h, fiber photometry, and extracellular recordings in anesthetized mice to show that noxious mechanical and thermal stimuli activate cNTS neurons. These stimuli also produce prolonged NE transients in PB that far outlast the noxious stimuli. Similar NE transients can be evoked by focal electrical stimulation of cNTS, a region that contains the noradrenergic A2 cell group that projects densely on PB. In vitro , optical stimulation of cNTS cat terminals depolarized PB neurons and caused a prolonged increase the frequency of excitatory synaptic activity. A dual opsin approach showed that sensory afferents from the caudal spinal trigeminal nucleus are potentiated by cNTS cat terminal activation. This potentiation was coupled with a decrease in the paired pulse ratio (PPR), consistent with an cNTS cat -mediated increase in the probability of release at SpVc synapses. Together, these data suggest that A2 neurons of the cNTS generate long lasting NE transients in PB which increase excitability and potentiate responses of PB neurons to sensory inputs. These reveal a mechanism through which stressors from multiple modalities may potentiate the aversiveness of nociceptive stimuli.
... The relatively large number of neurons in the LPB compared to the rest of the brainstem is also consistent with our quantitative analysis of retrograde labeling in the brain following small restricted injections of CTB in the aPVT and pPVT(Li and Kirouac 2012). It is generally understood that the PB relays brainstem and spinal cord viscerosensory, somatosensory and taste related signals to widespread regions of the forebrain(Chiang et al. 2019;Palmiter 2018;Herbert et al. 1990;Saper and Loewy 1980) including the PVT (Li and Kirouac 2012; Krout and Loewy 2000a). Mapping of brain-wide sources of neurons that make synapses on PB-PVT projecting neurons in the TRIO experiments revealed that the largest source of input cells is from neurons that are scattered in the brainstem reticular formation. ...
The paraventricular nucleus of the thalamus (PVT) projects to areas of the forebrain involved in behavior. Homeostatic challenges and salient cues activate the PVT and evidence shows that the PVT regulates appetitive and aversive responses. The brainstem is a source of afferents to the PVT and the present study was done to determine if the lateral parabrachial nucleus (LPB) is a relay for inputs to the PVT. Retrograde tracing experiments with cholera toxin B (CTB) demonstrate that the LPB contains more PVT projecting neurons than other regions of the brainstem including the catecholamine cell groups. The hypothesis that the LPB is a relay for brainstem signals to the PVT was assessed using an intersectional monosynaptic rabies tracing approach. Sources of inputs included the reticular formation, periaqueductal gray (PAG), nucleus cuneiformis, superior and inferior colliculi, and the LPB. Distinctive clusters of input cells to LPB-PVT projecting neurons were also found in the dorsolateral bed nucleus of the stria terminalis (BSTDL) and the lateral central nucleus of the amygdala (CeL). Anterograde viral tracing demonstrates that LPB-PVT neurons densely innervate all of the PVT in addition to providing collateral innervation to the preoptic area, lateral hypothalamus, zona incerta and PAG but not the BSTDL and CeL. The paper discusses the anatomical evidence that suggests that the PVT is part of a network of interconnected neurons involved in arousal, homeostasis, and the regulation of behavioral states with forebrain regions potentially providing descending modulation or gating of signals relayed from the LPB to the PVT.
... Therefore, CGRP may induce anorexigenic neuropep such as CCK and/or inhibit orexigenic neuropeptides, such as NPY and MCH, res in suppression of food intake, functionally coupled to cAMP (Figure 3). Anorexigenic behavior in rodents and primates is regulated by the lateral parabrachial nucleus, which is a duct for visceral signals from the caudal hindbrain to forebrain areas linked with appetite control [80,81]. It was identified as a subset of neurons placed in the external lateral parabrachial nucleus (PBel) that expressed CGRP and suppressed feeding and mediated taste aversion when activated by illness mimetics [82]. ...
Targeting calcitonin gene-related peptide (CGRP) and its receptor by antibodies and antagonists was a breakthrough in migraine prevention and treatment. However, not all migraine patients respond to CGRP-based therapy and a fraction of those who respond complain of aliments mainly in the gastrointestinal tract. In addition, CGRP and migraine are associated with obesity and metabolic diseases, including diabetes. Therefore, CGRP may play an important role in the functioning of the gut-brain-microflora axis. CGRP secretion may be modulated by dietary compounds associated with the disruption of calcium signaling and upregulation of mitogen-activated kinase phosphatases 1 and 3. CGRP may display anorexigenic properties through induction of anorexigenic neuropeptides, such as cholecystokinin and/or inhibit orexigenic neuropeptides, such as neuropeptide Y and melanin-concentrating hormone CH, resulting in the suppression of food intake, functionally coupled to the activation of the hypothalamic 3′,5′-cyclic adenosine monophosphate. The anorexigenic action of CGRP observed in animal studies may reflect its general potential to control appetite/satiety or general food intake. Therefore, dietary nutrients may modulate CGRP, and CGRP may modulate their intake. Therefore, anti-CGRP therapy should consider this mutual dependence to increase the efficacy of the therapy and reduce its unwanted side effects. This narrative review presents information on molecular aspects of the interaction between dietary nutrients and CGRP and their reported and prospective use to improve anti-CGRP therapy in migraine.
... In addition, aldosterone sensitive cells in the parabrachial nucleus (PB) and pre-locus coeruleus (pre-LC) send projections to several forebrain sites, including bed nucleus of the stria terminalis, the ventral tegmental region, paraventricular nucleus and central/ medial amygdala. These PB and pre-LC to forebrain projections are likely critical for both activating and satiating sodium appetite [102][103][104][105][106][107][108]. ...
Salt ingestion by animals and humans has been noted from prehistory. The search for salt is largely driven by a physiological need for sodium. There is a large body of literature on sodium intake in laboratory rats, but the vast majority of this work has used male rats. The limited work conducted in both male and female rats, however, reveals sex differences in sodium intake. Importantly, while humans ingest salt every day, with every meal and with many foods, we do not know how many of these findings from rodent studies can be generalized to men and women. This review provides a synthesis of the literature that examines sex differences in sodium intake and highlights open questions. Sodium serves many important physiological functions and is inextricably linked to the maintenance of body fluid homeostasis. Indeed, from a motivated behavior perspective, the drive to consume sodium has largely been studied in conjunction with the study of thirst. This review will describe the neuroendocrine controls of fluid balance, mechanisms underlying sex differences, sex differences in sodium intake, changes in sodium intake during pregnancy, and the possible neuronal mechanisms underlying these differences in behavior. Having reviewed the mechanisms that can only be studied in animal experiments, we address sex differences in human dietary sodium intake in reproduction, and with age.
... In fact, both the PVH Ericsson et al., 1994;Fulwiler and Saper, 1984;Moga et al., 1990;Sagar et al., 1995) and the PBN Mascarucci et al., 1998) have already been implicated in the central nervous system proinflammatory response originating from the NTS. Catecholaminergic neurons from the NTS directly target PVH neurons to activate the HPA axis, while glutamatergic signaling by NTS neurons in the PBN initiates visceral reflexes and transmits immune-sensory information to forebrain structures (Goehler et al., 2000;Herbert et al., 1990). Because AgRP neurons are inhibitory, it is possible that they block proinflammatory outputs from these pathways ...
Homeostasis is established through bidirectional communication between the periphery and the central nervous system. To maintain homeostasis, some biological drives can become prioritized over others. This changing balance between biological drives encourages peak performance and survival. However, when homeostasis is disturbed, chronic inflammatory diseases such as obesity, chronic pain, and arthritis can arise. We became interested in understanding if competing biological drives could be leveraged for therapeutic purposes. Food restriction inhibits inflammation; therefore, we explored how hunger and feeding neural circuits affect responses to noxious agents. Our first study investigated the role of hunger to alleviate pain behavior. We found that hunger significantly reduces time spent licking during the inflammatory phase of a formalin pain assay but leaves intact pain responses to acute threats. We next evaluated if hypothalamic hunger neurons are involved in this behavioral change. Stimulation of agouti-related protein expressing (AgRP) neurons significantly reduced formalin pain behavior. To determine the central nodes that mediate this effect, we systematically screened AgRP neuron projections for their ability to suppress pain. Only AgRP neurons projecting to the hindbrain parabrachial nucleus was able to reduce inflammatory pain behavior. Our second study investigated the role of hunger to influence inflammatory responses of an injury site. Using two models of localized inflammation, we found that food deprivation robustly reduces inflammation, pro-inflammatory cytokine levels, and associated temperature increases induced by injection of noxious stimuli [complete Freund’s adjuvant (CFA) or formalin]. Activation of AgRP neurons recapitulated the effect of food deprivation on inflammation. We then evaluated the role of each AgRP axonal target structure to reduce inflammation. Interestingly, stimulation of AgRP neurons that project to the paraventricular nucleus of the hypothalamus or the parabrachial nucleus were sufficient to reduce CFA-induced inflammation. Finally, we identified the vagus nerve as a key pathway for the anti-inflammatory effect of hunger. We propose that hunger, through AgRP neurons, inhibits pro-inflammatory responses from the central nervous system and changes the output of efferent vagal fibers. This body of work reveals a central node for the reduction of pain and inflammation, highlighting a novel role for hypothalamic circuits to influence injury responses.
... The PB is known to receive inputs from the nucleus tractus solitaries, the dorsal laminae of the spinal cord and from various forebrain regions [286][287][288][289][290][291][292][293] . Its main projections include forebrain regions such as the thalamus (the PVT, among others), the amygdala, the cortex, the BNST and the hypothalamus 177,294-296 . ...
NMDA receptors (NMDARs) are glutamate-gated ion channels of the CNS. The best characterized and most common forms of NMDARs are composed by two GluN1 subunits binding glycine and two GluN2 subunits binding glutamate. Our attention focused on the less known glycine-binding GluN3A subunit of the third NMDAR group. GluN3A can form two distinct NMDAR flavors. First, GluN3A can constitute diheteromeric GluN1/GluN3ARs activated by glycine and insensitive to glutamate. GluN3A can also generate with GluN1 and GluN2 glutamate-sensitive triheteromeric GluN1/GluN2/GluN3ARs with different properties from classic NMDARs. GluN3A expression is assumed to be limited to the first postnatal weeks. Therefore, its identification in neurons has so far been limited to the juvenile brain, where triheteromers were shown to play a role in synaptic maturation. GluN1/GluN3ARs had however never been identified in native tissues. During my thesis, on the basis of novel immunohistological evidence on GluN3A expression in the adult brain, and using a unique compound, CGP78608, I showed that GluN1/GluN3ARs are functional in several nuclei, comprising the adult Medial Habenula and juvenile hippocampus. Concerning GluN1/GluN2/GluN3ARs, I could demonstrate that they are functional in the paraventricular nucleus of the adult thalamus. Among several cell subgroups examined, I could show that neurons expressing calbindin 2 and melanocortin receptors 4 from the parabrachial nucleus are physiological activators of these receptors. In conclusion, my work led to a shift in our perception of how GluN3A subunits are expressed and opens new hypotheses on how they can contribute to the activity of neural circuits.
... The PB neurons relay via gustatory and general visceral input to the "gustatory/visceral" thalamic region that also receives input from the ST directly ( Figure 3A). The thalamic gustatory relay is referred to as ventral posterior thalamic nucleus parvocellular (VPPC) and is defined as a 'taste relay' (Herbert et al., 1990;Lundy and Norgren, 2015). This unique, predominantly ipsilateral connection breaks down into a complex interaction from the VPPC that receives fibers from the ipsi-and, to a lesser extent, the contralateral PB. ...
Somatosensory, taste, vestibular, and auditory information is first processed in the brainstem. From the brainstem, the respective information is relayed to specific regions within the cortex, where these inputs are further processed and integrated with other sensory systems to provide a comprehensive sensory experience. We provide the organization, genetics, and various neuronal connections of four sensory systems: trigeminal, taste, vestibular, and auditory systems. The development of trigeminal fibers is comparable to many sensory systems, for they project mostly contralaterally from the brainstem or spinal cord to the telencephalon. Taste bud information is primarily projected ipsilaterally through the thalamus to reach the insula. The vestibular fibers develop bilateral connections that eventually reach multiple areas of the cortex to provide a complex map. The auditory fibers project in a tonotopic contour to the auditory cortex. The spatial and tonotopic organization of trigeminal and auditory neuron projections are distinct from the taste and vestibular systems. The individual sensory projections within the cortex provide multi-sensory integration in the telencephalon that depends on context-dependent tertiary connections to integrate other cortical sensory systems across the four modalities.
... indicating an abnormal modulation of serotonin and GABA transmission from the ascending arousal system to the cortical cortex. The PBC receives visceral afferent information from the brainstem and outputs this information to the hypothalamus, amygdala, and cortical cortex (Herbert et al., 1990). Recent research has linked PBC to facilitating arousal in the cerebral cortex (Fuller et al., 2011) and to the pathological mechanism of obstructive sleep apnea (Kaur et al., 2013). ...
The ascending arousal system plays a crucial role in individuals' consciousness. Recently, advanced functional magnetic resonance imaging (fMRI) has made it possible to investigate the ascending arousal network (AAN) in vivo. However, the role of AAN in the neuropathology of human insomnia remains unclear. Our study aimed to explore alterations in AAN and its connections with cortical networks in chronic insomnia disorder (CID). Resting-state fMRI data were acquired from 60 patients with CID and 60 good sleeper controls (GSCs). Changes in the brain's functional connectivity (FC) between the AAN and eight cortical networks were detected in patients with CID and GSCs. Multivariate pattern analysis (MVPA) was employed to differentiate CID patients from GSCs and predict clinical symptoms in patients with CID. Finally, these MVPA findings were further verified using an external data set (32 patients with CID and 33 GSCs). Compared to GSCs, patients with CID exhibited increased FC within the AAN, as well as increased FC between the AAN and default mode, cerebellar, sensorimotor, and dorsal attention networks. These AAN-related FC patterns and the MVPA classification model could be used to differentiate CID patients from GSCs with 88% accuracy in the first cohort and 77% accuracy in the validation cohort. Moreover, the MVPA prediction models could separately predict insomnia (data set 1, R2 = .34; data set 2, R2 = .15) and anxiety symptoms (data set 1, R2 = .35; data set 2, R2 = .34) in the two independent cohorts of patients. Our findings indicated that AAN contributed to the neurobiological mechanism of insomnia and highlighted that fMRI-based markers and machine learning techniques might facilitate the evaluation of insomnia and its comorbid mental symptoms.
... The different NTS subnuclei engage in complex reciprocal connections with the PBN including the Kölliker-Fuse nucleus in the rostral pons (Ganchrow et al., 2014;Herbert et al., 1990;Roman et al., 2016) and project to the locus coeruleus (Van Bockstaele et al., 1999). In particular, the Kölliker-Fuse nucleus forms part of the respiratory network and is considered a major source of cardiac vagal tone and RSA (Farmer et al., 2016). ...
Due to its pivotal role in autonomic networks and interoception, the vagus attracts continued interest from both basic scientists and therapists of various clinical disciplines. In particular, the widespread use of heart rate variability as an index of autonomic cardiac control and a proposed central role of the vagus in biopsychological concepts, e.g., the polyvagal theory, provide a good opportunity to recall basic features of vagal anatomy. In addition to the “classical” vagal brainstem nuclei, i.e., dorsal motor nucleus, nucleus ambiguus and nucleus tractus solitarii, the spinal trigeminal and paratrigeminal nuclei come into play as targets of vagal afferents. On the other hand, the nucleus of the solitary tract receives and integrates not only visceral but also somatic afferents.
... The lPB/KF is implicated in respiratory phase transition (Dutschmann and Herbert, 2006;Mörschel and Dutschmann, 2009). The lPB/KF receives principal inputs from the NTS (Herbert et al., 1990) and the dorsal horn of the spinal cord (Cordero-Erausquin et al., 2009;Cameron et al., 2015), and projects to numerous forebrain structures including the amygdala, hypothalamus, cortex and thalamus. Thus, the lPB/KF relays multiple sensory information about respiratory and cardiovascular function and also about nociception, pain, and temperature (Jiang et al., 2004;Davern, 2014;Barik et al., 2018;Palmiter, 2018;Chiang et al., 2019). ...
During running, ventilation increases to match the augmented energetic demand. Yet the presumed neuronal substrates for this running hyperpnea have remained elusive. To fill this gap, we have, in mice, examined the interactions between i) limb movements and respiratory cycles, and ii) locomotor and respiratory neural networks. First, by combining electromyographic recordings (EMG) of the diaphragm with limb video-tracking in running mice, we show that, for a wide range of trotting speeds on a treadmill, breathing rate increases to a fixed value, irrespective of running speeds. Importantly, breaths are never temporally synchronized to strides, highlighting that exercise hyperpnea can operate without phasic signals from limb sensory feedbacks. We next sought to identify candidate trigger neurons in the locomotor central network, and their partners in respiratory centers. Combining EMG recordings, viral tracing, and activity interference tools, we first show that the prime supraspinal center for locomotor initiation (the mesencephalic locomotor region, MLR) can upregulate breathing during, and even before, running. Indeed, the MLR contacts directly and modulates the main inspiratory generator, the preBötzinger complex. We show that the lumbar locomotor circuits also have an excitatory action onto respiratory activity, but that this ascending drive targets another essential respiratory group, the retrotrapezoid nucleus. This work highlights the multifunctional nature of locomotor command and executive centers, and points to multiple neuronal pathways capable of upregulating breathing during, or possibly even prior to, running.
... Afferent signals sent to the caudal nucleus tractus solitarius (NTS) via the glossopharyngeal or vagus nerves (Loewy, 1990) are integrated with respiratory pacemaker output to adjust respiratory drive; a pathway also identified as part of the ascending, afferent pathway for other interoceptive networks (J€ anig, 1996;Saper, 2002). The parabrachial nucleus (PBN) in the dorsolateral pons receives sensory inputs from the NTS and medullary reticular formation (Herbert et al., 1990) and is considered a "hub" for pain and other aversive stimuli (Chiang et al., 2019). Brain imaging studies that included the PBN in the field-of-view show it is activated by hypercapnia Pattinson et al., 2009), but it is not clear whether this activation is part of the ventilatory response or air hunger. ...
The clinical term dyspnea (a.k.a. breathlessness or shortness of breath) encompasses at least three qualitatively distinct sensations that warn of threats to breathing: air hunger, effort to breathe, and chest tightness. Air hunger is a primal homeostatic warning signal of insufficient alveolar ventilation that can produce fear and anxiety and severely impacts the lives of patients with cardiopulmonary, neuromuscular, psychological, and end-stage disease. The sense of effort to breathe informs of increased respiratory muscle activity and warns of potential impediments to breathing. Most frequently associated with bronchoconstriction, chest tightness may warn of airway inflammation and constriction through activation of airway sensory nerves. This chapter reviews human and functional brain imaging studies with comparison to pertinent neurorespiratory studies in animals to propose the interoceptive networks underlying each sensation. The neural origins of their distinct sensory and affective dimensions are discussed, and areas for future research are proposed. Despite dyspnea's clinical prevalence and impact, management of dyspnea languishes decades behind the treatment of pain. The neurophysiological bases of current therapeutic approaches are reviewed; however, a better understanding of the neural mechanisms of dyspnea may lead to development of novel therapies and improved patient care.
... In addition, the reticular nuclei and vagal complex, which are both important nuclei locations in the brainstem, display abundant interaction with each other. The projection from the NTS (Sawchenko and Swanson, 1982) and the parabrachial nuclei (PB) (Herbert et al., 1990) can reach NA and DMV due to the lap of inputs to the NA and DMV. The IML mainly receives projection from the brainstem and hypothalamus (Loewy, 1981;Schwanzel-Fukuda et al., 1984). ...
Anxiety disorder is a prevalent psychiatric disease and imposes a significant influence on cardiovascular disease (CVD). Numerous evidence support that anxiety contributes to the onset and progression of various CVDs through different physiological and behavioral mechanisms. However, the exact role of nuclei and the association between the neural circuit and anxiety disorder in CVD remains unknown. Several anxiety-related nuclei, including that of the amygdala, hippocampus, bed nucleus of stria terminalis, and medial prefrontal cortex, along with the relevant neural circuit are crucial in CVD. A strong connection between these nuclei and the autonomic nervous system has been proven. Therefore, anxiety may influence CVD through these autonomic neural circuits consisting of anxiety-related nuclei and the autonomic nervous system. Neuromodulation, which can offer targeted intervention on these nuclei, may promote the development of treatment for comorbidities of CVD and anxiety disorders. The present review focuses on the association between anxiety-relevant nuclei and CVD, as well as discusses several non-invasive neuromodulations which may treat anxiety and CVD.
... In rodents, the NTS is traditionally, if somewhat arbitrarily, divided into two parts, sometimes three, 13 based on their relative rostrocaudal location 10 Figure 1C). In coronal sections, the NTS is oval in appearance at more rostral levels ( Figure 1D) but takes a triangular shape at the level of the AP, with the DMV situated at its ventral border. ...
The body and brain are in constant two‐way communication. Driving this communication is a region in the lower brainstem: the dorsal vagal complex. Within the dorsal vagal complex, the caudal nucleus of the solitary tract (cNTS) is a major first stop for incoming information from the body to the brain carried by the vagus nerve. The anatomy of this region makes it ideally positioned to respond to signals of change in both emotional and bodily states. In turn, the cNTS controls the activity of regions throughout the brain that are involved in the control of both behaviour and physiology. This review is intended as a help for anyone with an interest in the cNTS. First, I provide an overview of the architecture of the cNTS and outline the wide range of neurotransmitters expressed in subsets of neurons in the cNTS. I then in detail discuss the known inputs and outputs of the cNTS and briefly highlight what is known regarding the neurochemical makeup and function of those connections. I then discuss one group of cNTS neurons: glucagon‐like peptide‐1 (GLP‐1)‐expressing neurons. GLP‐1 neurons serve as a good example of a group of cNTS neurons, which receive input from varied sources and have the ability to modulate both behaviour and physiology. Finally, I consider what we might learn about other cNTS neurons from our study of GLP‐1 neurons and why it is important to remember that the manipulation of molecularly defined subsets of cNTS neurons is likely to affect physiology and behaviours beyond those monitored in individual experiments. This article is protected by copyright. All rights reserved.
... It remains to be elucidated whether other neurological and behavioral processes, in addition to enhanced satiation, contribute to differential effects of amylin and sCT. The LPBN receives a variety of visceral signals from the caudal hindbrain and also communicates with forebrain areas, including the CeA [12,18,19]. Ablation of the LPBN reduces the anorectic effect of amylin and its ability to activate CeA neurons [7]. ...
Background
The pancreatic hormone amylin and its long-acting analogs (e.g., salmon calcitonin (sCT)) are potential anti-obesity treatments. Amylin and sCT act centrally to reduce food intake by activating neurons in the area postrema (AP) that project to the lateral parabrachial nucleus (LPBN).
Objectives
The behavioral mechanisms and the neuronal pathways mediated by amylin and sCT are not fully understood and it is unclear to what extent sCT and amylin engage overlapping or distinct neuronal subpopulations to reduce food intake. We here hypothesize that amylin and sCT recruit different LPBN neuronal population to mediate their anorectic effects.
Results
Our results indicate that permanent or transient inhibition of calcitonin gene related peptide (CGRP) neurons in LPBN blunts sCT-, but not amylin-induced anorexia and neuronal activation. Importantly, sCT but not amylin induces behaviors indicative of malaise including conditioned affective aversion, nausea, emesis, and conditioned avoidance; the latter mediated by CGRPLPBN neurons.
Conclusions
Together, the present study highlights that although amylin and sCT comparably decrease food intake, sCT is distinctive from amylin in the activation of anorectic neuronal pathways associated with malaise.
... 123 ), whereas neurons in the mesencephalic nucleus of the trigeminal nerve are mostly tuned to the mechanical stimulation of the teeth 124 . Projections from both the NTS and sen sory trigeminal nerve nuclei converge on the pontine parabrachial nucleus 125 , which contains many neurons that respond to mechanical stimulation of multiple oral sites 126 . Notably, a recent study found that Pdyn + parabrachial nucleus neurons are activated by tactile stimulation of the oral and pharyngeal cavities and that these neurons receive monosynaptic inputs from the rostral NTS and trigeminal nerve nuclei 17 . ...
Eating and drinking generate sequential mechanosensory signals along the digestive tract. These signals are communicated to the brain for the timely initiation and regulation of diverse ingestive and digestive processes - ranging from appetite control and tactile perception to gut motility, digestive fluid secretion and defecation - that are vital for the proper intake, breakdown and absorption of nutrients and water. Gut mechanosensation has been investigated for over a century as a common pillar of energy, fluid and gastrointestinal homeostasis, and recent discoveries of specific mechanoreceptors, contributing ion channels and the well-defined circuits underlying gut mechanosensation signalling and function have further expanded our understanding of ingestive and digestive processes at the molecular and cellular levels. In this Review, we discuss our current understanding of the generation of mechanosensory signals from the digestive periphery, the neural afferent pathways that relay these signals to the brain and the neural circuit mechanisms that control ingestive and digestive processes, focusing on the four major digestive tract parts: the oral and pharyngeal cavities, oesophagus, stomach and intestines. We also discuss the clinical implications of gut mechanosensation in ingestive and digestive disorders.
... Furthermore, the laryngeal and articulatory proprioceptive and tactile information from most laryngeal and articulatory muscles are also transferred to NST via the vagus nerve (Altschuler et al., 1989;Hayakawa et al., 2001;Mifflin, 1993;Patrickson et al., 1991;Travers and Norgren, 1995). The NST itself has strong connections to several relay stations of the vocal motor network in the brainstem (Hage and Nieder, 2016) such as the PAG (Bandler and Tork, 1987;Keay et al., 1997;Mantyh, 1982), the ventrolateral parabrachial region as well as the reticular formation encompassing parts of the putative vocal pattern generator (Beckstead et al., 1980;Ezure et al., 1998;Fort et al., 1994;Herbert et al., 1990;Slugg and Light, 1994), which has direct access to all phonatory motoneuron pools (Mantyh, 1983;Meller and Dennis, 1991). Our findings suggest that the somatosensory inputs derived from the cardiorespiratory, phonatory, and articulatory systems are key aspects for gating vocal initiation being essential for the optimization of the cardiorespiratory status during natural vocal production to minimize energy expenditure. ...
Communication is a keystone of animal behavior. However, the physiological states underlying natural vocal signaling are still largely unknown. In this study, we investigated the correlation of affective vocal utterances with concomitant cardiorespiratory mechanisms. We telemetrically recorded electrocardiography, blood pressure, and physical activity in six freely moving and interacting cynomolgus monkeys (Macaca fascicularis). Our results demonstrate that vocal onsets are strengthened during states of sympathetic activation, and are phase locked to a slower Mayer wave and a faster heart rate signal at ∼2.5 Hz. Vocalizations are coupled with a distinct peri-vocal physiological signature based on which we were able to predict the onset of vocal output using three machine learning classification models. These findings emphasize the role of cardiorespiratory mechanisms correlated with vocal onsets to optimize arousal levels and minimize energy expenditure during natural vocal production.
... Most studies traced projections of mature nuclei in adult brains. For example, projections from the NTS were examined in adult rodent brains by multiple antero/retrograde labeling approaches, revealing complex projections that ascend in ipsi/contralateral ventral/dorsal paths to innervate different sub-nuclear sites in the parabrachial nucleus (PBN), RTN, rostral ventrolateral medullary nucleus as well as within the respiratory compartments of the rostroventral respiratory group, preBötC and BötC nuclei (Herbert et al., 1990;Williams et al., 1996;Cunningham and Sawchenko, 2000;Karimnamazi et al., 2002;Alheid et al., 2011;Fu et al., 2019). Recently, a subpopulation of aldosterone-sensitive neurons, which express the dA3 markers Phox2B/Lmx1b, were also found to localize in the NTS and to control sodium appetite by projecting anteriorly to the PBN and pre-locus coeruleus (pLC) complex in the prepontine hindbrain (r1) as well as to the bed nucleus of the stria terminalis in the forebrain (Gasparini et al., 2018). ...
Unraveling the inner workings of neural circuits entails understanding the cellular origin and axonal pathfinding of various neuronal groups during development. In the embryonic hindbrain, different subtypes of dorsal interneurons (dINs) evolve along the dorsal-ventral (DV) axis of rhombomeres and are imperative for the assembly of central brainstem circuits. dINs are divided into two classes, class A and class B, each containing four neuronal subgroups (dA1-4 and dB1-4) that are born in well-defined DV positions. While all interneurons belonging to class A express the transcription factor Olig3 and become excitatory, all class B interneurons express the transcription factor Lbx1 but are diverse in their excitatory or inhibitory fate. Moreover, within every class, each interneuron subtype displays its own specification genes and axonal projection patterns which are required to govern the stage-by-stage assembly of their connectivity toward their target sites. Remarkably, despite the similar genetic landmark of each dINs subgroup along the anterior-posterior (AP) axis of the hindbrain, genetic fate maps of some dA/dB neuronal subtypes uncovered their contribution to different nuclei centers in relation to their rhombomeric origin. Thus, DV and AP positional information has to be orchestrated in each dA/dB subpopulation to form distinct neuronal circuits in the hindbrain. Over the span of several decades, different axonal routes have been well-documented to dynamically emerge and grow throughout the hindbrain DV and AP positions. Yet, the genetic link between these distinct axonal bundles and their neuronal origin is not fully clear. In this study, we reviewed the available data regarding the association between the specification of early-born dorsal interneuron subpopulations in the hindbrain and their axonal circuitry development and fate, as well as the present existing knowledge on molecular effectors underlying the process of axonal growth.
Oxytocin (OXT), a neuropeptide originating from the hypothalamus and traditionally associated with peripheral functions in parturition and lactation, has emerged as a pivotal player in the central regulation of the autonomic nervous system (ANS). This comprehensive ANS, comprising sympathetic, parasympathetic, and enteric components, intricately combines sympathetic and parasympathetic influences to provide unified control. The central oversight of sympathetic and parasympathetic outputs involves a network of interconnected regions spanning the neuroaxis, playing a pivotal role in the real-time regulation of visceral function, homeostasis, and adaptation to challenges. This review unveils the significant involvement of the central OXT system in modulating autonomic functions, shedding light on diverse subpopulations of OXT neurons within the paraventricular nucleus of the hypothalamus and their intricate projections. The narrative progresses from the basics of central ANS regulation to a detailed discussion of the central controls of sympathetic and parasympathetic outflows. The subsequent segment focuses specifically on the central OXT system, providing a foundation for exploring the central role of OXT in ANS regulation. This review synthesizes current knowledge, paving the way for future research endeavors to unravel the full scope of autonomic control and understand multifaceted impact of OXT on physiological outcomes.
Autism spectrum disorder (ASD) is a complex neurodevelopmental condition mainly characterized by social impairments and repetitive behaviors. Among these core symptoms, a notable aspect of ASD is the presence of emotional complexities, including high rates of anxiety disorders. The inherent heterogeneity of ASD poses a unique challenge in understanding its etiological origins, yet the utilization of diverse animal models replicating ASD traits has enabled researchers to dissect the intricate relationship between autism and atypical emotional processing. In this review, we delve into the general findings about the neural circuits underpinning one of the most extensively researched and evolutionarily conserved emotional states: fear and anxiety. Additionally, we explore how distinct ASD animal models exhibit various anxiety phenotypes, making them a crucial tool for dissecting ASD's multifaceted nature. Overall, to a proper display of fear response, it is crucial to properly process and integrate sensorial and visceral cues to the fear‐induced stimuli. ASD individuals exhibit altered sensory processing, possibly contributing to the emergence of atypical phobias, a prevailing anxiety disorder manifested in this population. Moreover, these individuals display distinctive alterations in a pivotal fear and anxiety processing hub, the amygdala. By examining the neurobiological mechanisms underlying fear and anxiety regulation, we can gain insights into the factors contributing to the distinctive emotional profile observed in individuals with ASD. Such insights hold the potential to pave the way for more targeted interventions and therapies that address the emotional challenges faced by individuals within the autism spectrum.
The secondary general visceral sensory nucleus (SVN) receives ascending fibers from the commissural nucleus of Cajal (NCC), or the primary general visceral sensoru in the medulla oblongata of teleosts. However, the full set of fiber connections of the SVN have been studied only in the Nile tilapia. We have investigated the connections of the SVN in goldfish by tracer injection experiments to the nucleus. We paid special attention to the possible presence of spinal afferents, since the spinal cord projects to the lateral parabrachial nucleus, or the presumed homologue of SVN, in mammals. We found that the SVN indeed receives spinal projections. Spinal terminals were restricted to a region ventrolaterally adjacent to the terminal zone of NCC fibers, suggesting that the SVN can be subdivided into two subnuclei: the commissural nucleus‐recipient (SVNc) and spinal‐recipient (SVNsp) subnuclei. Tracer injections to the SVNc and SVNsp as well as reciprocal injections to the diencephalon revealed that both subnuclei project directly to diencephalic structures, such as the posterior thalamic nucleus and nucleus of lateral recess, although diencephalic projections of the SVNsp were rather sparse. The SVNsp appears to send fibers to more wide‐spread targets in the preoptic area than the SVNc does. The SVNc projects to the telencephalon, while the SVNsp sends scarce or possibly no fibers to the telencephalon. Another notable difference was that the SVNsp gives rise to massive projections to the dorsal diencephalon (ventromedial thalamic, central posterior thalamic, and periventricular posterior tubercular nuclei). These differential connections of the subnuclei may reflect discrete functional significances of the general visceral sensory information mediated by the medulla oblongata and spinal cord.
A previous study (T. V. Jaeger & D. van der Kooy, 1993) has implicated a visceral and taste region (parabrachial nucleus), but not mesolimbic dopamine terminal fields (nucleus accumbens), as a substrate for opiate discriminative effects. The authors now show that (a) morphine's discriminative effects in the parabrachial nucleus (PBN) require the activation of opiate receptors; (b) in rats trained to discriminate morphine from saline, infusions of morphine into the ventral tegmental area (VTA) do not generalize to the systemic training condition; (c) infusions of morphine into the PBN, but not the VTA, serve as a stimulus for the acquisition of discrimination learning; and (d) morphine applied to the VTA, but not the PBN, is motivating. The data show that the motivating and discriminative effects of morphine are processed separately by the brain. Further, discriminative drug effects are neither necessary nor sufficient for opiate motivational effects.
Lesions in the gustatory zone of the parabrachial nuclei (PBN) severely impair acquisition of a conditioned taste aversion (CTA) in rats. To test whether this deficit has a memorial basis, intact rats (n = 15) and rats with PBN lesions (PBNX; n = 10) received seven intraoral taste stimulus infusions (30 s, 0.5 ml) distributed over a 30.5-min period after either LiCl or NaCl injection. This task measures the rapid formation of a CTA and has minimum demands on memory. LiCl-injected intact rats progressively changed their oromotor response profile from one of ingestion to one of aversion. NaCl-injected intact rats did not change their ingestive pattern of responding. In contrast, there was no difference between LiCl- and NaCl-injected PBNX rats. These same PBNX rats failed to avoid licking the taste stimulus when tested in a different paradigm. A simple impairment in a memorial process is not likely the basis for the CTA deficit.
Vagal sensory inputs to the brainstem can alter breathing through the modulation of pontomedullary respiratory circuits. In this study, we set out to investigate the localised effects of modulating lateral parabrachial nucleus (LPB) activity on vagally-evoked changes in breathing pattern. In isoflurane-anaesthetised and instrumented mice, electrical stimulation of the vagus nerve (eVNS) produced stimulation frequency-dependent changes in diaphragm electromyograph (dEMG) activity with an evoked tachypnoea and apnoea at low and high stimulation frequencies, respectively. Muscimol microinjections into the LPB significantly attenuated eVNS-evoked respiratory rate responses. Notably, muscimol injections reaching the caudal LPB, previously unrecognised for respiratory modulation, potently modulated eVNS-evoked apnoea, whilst muscimol injections reaching the intermediate LPB selectively modulated the eVNS-evoked tachypnoea. The effects of muscimol on eVNS-evoked breathing rate changes occurred without altering basal eupneic breathing. These results highlight novel roles for the LPB in regulating vagally-evoked respiratory reflexes.
Excitatory interneurons in the superficial dorsal horn (SDH) are heterogeneous, and include a class known as vertical cells, which convey information to lamina I projection neurons. We recently used pro-NPFF antibody to reveal a discrete population of excitatory interneurons that express neuropeptide FF (NPFF). Here, we generated a new mouse line (NPFFCre) in which Cre is knocked into the Npff locus, and used Cre-dependent viruses and reporter mice to characterise NPFF cell properties. Both viral and reporter strategies labelled many cells in the SDH, and captured most pro-NPFF-immunoreactive neurons (75–80%). However, the majority of labelled cells lacked pro-NPFF, and we found considerable overlap with a population of neurons that express the gastrin-releasing peptide receptor (GRPR). Morphological reconstruction revealed that most pro-NPFF-containing neurons were vertical cells, but these differed from GRPR neurons (which are also vertical cells) in having a far higher dendritic spine density. Electrophysiological recording showed that NPFF cells also differed from GRPR cells in having a higher frequency of miniature EPSCs, being more electrically excitable and responding to a NPY Y1 receptor agonist. Together, these findings indicate that there are at least two distinct classes of vertical cells, which may have differing roles in somatosensory processing.
Taste neophobia, the rejection of novel tastes or foods, involves an interplay of various brain regions encompassing areas within the central gustatory system, as well as nuclei serving other functions. Previous findings, utilising c-Fos imaging, identified several brain regions which displayed higher activity after ingestion of a novel taste as compared to a familiar taste. The present study extends this analysis to include additional regions suspected of contributing to the neurocircuitry involved in evoking taste neophobia. Our data show increased c-Fos expression in the basolateral amygdala, central nucleus of the amygdala, gustatory portion of the thalamus, gustatory portion of the insular cortex and the medial and lateral regions of the parabrachial nucleus. These results confirm the contribution of areas previously identified as active during ingestion of novel tastes and expose additional areas that express elevated levels of c-Fos under these conditions, thus adding to the neural network involved in the detection and initial processing of taste novelty.
Objectives
To examine the role of neurons of the pontine respiratory group (PRG) overlapping with the Kölliker-Fuse nucleus in the regulation of swallowing, we compared the activity of swallowing motor activities and interneuron discharge in the dorsal swallowing group in the medulla before and after pharmacological inhibition of the PRG.
Methods
In 23 in situ perfused brainstem preparation of rats, we recorded the activities of the vagus (VNA), hypoglossal (HNA), and phrenic nerves (PNA), and swallowing interneurons of the dorsal medulla during fictive swallowing elicited by electrical stimulation of the superior laryngeal nerve or oral water injection. Subsequently, respiratory- and swallow-related motor activities and single unit cell discharge were assessed before and after local microinjection of the GABA-receptor agonist muscimol into the area of PRG ipsilateral to the recording sites of swallowing interneurons.
Results
After muscimol injection, the amplitude and duration of swallow-related VNA bursts decreased to 71.3 ± 2.84 and 68.1 ± 2.76% during electrically induced swallowing and VNA interburst intervals during repetitive swallowing decreased. Similar effects were observed for swallowing-related HNA. The swallowing motor activity was similarly qualitatively altered during physiologically induced swallowing. All 23 neurons were changed in either discharge duration or frequency after PRG inhibition, however, the general discharge patterns in relation to the motor output remained unchanged.
Conclusion
Descending synaptic inputs from PRG provide control of the primary laryngeal sensory gate and synaptic activity of the PRG partially determine medullary cell and cranial motor nerve activities that govern the pharyngeal stage of swallowing.
The depth, rate, and regularity of breathing change following transition from wakefulness to sleep. Interactions between sleep and breathing involve direct effects of the central mechanisms that generate sleep states exerted at multiple respiratory regulatory sites, such as the central respiratory pattern generator, respiratory premotor pathways, and motoneurons that innervate the respiratory pump and upper airway muscles, as well as effects secondary to sleep-related changes in metabolism. This chapter discusses respiratory effects of sleep as they occur under physiologic conditions. Breathing and central respiratory neuronal activities during nonrapid eye movement (NREM) sleep and REM sleep are characterized in relation to activity of central wake-active and sleep-active neurons. Consideration is given to the obstructive sleep apnea syndrome because in this common disorder, state-dependent control of upper airway patency by upper airway muscles attains high significance and recurrent arousals from sleep are triggered by hypercapnic and hypoxic episodes. Selected clinical trials are discussed in which pharmacological interventions targeted transmission in noradrenergic, serotonergic, cholinergic, and other state-dependent pathways identified as mediators of ventilatory changes during sleep. Central pathways for arousals elicited by chemical stimulation of breathing are given special attention for their important role in sleep loss and fragmentation in sleep-related respiratory disorders.
Extracellular fluids, including blood, lymphatic fluid, and cerebrospinal fluid, are collectively called body fluids. The Na+ concentration ([Na+]) in body fluids is maintained at 135-145 mM and is broadly conserved among terrestrial animals. Homeostatic osmoregulation by Na+ is vital for life because severe hyper- or hypotonicity elicits irreversible organ damage and lethal neurological trauma. To achieve "body fluid homeostasis" or "Na homeostasis", the brain continuously monitors [Na+] in body fluids and controls water/salt intake and water/salt excretion by the kidneys. These physiological functions are primarily regulated based on information on [Na+] and relevant circulating hormones, such as angiotensin II, aldosterone, and vasopressin. In this review, we discuss sensing mechanisms for [Na+] and hormones in the brain that control water/salt intake behaviors, together with the responsible sensors (receptors) and relevant neural pathways. We also describe mechanisms in the brain by which [Na+] increases in body fluids activate the sympathetic neural activity leading to hypertension.
Vocalizations are often elaborate, rhythmically structured behaviors. Vocal motor patterns require close coordination of neural circuits governing the muscles of the larynx, jaw, and respiratory system. In the elaborate vocalization of Alston's singing mouse (Scotinomys teguina) each note of its rapid, frequency-modulated trill is accompanied by equally rapid modulation of breath and gape. To elucidate the neural circuitry underlying this behavior, we introduced the polysynaptic retrograde neuronal tracer pseudorabies virus (PRV) into the cricothyroid and digastricus muscles, which control frequency modulation and jaw opening, respectively. Each virus singly labels ipsilateral motoneurons (nucleus ambiguus for cricothyroid, and motor trigeminal nucleus for digastricus). We find that the two isogenic viruses heavily and bilaterally colabel neurons in the gigantocellular reticular formation, a putative central pattern generator. The viruses also show strong colabeling in compartments of the midbrain including the ventrolateral periaqueductal gray and the parabrachial nucleus, two structures strongly implicated in vocalizations. In the forebrain, regions important to social cognition and energy balance both exhibit extensive colabeling. This includes the paraventricular and arcuate nuclei of the hypothalamus, the lateral hypothalamus, preoptic area, extended amygdala, central amygdala, and the bed nucleus of the stria terminalis. Finally, we find doubly labeled neurons in M1 motor cortex previously described as laryngeal, as well as in the prelimbic cortex, which indicate these cortical regions play a role in vocal production. The progress of both viruses is broadly consistent with vertebrate-general patterns of vocal circuitry, as well as with circuit models derived from primate literature.
GABAA receptor activation with agonist muscimol in the lateral parabrachial nucleus (LPBN) induces 0.3 M NaCl intake. In the present study, we investigated water and 0.3 M NaCl intake in male adult rats treated with losartan (angiotensin AT1 receptor antagonist) or MeT-AVP (V1-type vasopressin receptor antagonist) combined with muscimol or methysergide (5-HT2 antagonist) into the LPBN in rats treated with intragastric 2 M NaCl. After 2 M NaCl load and bilateral injections of muscimol (0.5 nmol/0.2 µL) into the LPBN, rats ingested water and 0.3 M NaCl. The pre-treatment of the LPBN with MeT-AVP (1 nmol/0.2 µL) but not losartan (50 µg/0.2 µL) in muscimol treated rats reduced 0.3 M NaCl intake. The pre-treatment of the LPBN with MeT-AVP did not modify the increased 0.3 M NaCl intake in rats treated with methysergide (4 µg/0.2 µL), suggesting that the effect of MeT-AVP was not due to non-specific inhibition of ingestive behavior. The results suggest that endogenous vasopressin in the LPBN facilitates the effects of GABAergic activation driving cell-dehydrated male rats to ingest 0.3 M NaCl.
Diverse neurons in the parabrachial nucleus (PB) communicate with widespread brain regions. Despite evidence linking them to a variety of homeostatic functions, it remains difficult to determine which PB neurons influence which functions because their subpopulations intermingle extensively. An improved framework for identifying these intermingled subpopulations would help advance our understanding of neural circuit functions linked to this region. Here, we present the foundation of a developmental-genetic ontology that classifies PB neurons based on their intrinsic, molecular features. By combining transcription factor labeling with Cre fate-mapping, we find that the PB is a blend of two, developmentally distinct macropopulations of glutamatergic neurons. Neurons in the first macropopulation express Lmx1b (and, to a lesser extent, Lmx1a) and are mutually exclusive with those in a second macropopulation, which derive from precursors expressing Atoh1. This second, Atoh1-derived macropopulation includes many Foxp2-expressing neurons, but Foxp2 also identifies a subset of Lmx1b-expressing neurons in the Kölliker-Fuse nucleus (KF) and a population of GABAergic neurons ventrolateral to the PB ("caudal KF"). Immediately ventral to the PB, Phox2b-expressing glutamatergic neurons (some co-expressing Lmx1b) occupy the KF, supratrigeminal nucleus, and reticular formation. We show that this molecular framework organizes subsidiary patterns of adult gene expression (including Satb2, Calca, Grp, Pdyn) and predicts output projections to the amygdala (Lmx1b), hypothalamus (Atoh1), and hindbrain (Phox2b/Lmx1b). Using this molecular ontology to organize, interpret, and communicate PB-related information could accelerate the translation of experimental findings from animal models to human patients. This article is protected by copyright. All rights reserved.
In this review, we provide an overview of essential clinical trials examining the effect of vagal nerve stimulation (VNS) in treatment-resistant depression (TRD), the applicable neuroanatomy of the vagus nerve, and the proposed mechanism of action (MOA) of VNS in TRD.
Vagal nerve stimulation (VNS) is currently the only FDA-approved neurostimulation treatment for severe treatment-resistant depression (TRD). The implanted VNS device sends electrical impulses to the left cervical vagus nerve, resulting in stimulation of afferent vagal brainstem pathways known to be associated with mood regulation. Within the last decade, several clinical trials have attempted to further elucidate this effect specifically in TRD. Early clinical trials including the D01, D02, and D03 trials showed promising evidence of the antidepressant efficacy and durability of VNS as a treatment for TRD. Later trials comparing VNS and treatment-as-usual (TAU) resulted in similar findings regarding antidepressant efficacy and durability. VNS was additionally found to be beneficial in improving quality of life and suicidality among unipolar TRD patients and depression among bipolar TRD patients. Ongoing and future studies such as the RECOVER trial continue to investigate the psychiatric benefits of VNS within the TRD population. Although the MOA of VNS in TRD is still not fully understood, recent brain imaging studies and animal studies have proven instrumental in addressing this knowledge gap.
In a previous study (Herbert et al., J. Comp. Neurol. [1990];293:540-580), we demonstrated that the ascending afferent projections from the medulla to the parabrachial nucleus (PB) mark out functionally specific terminal domains within the PB. In this study, we examine the organization of the forebrain afferents to the PB. The PB was found to recive afferents from the infralimbic, the lateral prefrontal, and the insular cortical areas; the dorsomedial, the ventromedial, the median preoptic, and the paraventricualr hypothalamic nuclei; the dorsal, the retrochiasmatic, and the lateral hypothalamic areas; the central nucleus of the amygdala; the substantia innominata; and the bed nucleus of the stria terminalis. In general, forebrain areas tend to innervate the same PB subnuclei from which they receive their input. Three major patterns of afferent termination were noted in the PB; these corresponded to the three primary sources of forebrain input to the PB: the cerebral cortex, the hypothalamus, and the basal forebrain. Hypothalamic afferents innervate predominantly rostral portions of the PB, particularly the central lateral and dorsal lateral subnuclei. The basal forebrain projection to the PB ends densely in the external lateral and waist subnuclei. Cortical afferents terminate most heavily in the caudal half of the PB, particularly in the ventral lateral and medial subnuclei. In addition, considerable topography organization was found within the individual projections. For example, tuberal lateral hypothalamic neurons project heavily to the central lateral subnucleus and lightly to the waist area; in contrast, caudal lateral hypothalamic neurons send a moderately heavy projection to both the central lateral and waist subnuclei. Our results show that the forebrain afferents of the PB are topographically organized. These topographical differences may provide a substrate for the diversity of visceral functions associated with the PB.
The CNS control of the cardiovascular system involves the coordination of a series of complex neural mechanisms which integrate afferent information from a variety of peripheral receptors and produce control signals to effector organs for appropriate physiological responses. Although it is generally thought that these control signals are generated by a network of neural circuits that are widely distributed in the CNS, over the last two decades a considerable body of experimental evidence has accumulated suggesting that several of these circuits involve neurons found on or near the ventral surface of the medulla oblongata. Neurons in the VLM have been shown to be involved in the maintenance of vasomotor tone, in baroreceptor and chemoreceptor (central and peripheral) reflex mechanisms, in mediating the CIR and somatosympathetic reflexes and in the control of the secretion of vasopressin. These physiological functions of VLM neurons have been supported by neuroanatomical and electrophysiological studies demonstrating direct connections with a number of central structures previously implicated in the control of the circulation, including the IML, the site of origin of sympathetic preganglionic axons, and the SON and PVH, the site of origin of neurohypophyseal projecting axons containing AVP.Considerable suggestive evidence has also been obtained regarding the chemical messengers involved in transmitting information from VLM neurons to other central structures. There have been developments suggesting a role for monoamines and neuropeptides in mediating the neural and humoral control of SAP by neurons in the VLM.This review presents a synthesis of the literature suggesting a main role for VLM neurons in the control of the circulation.
A new neuroanatomical method for tracing connections in the central nervous system based on the anterograde axonal transport of the kidney bean lectin,Phaseolus vulgaris-leucoagglutinin (PHA-L) is described. The method, for which a detailed protocol is presented, offers several advantages over present techniques. First, when the lectin is delivered iontophoretically, PHA-L injection sites as small as 50–200 μm in diameter can be produced, and are clearly demarcated since the neurons within the labeled zone are completely filled. Second, many morphological features of such filled neurons are clearly demonstrated including their cell bodies, axons, dendritic arbors and even dendritic spines. Third, there is some evidence to suggest that only the neurons at the injection site that are filled transport demonstrable amounts of the tracer, raising the possibility that the effective injection site can be defined quite precisely. Fourth, even with the most restricted injections, the morphology of the labeled axons and axon terminals is clearly demonstrated; this includes boutons en passant, fine collateral branches, and various terminal specialization, all of which can be visualized as well as in the best rapid Golgi preparations. Fifth, when introduced iontophoretically, PHA-L appears to be transported preferentially in the anterograde direction; only rarely is it transported retrogradely. Sixth, PHA-L does not appear to be taken up and transported effectively by fibers of passage. Seventh, there is no discernible degradation of the transported PHA-L with survival times of up to 17 days. Finally, since the transported marker can be demonstrated with either peroxidase or fluorescent antibody techniques, it may be used in conjunction with other neuroanatomical methods. For example, double anterograde labeling experiments can be done using the autoradiographic method along with immunoperoxidase localization of PHA-L, and the retrogradely transported fluorescent dyes can be visualized in the same tissue sections as PHA-L localized with immunofluorescence techniques.
Axonal transport and immunohistochemical methods were used to investigate the anatomical and biochemical organization of projections from the nucleus of the solitary tract (NTS) to the rostral, esophageal, part of the nucleus ambiguus (NA) in the rat. Discrete iontophoretic deposits of a retrogradely transported tracer, fluorogold, placed in the rostral NA labeled a column of cells within the NTS, termed the central part of the NTS (after Ross et al., 1985), situated just medial to the solitary tract and extending from about 300 to 1000 microns rostral to the obex. Iontophoretic deposits of the anterogradely transported tracer, Phaseolus vulgaris-leucoagglutinin (PHA-L), placed in the central part of the NTS gave rise to dense and topographically restricted projections to the rostral NA. More caudal and ventral aspects of the NA did not receive prominent inputs from the central part of the NTS, and deposits that spared the central part of the NTS gave rise to only sparse projections to the rostral NA. Antisera against somatostatin-28 (SS-28) stained cell bodies within the central part of the NTS. In addition, a double-labeling procedure, capable of colocalizing anterogradely transported PHA-L and endogenous peptides to individual fibers and/or terminals, demonstrated an appreciable number of SS-28-immunoreactive terminals within the rostral NA that arose from the NTS. Correspondingly, unilateral lesions that involved the central part of the NTS resulted in a marked depletion of SS-28 immunoreactivity in the ipsilateral rostral NA. These data provide evidence for a discrete, partly somatostatinergic, projection from the central part of the NTS to the rostral NA. Anatomical and physiological studies implicating the central part of the NTS and the rostral NA in esophageal function suggest this pathway to be involved in the reflex control of esophageal motility.
We sought to determine the ultrastructural localization and the extrinsic sources of the catecholamine-synthesizing enzyme, tyrosine hydroxylase (TH), in the lateral parabrachial region (PBR) of adult male rats. In the first portion of the study, a rabbit antiserum to TH was immunocytochemically localized in coronal sections through the lateral PBR from acrolein-fixed brains using the peroxidase-antiperoxidase method. Electron-microscopic analysis revealed that perikarya and dendrites with peroxidase immunoreactivity for TH constituted only 17% of the total labeled profiles. Afferents to the TH-labeled perikarya and dendrites usually failed to exhibit immunoreactivity and were thus considered noncatecholaminergic. Somatic synapses were most commonly detected on small immunoreactive perikarya in the central lateral nucleus of the PBR. Other labeled perikarya located in the dorsal lateral or ventral lateral nuclei received few somatic synapses and were morphologically distinct in terms of their larger size, infolded nuclear membrane, and abundance of cytoplasmic organelles. Axons and axon terminals with peroxidase immunoreactivity constituted the remaining labeled profiles in the lateral PBR. These terminals primarily formed symmetric synapses with unlabeled and a few labeled dendrites. The labeled axon terminals were categorized into 2 types: Type I was small (0.3-0.6 micron), contained many small clear vesicles, and exhibited few well-defined synaptic densities. The second type was large (0.8-1.4 micron), contained both small clear and large dense core vesicles, and exhibited well-defined synaptic densities. The 2 types of terminals were morphologically similar to dopaminergic terminals. The location of catecholaminergic neurons contributing to the TH-labeled terminals was determined by combining peroxidase-antiperoxidase immunocytochemistry for TH with retrograde transport of wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP). The tracer was unilaterally injected into the PBR of anesthetized adult rats. Immunocytochemical labeling for TH was seen as a brown reaction product within neurons in known catecholaminergic cell groups. A black granular reaction product formed by a cobalt-intensified and diaminobenzidine-stabilized tetramethyl benzidine reaction for WGA-HRP was evident within many TH-labeled and unlabeled neurons.(ABSTRACT TRUNCATED AT 400 WORDS)
Neurons immunocytochemically labeled with the adrenaline‐synthesizing enzyme phenylethanolamine N‐methyltransferase were mapped in the brain of rat pretreated with colchicine. In medulla, immunoreactive cells in the C1 and C2 groups were distributed in a more complex manner than described previously.
C1 neurons were identified in the reticular formation of ventrolateral medulla and were organized into two populations:(1) a cell column extending throughout the ventrolateral medulla, and lying ventral to the ambiguus cell group and either dorsal to the precerebellar lateral reticular nucleus or interposed between its two subdivisions; (2) a rostral cell cluster forming medial to the column at caudal levels and enlarging close to and in parallel with the ventral surface of the rostral ventrolateral medulla. A large proportion of cells and processes of the rostral cell group were oriented medially and ventromedially. Processes of C1 neurons were traced dorsally toward the nucleus tractus solitarii, dorsal motor nucleus, and principal tegmental adrenergic bundle, ventrally toward the ventral surface, laterally toward the trigeminal complex, and medially or ventromedially toward the raphe.
C2 neurons were located in the dorsomedial medulla and were subdivided into four distinct populations:(1) neurons in the rostral nucleus paragigantocellularis pars dorsalis (NGCd) and medial longitudinal fasciculus (MLF) were contiguous and similar in size and shape, with their long diameters oriented horizontally or diagonally along several axes; (2) neurons of the periventricular gray were located in a cytoarchitecturally undefined area dorsal to the MLF; these cells were ovoid, smaller, and organized more compactly than those in the NGCd‐MLF; (3) a cell group in the rostromedial nucleus tractus solitarii (NTS) and dorsal motor nucleus overflowed caudally into the intermediate thirds of both structures; and (4) a parvicellular group in the NTS was compactly organized in the dorsolateral NTS and was best developed at the level of the area postrema. Processes of C2 neurons were generally directed sagitally, medially, and laterally along the ventricular floor and ventrally or medially toward the raphe; other fibers arborized and terminated within the NTS and dorsal motor nucleus.
In the medulla, local processes were traced from C1 and C2 neurons directly into respective ventral and dorsal parts of the medullary raphe and surrounding intraparenchymal blood vessels. Fibers from these neurons were also followed, respectively, onto the ventral subpial surface and the floor of the fourth ventricle.
A new system of hypothalamic neurons expression catalytically active PNMT but none of the other enzymes required for catecholamine synthesis was identified in the lateral and perifornical nuclei and zona incerta; a substantial, although lower, number of cells were also seen in dorsal andmedial hypothalamus. The absence of tyrosine hydroxylase, aromatic L‐amino acid decarboxylase, and dopamine‐B‐hydroxylase in areas populated by the majority of these neurons suggests either that (1) quantities of these enzymes may normally be too low for immunocytochemical detection or that (2) noradrenaline may be taken up by and converted in situ to adrenaline or that (3) PNMT‐stained cells in the hypothalamus may methylate as‐yet‐ unrecognized amines.
The present series of experiments was designed to study the organization of preterminai processes and synaptic boutons of single physiologically identified slowly adapting receptor (SAR) pulmonary stretch afferent fibers. Intra‐axonally injected horseradish peroxidase‐wheat germ agglutinin (HRP‐WGA) conjugate was used as the label. In the first paper, we describe the pattern of arborization of axon collaterals from single physiologically identified SAR afferent fibers evident in the various subnuclei of the nucleus of the tractus solitarius (nTS). In the second paper, details are presented regarding the ultrastructure of these synaptic boutons and axon collaterals.
A number of significant findings resulted from this study: (1) A single lung stretch SAR afferent fiber arborized over a considerable distance rostrocaudally in the brain stem (1,700–2,100 μm). (2) A single lung stretch SAR afferent fiber terminated as hundreds of bouton terminals (650–1,180). (3) There was a remarkable consistency in the subnuclei of the nTS that received these terminal arborizations of SAR afferents. (4) The ventral (vnTS), intermediate (nI), ventrolateral (vInTS), and interstitial (ni) subnuclei of the nTS were the only regions of the nTS receiving bouton terminals of SAR afferent fibers. (5) Under the light microscope the pattern of termination of SAR afferents was similar in all the axons studied in this series. (6) The injected parent axon in each case could be followed in the TS at all levels and remained consistent with regard to position and orientation and could be traced rostrally to levels as far as 3.5 mm rostral to the obex whereas the region of terminal arborization was located around 1.7–2.1 mm rostral to the obex. This pattern indicates that a single lung stretch SAR afferent fiber descends caudally upon entering the nTS. In the cat vagal afferent fibers are known to enter the medulla at levels between 0.5 mm and 3.2 mm rostral to the obex (Kalia and Mesulam, '80a).
The results of the light microscopic analysis presented in this article indicate that lung stretch (SAR) afferents from the lungs and tracheobronchial tree have distinctly localized patterns of distribution in the nTS. In addition, these findings support the concept that representation of pulmonary afferents in the medulla is constituted by a differentiated distribution of nerve terminals in the various subnuclei of the nTS. Modality‐specific localization (SAR afferents in this case) appears to be predominant in the n'1'S. The widespread rostrocaudal distribution of the terminal field of a single lung stretch SAR afferent is remarkable. In addition, the finding that the terminals of different SAR afferents are localized in only a few subnuclei of the nTS suggests that specificity exists in this afferent system which could provide the morphological substrate for focussed physiological effects.
The sensory modalities of taste and touch, for the anterior tongue, are relegated to separate cranial nerves. The lingual branch of the trigeminal nerve mediates touch; the chorda tympani branch of the facial nerve mediates taste. The chorda tympani also contains efferent axons which originate in the superior salivatory nucleus. The central projections of these two nerves have been visualized in the hamster by anterograde labelling with horseradish peroxidase (HRP).
Afferent fibers of the chorda tympani distribute to all rostral-caudal levels of the solitary nucleus. They synapse heavily in the dorsal half of the nucleus at its rostral extreme; synaptic endings are sparser, and located lat-erally in caudal region. These taste afferents trave caudally in the solitary tract and reach different levels by a series of collateral branches which extend medially into the solitary nucleus, where they exhibit preterminal and terminal swellings. Taste atferentaxons range in diameter from 0.2 μm to 1.5 μm. The thickest axons project exclusively to the rostral and intermediate subdivisions of the solitary nucleus; the fine ones may distribute predominantly to the caudal subdivision.
Afferent fibers of the lingual nerve terminate heavily in the dorsal one-third of the spinal nucleus of the trigeminal nerve and also as a dense patch in the lateral solitary nucleus at the midpoint between its rostral and caudal poles. This latter projection overlaps that of the chorda tympani. Thus the two sensory nerves which subserve taste and touch from coincident peripheral fields on the tongue converge centrally on the intermediate subdivision of the solitary nucleus.
Efferent neurons of the superior salivatory nucleus were labelled retro-gradely following application of HRP to the chorda tympani. These cells are located ipsilaterally in the medullary reticular formation ventral to the rostral pole of the solitary nucleus; their dendrites are oriented dorsoventrally. The efferent axons course dorsally, form a genu lateral to the facial somato-motor genu, and course ventrolaterally through the spinal nucleus of the trigeminal nerve to exit the brain ventral to the entering facial afferents.
We employed the neural tracers cholera toxin-norseradish peroxidase and wheat germ agglutinin-horseradisn peroxidase to examine the organization of the afferent and efferent connections of the stomach within the medulla oblongata of the rat. The major finding of this study is that gastric motoneurons of the dorsal motor nucleus (DMN) possess numerous dendrites penetrating discrete regions of the overlying nucleus of the solitary tract (NTS). In particular, dendritic labelling was present in areas of NTS which also received terminals of gastric vagal afferent fibers such as the subnucleus gelatinosus, nucleus commissuralis, and medial nucleus of NTS. This codistribution of afferent and efferent elements of the gastric vagus may provide loci for monosynaptic vagovagal interactions. A small number of dendrites of DMN neurons penetrated the ependyma of the fourth ventricle and a few others entered the ventral aspect of the area postrema, thus making possible the direct contact of preganglionic neurons with humoral input from the cerebrospinal fluid and/or the peripheral plasma. Nucleus ambiguus neurons projecting to the stomach predominantly innervate the forestomach. The dendrites of these cells, when labelled, were generally short, and extended beyond the compact cluster of ambiguus neurons in a ventrolateral direction, parallel to the fascicles of vagal efferent fibers traversing the medulla.
The immunocytochemical localization of the biosynthetic enzymes-tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH), and phen-ylethanolamine-N-methyltransferase (PNMT)-was used to determine the cytological features and precise neuroanatomical location of catecholami-nergic neurons in the medulla oblongata of rat. Perikarya labeled with TH were detected in two bilaterally symmetrical columns located in the ventrolateral and dorsomedial medulla. The distribution and the number of neuronal perikarya containing TH were the same as those containing DBH, except in the dorsal motor nucleus of the vagus at the level of the area postrema where the number of neurons immunocytochemically labeled for TH was considerably greater than those labeled for DBH. The detection of perikarya which show immunoreactivity for TH, used in the biosynthesis of dopamine, noradrenaline, and adrenaline, but not DBH, which converts dopamine to noradrenaline, suggests the existence of dopamine-synthesiz-ing neurons in the medulla.
Brainstem projections of the aortic nerve in the rat were studied using the transganglionic transport of horseradish peroxidase. Labeled axons were found to project predominantly to the ipsilateral interstitial nucleus and to the ipsilateral dorsolateral aspect of the nucleus of the solitary tract near the level of the obex. Lighter bilateral projections were also found to the medial, ventrolateral and dorsolateral aspects of the solitary complex, and to the commissural nucleus. These data provide evidence of direct aortic baroreceptor afferent projections to restricted regions of the solitary complex and indicate that these specific areas function in the intergration of the baroreceptor reflex.
Using the cobalt labelling technique in the rat, mesencephalic afferent fibres were shown in all three divisions of the trigeminal nerve. The descending branches of mesencephalic trigeminal neurones extend to the 3rd cervical segment of the spinal cord. Collaterals of this tract terminate in the following structures: the supratrigeminal nucleus, the motor nuclei of V, VII and XII cranial nerves, the reticular formation, a distinct nucleus in the reticular formation and the solitary nucleus.
The medullary distribution of afferent fibers and cells of origin of the cervical vagal trunk and of the vagal innervation of the stomach have been studied using the anterograde and retrograde transport of horseradish peroxidase (HRP). Injections of HRP were made into the cervical vagus nerve, the stomach wall, the proximal small intestine, or the peritoneal cavity. Two to four days following the injections, the rats were perfused and the medullae oblongatae and nodose ganglia were processed using the tetramethyl benzidine method. Cervical vagus nerve injections of HRP resulted in heavy anterograde labeling in the ipsilateral nucleus of the tractus solitarius (NTS) and the commissural nucleus. Lighter labeling was seen in these regions on the contralateral side, but did not extend as far rostrally in the NTS. Labeling was also seen in the area postrema. Retrogade labeling of somata was present in the ipsilateral side in the nodose ganglion, throughout the whole extent of the dorsal motor nucleus of the vagus, much of the nucleus ambiguus and in rostral levels of the cervical spinal cord. After stomach injections, labeling indicative of afferent fibers was observed bilaterally in the dorsomedial and medial portions of the NTS and in the commissural nucleus. Labeled efferent fibres arose from neurons in the dorsal motor nucleus of the vagus, nucleus ambiguus and the cervical spinal cord. Retrogradely labeled somata were found bilaterally, throughout the rostrocaudal length of the dorsal motor nucleus in all cases with stomach injections. In some, but not all cases, labeled somata were seen bilaterally in compact areas within the nucleus ambiguus, particularly rostrally. Control injections of HRP into the intestinal wall and peritoneal cavity indicated that the stomach was the primary source of afferent and efferent labeling in the medulla following subdiaphragmatic injections.
Autonomic preganglionic, sensory, and lower motoneuron perikarya within the central nervous system, as well as cell bodies with axons projecting to the circumventricular organs, are retrogradely labeled with horseradish peroxidase (HRP) delivered to their axon terminals by cerebral and extracerebral blood. Subsequent to vascular injection of HRP into mice, blood‐borne peroxidase passes across permeable vessels in muscle, ganglia, and in all circumventricular organs except for the subcommissural organ in which no leak could be discerned. Brain parenchyma adjacent to each of the permeable circumventricular organs quickly becomes inundated with the protein. By four to six hours post‐injection, this extracellular HRP reaction product has disappeared, and by eight hours perikarya of specific hypothalamic nuclei contain HRP‐positive granules indicative of the intra‐axonal retrograde transport of the protein. Hypothalamic neurons so labeled are presumed to send axons to such circumventricular organs as the median eminence or neurohypophysis and include neurons of the magnocellular neurosecretory supraoptic and paraventricular nuclei, the accessory magnocellular nuclei, the parvicellular arcuate nucleus, and a band of periventricular cells extending rostrally into the medial preoptic area. Labeled somata are also adjacent to the organum vasculosum of the lamina terminalis and in the vertical limb of the nucleus of the diagonal band of Broca. No similarly labeled cell bodies were identified near the subfornical organ.
At 12 hours post‐injection, HRP labeling of specific brain stem and spinal cord somata with axons efferent from the central nervous system indicates that protein from the peripheral blood can be incorporated by neurons of different functional categories for retrograde transport. Thus, blood‐borne peroxidase, imbibed presumably from myoneural clefts by motoneuron axon terminals, is transported to perikarya in cranial motor nerve nuclei III, IV, V, VI, VII, XII, the ambiguus nucleus, and in the ventral horn of the spinal cord. Sensory endings afferent to muscle spindles also take up HRP for retrograde transport, as manifested by the labeling of cell bodies in the mesencephalic nucleus of V. Autonomic preganglionic terminals take up HRP for transport back to their cell bodies in the intermediolateral sympathetic cell column in the spinal cord and to parasympathetic cell groups such as the brain stem dorsal motor vagus and salivatory nuclei.
Three cell groups in the brain stem that presumably have their efferent projections intrinsic to the central nervous system contain peroxidase‐labeled perikarya. These cell groups include a portion of the nucleus of the solitary tract rostral to the area postrema and the noradrenergic A1 and A5 nuclei of Dahlström and Fuxe ('64). The area postrema is thought to receive axon collaterals from the nucleus of the solitary tract (Morest, '60). Of the circumventricular organs, only the median eminence is believed to have a prominent noradrenergic innervation originating from somewhere in the brainstem. The peroxidase‐labeled A1 and A5 neurons may represent the origin of this innervation.
Vascular infusion of peroxidase results in retrograde neuronal labeling of neurosecretory, motor, sensory, and autonomic systems. The inference is made that other substances, such as toxins and neurovirulent viruses, can also enter these neuronal systems, as does peroxidase, from cerebral and extracerebral blood.
Endogenous cytochrome oxidase activity within the mitochondria of neurons and neuropil was demonstrated histochemically under normal and experimental conditions. Since enzymatic changes were noted with chronic neuronal inactivity in the auditory system (Wong-Riley et al), the present study sought to examine functionally induced enzymatic changes in the visual system of kittens. Eight kittens were used experimentally: 5 had monocular lid suture for varying periods of time; one had binocular lid suture followed by monocular suture followed by binocular opening; two had monocular enucleation. All initial procedures were performed before eye opening. Materials from other normal kittens and cats were also used as controls. At the end of the experiments, the animals were perfused with aldehyde solutions and frozen sections of the brains were incubated for cytochrome oxidase activity (a detailed protocol was outlined). The results indicated that the deprivation caused by monocular suture produced a decrease in the cytochrome oxidase staining of the binocular segment of the deprived geniculate laminae. Enucleation yielded a greater decrease in the cytochrome oxidase activity in the affected geniculate laminae. However, the staining in the 'normal' lamina extended across the interlaminar border to include a row of surviving large cells in the 'denervated' lamina. The staining of the monocular segment appeared not to be affected by lid suture, but was decreased by enucleation. At the cortical level, lamina IV in area 17 of normal cats was stained darkly as a continuous band. Following lid suture, this pattern was replaced in part by alternating columns of light and dark staining, suggestive of ocular dominance columns. Thus, a decrease in neuronal activity due to reduced visual stimulation or destruction of the primary afferent nerves led to a significant decrease in the level of oxidative enzyme activity one to several synapses away.
Ascending projections from the caudal (general-visceroceptive) part of the nucleus of the solitary tract (NTS) were studied experimentally in the rat by the aid of the anterograde autoradiographic and the retrograde horseradish peroxidase (HRP) tracer techniques. Microelectrophoretic deposits of tritiated proline and leucine which involved the caudal part of the NTS, the dorsal motor nucleus of the vagus (dmX), and portions of the hypoglossal nucleus, nucleus intercalatus and/or nucleus gracilis were found to label ascending fibers that, besides going to numerous brain stem territories that included prominently the parabrachial area, could also be traced to several forebrain structures, namely, the bed nucleus of the stria terminalis (BST), the paraventricular (PA), dorsomedial (HDM) and arcuate (ARC) nuclei of the hypothalamus, the central nucleus of the amygdaloid complex (AC), the medial preoptic area (PM) and the periventricular nucleus of the thalamus (TPV). Smaller isotope injections almost completely confined to the NTS and dmX resulted in lighter labeling of a similar set of parabrachial and forebrain projections, whereas in another case, in which the deposit was almost exclusively limited to the nucleus gracilis, no label was seen in the aforementioned structures. In another series of experiments, aimed at further localizing the neurons of origin of the prosencephalic projections under consideration, small microelectrophoretic HRP injections confined almost totally to BST, PA, HDM, AC, PM or TPV, as well as both small and large injections involving ARC, resulted in labeled neurons situated in the dorsal medullary region, mainly in the medial portion of the NTS at the level of and caudal to the area postrema.
The efferent projections from the solitary complex to the lower brain stem and spinal cord were studied in the cat with the autoradiographic anterograde axonal transport and retrograde horseradish peroxidase (HRP) techniques. A revised cytoarchitectonic description of the caudal two-thirds of the complex is presented in which the complex was subdivided into six nuclei: lateral, ventrolateral, intermediate, medial, parvocellular, and commissural solitary tract nuclei. Following injections of ³H amino acids into electrophysiologically defined regions of the complex in which cardiac or respiratory units were recorded, labeled fibers could be traced to a number of sites in the caudal brain stem including the medial and lateral parabrachial nuclei, Kölliker-Fuse nucleus and the area ventral to this nucleus, lateral periaqueductal gray matter, ambiguus complex, which consists of the retrofacial, ambiguus and retroambiguus nuclei, ventrolateral reticular nucleus (in an area equivalent to the A1 cell group of Dahlström and Fuxe, '64), medial accessory olive, paramedian reticular formation, and lateral cuneate nucleus. Descending solitario-spinal projections have been traced bilaterally, but predominantly to the contralateral side, to the region of the phrenic motor neurons in the C4-C6 ventral horn, to the thoracic ventral horn, and intermediolateral cell column.
The axonal projections of neurons in and near the nucleus of the solitary tract have been visualized using titrated amino acid autoradiography. Axons of neurons of this nucleus ramify extensively within the nucleus itself, but much less so in the nucleus commissuralis. They also enter cranial motor nuclei within the medulla. Axons originating in the anterior part of the nucleus of the solitary tract extend to the hypoglossal, facial and probably trigeminal motor nuclei, but not to the dorsal motor nucleus of the vagus or the nucleus ambiguus. The posterior part of the nucleus of the solitary tract projects to all these motor nuclei. In the spinal cord solitary nucleus axons remain in the medial gray directly caudal to the solitary nucleus itself. The distribution becomes very weak by C3 after some fibers spread laterally into the caudal trigeminal nucleus. Fibers are labeled in the contralateral ventral columns, but they could not be unequivocably attributed to solitary neurons. Axons ascending from the nucleus of the solitary tract extend no further rostrally than the pons, where they terminate in the caudal end of the parabrachial nuclei.Although often treated as entirely separate systems, the present results indicate that secondary gustatory neurons in the anterior solitary nucleus and secondary visceral afferent neurons in the posterior solitary nucleus have very similar rostral and caudal projections. The pontine parabrachial nuclei, the rostral termination of solitary nucleus neurons, have extensive direct connections to the thalamus, the hypothalamus and the limbic forebrain. Assuming similar connections occur in other mammals, these findings establish the existence of di-synaptic visceral afferent access to the highest autonomic integrative centers in the brain.
In 34 cats 3H-leucine was injected in the pontine and medullary tegmentum. The location of the labelled neurons and the distribution of the labelled fibres and terminals were studied autoradiographically. The findings indicate that the neurons in the bulbar lateral tegmental field (Berman, 1968) represent the main source of the propriobulbar projections to the hypoglossal, facial and motor V nuclei, while those in the medial tegmental field distribute their fibres mainly to the spinal cord. The neurons in the lateral part of the lateral tegmental field give rise to ascending and descending fibres which compose the lateral propriobulbar system, and distribute fibres mainly to ipsilateral bulbar motor nuclei. The neurons in the medial part of the lateral tegmental field compose the medial propriobulbar system, which is organized bilaterally and tends to distribute fibres to the motor nuclei bilaterally. The various neuronal cell groups which project through the medial propriobulbar system to the different motor nuclei bilaterally show relatively less spatial segregation than those which project through the lateral system to these motor nuclei.
The local bulbar connections to the V, VII and XII motor nuclei in the cat have been studied by means of the anterograde fibre degeneration technique in combination with the Fink-Heimer silver impregnation procedure. For this purpose electrolytic lesions were made mainly in the reticular formation of the medulla oblongata and the pons. For control purposes also, extrabulbar lesions were made in the cervical cord and the upper brain-stem and in addition, primary afferent fibres were interrupted by section of the upper cervical and trigeminal roots. The findings indicated the existence of a lateral and a medial propriobulbar fibre system, the former of which projects to the motor nuclei mainly ipsilaterally, while the latter tends to project bilaterally. Since the cells of origin of the propriobulbar fibre systems are difficult to determine by means of the anterograde degeneration technique these systems have also been investigated by means of the labelled amino-acid tracing technique. The findings thus obtained are reported in the adjoining paper.
The projections of a third order gustatory relay in the dorsal pons of rats have been traced using tritiated proline autoradiography and antidromic activation of pontine neurons from electrodes in the thalamus and amygdala. Labelled axons collect in the central tegmental tract and ascend to the thalamic taste area in the medial extension of the ventrobasal complex. The majority of the fibers remain ipsilateral, but a few cross in the rostral pons and midbrain. The largest crossing occurs at the level of the thalamic termination. Many fascicles of fibers continue rostrally by passing beneath the thalamic taste area, piercing the medial lemniscus, and spreading out along the dorsomedial corner of the internal capsule (IC). The terminal field at this level caps IC from the subthalamic nucleus down into the far-lateral hypothalamus. Labelled axons grandually penetrate through the internal capsule, and ramify throughout the underlying substantia innominata. This terminal zone extends laterally into the rostral end of the central nucleus of the amygdala, which is densely labelled to its caudal exremity. At the caudal end of the amygdala labelled fibers are visible in one component of the stria terminalis. These fibers can be followed over the dorsal thalamus into a smaller, but equally dense terminal area in the dorsolateral bed nucleus of the stria terminalis. The electrophysiological data demonstrate that pontine gustatory units can be antidromically activated by electrodes located in or near the central nucleus of the amygdala. Since many of the same units can also be driven from the thalamic taste area, at least some of the axons traced autoradiographically probably convey gustatory information to the hypothalamus and amygdala.
The parabrachial nucleus (PB) is the main relay for ascending visceral afferent information from the nucleus of the solitary tract (NTS) to the forebrain. We examined the chemical organization of solitary-parabrachial afferents by using combined retrograde transport of fluorescent tracers and immunohistochemistry for galanin (GAL), cholecystokinin (CCK), and corticotropin-releasing factor (CRF).
Each peptide demonstrated a unique pattern of immunoreactive staining. GAL-like immunoreactive (-ir) fibers were most prominent in the “waist” area, the inner portion of external lateral PB, and the central and dorsal lateral PB subnuclei. Additional GAL-ir innervation was seen in the medial and external medial PB subnuclei. GAL-ir perikarya were observed mainly rostrally in the dorsal lateral, superior lateral, and extreme lateral PB.
CCK-ir fibers and terminals were most prominent in the outer portion of the external lateral PB; some weaker labeling was also present in the central lateral PB. CCK-ir cell bodies were almost exclusively confined to the superior lateral PB and the “waist” area, although a few cells were seen in the Kölliker-Fuse nucleus.
The distribution of CRF-ir terminal fibers in general resembled that of GAL, but showed considerably less terminal labeling in the lateral parts of the dorsal and central lateral PB, and the external medial and KöUlliker-Fuse subnuclei. The CRF-ir cells were most numerous in the dorsal lateral PB and the outer portion of the external lateral PB; rostrally, scattered CRF-ir neurons were seen mainly in the central lateral PB.
After injecting the fluorescent tracer Fast Blue into the PB, the distribution of double-labeled neurons in the NTS was mapped. GAL-ir cells were mainly located in the medial NTS subnucleus; 34% of GAL-ir cells were double-labeled ipsilaterally and 7% contralaterally. Conversely, 17% of the retrogradely labeled cells ipsilaterally and 16% contralaterally were GAL-ir. CCK-ir neurons were most numerous in the dorsomedial subnucleus of the NTS and the outer rim of the area postrema. Of the CCK-ir cells, 68% in the ipsilateral and 10% in the contralateral NTS were double-labeled, whereas 15% and 10%, respectively, of retrogradely labeled cells were CCK-ir. In the area postrema, 36% of the CCK-ir cells and 9% of the Fast Blue cells were double-labelled CRF-ir neurons were more widely distributed in the medial, dorsomedial, and ventrolateral NTS subnuclei, but double-labeled cells were mainly seen in the medial NTS. Of CRF-ir cells in the NTS, 26% ipsilaterally and 8%contralaterally were retrogradely labeled by the PB injections. Conversely, of retrogradely labeled cells in the NTS, 4% ipsilaterally and 6% contralaterally were CRF-ir.
Our results suggest that the functional specificity of NTS afferents may be maintained by their selective termination in particular PB subnuclei. In addition, the neuropeptides found in these pathways may provide chemical coding for the relay of specific types of visceral sensory information to the PB.
The antioxidant beta-mercaptoethanol (BME) used in conjunction with the permanent mountant DPX (DPX-BME) retarded fluorescent fading of mithramycin, acridine orange and Hoechst 33258 stained chicken erythrocytes, each to a varying degree. The initial fluorescence of all dyes examined was more intense with DPX-BME than with DPX alone. Specimens mounted in DPX-BME showed strong fluorescence and excellent morphology; if kept in the dark, they could be stored indefinitely without deterioration. Retarding fading of fluorescence with DPX-BME faciliated quantitation of DNA using fluorescence cytophotometry.
Projections from the nucleus tractus solitarii (NTS) to autonomic control regions of the ventrolateral medulla, particularly the nucleus reticularis rostroventrolateralis (RVL), which serves as a tonic vasomotor center, were analyzed in rat by anterograde, retrograde, and combined axonal transport techniques.
Autonomic portions of the NTS, including its commissural, dorsal, intermediate, interstitial, ventral, and ventrolateral subnuclei directly project to RVL as well as to other regions of the ventrolateral medulla. The projections are organized topographically. Rostrally, a small cluster of neurons in the intermediate third of NTS, the subnucleus centralis, and neurons in proximity to the solitary tract selectively innervate neurons in the retrofacial nucleus and nucleus ambiguus. Neurons generally located in more caudal and lateral sites in the NTS innervate the caudal ventrolateral medulla (CVL). The RVL, CVL, and nucleus retroambiguus are interconnected.
A combined retrograde and anterograde transport technique was developed so as to prove that projections from NTS to the ventrolateral medulla specifically innervate the region of RVL containing neurons projecting to the thoracic spinal cord or the region of the nucleus containing vagal preganglionic neurons.
When the retrograde tracer, fast blue, was injected into the thoracic spinal cord, and wheat germ agglutinin-conjugate horseradish peroxidase (HRP) was injected into the NTS, anterogradely labeled terminals from the NTS surrounded the retrogradely labeled neurons in the RVL and in the nucleus retroambiguus in the caudal medulla. Among the bulbospinal neurons in the RVL innervated by the NTS were adrenaline-synthesizing neurons of the C1 group.
When fast blue was applied to the cervical vagus, and HRP was injected into the NTS, anterogradely labeled terminals from the NTS surrounded retrogradely labeled neurons in the rostral dorsal motor nucleus of the vagus, the region of the nucleus ambiguus, the retrofacial nucleus, and the dorsal portion of the RVL, a region previously, shown to contain cardiac vagal preganglionic neurons. This combined anterograde and retrograde transport technique provides a useful method; for tracing disynaptic connections in the brain.
These data suggest that the RVL is part of a complex of visceral output regions in the ventrolateral medulla, all of which receive afferent projections from autonomic portions of the NTS. Bulbospinal neurons in the RVL, in particular the C1 adrenaline neurons, may provide a portion of the anatomic substrate of the baroreceptor and other visceral reflexes.
The ultrastructural morphology and afferent sources of terminals containing substance P-like immunoreactivity were examined in the rat parabrachial region. In the first portion of the study, a polyclonal antiserum to substance P was localized in the ventrolateral parabrachial region using the peroxidase-antiperoxidase labeling technique combined with electron microscopy. The antiserum was tested for cross-reaction with substance P, physalaemin, substance K and neuromedins B, C and K. Cross-reactivity was most intense with substance P. However, substance K, neuromedin K and physalaemin also exhibited limited cross-reactions with the antiserum. In the ventrolateral parabrachial region of untreated adult animals, substance P-like immunoreactivity was localized in axon terminals containing numerous small (40–60 nm) clear vesicle and 1–3 large (90–120 nm) dense-core vesicles. At least 54% of the labeled terminals formed asymmetric synapses with unlabeled dendrites; and at least 30% of the recipient dendrites received more than one labeled axon terminal. In addition, the labeled terminals were associated less frequently with other unlabeled soma, axon terminals and blood vessels.
The functional organization of the insular cortex was studied by recording neuronal responses to visceral sensory stimuli. Horseradish peroxidase (HRP) was then iontophoresed at the recording sites to identify afferents from the ventrobasal thalamus to specific visceroceptive sites in the insular cortex. The relationship of the ventrobasal thalamus to the insular cortex and to brainstem relay nuclei for the ascending visceral projections was then examined by using the axonal transport of HRP, wheat germ agglutinin conjugated to HRP (WGA-HRP), and fluorescent dyes. Of a total of 55 neurons that were tested for responses to visceral sensory stimuli, 33 units responded to at least one visceral sensory modality: 6 received gastric mechanoreceptor input, 8 responded to taste inputs, 13 were activated by arterial chemoreceptors and/or showed respiratory related activity, and 6 responded to cardiovascular baroreceptor stimulation. On the basis of its cytoarchitecture and connections with the thalamus, the insular cortex was divided into a dorsal granular area, an intermediate dysgranular region, and a ventral agranular strip. Taste-responsive neurons were located anteriorly, primarily in the dysgranular region, whereas unit responses to general visceral modalities were distributed dorsally and posteriorly in the granular insular cortex. Gastric mechanoreceptor-responsive units were situated more dorsally and anteriorly in the granular insular cortex, while cardiopulmonary inputs were located more ventrally and posteriorly. Injections of HRP into the gustatory insular cortex resulted in retrograde labeling of neurons in the parvicellular part of the ventroposterior medial thalamic nucleus (VPMpc). Injections into the general visceral insular cortex retrogradely labeled neurons lateral to VPMpc in the ventroposterior lateral parvicellular thalamic nucleus (VPLpc). Injections of HRP, WGA-HRP, and fluorescent dyes into VPMpc and VPLpc verified that their projection to the insular cortex is topographically organized. In the same experiments, retrogradely labeled neurons in the parabrachial nucleus identified the likely subnuclei within this nucleus for relay of visceral sensory information to the thalamus. Injections of WGA-HRP into the parabrachial nucleus demonstrated that its projection to the ventrobasal thalamus is also topographically organized. These results demonstrate the relationship of general visceral and special visceral (taste) representations in the insular cortex. The ascending pathway for visceral sensory information appears to be viscerotopically organized at all levels of the neuraxis, including the insular cortex.
Iontophoretic administration of PHA-L into the globus pallidus of rats resulted in the labeling of neuronal perikarya in the striatum as well as axons and terminals in the striatum, entopeduncular nucleus, subthalamus and substantia nigra. The labeled striatal perikarya were densely stained in Golgi fashion with virtually complete filling of the dendrites and spines. It is concluded that the striatal cells were filled by the retrograde transport of PHA-L and represent either striatopallidal cells, or striatonigral cells whose axons were interrupted as they passed through the injection site. The anterogradely labeled axon terminals in the striatum were observed in close apposition to the dendrites of the retrogradely labeled neurons suggesting the existence of synaptic contacts between the two groups of cells. This study demonstrates that PHA-L can be transported retrogradely as well as anterogradely following iontophoretic injections.
This study provides a scheme for subdividing the nucleus of the solitary tract of the hamster on the basis of cytoarchitectonic criteria, cell measurements, and neuronal cell types identified with the Golgi method. Reduced silver-stained sections revealed the feltlike neuropil that characterizes the nucleus of the solitary tract and were used to define the boundaries of the nuclear complex. Adjacent sections stained for Nissl substance revealed ten subdivisions, each with a characteristic neuronal architecture based on cell sizes, shapes, and packing density. Some subdivisions, e.g., the ventral and medial subnuclei, were identified at all rostrocaudal levels of the nuclear complex, while other subdivisions, e.g., the caudally located dorsolateral and ventrolateral subnuclei, were restricted to particular levels. Golgi preparations were counterstained for Nissl substance, thus allowing dendro- and cytoarchitecture to be compared directly. This material permitted the identification of a number of functionally relevant features of the neuronal constituents of the subdivisions. This approach, employing three cytological methods, has permitted the assembly of a detailed atlas of the nucleus of the solitary tract. The subdivisions of the present atlas have been compared with their likely counterparts identified in previous investigations of the mammalian nucleus of the solitary tract. In order to relate cytoarchitecture with primary afferent termination sites and to define the gustatory-recipient subdivisions, the differential relationships of the subdivisions with lingual afferent projections in the hamster are also described. The present parcellation scheme is intended to facilitate anatomical and physiological investigations of the types of circuits that compose the medullary gustatory and general visceral sensory systems.
Previous studies have shown that behavioral and neurophysiological responses to tastes develop during rat's postnatal life. The present experiments evaluated morphological and metabolic development of neurons in the gustatory zone of the caudal parabrachial nucleus (PBNc) of rat. Histological reconstruction studies were conducted to establish coordinate systems for PBNc gustatory zones in developing rats. Reliability of coordinate systems were evaluated in separate experiments following infusions of horseradish peroxidase in the thalamic taste area. Morphological and Golgi impregnation studies were performed to characterize neuronal and dendritic architecture in PBNc gustatory zones defined by coordinates. Conventional histochemical studies were performed for the mitochondrial respiratory enzymes cytochrome C oxidase (CO; EC 1.9.3.1) succinate dehydrogenase (SDH; EC 1.3.99.1), and NADH-dehydrogenase (NADH-DH; EC 1.6.99.3). Results show that two somatic morphologies can be statistically characterized in PBNc gustatory zones: Multipolar somatic types and fusiform somatic types. Multipolar and fusiform neurons of neonatal and adult rats project axons to the thalamic taste area, and dendrites of these neurons grow extensively between approximately 16 days after birth to approximately 35 days after birth. Activity of CO, SDH, and NADH-DH increases in the PBNc gustatory zones during the period of dendritic growth, and continues to increase slightly to approximately 45 days. These results provide the first demonstration of postnatal morphological and metabolic developmental in a central gustatory relay. Postnatal development of gustatory system therefore appears similar to that reported for other sensory systems, to the extent that morphological and metabolic development accompanies the ontogeny of taste responses.
The somal shapes, dendritic features, and orientations of the neurons within the gustatory zone of the nucleus of the solitary tract were studied with the rapid Golgi method in the adult hamster. These Golgi studies complement previous quantitative morphometric analyses of the distributions of large and small neurons within the gustatory zone. Class 1 neurons are usually fusiform and possess long, relatively unbranched dendrites that often extend beyond the cytoarchitectonic boundaries of the gustatory zone. Class II neurons are multipolar and possess more dendrites that are significantly shorter than those of class I neurons. Both classes of neurons are spine poor. Computer-generated three-dimensional rotational analyses demonstrate that the dendritic arborizations of neurons of the gustatory zone are oriented preferentially in the horizontal plane. Dendrites extend in parallel or perpendicular to the solitary tract, the source of peripheral gustatory inputs, and appear to be positioned spatially to maximize synaptic interactions with these peripheral fibers. These Golgi studies also suggest that individual gustatory neurons may be influenced by incoming gustatory fibers that innervate separate populations of taste buds, a finding that is not predictable from the topographical organization of the gustatory zone.
The organization of axon collaterals, preterminal processes, and presumptive synaptic boutons of single physiologically identified rapidly adapting receptor (RAR) pulmonary afferent fibers was examined following the intraaxonal application of wheat germ agglutinin conjugated with horseradish peroxidase (WGA‐HRP). The RAR axons were injected 200–300 μm lateral to the nucleus of the tractus solitarius (nTS) at a number of different rostrocaudal levels in seven individual experiments. The trajectories of the stained axons were reconstructed from individual 50‐μm‐thick serial sections. The rostrocaudal extent, as well as the distribution of the trajectory of each RAR afferent, was reconstructed from every section by using a camera lucida attachment. In this first of two papers, we describe the pattern of organization of bouton terminals of RAR afferents related to cytoarchitectonically distinct subnuclei of the nTS. In the companion paper, morphological details of the fine structure of these synaptic boutons and axonal branches are described in different subnuclei in order to illustrate morphological differences in these functionally distinct regions.
A number of significant findings have resulted from this light microscopic study. The central process of a single RAR afferent fiber arborized in the medulla oblongata over a considerable distance in the rostrocaudal plane (2.5 mm rostral to 1.4 mm caudal to the obex). A single RAR afferent fiber terminated in numerous bouton terminals (range 500–1,050), and these terminals arose from over 400 segments of branches of the parent injected axon. A small number of en passant bouton terminals were found. There appeared to be a remarkable degree of consistency in the subnuclei of the nTS where these terminals arborized. The dorsal and dorsolateral subnuclei of the nTS received 144–647 bouton terminals. The second‐largest concentration of bouton terminals of RAR afferents was found in the intermediate (nI) subnucleus of the nTS. No labeled bouton terminal was found in the ventral and ventrolateral subnuclei of the nTS. This finding is in sharp contrast to the terminations of SAR afferents which terminated predominantly in the ventral and ventrolateral nuclei of the nTS, the interstitial nucleus of the nTS, and the nI.
The parent RAR axon could be traced as far rostrally as 2.5 mm, even though the region of terminal arborization could not be followed beyond 0.8 mm. The destination of this rostrally projecting RAR afferent could not be determined in this study. This pattern indicates that a single RAR afferent fiber ascends rostrally in the tractus solitarius giving off branches at a number of different levels.
Since the rostrocaudal location of the randomly selected RAR afferent impaled in the medulla varied considerably in all seven cases examined, it is likely the location of their peripheral endings was different in each case. In spite of this viscerotopic difference between the injected axons, the patern of distribution of the axon collaterals and synaptic boutons in the nTS was very similar in all cases.
This illustrates that modality specificity, and not viscerotopic specificity, is an important feature of the central organization of these afferents. These findings are similar to the modality specificity observed with SAR afferents (Kalia and Richter: J. Comp. Neurol. 233 : 308‐332, '85a). In addition, these results further support the concept of functional organization of the nTS along cytoarchitectonic boundaries.
It has been proposed that calcitonin gene‐related peptide (CGRP) may serve as a major neuromodulator in visceral sensory pathways, but its exact role in the visceral sensory thalamus and cortex has not been determined. We therefore examined the distribution of CGRP‐like immunoreactive (CGRPir) innervation of the insular cortex and the parvicellular division of the ventroposterior nucleus of the thalamus (VPpc) in the rat by using immunohistochemistry for CGRP combined with retrograde transport of the fluorescent dye fluoro‐gold.
Modest numbers of CGRPir fibers were distributed in the dysgranular and agranular insular cortex, but few were observed in the granular insular cortex. The density of CGRPir innervation increased caudally along the rhinal fissure and was considerably greater in the perirhinal cortex. When fluorogold was injected into the insular cortex numerous retrogradely labeled neurons were seen in the VPpc, but few of these were CGRPir. Retrogradely labeled CGRPir neurons were, however, seen in the ventral lateral and medial parabrachial (PB) subnuclei. Injection of fluoro‐gold into the perirhinal cortex (which is just caudal to the insular cortex along the rhinal fissure) resulted in many retrogradely labeled CGRPir neurons in the posterior thalamic region, including the subparafascicular, the lateral subparafascicular, and the posterior intralaminar nuclei.
The VPpc was heavily innervated by CGRPir fibers but contained few CGRPir cell bodies. Injection of fluoro‐gold into the VPpc resulted in many retrogradely labeled CGRPir neurons in the external medial PB subnucleus bilaterally, but with a contralateral predominance. Smaller numbers of retrogradely labeled CGRPir neurons were also observed in the ventrolateral PB subnucleus, bilaterally with an ipsilateral predominance. These results suggest that CGRP may be a neuromodulator in the ascending visceral sensory pathways from the PB to the VPpc and the insular cortex, but not between the latter two structures.
The aim of this study was to map the viscerotopic representation of the upper alimentary tract in the sensory ganglia of the IXth and Xth cranial nerves and in the subnuclei of the solitary and spinal trigeminal tracts. Therefore, in 172 rats 0.5–65 μl of horseradish peroxidase (HRP), wheat germ agglutinin-HRP, or cholera toxin-HRP were injected into the trunks and major branches of the IXth and Xth cranial nerves as well as into the musculature and mucosa of different levels of the upper alimentary and respiratory tracts.
The results demonstrate that the sensory ganglia of the IXth and Xth nerves form a fused ganglionic mass with continuous bridges of cells connecting the proximal and distal portions of the ganglionic complex. Ganglionic perikarya were labeled in crude, overlapping topographical patterns after injections of tracers into nerves and different parts of the upper alimentary tract. After injections into the soft palate, pharynx, esophagus, and stomach, anterograde labeling was differentially distributed in distinct subnuclei in the nucleus of the tractus solitarius (NTS). Palatal and pharyngeal injections resulted primarily in labeling of the interstitial and intermediate subnuclei of the NTS and in the paratrigeminal islands (PTI) and spinal trigeminal complex. Esophageal and stomach wall injections resulted in labeling primarily of the subnucleus centralis and subnucleus gelatinosus, respectively.
The distribution of upper alimentary tract vagal-glossopharyngeal afferents in the medulla oblongata has two primary groups of components, i.e., a viscertopic distribution in the NTS involved in ingestive and respiratory reflexes and a distribution coextensive with fluoride-resistant acid-phosphatase-positive regions of the PTI and spinal trigeminal nucleus presumably involved in visceral reflexes mediated by nociceptive or chemosensitive C fibers.
The purpose of our study was to determine the cardiorespiratory effects of exciting cell bodies of the area postrema of the cat. This was accomplished by local application of L-glutamic acid (bilateral application of 5 microliter of a 250-1000 mM solution) and kainic acid (bilateral application of 5 microliter of a 40 mM solution) to the area postrema of chloralose-anesthetized cats while monitoring arterial pressure, heart rate, tidal volume and respiratory rate. These excitatory amino acids activate neuronal cell bodies but not axons of passage. L-Glutamic acid produced a dose-dependent increase in arterial pressure, decreases in respiratory rate and minute volume and, occasionally, ventricular tachyarrhythmias. Kainic acid produced effects similar to those seen with L-glutamic acid except the changes in respiratory activity were more pronounced with each animal exhibiting respiratory arrest. In artificially respired animals, kainic acid produced similar cardiovascular changes as those occurring in spontaneously breathing animals (i.e. increases in arterial pressure of 61 +/- 5.7 mm Hg, and in heart rate of 32 +/- 8.3 beats/min). Finally, application of kainic acid to the area postrema abolished the pressor and tachycardic responses to bilateral occlusion of the carotid arteries. These results suggest that activation of cell bodies in the area postrema can result in pronounced cardiorespiratory changes.
Co-localization of neurotensin and cholecystokinin in tyrosine hydroxylase-containing neurons in the nucleus tractus solitarius of the rat was demonstrated by immunocytochemistry with fluorescent double-staining combined with the peroxidase-antiperoxidase method. Co-localization of neurotensin/tyrosine hydroxylase or cholecystokinin/tyrosine hydroxylase was consistently found in small neurons in the region dorsomedial to the tractus solitarius at the level of the area postrema with high percentages of co-existence: 91.0% tyrosine hydroxylase-immunoreactive neurons contained neurotensin and 91.1% cholecystokinin, suggesting that they represent the same neurons. Accordingly, co-localization of neurotensin and cholecystokinin was assessed on tyrosine hydroxylase-containing neurons bisected into two adjacent sections, and then identified in a certain number of the catecholamine neurons in this region. Furthermore these catecholamine neurons exhibited immunoreactivity for an adrenaline-synthesizing enzyme, phenylethanolamine N-methyltransferase. It was concluded that catecholamine, in particular adrenaline, neurons, characterized by co-localization of neurotensin and cholecystokinin, established a distinct subpopulation in the catecholaminergic system in the dorsomedial medulla of the rat.
Efferent and afferent connections of the supratrigeminal region were studied in the rat using iontophoretically delivered horseradish peroxidase and Phaseolus vulgaris leuco-agglutinin. Projections of supratrigeminal efferents were found to the contralateral supratrigeminal region, to the ipsi- and contralateral trigeminal motor nuclei and the medullary reticular formation, and to the ipsilateral facial and hypoglossal motor nuclei. Neurons projecting to the supratrigeminal region were located in the contralateral supratrigeminal nucleus, in the ipsilateral mesencephalic trigeminal nucleus and bilaterally in the medullary reticular formation. This organization is discussed with respect to bilateral oral motor control mechanisms.
In anesthetized and artificially ventilated cats, the physiological and morphological properties of expiratory neurons or their axons of the Bötzinger complex (BOT) were studied using intracellular recording and intracellular HRP labeling techniques. Thirteen expiratory neurons (nine cell somata and four axons) were successfully stained. Four of them were motoneurons, having relatively large cell somata in the retrofacial nucleus (RFN) and axons without any collaterals inside the brainstem. All the motoneurons showed a plateau shape of depolarization potentials during the expiratory phase. Any of the other nine expiratory neurons exhibited augmenting type firing or membrane potential changes during the expiratory phase. In five out of nine augmenting neurons, cell somata were stained and located ventral to the RFN. In four, only axons were stained. The majority of the augmenting neurons had two major axonal branches: one traveling toward the contralateral side and the other descending ipsilaterally in the brainstem. The most striking feature of the axonal trajectory was that all of the stained augmenting expiratory neurons, including the axons, had collateral branches with synaptic boutons in the BOT area, thus indicating that BOT expiratory neurons interact with some respiratory neurons in the BOT area and its vicinity.
We studied projection patterns of the augmenting expiratory neurons of the Bötzinger complex (BOT) in the contralateral brainstem. Three experimental approaches were used: 1) electrophysiological analysis using antidromic microstimulation, and morphological analyses using 2) intraaxonal injection of HRP, and 3) application of the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L). Taken together, the three methods revealed morphological details of the axonal arborizations of the expiratory neurons in the BOT and the ventral respiratory group (VRG). The majority of augmenting expiratory neurons of the BOT had axonal collaterals in the contralateral brainstem. The stem axons to the contralateral side crossed the midline almost at the level of the cell somata. They descended dorsomedial to the ventral spinocerebellar tract and gave off collateral branches directed dorsomedially. Terminal boutons were distributed abundantly in the caudal part of the BOT and in the more caudally situated VRG. Axon collaterals sometimes ran to the dorsal respiratory group (DRG) and distributed terminal boutons there. Together with the fact of extensive ipsilateral arborizations shown previously, the present results indicate that the augmenting expiratory neurons of the BOT have wide bilateral influence on the BOT, VRG, DRG, and spinal cord.
Injections of WGA-HRP were made in the rat trigeminal ganglion and C1-3 dorsal root ganglia (DRGs) to study the central projection patterns and their relations to each other. Trigeminal ganglion injections resulted in heavy terminal labeling in all trigeminal sensory nuclei. Prominent labeling was also observed in the solitary tract nucleus and in the medial parts of the dorsal horn at C1-3 levels, but labeling could be followed caudally to the C7 segment. Contralateral trigeminal projections were found in the nucleus caudalis and in the dorsal horn at C1-3 levels. The C1 DRG was found to be inconstant in the rat. When it was present, small amounts of terminal labeling were found in the external cuneate nucleus (ECN) and the central cervical nucleus (CCN). No dorsal horn projections were seen from the C1 DRG. Injections in the C2 DRG resulted in heavy labeling in the ECN, nucleus X, CCN, and dorsal horn, where it was mainly located in lateral areas. Labeling could be followed caudally to the Th 7 segment. C2 DRG projections also appeared in the cuneate nucleus (Cun), in all the trigeminal sensory nuclei, and in the spinal, medial, and lateral vestibular nuclei. A small C2 DRG projection was observed in the ventral cochlear nucleus. C3 DRG injections resulted in heavy labeling in both medial middle and lateral parts of the dorsal horn, in the ECN, and in nucleus X, whereas the labeling in the CCN was somewhat weaker. Smaller projections were seen to trigeminal nuclei, Cun, and the column of Clarke. Comparisons of the central projection fields of trigeminal and upper cervical primary afferents indicated a somatotopic organization but with a certain degree of overlap.
The area postrema (AP) of the dog mediates pressor responses to angiotensin II and plays a role in the maintenance of normal arterial pressure. Ablation of the AP (APX) in the rat has been reported to have little or no effect on cardiovascular regulation. In the present study, computer data acquisition techniques were used to investigate this question. APX in the rat significantly lowered resting mean arterial pressure within 1 h (P less than 0.005) and lowered heart rate within 1 day (P less than 0.05) following the lesion. Increases in heart rate following atropine injections were significantly greater (P less than 0.05) in AP relative to sham lesion rats, suggesting higher vagal tone in the AP lesion rats. In addition, APX significantly enhanced the baroreflex control of heart rate in response to intravenous phenylephrine (P less than 0.05). Lability of pressure was not affected by the lesion. The hypotension and bradycardia produced by APX were still present 1 wk after APX. These AP lesions apparently did not produce significant damage to the function of the nearby NTS, since 1) histological analysis revealed minimal NTS damage, 2) arterial pressure lability was not increased, and 3) APX enhanced rather than impaired baroreflex control of heart rate. We conclude that the AP may have a role in the maintenance of resting arterial pressure and heart rate in the rat.
In Nembutal-anesthetized and spontaneously breathing rats, a total of 226 respiratory neurons were recorded in the medulla extending from the caudal end of the facial nucleus to 1 mm caudal to the obex. They were classified into inspiratory (I) and expiratory (E) neurons by their temporal relationships to diaphragm EMGs. One hundred and seventeen I and 108 E neurons were identified. I and E neurons were further classified into augmenting, decrementing, and other types based on their firing patterns. Almost all the respiratory neurons recorded were located around the nucleus ambiguus and the nucleus retroambigualis, corresponding to the ventral respiratory group (VRG) of the cat. On the other hand, only a few respiratory neurons were identified around the ventrolateral nucleus of the solitary tract, corresponding to the dorsal respiratory group of the cat. In the VRG, 3 subgroups were distinguished rostrocaudally. One group of E neurons was located ventrally to the rostral part of the nucleus ambiguus, presumably corresponding to the Bötzinger complex defined in the cat. Another group of E neurons extended caudally beyond the obex, from the caudal portion of the nucleus ambiguus through the nucleus retroambigualis. Between these two groups of E neurons, an assembly of predominantly I neurons existed in the vicinity of the nucleus ambiguus. These characteristics of distributions were basically similar to those of the VRG of the cat.
In the rat, the subdiaphragmatic vagus nerves (SDX) have five major branches--the right gastric, the left gastric, the coeliac, the accessory coeliac, and the hepatic. Although these branches innervate more than the organs after which they are named, some mediate specific behavioral functions. In addition to the SDX trunk, the central stump of each of these branches was incubated in horseradish peroxidase (HRP) for 6 hours in anesthetized rats. After processing the vagal ganglia, pons, medulla, and upper cervical spinal cord of each preparation, the sections were examined for both retrogradely and anterogradely transported HRP reaction product. When only one nerve had been incubated, retrogradely labeled neurons were confined primarily to the ipsilateral ganglion, medulla, and spinal cord. Within the brain, a few labeled neurons occurred within the nucleus ambiguus (NA) and the reticular formation caudal to the NA, but the vast majority appeared in the dorsal motor nucleus of the vagus (DMX). The axons of most labeled neurons in the NA distributed in the gastric branches; those from cells caudal to the NA, probably distributed in the coeliac branch. Most labeled DMX cells also distributed with the gastric branches. Those on the lateral tip of the right DMX, however, had axons in the coeliac branch; those on the left DMX tip, in the accessory coeliac. After incubation of the SDX trunk, anterograde HRP reaction product occurred in the caudomedial nucleus of the solitary tract (NST) just rostral and subjacent to the area postrema (AP). Unlike the retrograde label, anterograde reaction product was bilateral, but always weaker contralaterally. Within the SDX distribution, the afferent axons from the gastric branches exhibited one pattern of termination; those from the coeliac, accessory coeliac, and hepatic branches, another. The gastric branch distributions began dorsolaterally in the SDX termination zone and continued caudally beneath the AP. Immediately subjacent to the AP, gastric branch terminals were never dense and the entire distribution faded at the level of the obex. The coeliac and accessory coeliac distributions began dorsomedially within the SDX termination zone and intensified caudally in a thin band immediately subjacent to the AP. The densest label was associated with the caudal half of the AP, but the distribution thinned rapidly caudal to the obex. The hepatic distribution was similar to that of the coeliac branches but never achieved similar density. Physiological and behavioral data correlate with the anatomical picture in that the efferent functions appear to be more densely localized than the afferent functions.
Rats with lesions of the area postrema and the immediately subjacent nucleus of the solitary tract (AP lesions) ingest greater quantities of palatable foods than intact rats. Because AP lesions destroy some abdominal vagal sensory terminals and may damage vagal motor neurons as well, it is possible that lesion-induced alteration of vagal function causes overingestion of palatable foods. To test this hypothesis, we have examined ingestion of a highly palatable solid food by AP- and sham-lesioned rats with total subdiaphragmatic vagotomies and examined ingestion of a highly palatable sucrose solution by AP- and sham-lesioned rats with open gastric fistulas (sham feeding). Vagotomy in sham-lesioned rats failed to cause overingestion of palatable food. Furthermore, vagotomy in AP-lesioned rats did not abolish their overingestion of palatable food, although AP lesion-induced overingestion was attenuated by vagotomy. Finally, sham-feeding AP-lesioned rats consumed significantly more sucrose solution than sham-lesioned rats. These results indicate that overingestion of palatable foods and solutions by AP-lesioned rats is not due to impaired abdominal visceral afferent function and probably is not due to altered vagal efferent function. The data are consistent with our previous suggestion that overingestion by AP-lesioned rats results from a primary change in responsiveness to orosensory cues.
Responses of neurons of the canine area postrema were recorded to ionophoretic application of insulin, apomorphine, leucine-enkephalin and glutamate. Each excited the neurons directly in a dose-dependent fashion. Like apomorphine and leucine enkephalin, which are known to induce emesis by activation of area postrema neurons, insulin given systemically induced emesis in intact dogs but not in animals with area postrema ablations. These results provide further support for a critical role of the area postrema in triggering the emetic reflex, and are the first definitive demonstration of a direct excitatory action of insulin on mammalian neurons.
We sought to determine (1) the ultrastructural localization and (2) the extrinsic sources of neurotensin‐like immunoreactivity (NTLI) in the parabrachial region (PBR). The brains from untreated adult male rats and from others that received intraventricular injections of colchicine (100 μg/7.5 μl saline) 24 hours prior to death were fixed by perfusion with acrolein or glutaraldehyde and paraformaldehyde. Coronal sections were immunocytochemically labeled with a polyclonal rabbit antiserum to neurotensin and the PAP method. Western dot‐blots and immunocytochemical labeling with adsorbed antiserum revealed significant cross‐reaction only against NT, NT 8‐13 , and glutamine (Gln) ⁴ ‐NT.
In the ultrastructural study, the most numerous labeled profiles were axons and axon terminals in both colchicine‐treated and control animals. The terminals containing NTLI were characterized by a mixed population of small, clear and large, dense core vesicles; asymmetric junctions principally with unlabeled dendrites; and a few synaptic specializations with unlabeled axon terminals. Compared to axon terminals, relatively few perikarya or dendrites had detectable levels of NTLI in either untreated or colchicine‐treated animals. The labeled perikarya measured 8‐10 μm in longest cross‐sectional diameter, contained NTLI throughout a narrow rim of cytoplasm, and received a few somatic synapses from unlabeled terminals. From the relative density of axon terminals and sparsity of perikarya and dendrites, we conclude that the NTLI in the PBR is principally derived from extrinsic neurons. However, the intrinsic neurons with NTLI may also contribute to the immunoreactivity in the axon terminals of the PBR.
We sought to determine the precise location of the extrinsic neurons that contribute to the NTLI in axon terminals in the PBR. Following unilateral injections of wheat germ agglutinin‐conjugated horseradish peroxidase (WGA‐HRP), dual labeling was most evident in a large population of neurons located in the dorsal, medial and commissural nuclei of the solitary tracts, ipsilateral to the side of the injection. However, a few perikarya containing both the retrogradely transported WGA‐HRP and immunocytochemical labels for NT were also detected in the caudal ventrolateral reticular formation, the locus coeruleus, and the paraventricular and lateral hypothalamic nuclei. We conclude that (1) NT or a closely related peptide is present in intrinsic neurons and multiple afferent pathways to the PBR; and (2) the axon terminals with NTLI have synaptic interactions with dendrites of intrinsic neurons and with axon terminals that may have either extrinsic or intrinsic origins.
The effect of surgical ablation of the area postrema on acute (5-10 minutes) and chronic (5-10 days) increases in mean arterial pressure produced by intravenous infusion of angiotensin II in conscious, instrumented rats was studied. In agreement with previous studies, pressor responses of area postrema-ablated rats (n = 11) to acute angiotensin II infusion were identical to those of control sham-lesioned rats (n = 13). In these same rats, however, a 5-day infusion of angiotensin II produced a sustained hypertension in the sham-lesioned group whereas mean arterial pressure was increased only transiently (1-3 days) in the area postrema-ablated rats. No differences before infusion of arterial pressure, heart rate, water intake, urinary sodium excretion, and urinary potassium excretion were observed between sham-lesioned and area postrema-ablated rats; only arterial pressure was changed significantly during angiotensin II infusion in either group. Twenty-four hours after terminating angiotensin II infusion, mean arterial pressure was within the normotensive range in both sham-lesioned and area postrema-ablated rats. In a separate group of sham-lesioned (n = 13) and area postrema-ablated (n = 12) rats, angiotensin II was infused intravenously for a 10-day period; mean arterial pressure was increased significantly over the entire 10-day infusion in sham-lesioned rats, but for only 1 day in area postrema-ablated rats. An intact area postrema appears necessary for the development of chronic, but not acute, hypertension during intravenous infusion of angiotensin II in the rat.
We determined the temporal changes in effectiveness of inspiratory-shortening expiratory-prolonging stimulus trains delivered in the region of the nucleus parabrachialis medialis and compared the responses to those observed during trains delivered to the vagus in the same animals (pentobarbital, sodium-anesthetized paralyzed cats). The inspiratory inhibitory effect of the pontine stimulus was assessed from the effect the stimulus has on threshold for terminating inspiration. Stimulus effect increased gradually, reached a peak at 0.2-0.4 s, and declined thereafter. The time of occurrence of peak effect was different from that observed in the course of vagal stimulus trains. With long stimulus trains (19-40 s), the initial effect on inspiratory duration (TI) (i.e., shortening) rapidly subsided and, in six of eight animals, was replaced by TI prolongation. The initial effect on expiratory duration (TE) (i.e., prolongation) also gradually declined with time but TE remained above control throughout. The time constant of adaptation was very similar with vagal and pontine stimulus trains (12.2 and 11.0 s, respectively), but the gain of the adapting response was much more pronounced with pontine stimuli, resulting in a paradoxical effect while stimulation continued. We conclude that the response to pontine stimuli, as with vagal stimuli, displays both integrative and adaptive characteristics. The similarity of the time constants for vagal and pontine adaptation responses suggests that these two inputs share common processing pathways.
Transganglionic transport of horseradish peroxidase or lectin-conjugated horseradish peroxidase from an application site in the cervical trunk of the glossopharyngeal (IXth cranial) nerve of the rat produced extraperikaryal reaction product characteristic of axon terminal processes in three regions of the brain stem: (1) the nucleus of the tractus solitarius, from approximately 2.5 mm rostral to the obex to approximately 3 mm caudal to the obex; (2) the spinal trigeminal nucleus at the level of obex; (3) the cuneate fasciculus, approximately 3 mm caudal to the obex. In contrast, labelling of the carotid sinus nerve, a branch of the glossopharyngeal nerve which conveys chemoreceptor and baroreceptor afferent fibers from the carotid bifurcation, revealed a restricted central projection to within 1 mm of the obex and corresponding to the intermediate region of the glossopharyngeal nerve projection to the nucleus of the tractus solitarius. Two distinct aggregations of label were observed: (1) rostral to the obex, within the lateral and dorsomedial subnuclei of the nucleus of the tractus solitarius; (2) caudal to the obex, within the commissural and ventrolateral subnuclei of the nucleus of the tractus solitarius. Between these two sites the density of labelling was reduced. Retrogradely labelled neurons were demonstrated in the inferior salivatory nucleus and in the nucleus ambiguus after application of lectin-conjugated horseradish peroxidase to the glossopharyngeal nerve. Of the labelled neurons in the nucleus ambiguus (approximately 100), 25% contributed fibers to the carotid sinus nerve. The concentration of extraperikaryal reaction product located rostral to the obex after labelling of the carotid sinus nerve closely matches descriptions of the region of afferent terminations from carotid and aortic baroreceptors in the cat. The concentration of label caudal to the obex may therefore correspond to the region of afferent terminations from carotid chemoreceptors. This study may therefore provide some basis for a separation of the central synapses of primary afferent fibers from the carotid baroreceptors and chemoreceptors in the rat. The labelled neurons of the nucleus ambiguus provide the anatomical substrate for centrifugal control of carotid chemoreceptor activity.