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Localization of orexin-1 receptors to vagal afferent neurons in the rat and humans
Abstract
Orexin-A and -B are brain-gut peptides that stimulate food intake via orexin-R1 and -R2 receptors. Cholecystokinin (CCK) inhibits food intake via CCK(A) receptors expressed on vagal afferent neurons. The purpose of the study was to determine whether vagal afferent neurons express OX-R1 and OX-R2 and whether orexin-A inhibits responses to CCK.
OX-R1 and -R2 expression by rat and human nodose ganglia was examined by reverse-transcriptase polymerase chain reaction (RT-PCR). Receptor localization was determined by immunohistochemistry. Responses of rat jejunal afferent fibers were examined by electrophysiology.
Both rat and human nodose ganglia expressed OX-R1 as detected by RT-PCR, and humans also expressed OX-R2. The identity of the products was confirmed by sequencing. Immunohistochemistry indicated expression of OX-R1 in both species in neurons that also expressed CCK(A) and leptin receptors. In human ganglia there was also expression in glial cells that was absent in rats. Orexin-A had no effect on the resting discharge of afferent nerve fibers but inhibited responses to CCK.
OX-R1 and CCK(A) receptors are expressed by human and rat vagal afferent neurons. Orexin inhibits responses to CCK suggesting a role in modulation of gut to brain signaling.
... Over the last decade or so it has become clear that in addition to gut signals that limit nutrient delivery, there are also signalling molecules released in the absence of food that tend to increase food intake and accelerate gastric emptying -examples include ghrelin (Kojima et al. 1999;Date et al. 2002;Burdyga et al. 2006b), orexin-A (Kirchgessner & Liu, 1999;Burdyga et al. 2003) and endocannabinoids such as anandamide (Gomez et al. 2002;Burdyga et al. 2004). In each of these cases, vagal afferent neurons express the appropriate receptors and there is extensive overlap in the pattern of expression of these receptors and those of factors that inhibit nutrient delivery (CCK, leptin, PYY 3-36 and GLP-1; Fig. 2A and B). ...
... In each of these cases, vagal afferent neurons express the appropriate receptors and there is extensive overlap in the pattern of expression of these receptors and those of factors that inhibit nutrient delivery (CCK, leptin, PYY 3-36 and GLP-1; Fig. 2A and B). This clearly provides a basis for functional interactions and, for example, both orexin-A (Burdyga et al. 2003;Fig. 2C) and ghrelin inhibit vagal afferent activation in response CCK (Date et al. 2002). ...
... B, the same neurons can express receptors for multiple orexigenic and satiety factors: examples are shown for GHS1 and CCK1 receptor expression and for Y2 and CCK1 receptor expression. C, orexigenic factors, in this case orexin-A, inhibit the stimulation of vagal afferent discharge by satiety factors, in this case CCK (Burdyga et al. 2003). J Physiol 592.14 vagal afferent neurons with CCK1 receptors (Broberger et al. 1999), and is associated with inhibition of food intake; the other, MCH (melanin concentrating hormone) is expressed in the same neurons and is associated with stimulation of food intake (Burdyga et al. 2006a). ...
The landmark discovery by Bayliss and Starling in 1902 of the first hormone, secretin, emerged from earlier observations that a response (pancreatic secretion) following a stimulus (intestinal acidification) occurred after section of the relevant afferent nerve pathway. Nearly 80 years elapsed before it became clear that visceral afferent neurons could themselves also be targets for gut and other hormones. The action of gut hormones on vagal afferent neurons is now recognised to be an early step in controlling nutrient delivery to the intestine by regulating food intake and gastric emptying. Interest in these mechanisms has grown rapidly in view of the alarming global increase in obesity. Several of the gut hormones (cholecystokinin, CCK; PYY3-36; glucagon-like peptide-1, GLP-1) excite vagal afferent neurons to activate an ascending pathway leading to inhibition of food intake. Conversely others eg ghrelin, that are released in the inter-digestive period, inhibit vagal afferent neurons leading to increased food intake. Nutrient status determines the neurochemical phenotype of vagal afferent neurons by regulating a switch between states that promote orexigenic or anorexigenic signalling through mechanisms mediated, at least partly, by CCK. Gut-brain signalling is also influenced by leptin, by gut inflammation and by shifts in the gut microbiota including those that occur in obesity. Moreover, there is emerging evidence that diet-induced obesity locks the phenotype of vagal afferent neurons in a state similar to that normally occurring during fasting. Vagal afferent neurons are therefore early integrators of peripheral signals underling homeostatic mechanisms controlling nutrient intake. They may also provide new targets in developing treatments for obesity and feeding disorders.
... Notably, the NTS, the gateway of the gut and brain, contains neurons and circuits that are involved in feeding behavior and energy homeostasis [35]. Opioids and orexins are gut peptides that stimulate feeding when injected into the rostral NTS (rNTS) [36,37]. Meanwhile, NTS neurons, such as CCK and preproglucagon (GCG), can respond to satiety-related stimuli from vagal afferents [38,39]. ...
... Moreover, mechanical stimuli can also activate vagal nerves. Vagal afferent mechanoreceptors are activated by gastric distention [36,118]. Interestingly, food intake is sensitive to the stimulation of mechanoreceptors in the intestines. ...
Obesity has become a worldwide disease, posing a rapidly increasing challenge to the global healthcare system. The primary reason for obesity is that food intake exceeds the body’s needs. The central nervous system monitors the body’s energy status by continuously receiving peripheral gut-derived signals and functions as a master regulator in controlling feeding behaviors. Vagal afferents transmit gut-derived consumption signals from the periphery to the hindbrain (e.g., the nucleus of the solitary tract (NTS)). In contrast, vagal efferent nerves send commands to regulate peripheral organ activities. However, the precise role of the gut–vagus–NTS pathway and the gut–brain axis in regulating food intake is not yet fully understood. This review highlights the key roles of the NTS, vagal sensory neurons, and the gastrointestinal system in regulating feeding behaviors.
... Cholecystokinin (CCK) is secreted in response to nutrients in the intestinal lumen [116,117] where it delays gastric emptying and inhibits food intake. Vagal afferent neurons are targeted by peripheral signals for the modulatory control of food intake and ORX administration can inhibit the influence of CCK on these neurons [118]. CCK activates ORX cells via the CCK-A receptor [119], whereas it has been shown to directly downregulate MCH-1R on vagal afferent neurons [118] and inhibit MCH release [120,121,122,123]. ...
... Vagal afferent neurons are targeted by peripheral signals for the modulatory control of food intake and ORX administration can inhibit the influence of CCK on these neurons [118]. CCK activates ORX cells via the CCK-A receptor [119], whereas it has been shown to directly downregulate MCH-1R on vagal afferent neurons [118] and inhibit MCH release [120,121,122,123]. The pancreatic peptide amylin and its receptor salmon calcitonin (sCT) have an inhibitory influence over the LHA; however, while both amylin and sCT decrease mRNA expression of ORX, only sCT reduced expression of MCH mRNA [124]. ...
The lateral hypothalamic area (LHA) is a heterogeneous brain structure extensively studied for its potent role in regulating energy balance. The anatomical and molecular diversity of the LHA permits the orchestration of responses to energy sensing cues from the brain and periphery. Two of the primary cell populations within the LHA associated with integration of this information are Orexin (ORX) and Melanin Concentrating Hormone (MCH). While both of these non-overlapping populations exhibit orexigenic properties, the activities of these two systems support feeding behavior through contrasting mechanisms. We describe the anatomical and functional properties as well as interaction with other neuropeptides and brain reward and hedonic systems. Specific outputs relating to arousal, food seeking, feeding, and metabolism are coordinated through these mechanisms. We then discuss how both the ORX and MCH systems harmonize in a divergent yet overall cooperative manner to orchestrate feeding behavior through transitions between various appetitive states, and thus offer novel insights into LHA allostatic control of appetite.
... Because orexin-A as a brain-gut peptide mainly exerts its effects on feeding behavior, it has become more and more appealing (Sakurai et al. 1998). Intracerebroventricular and intravenous injection of orexin-A increased gastric function in rats (Burdyga et al. 2003). Orexin-A exerts its effect via orexin-A receptors that are localized to the vagal afferent terminal (Burdyga et al. 2003). ...
... Intracerebroventricular and intravenous injection of orexin-A increased gastric function in rats (Burdyga et al. 2003). Orexin-A exerts its effect via orexin-A receptors that are localized to the vagal afferent terminal (Burdyga et al. 2003). Moreover, orexin-A, as a potent stimulant for gastrointestinal movement, is expected to be clinically applied as a gastroprokinetic medicine to solve the problem of reduced gastric motility such as postoperative gastric ileus after abdominal surgery (Kermani and Eliassi 2012;Gemici et al. 2015). ...
It has been well‐known that hypothalamic orexigenic neuropeptides, orexin‐A, and melanin‐concentrating hormone ( MCH ), play important roles in regulation of gastric function. However, what neural pathway mediated by the two neuropeptides affects the gastric function remains unknown. In this study, by way of nucleic stimulation and extracellular recording of single unit electrophysiological properties, we found that electrically stimulating the lateral hypothalamic area ( LH ) or microinjection of orexin‐A into the arcuate nucleus ( ARC ) excited most gastric distension‐responsive neurons in the nuclei and enhanced the gastric function including motility, emptying, and acid secretion of conscious rats. The results indicated that LH ‐ ARC orexin‐A‐ergic projections may exist and the orexin‐A in the ARC affected afferent and efferent signal transmission between ARC and stomach. As expected, combination of retrograde tracing and immunohistochemistry showed that some orexin‐A‐ergic neurons projected from the LH to the ARC . In addition, microinjection of MCH and its receptor antagonist PMC ‐3881‐ PI into the ARC affected the role of orexin‐A in the ARC , indicating a possible involvement of the MCH pathway in the orexin‐A role. Our findings suggest that there was an orexin‐A‐ergic pathway between LH and ARC which participated in transmitting information between the central nuclei and the gastrointestinal tract and in regulating the gastric function of rats.
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... In addition to CCK1 and CCK2 receptors, vagal afferent neurons also express ghrelin type 1 (GHS-1), orexin type 1 (OX-R1), MCH type 1 (MCH-1), cannabinoid CB1, and leptin receptors ( *** Burdyga et al., 2003Burdyga et al., , 2004Burdyga et al., , 2002Burdyga, Varro, Dimaline, Thompson, & Dockray, 2006a;Burdyga et al., 2006b). An interaction between ghrelin and CCK has been described, since pretreatment with CCK inhibited the orexigenic effect of ghrelin and, conversely, the anorectic effect of CCK was blunted by preadministration of ghrelin. ...
... Interestingly, it is known that CCK1 and ghrelin receptors colocalize in the nodose ganglia, and, therefore, they might interfere with the signal transmission generated by each other ( Date et al., 2005). For example, ghrelin and orexin are capable of inhibiting the discharge of vagal afferent neurons in response to CCK ( Burdyga et al., 2003;Date et al., 2005). ...
The endocannabinoid system functions as a potent regulator of feeding behavior and energy balance through complex central and peripheral mechanisms. Recent findings have demonstrated the existence of cooperation between peripheral cannabinoid CB1 receptors and the satiety hormone cholecystokinin (CCK). The two systems have opposing actions in the modulation of feeding: while endocannabinoids such as anandamide promote feeding, CCK controls gastrointestinal motility and appetite suppression. In this review, we examine the individual contribution of endocannabinoids and CCK in the modulation of appetite and explore the interaction between the two systems. We also highlight the potential benefits of simultaneously targeting peripheral CB1 and CCK1 receptors to design new therapies to fight obesity.
... In addition to CCK-A receptors, vagal afferent neurons also express the leptin receptor (Ob-R)49 and receptors associated with stimulation of food intake including the ghrelin (GHS-1),50 cannabinoid (CB1),51 orexin (OX-R1)52 and melanin-concentrating hormone (MCH-1)53 receptors. Among these, ghrelin and orexin A inhibit the discharge of vagal afferent neurons in response to CCK.52,54 Feeding studies demonstrated that the anorexic effect of CCK was blocked by pre-administration of ghrelin in rats. ...
... In addition to CCK-A receptors, vagal afferent neurons also express the leptin receptor (Ob-R)49 and receptors associated with stimulation of food intake including the ghrelin (GHS-1),50 cannabinoid (CB1),51 orexin (OX-R1)52 and melanin-concentrating hormone (MCH-1)53 receptors. Among these, ghrelin and orexin A inhibit the discharge of vagal afferent neurons in response to CCK.52,54 Feeding studies demonstrated that the anorexic effect of CCK was blocked by pre-administration of ghrelin in rats. Conversely, pretreatment with CCK inhibited the orexigenic effect of ghrelin. ...
The paradigm for the control of feeding behavior has changed significantly. In this review, we present evidence that the separation of function in which cholecystokinin (CCK) controls short-term food intake and leptin regulate long-term eating behavior and body weight become less clear. In addition to the hypothalamus, the vagus nerve is critically involved in the control of feeding by transmitting signals arising from the upper gut to the nucleus of the solitary tract. Among the peripheral mediators, CCK is the key peptide involved in generating the satiety signal via the vagus. Leptin receptors have also been identified in the vagus nerve. Studies in the rodents clearly indicate that leptin and CCK interact synergistically to induce short-term inhibition of food intake and long-term reduction of body weight. The synergistic interaction between vagal CCK-A receptor and leptin is mediated by the phosphorylation of signal transducer and activator of transcription3 (STAT3), which in turn, activates closure of K(+) channels, leading to membrane depolarization and neuronal firing. This involves the interaction between CCK/SRC/phosphoinositide 3-kinase cascades and leptin/Janus kinase-2/phosphoinositide 3-kinase/STAT3 signaling pathways. It is conceivable that malfunctioning of these signaling molecules may result in eating disorders.
... Not only do cholecystokinin (CCK) and ghrelin affect the NTS through the vagal nerve, but also via the circulation through the area postrema (Bauer et al., 2016). A vast range of receptors have been detected for hormones controlling food consumption in the vagal afferent neurons of the brainstem: CCK-1R and 2R for CCK and gastrin (Moriarty et al., 1997), leptin (Burdyga et al., 2002), insulin, glucagon-like peptide-1 receptor (GLP-1R) (Nakagawa et al., 2004), glucagon-like peptide-2 receptor (GLP-2R) (Nelson et al., 2007), and orexin receptor called hypocretin receptor 1 (HCRTR1) (Burdyga et al., 2003). The NTS expresses Y1, Y5, and MC4R and produces glucagon-like peptide-1 (GLP-1), NPY, POMC-derived α-MSH (these POMC neurons are important for short-term regulation) (Roh and Kim, 2016). ...
According to the World Health Organization report published in 2016, 650 million people worldwide suffer from obesity, almost three times more than in 1975. Obesity is defined as excessive fat accumulation which may impair health with non-communicable diseases such as diabetes, cardiovascular diseases (hypertension, coronary artery disease, stroke), and some cancers. Despite medical advances, cardiovascular complications are still the leading causes of death arising from obesity. Excessive fat accumulation is caused by the imbalance between energy intake and expenditure. The pathogenesis of this process is complex and not fully understood, but current research is focused on the role of the complex crosstalk between the central nervous system (CNS), neuroendocrine and immune system including the autonomic nervous system, adipose tissue, digestive and cardiovascular systems. Additionally, special attention has been paid to newly discovered substances: neuropeptide 26RFa, preptin, and adropin. It was shown that the above peptides are synthesized both in numerous structures of the CNS and in many peripheral organs and tissues, such as the heart, adipose tissue, and the gastrointestinal tract. Recently, particular attention has been paid to the role of the presented peptides in the pathogenesis of obesity, metabolic and cardiovascular system diseases. This review summarizes the role of newly investigated peptides in the crosstalk between brain and peripheral organs in the pathogenesis of obesity, metabolic, and cardiovascular diseases.
... In addition to CCK, VAN are also responsive to tension [138,[155][156][157][158][159][160][161], mucosal stroking [158][159][160]162], and express receptors for other ingestive signals including anorexigenic signals such as leptin [141,155,[163][164][165], GLP1 [166], PYY [167], urocortins [168], insulin [169], and α-melanocyte stimulating hormone (α-MSH) [170] and orexigenic signals such as ghrelin [160,[171][172][173][174], endocannabinoids [175][176][177][178][179], melanocortin-concentrating hormone (MCH) [172], and orexin [180]. VAN also have receptors for bacterial byproducts (e.g. ...
In 1973, Gibbs, Young, and Smith showed that exogenous cholecystokinin (CCK) administration reduces food intake in rats. This initial report has led to thousands of studies investigating the physiological role of CCK in regulating feeding behavior. CCK is released from enteroendocrine I cells present along the gastrointestinal (GI) tract. CCK binding to its receptor CCK1R leads to vagal afferent activation providing post-ingestive feedback to the hindbrain. Vagal afferent neurons’ (VAN) sensitivity to CCK is modulated by energy status while CCK signaling regulates gene expression of other feeding related signals and receptors expressed by VAN. In addition to its satiation effects, CCK acts all along the GI tract to optimize digestion and nutrient absorption. Diet-induced obesity (DIO) is characterized by reduced sensitivity to CCK and every part of the CCK system is negatively affected by chronic intake of energy-dense foods. EEC have recently been shown to adapt to diet, CCK1R is affected by dietary fats consumption, and the VAN phenotypic flexibility is lost in DIO. Altered endocannabinoid tone, changes in gut microbiota composition, and chronic inflammation are currently being explored as potential mechanisms for diet driven loss in CCK signaling. This review discusses our current understanding of how CCK controls food intake in conditions of leanness and how control is lost in chronic energy excess and obesity, potentially perpetuating excessive intake.
... Kirchgessner and Liu reported that Orexins play a role in the gastric and intestinal phase of secretion [46]. In addition, many literature data report the role of Orexin-A and B in appetite control [47,48]. Furthermore, it is known that Orexin inhibited responses to CCK suggesting its role in modulating gut-to-brain signaling. ...
The accumulation of adipose tissue represents one of the characteristics of obesity, increasing the risk of developing correlated obesity diseases such as cardiovascular disease, type 2 diabetes, cancer, and immune diseases. Visceral adipose tissue accumulation leads to chronic low inflammation inducing an imbalanced adipokine secretion. Among these adipokines, Adiponectin is an important metabolic and inflammatory mediator. It is also known that adipose tissue is influenced by Orexin-A levels, a neuropeptide produced in the lateral hypothalamus. Adiponectin and Orexin-A are strongly decreased in obesity and are associated with metabolic and inflammatory pathways. The aim of this review was to investigate the involvement of the autonomic nervous system focusing on Adiponectin and Orexin-A after bariatric surgery. After bariatric surgery, Adiponectin and Orexin-A levels are strongly increased independently of weight loss showing that hormone increases are also attributable to a rearrangement of metabolic and inflammatory mediators. The restriction of food intake and malabsorption are not sufficient to clarify the clinical effects of bariatric surgery suggesting the involvement of neuro-hormonal feedback loops and also of mediators such as Adiponectin and Orexin-A.
... VANs express both CCKRs, with CCK 1 more abundant than CCK 2 (Moriarty et al., 1997). Studies have shown CCK 1 localization with receptors of orexigenic hormones (ghrelin (Date et al., 2005;Burdyga et al., 2006b), orexin-A (Burdyga et al., 2003) and melanin concentrating hormone (Burdyga et al., 2006a), anorexigenic hormones (PYY (Burdyga et al., 2008), GLP-1 (Williams et al., 2016), and leptin (Burdyga et al., 2002;Li et al., 2011), as well as TRPV1 channels (Burdyga et al., 2006b) and cannabinoid CB1 receptors (Burdyga et al., 2004). Thus, lesioning CCK 1 -positive nodose neurons also impairs satiety signals trafficking between the gut and the brain mediated by these receptors. ...
Gastrointestinal (GI) vagal afferents convey sensory signals from the GI tract to the brain. Numerous subtypes of GI vagal afferent have been identified but their individual roles in gut function and feeding regulation are unclear. In the past decade, technical approaches to selectively target vagal afferent subtypes and to assess their function has significantly progressed. This review examines the classification of GI vagal afferent subtypes and discusses the current available techniques to study vagal afferents. Investigating the distribution of GI vagal afferent subtypes and understanding how to access and modulate individual populations are essential to dissect their fundamental roles in the gut-brain axis.
... Ghre projections are described outside the hypothalamus including the amygdala (Burdyga et al. 2003). These findings hypothesize an involvement of Ghre in neural transmission and neuronal function (Lu et al. 2002). ...
Ghrelin, a gastrointestinal hormone, is a modulator of the sense of smell. The main source of ghrelin in the central nervous system has been mainly observed in specific populations of hypothalamic neurons. An increasing number of studies have reported ghrelin synthesis and its effect on neurons outside the hypothalamus. Ghrelin and its receptors are expressed in the olfactory bulbs and in other centres of the brain, such as the amygdala, for processing olfactory signals, pyramidal neurons of the cerebral cortex and the dorsal vagal complex of the medulla oblongata. It is known that ghrelin is involved in cognitive mechanisms and eating behaviours, in fact, its expression increases in anticipation of food intake. In order to identify the existence of centrifugal direct afferents from the main olfactory bulb to the medial amygdala and the hypothalamus arcuate nucleus, in this work we used two retrograde tracers, Dil and Fluoro Gold, and immunohistochemical procedure to visualize positive ghrelin neurons. Our paper provides neuroanatomic support for the ghrelin modulation of smell. Our results show that ghrelin neuron projections from mitral cells of bulbs can transmit olfactory information via branching connections to the amygdala and the hypothalamus. This pathway could play an important role in regulating feeding behaviour in response to odours.
... CCK binds A-type receptors, found either in the periphery or in the brain, and B-type receptors, found only in the brain (Fink et al., 1998). CCK may act directly on the CNS (Blessing, 1997) and/or peripherally via vagal afferent fibers (Corp et al., 1993;Burdyga et al., 2003). Some authors reported that the main mechanism trough which CCK regulates food intake is the inhibition of gastric emptying (Moran and Kinzig, 2004). ...
Obesity is reaching epidemic proportions globally and represents a major cause of comorbidities, mostly related to cardiovascular disease. The autonomic nervous system (ANS) dysfunction has a two-way relationship with obesity. Indeed, alterations of the ANS might be involved in the pathogenesis of obesity, acting on different pathways. On the other hand, the excess weight induces ANS dysfunction, which may be involved in the haemodynamic and metabolic alterations that increase the cardiovascular risk of obese individuals, i.e., hypertension, insulin resistance and dyslipidemia. This article will review current evidence about the role of the ANS in short-term and long-term regulation of energy homeostasis. Furthermore, an increased sympathetic activity has been demonstrated in obese patients, particularly in the muscle vasculature and in the kidneys, possibily contributing to increased cardiovascular risk. Selective leptin resistance, obstructive sleep apnea syndrome, hyperinsulinemia and low ghrelin levels are possible mechanisms underlying sympathetic activation in obesity. Weight loss is able to reverse metabolic and autonomic alterations associated with obesity. Given the crucial role of autonomic dysfunction in the pathophysiology of obesity and its cardiovascular complications, vagal nerve modulation and sympathetic inhibition may serve as therapeutic targets in this condition.
... It is important to note that CCK-SAP will cause cell death of CCK receptor-expressing neurons rather than selectively knockdown CCK receptors in the neurons. Previous studies have observed extensive colocalization of Y2 receptor (11), GLP-1 receptor (49), vanilloid receptor 1 (16), leptin receptor (14), cannabinoid receptor 1 (13), ghrelin receptor 1a and 1b (16), melanin-concentrating hormone receptor 1 (15), and orexin receptor 1 (12) in VAN that express CCK-A receptors. This suggests that CCK-SAP ablation will inhibit a range of signals from the gut to the brain. ...
There is a lack of tools that selectively target vagal afferent neurons (VAN) innervating the gut. We use saporin (SAP), a potent neurotoxin, conjugated to the gastronintestinal (GI) hormone cholecystokinin (CCK-SAP) injected into the nodose ganglia (NG) of male Wistar rats to specifically ablate GI‐VAN. We report that CCK-SAP ablates a subpopulation of VAN in culture. In vivo, CCK-SAP injection into the NG reduces VAN innervating the mucosal and muscular layers of the stomach and small intestine but not the colon, while leaving vagal efferent neurons intact. CCK-SAP abolishes feeding-induced c-Fos in the NTS, as well as satiation by CCK or glucagon like peptide-1 (GLP-1). CCK-SAP in the NG of mice also abolishes CCK-induced satiation. Therefore, we provide multiple lines of evidence that injection of CCK-SAP in NG is a novel selective vagal deafferentation technique of the upper GI tract that works in multiple vertebrate models. This method provides improved tissue specificity and superior separation of afferent and efferent signaling compared with vagotomy, capsaicin, and subdiaphragmatic deafferentation.
NEW & NOTEWORTHY We develop a new method that allows targeted lesioning of vagal afferent neurons that innervate the upper GI tract while sparing vagal efferent neurons. This reliable approach provides superior tissue specificity and selectivity for vagal afferent over efferent targeting than traditional approaches. It can be used to address questions about the role of gut to brain signaling in physiological and pathophysiological conditions.
... Diminuição significativa nos níveis de expressão de CCK RNAm ocorreram, após a alimentação, no cérebro de Ictalurus punctatus (PETERSON et al., 2012) e C. auratus (PEYON et al., 1999) e nos cecos pilóricos de Seriola quinqueradiata(MURASHITA et al., 2007).A ação da CCK de estimular descargas em neurônios do nervo vago aferente e assim inibir a ingestão de alimento é potencializada pela distensão gástrica, leptina e urocortina(PETERS et al., 2004;BARRACHINA et al., 1997;MORAN, 1993;MORAN, 1991). Em contraste, orexina-A e grelina inibem a ação da CCK nesses neurônios(DATE et al., 2005;BURDYGA et al., 2003). Assim, neurônios do nervo vago aferente são capazes de modular sua resposta, inibição ou estimulação, ao consumo de alimentos, associada à expressão de moléculas de sinalização, com ênfase nos peptídeos gastrintestinais(DOCKRAY, 2009). ...
The diffuse neuroendocrine system (DNES) constitutes various types of
cells of the gastrointestinal system. These cells produce and secrete different
peptides, which exert several effects on the digestive process and feeding
behavior. The objective was to study, using immunohistochemistry, the
distribution of endocrine cells of the DNES, immunoreactive to the peptides
GAS, CCK-8, NPY and CGRP in the digestive system of dourado (Salminus
brasiliensis). Twelve juvenile fish with weight of 144.8 ± 21.7 g and total length
of 25.5 ± 3.5 cm were used. After 24 hours of fasting, the fish were euthanized
and samples were collected of five different segments: stomach: pyloric region
(PE); medium intestine: pyloric caeca (CP), loop 1 (A1) and loop 2 (A2); and
posterior intestine (IP). The tissue samples were fixed in Bouin solution for 12
hours, placed in 70% alcohol and processed according to routine histological
methods. For the immunohistochemistry, all the reactions were performed in a
humid chamber and, in the washing procedures, PBS 0.1 M was used. The
obstruction of the endogenous peroxidase and of non-specific bonds was done
using commercial reagents Dako®. The samples were incubated with polyclonal
primary antibody (Bachem, USA) against GAS, CCK-8, NPY and CGRP.
Subsequently, they were incubated with anti-rabbit secondary antibody
EnVision+System/HRP, revealed by the enzymatic method using 3.3
tetrahydrochloride diaminobenzidine, DAB, and counterstained with Carazzi
hematoxylin. The average number of immunoreactive endocrine cells for each
peptide in each sampled segment and in each fish was determined by the total
count of immunostained cells. The total number of cells was determined using a
microscope, while the area was measured capturing the image (20x objective)
correspondent to the total area of epithelial mucosa ascertained using the
program Image J. The resulting data were submitted to ANAVA in factorial
scheme and the means compared by the Tukey test at 5%. The use of developed
antibodies against mammal peptides was shown, for the first time, to be efficient
in the immunolocalization of GAS, CCK-8, NPY and CGRP in dourado. All the
peptides were identified in all the samples segments, despite being scarce in
certain segments. The largest number of endocrine cells immunoreactive to
GAS, CCK-8 and CGRP were, mainly, in the pyloric region of the stomach and
in the pyloric caeca. As for the NPY, the immunostained cells were notably
restricted to the medium intestine of the dourado.
... Distribution of CCK(1) receptors in the human brain might be very close to that seen in other species, but its characterization has been neglected. There are only reports of its presence in the spinal cord (Hill et al., 1988b) and nodose ganglia (Burdyga et al., 2003). ...
The CCK(1) receptor is a G-protein-coupled receptor activated by the sulfated forms of cholecystokinin (CCK), a gastrin-like peptide released in the gastrointestinal tract and mammal brain. A substantial body of research supports the hypothesis that CCK(1)r stimulates gallbladder contraction and pancreatic secretion in the gut, as well as satiety in brain. However, this receptor may also fulfill relevant roles in behavior, thanks to its widespread distribution in the brain. The strategic location of CCK(1)r in mesolimbic structures and specific hypothalamic and brainstem nuclei lead to complex interactions with neurotransmitters like dopamine, serotonin, and glutamate, as well as hypothalamic hormones and neuropeptides. The activity of CCK(1)r maintains adequate levels of dopamine and regulates the activity of serotonin neurons of raphe nuclei, which makes CCK(1)r an interesting therapeutic target for the development of adjuvant treatments for schizophrenia, drug addiction, and mood disorders. Unexplored functions of CCK(1)r, like the transmission of interoceptive sensitivity in addition to the regulation of hypothalamic hormones and neurotransmitters affecting emotional states, well-being, and attachment behaviors, may open exciting roads of research. The absence of specific ligands for the CCK(1) receptor has complicated the study of its distribution in brain so that research about its impact on behavior has been published sporadically over the last 30 years. The present review reunites all this body of evidence in a comprehensive way to summarize our knowledge about the actual role of CCK in the neurobiology of mental illness.
... Th e DVC consists of the dorsal motor nucleus of the vagus (DVN), the area postrema (AP), and the NTS within which POMC neurons exist (Schwartz 2010). Receptors for a variety of hormones controlling food intake have been found to be expressed in the brainstem vagal aff erent neurons including cholecystokinin (CCK) 1R and CCK 2R at which both CCK and gastrin act (Moriarty et al. 1997), insulin receptors, GLP-1 (Nakagawa et al. 2004) and GLP-2R (Nelson et al. 2007), growth hormone secretagogue receptor (GHS)-R1 at which ghrelin acts (Date et al. 2002), the orexin receptor, OX-R1 (Burdyga et al. 2003), and leptin (Burdyga et al. 2002). ...
The maintenance of the body weight at a stable level is a major determinant in keeping the higher animals and mammals survive. Th e body weight depends on the balance between the energy intake and energy expenditure. Increased food intake over the energy expenditure of prolonged time period results in an obesity. Th e obesity has become an important worldwide health problem, even at low levels. The obesity has an evil effect on the health and is associated with a shorter life expectancy. A complex of central and peripheral physiological signals is involved in the control of the food intake. Centrally, the food intake is controlled by the hypothalamus, the brainstem, and endocannabinoids and peripherally by the satiety and adiposity signals. Comprehension of the signals that control food intake and energy balance may open a new therapeutic approaches directed against the obesity and its associated complications, as is the insulin resistance and others. In conclusion, the present review summarizes the current knowledge about the complex system of the peripheral and central regulatory mechanisms of food intake and their potential therapeutic implications in the treatment of obesity.
... This inhibition is GABA independent and mediated by galanin neuropeptide due to galanin-expressing LH neurons (LHGal) (Laque et al., 2013). OX neurons also project to NTS and reverse the foodintake suppression mediated in this brain region by reversing the stimulatory effect of CCK on NTS neurons, specifically onto catecholaminergic NTS (NTSCA) neurons (Asakawa et al., 2002;Burdyga et al., 2003;Parise et al., 2011). ...
Abstract Food-intake control is mediated by a heterogeneous network of different neural subtypes, distributed over various hypothalamic nuclei and other brain structures, in which each subtype can release more than one neurotransmitter or neurohormone. The complexity of the interactions of these subtypes poses a challenge to understanding their specific contributions to food-intake control, and apparent consistencies in the dataset can be contradicted by new findings. For example, the growing consensus that arcuate nucleus neurons expressing Agouti-related peptide (AgRP neurons) promote feeding, while those expressing pro-opiomelanocortin (POMC neurons) suppress feeding, is contradicted by findings that low AgRP neuron activity and high POMC neuron activity can be associated with high levels of food intake. Similarly, the growing consensus that GABAergic neurons in the lateral hypothalamus suppress feeding is contradicted by findings suggesting the opposite. Yet the complexity of the food-intake control network admits many different network behaviors. It is possible that anomalous associations between the responses of certain neural subtypes and feeding are actually consistent with known interactions, but their effect on feeding depends on the responses of the other neural subtypes in the network. We explored this possibility through computational analysis. We made a computer model of the interactions between the hypothalamic and other neural subtypes known to be involved in food-intake control, and optimized its parameters so that model behavior matched observed behavior over an extensive test battery. We then used specialized computational techniques to search the entire model state space, where each state represents a different configuration of the responses of the units (model neural subtypes) in the network. We found that the anomalous associations between the responses of certain hypothalamic neural subtypes and feeding are actually consistent with the known structure of the food-intake control network, and we could specify the ways in which the anomalous configurations differed from the expected ones. By analyzing the temporal relationships between different states we identified the conditions under which the anomalous associations can occur, and these stand as model predictions. Computer code and data sets used in this analysis are available at: https://github.com/SigmoidNetmaker/food-intake-neural-network
... In contrast, the orexin and CCK receptors are expressed in vagal afferent neurons in humans and rats. The vagal afferent discharge increased by CCK was attenuated by prior administration of orexin 54 . This is an example of the antagonistic interaction between anorectic and orexigenic peptides through the vagus nerve. ...
The hypothalamus is a center of food intake and energy metabolism regulation. Information signals from peripheral organs are mediated via the circulation or the vagal afferent pathway and input into the hypothalamus, where signals are integrated to determine various behaviors such as eating. Numerous appetite-regulating peptides are expressed in the central nervous system and the peripheral organs and interact in a complex manner. Of such peptides, gut peptides are known to bind to receptors at the vagal afferent pathway terminal that extend into the mucosal layer of the digestive tract, modulate the electrical activity of the vagus nerve, and subsequently send signals to the solitary nucleus and furthermore to the hypothalamus. All peripheral peptides other than ghrelin suppress appetite, and they synergistically suppress appetite via the vagus nerve. On the other hand, the appetite-enhancing peptide ghrelin antagonizes the actions of appetite-suppressing peptides via the vagus nerve, and appetite-suppressing peptides have attenuated effects in obesity due to inflammation in the vagus nerve. With greater understanding of the mechanism for food intake and energy metabolism regulation, medications that apply the effects of appetite-regulating peptides or implantable devices that electrically stimulate the vagus nerve are being investigated as novel treatments for obesity in basic and clinical studies. This article is protected by copyright. All rights reserved.
... The few studies on this topic show that SGCs in NG are quite similar to those in other sensory ganglia. There is evidence for orexin receptors in SGCs in rat and human NG (Burdyga et al., 2003) and for BDNF receptors on SGCs in NG of rats (Wetmore and Olson, 1995). A calcium imaging study has shown that SGCs in rat NG are sensitive to glutamate and to ATP (via P2YR) and can release GABA (Shoji et al., 2010;Yokoyama et al., 2015). ...
Gastrointestinal (GI) pain is a common clinical problem, for which effective therapy is quite limited. Sensations from the GI tract, including pain, are mediated largely by neurons in the dorsal root ganglia (DRG), and to a smaller extent by vagal afferents emerging from neurons in the nodose/jugular ganglia. Neurons in rodent DRG become hyperexcitable in models of GI pain (e.g., gastric or colonic inflammation), and can serve as a source for chronic pain. Glial cells are another element in the pain signaling pathways, and there is evidence that spinal glial cells (microglia and astrocytes) undergo activation (gliosis) in various pain models and contribute to pain. Recently it was found that satellite glial cells (SGCs), the main type of glial cells in sensory ganglia, might also contribute to chronic pain in rodent models. Most of that work focused on somatic pain, but in several studies GI pain was also investigated, and these are discussed in the present review. We have shown that colonic inflammation induced by dinitrobenzene sulfonic acid (DNBS) in mice leads to the activation of SGCs in DRG and increases gap junction-mediated coupling among these cells. This coupling appears to contribute to the hyperexcitability of DRG neurons that innervate the colon. Blocking gap junctions (GJ) in vitro reduced neuronal hyperexcitability induced by inflammation, suggesting that glial GJ participate in SGC-neuron interactions. Moreover, blocking GJ by carbenoxolone and other agents reduces pain behavior. Similar changes in SGCs were also found in the mouse nodose ganglia (NG), which provide sensory innervation to most of the GI tract. Following therapeutic approaches to both pain types may be similar. Future research in this field should include additional types of GI injury and also other types of visceral pain.
... Accumulating evidence suggests that the vagus plays an important role in the transmission of peripheral satiety and orexigenic signals to the CNS. In addition to receptors for anorexigenic hormones, such as CCK (Zarbin et al. 1981) and leptin (Burdyga et al. 2002), the vagal sensory neurons also express receptors for orexigenic agents, such as ghrelin (Sakata et al. 2003), orexin A (Burdyga et al. 2003), cannabinoid (Burdyga et al. 2004) and melanin-concentrating hormone (Burdyga et al. 2006b). The nodose ganglia probably serve as a site of interaction for various peripheral signals involved in peptide regulation. ...
Ghrelin is the only known hunger signal derived from the peripheral tissues. Ghrelin overcomes the satiety signals evoked by anorexigenic molecules, such as cholecystokinin (CCK) and leptin, to stimulate feeding. The mechanisms by which ghrelin reduces the sensory signals evoked by anorexigenic hormones, which act via the vagus nerve to stimulate feeding, are unknown. Patch clamp recordings of isolated rat vagal neurons showed that ghrelin hyperpolarizes neurons by activating K(+) conductance. Administering a KATP channel antagonist or silencing Kir6.2, a major subunit of the KATP channel, abolished ghrelin inhibition in vitro and in vivo. Patch clamp studies showed that ghrelin inhibits currents evoked by leptin and CCK-8, which operate through independent ionic channels. Ghrelin's inhibitory actions were abolished by treating the vagal ganglia neurons with pertussis toxin, and PI3K or Erk1/2 siRNA. In vivo gene silencing of PI3K and Erk1/2 in the nodose ganglia prevented ghrelin inhibition of leptin- or CCK-8-evoked vagal firing. Feeding experiments showed that silencing Kir6.2 in the vagal ganglia abolished the orexigenic action of ghrelin. These data indicate that ghrelin modulates vagal ganglia neuron excitability by activating KATP conductance via the GSH-R1a-Gαi -PI3K-Erk1/2-KATP pathway. The resulting hyperpolarization renders the neurons less responsive to signals evoked by anorexigenic hormones. This provides a mechanism to explain the action of ghrelin to overcome anorexigenic signals that act via the vagal afferent pathways. This article is protected by copyright. All rights reserved.
This article is protected by copyright. All rights reserved.
... Compared with other sensory ganglia, little is known on SGCs in the NG. There is evidence for orexin receptors in rat and human NG (Burdyga et al., 2003) and BDNF receptors on SGCs in rats (Wetmore and Olson, 1995). A calcium imaging study has shown that SGCs in rat NG are sensitive to glutamate and can release GABA (Shoji et al., 2010). ...
Satellite glial cell (SGCs) in trigeminal and dorsal root ganglia are altered structurally and functionally under pathological conditions associated with chronic pain. These changes include reactive gliosis, augmented coupling by gap junctions, and increased responses to ATP via purinergic P2 receptors. Similar information for nodose ganglia (NG), which receive sensory inputs from internal organs via the vagus nerves, is missing. Here, we investigated changes in SGCs in mouse NG after the intraperitoneal administration of lipopolysaccharide (LPS), which induces systemic inflammation. Using calcium imaging we found that SGCs in intact, freshly isolated NG are sensitive to ATP, acting largely via purinergic P2 receptors (mixed P2X and P2Y), with threshold at 0.1 μM. A single systemic injection of LPS (2.5 mg/kg) induced a 6-fold increase in the responses to ATP, largely by augmenting the sensitivity of P2X receptors. Immunohistochemical analysis revealed that at 1-14 days post-LPS injection the expression of glial fibrillary acidic protein in SGCs was 2-3-fold greater than controls. The expression of pannexin 1 channels increased 2-fold at day 7 after LPS injection. Using intracellular labeling we examined dye coupling among SGCs around different neurons, and observed an over 2-fold higher incidence of dye coupling after the induction of inflammation. Incubating the ganglia with ATP increased dye coupling by acting on neuronal P2X receptors, suggesting a role for ATP in the LPS-induced changes. We conclude that inflammation induces prominent changes in SGCs of NG, which might have a role in vagal afferent functions, such as the inflammatory reflex. GLIA 2015.
© 2015 Wiley Periodicals, Inc.
... However, there are other signalling molecules with opposite (orexigenic) effect. Ghrelin (Date et al., 2002a;Kojima et al., 1999), orexin-A (Burdyga et al., 2003) and endocannabinoids (Gomez et al., 2002) stimulate feeding and accelerate gastric emptying. Subdiaphragmatic vagotomy or capsaicin treatment completely abolishes feeding and GH response to ghrelin, indicating that these effects are mediated by the vagal nerve (Date, 2012). ...
Along with the increase in life expectancy over the last century comes the increased risk for development of age-related disorders, including metabolic and neurodegenerative diseases such as Alzheimer’s, Parkinson’s and Huntington’s disease. These chronic disorders share two main characteristics: 1) neuronal loss in motor, sensory or cognitive systems, leading to cognitive and motor decline; and 2) a strong correlation between metabolic changes and neurodegeneration. In order to treat them, a better understanding of their complexity is required: it is necessary to interpret the neuronal damage in light of the metabolic changes, and to find the disrupted link between the peripheral organs governing energy metabolism and the CNS. This review is an attempt to present ghrelin as part of molecular regulatory interface between energy metabolism, neuroendocrine and neurodegenerative processes. Ghrelin takes part in lipid and glucose metabolism, in higher brain functions such as sleep-wake state, learning and memory consolidation; it influences mitochondrial respiration and shows neuroprotective effect. All these make ghrelin an attractive target for development of biomarkers or therapeutics for prevention or treatment of disorders, in which cell protection and recruitment of new neurons or synapses are needed.
... fasting) [89], but there are examples of upregulation in response to high fat diet feeding [90] although this is not consistently reported [91]. The ability for CCK to activate CCK1 receptors on vagal afferents is inhibited by the orexigenic peptides ghrelin, orexin A and anandamide [76,[92][93][94]. The ability for CCK to reduce food intake appears to be compromised in response to changes in nutrient composition [95]. ...
Vagal afferents are a vital link between the peripheral tissue and central nervous system (CNS). There is an abundance of vagal afferents present within the proximal gastrointestinal tract which are responsible for monitoring and controlling gastrointestinal function. Whilst essential for maintaining homeostasis there is an abundance of literature emerging which describes remarkable plasticity of vagal afferents in response to endogenous as well as exogenous stimuli. This plasticity for the most part is vital in maintaining healthy processes; however, there are increased reports of vagal plasticity being disrupted in pathological states, such as obesity. Many of the disruptions, observed in obesity, have the potential to reduce vagal afferent satiety signalling which could ultimately perpetuate the obese state. Understanding how plasticity occurs within vagal afferents will open a whole new understanding of gut function as well as identify new treatment options for obesity.
... Guinea pig ileal submucosal and myenteric neurons are excited by low or mid-nanomolar orexin-A (184,191). Vagal afferent neurons (nodose ganglia) of humans and rats express orexin receptor mRNA, and orexin-A inhibits cholecystokinin response; orexins may thus contribute to gutto-CNS signaling (52). ...
The neuropeptides orexins and their G-protein-coupled receptors, OX(1) and OX(2), were discovered in 1998, and since then, their role has been investigated in many functions mediated by the central nervous system, including sleep and wakefulness, appetite/metabolism, stress response, reward/addiction and analgesia. Orexins also have peripheral actions of less clear physiological significance still. Cellular responses to the orexin receptor activity are highly diverse. The receptors couple to at least three families of heterotrimeric G-proteins and other proteins which ultimately regulate entities such as phospholipases and kinases, that impact on neuronal excitation, synaptic plasticity and cell death. This article is a 10-year update of my previous review on the physiology of the orexinergic/hypocretinergic system. I seek to provide a comprehensive update of orexin physiology that spans from the molecular players in orexin receptor signaling to the systemic responses yet emphasizing the cellular physiological aspects of this system.
... In addition to the hypothalamus, the vagus nerve plays a central role in regulating the feeding. Vagal afferent neurons have been shown to express a variety of receptors within the brainstem, which include cholecystokinin (CCK) 1R and CCK2R (at which both CCK and gastrin act [197] ), Ob- R [198], Y2R [29], GLP-1 [67], and GLP-2R [199], growth hormone secretagogue receptor (GHS)-R1 where ghrelin acts [118], and the orexin receptor, OX-R1 [200]. The vagal stretch and tension sensors detect nutrients stored in the stomach. ...
Obesity is one of the major challenges to human health worldwide; however, there are currently no effective pharmacological interventions for obesity. Recent studies have improved our understanding of energy homeostasis by identifying sophisticated neurohumoral networks which convey signals between the brain and gut in order to control food intake. The hypothalamus is a key region which possesses reciprocal connections between the higher cortical centres such as reward-related limbic pathways, and the brainstem. Furthermore, the hypothalamus integrates a number of peripheral signals which modulate food intake and energy expenditure. Gut hormones, such as peptide YY, pancreatic polypeptide, glucagon-like peptide-1, oxyntomodulin, and ghrelin, are modulated by acute food ingestion. In contrast, adiposity signals such as leptin and insulin are implicated in both short- and long-term energy homeostasis. In this paper, we focus on the role of gut hormones and their related neuronal networks (the gut-brain axis) in appetite control, and their potentials as novel therapies for obesity.
... In situ hybridizations studies have also shown an overlap between CART and CB1 mRNA in the retrochiasmatic and lateral hypothalamic areas, as well as in all parts of the dorsal vagal complex [Jelsing et al., 2008]. The vagal afferent neurons express receptors for the satiety hormones CCK, leptin, and peptide YY, as well as the receptors for the orexigenic substances, including orexin, MCH, and CB1 [Burdyga et al., 2003]. In response to fasting or food intake, these neurons carry information from both the stomach and duodenum. ...
The CB1 receptor is a Class A G-protein coupled receptor that has a high density and widespread distribution within the central nervous system. Because of its neuroanatomical distribution, the endocannabinoid system can modulate a wide variety of psychological and physiological functions. For example, CB1 receptors are found in brain regions regulating motor activity, cognitive processes, pain, satiety, appetitive behaviors and reward. In correspondence with this distribution, modulation of the endocannabinoid system has been shown to produce changes in coordination, executive function, memory, mood, perception, wakefulness, nociception and appetite. Administration of cannabinoid agonists has also been therapeutically used to reduce nausea, and is also known to decrease body temperature and neuronal excitability, pointing to additional roles for endocannabinoids in these and other physiological/neurological processes. The ongoing elucidation and characterization of the neuroanatomical circuitry within which the CB1 cannabinoid receptor and endocannabinoids are localized to modulate these psychological and physiological processes continues to suggest therapeutic applications for cannabinoid antagonists and inverse agonists. Drug Dev Res 70:527–554, 2009. © 2009 Wiley-Liss, Inc.
... As discussed earlier CCK binds to CCK1R receptors on the local vagus fibers decreasing gastric emptying and increasing satiety (Schwartz and Moran, 1994). OXA modulates the vagal response to CCK via the CC1R receptor indicating that OXA may regulate gut-brain signaling by CCK (Burdyga et al., 2003). ...
... Orexin A immunoreactivity has been found in endocrine cells in gastric pyloric glands of rodents, where a subset co-localizes with gastrin, in addition to endocrine cells in the human stomach (Kirchgessner and Liu, 1999;De Miguel and Burrell, 2002;Nakabayashi et al., 2003). Orexin-1 receptor has also been localized in vagal afferent neurons of humans and rats, while orexin A has been shown to inhibit jejunal vagal afferent responses to CCK (see later Burdyga et al., 2003;2010). Although not directly investigated, it is possible that orexin A released from gastric endocrine cells could modulate the response of gastric vagal afferents to mechanical stimulation, thereby influencing gastric vagal afferent signalling of satiety. ...
Interest in pharmacological treatments for obesity that act in the brain to reduce appetite has increased exponentially over recent years, but failures of clinical trials and withdrawals due to adverse effects have so far precluded any success. Treatments that do not act within the brain are, in contrast, a neglected area of research and development. This is despite the fact that a vast wealth of molecular mechanisms exists within the gut epithelium and vagal afferent system that could be manipulated to increase satiety. Here we discuss mechano- and chemosensory pathways from the gut involved in appetite suppression, and distinguish between gastric and intestinal vagal afferent pathways in terms of their basic physiology and activation by enteroendocrine factors. Gastric bypass surgery makes use of this system by exposing areas of the intestine to greater nutrient loads resulting in greater satiety hormone release and reduced food intake. A non-surgical approach to this system is preferable for many reasons. This review details where the opportunities may lie for such approaches by describing nutrient-sensing mechanisms throughout the gastrointestinal tract.
Both brown and white adipose tissues (BAT/WAT) are innervated by the peripheral nervous system, including efferent sympathetic nerves that communicate from the brain/central nervous system out to the tissue, and afferent sensory nerves that communicate from the tissue back to the brain and locally release neuropeptides to the tissue upon stimulation. This bidirectional neural communication is important for energy balance and metabolic control, as well as maintaining adipose tissue health through processes like browning (development of metabolically healthy brown adipocytes in WAT), thermogenesis, lipolysis, and adipogenesis. Decades of sensory nerve denervation studies have demonstrated the particular importance of adipose sensory nerves for brown adipose tissue and WAT functions, but far less is known about the tissue’s sensory innervation compared to the better-studied sympathetic nerves and their neurotransmitter norepinephrine. In this review, we cover what is known and not yet known about sensory nerve activities in adipose, focusing on their effector neuropeptide actions in the tissue.
It is increasingly evident that bidirectional gut-brain signaling provides a communication pathway that uses neural, hormonal, and immunological routes to regulate homeostatic mechanisms such as hunger/satiety as well as emotions and inflammation. Hence, disruption of the gut-brain axis can cause numerous pathophysiologies, including obesity and intestinal inflammatory diseases. One chemical mediator in the gut-brain axis is orexin-A, given that hypothalamic orexin-A affects gastrointestinal motility and secretion, and peripheral orexin in the intestinal mucosa can modulate brain functions, making possible an orexinergic gut-brain network. It has been proposed that orexin-A acts on this axis to regulate nutritional processes, such as short-term intake, gastric acid secretion, and motor activity associated with the cephalic phase of feeding. Orexin-A has also been related to stress systems and stress responses via the hypothalamic-pituitary-adrenal axis. Recent studies on the relationship of orexin with immune system-brain communications in an animal model of colitis suggested an immunomodulatory role for orexin-A in signaling and responding to infection by reducing the production of pro-inflammatory cytokines (e.g., tumor necrosis factor α, interleukin-6, and monocyte chemoattractant protein-1). These studies suggested that orexin administration might be of potential therapeutic value in irritable bowel syndrome or chronic intestinal inflammatory diseases, in which gastrointestinal symptoms frequently coexist with behavioral disorders, including loss of appetite, anxiety, depression, and sleeping disorders. Interventions in the orexinergic system have been proposed as a therapeutic approach to these diseases and for the treatment of chemotherapeutic drug-related hyperalgesia and fatigue in cancer patients.
The regulation of energy and glucose balance contributes to whole-body metabolic homeostasis, and such metabolic regulation is disrupted in obesity and diabetes. Metabolic homeostasis is orchestrated partly in response to nutrient and vagal-dependent gut-initiated functions. Specifically, the sensory and motor fibres of the vagus nerve transmit intestinal signals to the central nervous system and exert biological and physiological responses. In the past decade, the understanding of the regulation of vagal afferent signals and of the associated metabolic effect on whole-body energy and glucose balance has progressed. This Review highlights the contributions made to the understanding of the vagal afferent system and examines the integrative role of the vagal afferent in gastrointestinal regulation of appetite and glucose homeostasis. Investigating the integrative and metabolic role of vagal afferent signalling represents a potential strategy to discover novel therapeutic targets to restore energy and glucose balance in diabetes and obesity.
A cell sheath enveloping the body of the neurons in sensory ganglia was mentioned for the first time in 1836 by Valentin, a pupil of Purkinje. In some illustrations of his paper, the nuclei of cells adjacent to the surface of the nerve cell body, both in the trigeminal ganglion and in the ganglia of the autonomic nervous system, were clearly shown (Fig. 1.1a) even though they were misinterpreted as pigment granules. Since Remak (1838) denied the existence of this perineuronal sheath, Valentin (1839) provided a more detailed description of it, illustrated with new drawings (Fig. 1.1b), the captions of which gave a correct interpretation of the satellite cell nuclei.
Cholecystokinin (CCK) regulates appetite and reduces food intake by activating the type 1 CCK receptor (CCK1R). Attempts to develop CCK1R agonists for obesity have yielded active agents that have not reached clinical practice. Here we discuss why, along with new strategies to target CCK1R more effectively. We examine signaling events and the possibility of developing agents that exhibit ligand-directed bias, to dissociate satiety activity from undesirable side effects. Potential allosteric sites of modulation are also discussed, along with desired properties of a positive allosteric modulator (PAM) without intrinsic agonist action as another strategy to treat obesity. These new types of CCK1R-active drugs could be useful as standalone agents or as part of a rational drug combination for management of obesity.
Orexin-A is mainly produced in the lateral hypothalamus (LHA) and the perifornical area (PeF). Here, we aim to elucidate the effects of orexin-A in the hippocampus (Hi) on gastric distention (GD)-sensitive neurons and gastric motility, and potential regulation mechanisms by the PeF. Retrograde tracing and fluorescent-immunohistochemical staining were used to determine orexin-A neuronal projections. Single unit discharges in the Hi were recorded extracellularly and gastric motility in conscious rats was monitored during administration of orexin-A to the Hi or electrical stimulation of the PeF. Orexin-A administration to the Hi excited most of the GD-excitatory (GD-E) neurons and GD-inhibitory (GD-I) neurons, and increased gastric motility in a dose-dependent manner. All of effects induced by orexin-A could be partly blocked by pretreatment with orexin-A antagonist, SB-334867. Electrical stimulation of the PeF excited the majority of the orexin-A-responsive GD neurons in the Hi and promoted gastric motility. Additionally, pretreatment with SB-334867 in the Hi increased the firing rate of GDI and GDE neurons following electrical stimulation of the PeF. These findings suggest that orexin-A could regulate activities of GD-sensitive neurons and gastric motility. Furthermore, the PeF may be involved in this regulatory pathway.
The progress in basic and clinical gastrology indicates that gastric mucosal integrity represents a balance between offensive and defensive factors, The main offensive factors appear to be gastric acid and pepsin under health conditions, while the nonsteroidal anti-inflammatory drugs (NSAID) and Helicobacter pylori (H. pylori), infecting this mucosa, are currently considered the most important "aggressive" factors under pathological conditions. To the list of the aggressive factors, also stress, certain cytokines (TNF-alpha, IL-8, IL-11 and IL-18) and oxygen or nitrogen free radicals should be added. The aims of this review is the presentation of the involvement of aggressive and protective factors in the control of gastric acid secretion and appetite regulating hormones in maintaining gastric mucosal integrity and its protection against damaging factors.
The orexins (from the Greek for "appetite", orexin A (synonymous with hypocretin-1; 33 amino acids) and orexin B (hypocretin-2; 28 residues)) are derived from the preprohcrt/orexin (preprohypocretin) gene. These two peptides interact with two G-proteincoupled receptors, hcrt/orexin receptor-1 and hcrt/orexin receptor-2. The hcrt/orexin receptor-1 is selective for hcrt 1/orexin A and the hcrt/orexin receptor-2 exhibits similar affinity for hcrt1 and 2/orexin A and B.1 (N.E. See note on nomenclature). © 2005 Springer Science Business Media, Inc. All rights reserved.
The role of the hypothalamus in the regulation of endocrine and autonomic functions has been known for more than fifty years. These co-ordinate actions are responsible for the control of several processes such as feeding, drinking, reproduction, lactation, cardiovascular function, metabolic control, thermoregulation, sleep-wake cycle and hormone secretion.1-3 The lateral hypothalamic area (LHA) is not part of the hypophysiotropic area (HTA) of the hypothalamus.3 However, compelling evidence has pointed out its implication in neuroendocrine control and hormonal secretion from pituitary.2,4,5. © 2005 Springer Science Business Media, Inc. All rights reserved.
Vagal afferent neurons receive signal stimuli of brain-gut peptides and then transfer them to hypothalamus to regulate food intake. As an important gastrointestinal hormone, cholecystokinin (CCK) plays a key role in the regulatory mechanism of brain-gut axis. CCK excites vagal afferent neurons and regulates the excitability of some G protein-coupled receptors. It also promotes the release of other peptide neurotransmitters. This article reviewed the advances in study on involvement of gastrointestinal hormones in the regulatory mechanism of brain-gut axis, especially the 'pivotal' role of CCK in vagal afferent pathway.
DefinitionThe time-derivative of the velocity vector of a specific particle. For a material body, at each instant of time there exists an acceleration field, namely an acceleration vector assigned to each particle of the body.MechanicsMeasurement Techniques
Nutrient perception in the gut is important for the maintenance of nutrient and energy balance in the body. Recently, nutrient perception has attracted the attention of medical researchers, as it may provide an opportunity to prevent obesity and associated disease. Recent progress in functional MRI (fMRI) techniques have enabled noninvasive investigation of whole brain function during the processing of information regarding ingested nutrients from the gut depending on the feeding status in both rodents and human subjects. However, the fMRI technique still has substantial problems because it relies on blood oxygenation levels. Here, a novel fMRI technique is introduced that solves this problem for rodent fMRI studies and fMRI studies of the gut-brain axis.
Background:
Ghrelin is the only known peripherally active orexigenic hormone produced by the stomach that activates vagal afferents to stimulate food intake and to accelerate gastric emptying. Vagal sensory neurons within the nodose ganglia are surrounded by glial cells, which are able to receive and transmit chemical signals. We aimed to investigate whether ghrelin activates or influences the interaction between both types of cells. The effect of ghrelin was compared with that of leptin and cholecystokinin (CCK).
Methods:
Cultures of rat nodose ganglia were characterized by immunohistochemistry and the functional effects of peptides, neurotransmitters, and pharmacological blockers were measured by Ca(2+) imaging using Fluo-4-AM as an indicator.
Key results:
Neurons responded to KCl and were immunoreactive for PGP-9.5 whereas glial cells responded to lysophosphatidic acid and had the typical SOX-10-positive nuclear staining. Neurons were only responsive to CCK (31 ± 5%) whereas glial cells responded equally to the applied stimuli: ghrelin (27 ± 2%), leptin (21 ± 2%), and CCK (30 ± 2%). In contrast, neurons stained more intensively for the ghrelin receptor than glial cells. ATP induced [Ca(2+) ]i rises in 90% of the neurons whereas ACh and the NO donor, SIN-1, mainly induced [Ca(2+) ]i changes in glial cells (41 and 51%, respectively). The percentage of ghrelin-responsive glial cells was not affected by pretreatment with suramin, atropine, hexamethonium or 1400 W, but was reduced by l-NAME and by tetrodotoxin. Neurons were shown to be immunoreactive for neuronal NO-synthase (nNOS).
Conclusions & inferences:
Our data show that ghrelin induces Ca(2+) signaling in glial cells of the nodose ganglion via the release of NO originating from the neurons.
Recent studies have identified a novel role for gut-derived peptides in the physiological regulation of appetite and body weight. This data is reviewed and the potential of peptide hormones, particularly ghrelin, PYY, GLP-1 and oxyntomodulin, as therapies for anorexia and obesity is explored.
Orexins play a role in many biological functions include sleep, feeding, and energy balance. They also regulate circadian rhythms and the way that we feel pain. Orexins have been identified in a variety of tissues including the cerebrospinal fluid, blood, hypothalamus, spinal cord, sensory ganglion, enteric nervous system, pituitary, adrenal, salivary and lacrimal glands, testis, vestibular gland, and skin. Orexins play a role in a variety of biological functions including arousal, sleeping, food and fluid intake, pain, memory, perception of odor, and sexual activity. Orexins have also been implicated in the regulation of glucose metabolism. The expression of orexin is induced by hypoglycemia, low food, pregnancy, and hemodialysis. In contrast, factors that inhibit the expression of orexins include obstructive sleep apnea, aging, depression, obesity, traumatic brain injury, and inflammatory molecules such as liposaccharide. In conclusion, orexins are widely distributed and involved in a large variety of biological activities.
The enteric nervous system is an integrative brain with collection of neurons in the gastrointestinal tract which is capable of functioning independently of the central nervous system (CNS). The enteric nervous system modulates motility, secretions, microcirculation, immune and inflammatory responses of the gastrointestinal tract. Dysphagia, feeding intolerance, gastroesophageal reflux, abdominal pain, and constipation are few of the medical problems frequently encountered in children with developmental disabilities. Alteration in bowel motility have been described in most of these disorders and can results from a primary defect in the enteric neurons or central modulation. The development and physiology of the enteric nervous system is discussed along with the basic mechanisms involved in controlling various functions of the gastrointestinal tract. The intestinal motility, neurogastric reflexes, and brain perception of visceral hyperalgesia are also discussed. This will help better understand the pathophysiology of these disorders in children with developmental disabilities.
We have investigated the pathway and the mechanism by which cholecystokinin octapeptide (CCK-8), given systemically, may influence the discharge of brain stem neurons that have an input from the stomach. Extracellular recordings were made from neurons in the nucleus of the solitary tract (NTS), where vagal afferents terminate, and from neighboring regions of the dorsal medial medulla. Gastric distension and CCK-8 injected intra-aortically close to the stomach evoked either excitatory or inhibitory responses that were abolished by cervical vagal section. In animals from which the celiac/superior mesenteric ganglia were removed, or the gastric antrum resected 2 weeks earlier, responses to gastric distension and CCK-8 were maintained. The effects of CCK-8 are unlikely to be secondary to changes in smooth muscle tone because CCK-8 decreased pressure in the body of the stomach, while distension increased it. Moreover, intravenous noradrenaline and vasoactive intestinal peptide had effects similar to CCK-8 on intragastric pressure, but evoked different patterns of responses from brain stem neurons. The results are consistent with the idea that CCK-8 acts directly on vagal mechanoreceptive endings in the gastric corpus wall. It is well known that peripheral administration of CCK-8 influences short-term regulation of food intake. The effects described here may reflect the pathway by which peripheral CCK influences CNS function.
We examined the effect of intravenously infused glucagon-like peptide 1 (GLP-1) on subjective appetite sensations after an energy-fixed breakfast, and on spontaneous energy intake at an ad libitum lunch. 20 young, healthy, normal-weight men participated in a placebo-controlled, randomized, blinded, crossover study. Infusion (GLP-1, 50 pmol/ kg.h or saline) was started simultaneously with initiation of the test meals. Visual analogue scales were used to assess appetite sensations throughout the experiment and the palatability of the test meals. Blood was sampled throughout the day for analysis of plasma hormone and substrate levels. After the energy-fixed breakfast, GLP-1 infusion enhanced satiety and fullness compared with placebo (treatment effect: P < 0.03). Furthermore, spontaneous energy intake at the ad libitum lunch was reduced by 12% by GLP-1 infusion compared with saline (P = 0.002). Plasma GLP-1, insulin, glucagon, and blood glucose profiles were affected significantly by the treatment (P < 0.002). In conclusion, the results show that GLP-1 enhanced satiety and reduced energy intake and thus may play a physiological regulatory role in controlling appetite and energy intake in humans.
Studies in animals suggest a physiological role for glucagon-like peptide-1-(7-36)-amide (GLP-1) in regulating satiety. The role of GLP-1 in regulating food intake in man has, however, not been investigated. Subjects-Sixteen healthy male subjects were examined in a double blind placebo controlled fashion.
The effect of graded intravenous doses (0, 0.375, 0.75, and 1.5 pmol/kg/min) of synthetic human GLP-1 on food intake and feelings of hunger and satiety was tested in healthy volunteers.
Graded GLP-1 infusions resulted in a dose dependent reduction in food intake (maximal inhibition 35%, p<0.001 v control) and a similar reduction in calorie intake (32%; p<0.001). Fluid ingestion was also reduced by GLP-1 (18% reduction, p<0.01). No overt side effects were produced by GLP-1, but subjects experienced less hunger and early fullness in the period before a meal during GLP-1 infusion at the highest dose (p<0.05).
Intravenous infusions of GLP-1 decrease spontaneous food intake even at physiological plasma concentrations, implying an important role for GLP-1 in the regulation of the early satiety response in humans.
Cocaine- and amphetamine-regulated transcript (CART) is widely expressed in the central nervous system. Recent studies have pointed to a role for CART-derived peptides in inhibiting feeding behavior. Although these actions have generally been attributed to hypothalamic CART, it remains to be determined whether additional CART pathways exist that link signals from the gastrointestinal tract to the central control of food intake. In the present study, we have investigated the presence of CART in the rat vagus nerve and nodose ganglion. In the viscerosensory nodose ganglion, half of the neuron profiles expressed CART and its predicted peptide, as determined by in situ hybridization and immunohistochemistry. CART expression was markedly attenuated after vagotomy, but no modulation was observed after food restriction or high-fat regimes. A large proportion of CART-labeled neuron profiles also expressed cholecystokinin A receptor mRNA. CART-peptide-like immunoreactivity was transported in the vagus nerve and found in a dense fiber plexus in the nucleus tractus solitarii. Studies on CART in the spinal somatosensory system revealed strong immunostaining of the dorsal horn but only a small number of stained cell bodies in dorsal root ganglia. The present results suggest that CART-derived peptides are present in vagal afferent neurons sensitive to cholecystokinin, suggesting that the role of these peptides in feeding may be explained partly by mediating postprandial satiety effects of cholecystokinin.
Orexin (hypocretin) appears to play a role in the regulation of energy balances. Previous reports have indicated that orexin-containing neurons are found only in the lateral hypothalamic (LH) area. We show that a subset of neurons in the gut which also express leptin receptors display orexin-like immunoreactivity and express functional orexin receptors. Orexin excites secretomotor neurons in the guinea pig submucosal plexus and increases motility. Moreover, fasting upregulates the phosphorylated form of cAMP response element-binding protein (pCREB) in orexin-immunoreactive neurons, indicating a functional response to food status in these cells. Together, these data suggest that orexin in the gut may play an even more intimate role in regulating energy homeostasis than it does in the CNS.
Leptin, neuropeptide-Y (NPY) and orexin are peptides regulating energy metabolism and appetite control. NPY and orexin are mainly found in the central nervous system and they have also recently been found in the peripheral nervous system. We investigated how fasting affects changes in circulating concentrations of these peptides and their association with nutritional and metabolic parameters in humans.
Ten non-obese female patients with psychosomatic disorders fasted for 7 or 10 days. Blood samples were collected at 0800 h before fasting, on the 3rd and 7th days during the fast (with an additional sample taken on the 10th day when the fasting continued for 10 days) and on the 3rd and 7th days of refeeding. We measured blood concentrations of orexin-A, NPY, leptin, adrenocorticotropin, cortisol, insulin, C-peptide, glucose, and beta-hydroxybutyrate.
Body mass index and plasma leptin concentrations concomitantly and significantly decreased during fasting, whereas serum orexin-A concentrations significantly increased and were negatively correlated with plasma leptin concentrations. Plasma NPY concentrations decreased slightly but were not significantly different from the prefasting values, and no significant relationship with leptin or orexin-A was found. Orexin-A and leptin concentrations showed a significant inverse correlation with serum glucose, insulin, C-peptide, and beta-hydroxybutyrate concentrations. Only changes in plasma leptin concentrations showed a significant negative correlation with serum cortisol concentrations. All the measured indices which changed during fasting returned to the prefasting concentrations by the 7th day of refeeding.
Peripheral orexin-A and leptin concentrations inversely change during fasting, which is significantly correlated with energy metabolism in humans.
BACKGROUND AND AIM The circulating peptide leptin produced by fat cells acts on central receptors to control food intake and body weight homeostasis. Contrary to initial reports, leptin expression has also been detected in the human placenta, muscles, and recently, in rat gastric chief cells. Here we investigate the possible presence of leptin and leptin receptor in the human stomach.
METHODS Leptin and leptin receptor expression were assessed by immunohistochemistry, reverse transcriptase-polymerase chain reaction (RT-PCR), and western blot analysis on biopsy samples from 24 normal individuals. Fourteen (10 healthy volunteers and four patients with non-ulcer dyspepsia and normal gastric mucosa histology) were analysed for gastric secretions. Plasma and fundic mucosa leptin content was determined by radioimmunoassay.
RESULTS In fundic biopsies from normal individuals, immunoreactive leptin cells were found in the lower half of the fundic glands. mRNA encoding ob protein was detected in the corpus of the human stomach. The amount of fundic leptin was 10.4 (3.7) ng leptin/g mucosa, as determined by radioimmunoassay. Intravenous infusions of pentagastrin or secretin caused an increase in circulating leptin levels and leptin release into the gastric juice. The leptin receptor was present in the basolateral membranes of fundic and antral gastric cells. mRNA encoding Ob-RL was detected in both the corpus and antrum, consistent with a protein of ∼120 kDa detected by immunoblotting.
CONCLUSION These data provide the first evidence of the presence of leptin and leptin receptor proteins in the human stomach and suggest that gastric epithelial cells may be direct targets for leptin. Therefore, we conclude that leptin may have a physiological role in the human stomach, although much work is required to establish this.
The role of cholecystokinin (CCK) in the effect of dietary lipid on proximal gastrointestinal function and satiety is controversial. Recent work suggests that fatty acid chain length may be a determining factor. We investigated the mechanism by which long- and short-chain fatty acids activate jejunal afferent nerves in rats. Whole mesenteric afferent nerve discharge was recorded in anaesthetized male Wistar rats during luminal perfusion of saline, sodium oleate, and sodium butyrate (both 10 mM). Both fatty acids evoked characteristic afferent nerve responses, distinct from the mechanical response to saline, that were abolished in rats following chronic subdiaphragmatic vagotomy. The effect of oleate was abolished by the CCK-A receptor antagonist Devazepide (0.5 mg/kg), whereas the effect of butyrate persisted despite pretreatment with either Devazepide or a combination of the calcium channel inhibitors nifedipine (1 mg/kg) and the omega -conotoxins GVIA and SVIB (each 25 mug/kg). In summary, long- and short-chain fatty acids activate intestinal vagal afferents by different mechanisms; oleate acts via a CCK-mediated mechanism and butyrate appears to have a direct effect on afferent terminals.
Leptin, the product of the ob gene, plays a key role in the regulation of food intake via a cross-talk between hypothalamic leptin receptors and neuropeptides that affect feeding behaviour. Recent studies have shown a synergistic interaction between leptin and cholecystokinin (CCK) leading to suppression of food intake, which involves CCK-1 receptors and capsaicin-sensitive vagal fibres. In this study, we have investigated the presence of leptin receptors in afferent and efferent neurons of the vagus nerve. By using reverse transcription-polymerase chain reaction, mRNAs encoding long (Ob-Rb) and short (Ob-Ra) leptin receptor isoforms were detected in the rat nodose ganglion, which contains the cell bodies of the vagal afferent neurons. Western blot analysis confirmed the presence of leptin receptor-immunoreactive proteins in extracts from the vagal trunk. Immunohistochemistry showed the presence of leptin receptors and the leptin-induced transcription factor STAT3 in the cytoplasm of nodose ganglion cells. In cervical vagal segments, levels of leptin receptor protein displayed physiological regulation, with decreased amounts after feeding and increased levels after food restriction. In addition, leptin receptor and STAT3 immunoreactivities were detected in neurons of the nucleus of tractus solitarius (NTS) and the dorsal motor nucleus of the vagus nerve (DMNX) by immunofluorescence histochemistry. Furthermore, direct double-labelling demonstrated colocalization of Ob-Rb and STAT3 immunoreactivities in cholinergic vagal efferent cell bodies of the DMNX. It is speculated that vagal leptin receptors, apart from being activated by adipocyte-derived leptin, may also be influenced by leptin produced by the stomach. This may explain the synergistic action of leptin and CCK on neuronal activity in the NTS and on food intake.
Orexins are novel neuropeptides that are localized in neurons within the lateral hypothalamus and regulate feeding behavior. The lateral hypothalamus also plays an important role in the central regulation of gut function. We therefore hypothesized that orexins might be involved in the central control of gastric acid secretion. To address this question, we examined the effect of central injection of orexins on gastric acid secretion in rats. Intracisternal injection of synthetic orexin-A but not orexin-B dose-dependently stimulated acid secretion while intraperitoneal administration of orexin-A failed to stimulate acid secretion. Vagotomy or atropine abolished the action by central orexin-A. These data suggest for the first time that orexin-A may act in the brain to stimulate gastric acid secretion by modulating the vagal system. Considering its stimulatory action on feeding, we hypothesize here that orexin-A is a candidate mediator of cephalic phase gastric secretion.
Leptin administered (either intracerebroventricularly, icv, or intraperitoneally, ip) acts in synergy with CCK to suppress food intake and body weight in lean mice or rats. The potentiating effect induced by the co-injection of ip CCK and leptin to inhibit food consumption in mice is mediated by the CCK-A receptor and capsaicin sensitive afferents. In vitro, studies in rats showed that a subset of gastric vagal afferent fibers responded to leptin injected directly into the gastric artery only after a prior intra-arterial CCK injection. Moreover, the tonic activity of gastric-related neurons in the nucleus tractus solitarius (NTS) increased when leptin was delivered into the gastric chamber of an in vitro stomach–brainstem preparation. CCK co-injected with leptin potentiated Fos expression selectively in the area postrema, NTS and paraventricular nucleus of the hypothalamus (PVN), which points to the PVN as part of the afferent and efferent limbs of the circuitry involved in the synergistic interaction between leptin and CCK. The dampening of CCK or leptin inhibitory action on ingestive behavior when either factor is not present or their receptors are non functional supports the notion that such leptin-CCK interaction may have a physiological relevance. These observations provide a mean through which leptin and CCK integrate short- and mid-term meal-related input signals into long-term control of energy balance.
The nucleus tractus solitarius is a key brain centre involved in the regulation of numerous autonomic functions. The present study has employed in vitro autoradiography and in vivo microdialysis to investigate the presence and function of nicotinic acetylcholine receptors located in the medial nucleus tractus solitarius of the rat. Autoradiography using [125I]α-bungarotoxin (0.5 nM) enabled visualization of binding sites on sections of rat and monkey brainstem. Specific binding was highest in the medial nucleus tractus solitarius. The presence of binding sites was also apparent on sections of rat nodose ganglia/vagus nerve and human inferior vagal ganglia. Subsequent to unilateral ligation of the vagus nerve in the rat, an accumulation of binding sites was visualized adjacent to the ligature. Unilateral nodose ganglionectomy in the rat caused an approximate 97% reduction in [125I]α-bungarotoxin binding site density in the medial nucleus tractus solitarius from 814±183 to 27±2 d.p.m./mm2. Microdialysis results indicated that local adminstration of nicotine (1 mM) into the nucleus tractus solitarius of the rat resulted in increases of extracellular l-glutamate of 146±9% of basal levels. This effect was not reproducible following a second stimulation and was also blocked by prior and co-administration of the nicotinic acetylcholine receptor antagonist mecamylamine (100 μM). Extracellular levels of l-aspartate exhibited a similar pattern although results were not significant.
The neurophysiological responses to 2-ml intragastric saline loads and 100-pmol celiac artery infusions of cholecystokinin (CCK) were obtained from 20 vagal afferent fibers in 14 rats. Two groups of fibers were identified. Discharge rates of group I fibers (n = 16) were significantly increased by gastric loading, adapted slowly to maintained gastric volume, and were inhibited by load withdrawal. CCK elicited a significant increase in the discharge rate of these group I fibers. Prior exposure to CCK nearly doubled the response of these fibers to a subsequent gastric load. In contrast, group II fibers (n = 4) increased firing rate only during infusion of a gastric load and showed rapid adaptation and no response to CCK. CCK failed to alter subsequent responses to gastric loads in these fibers. These results 1) demonstrate an integration of signals elicited by exogenous CCK and gastric loads at the level of vagal afferent fibers and 2) imply that aspects of CCK's inhibition of food intake may derive from CCK's ability to mimic and amplify vagal afferent activity provoked by meal-related gastric events.
The effects of various vagal lesions on cholecystokinin (CCK) binding sites in the nucleus tractus solitarii (NTS) and area postrema (AP) and the peripheral transport of CCK binding sites in the cervical vagus were examined in rats by in vitro autoradiography with [125I]CCK-8. Unilateral supraganglionic, but not subdiaphragmatic vagotomy significantly reduced CCK binding in the ipsilateral NTS. Specific unilateral afferent, but not efferent, vagal rootlet transections also significantly reduced NTS CCK binding ipsilateral to the transections. None of the vagal lesions altered CCK binding in the AP. Infraganglionic but not supraganglionic vagotomy eliminated the peripheral transport of vagal CCK binding sites. Together these results demonstrate that CCK receptors in the NTS are located on vagal afferent terminals, that CCK receptors in the AP are likely postsynaptic to a vagal afferent input and that the peripheral and central transport of vagal CCK binding sites occurs in afferent fibers.
In order to investigate the vagal afferent pathway responsible for the previously reported effects of cholecystokinin (CCK) on gastric emptying and food intake, single afferent fibres were recorded from the cervical vagus of urethane-anaesthetized ferrets. Sixty tension receptor afferents with receptive fields in the corpus, antrum, duodenum, jejunum and ileum all showed a resting level of discharge which was augmented powerfully by distension of the segment containing the ending. Close intraarterial injection of CCK-8 (100-200 pmol) caused relaxation in proximal regions, but enhanced contractile activity in more distal regions. Mechanoreceptor discharge closely followed intraluminal pressure at all times, indicating a sensitivity primarily to tension and no direct sensitivity to CCK. Only duodenal tension receptors were significantly excited by CCK (due to increased contractile activity), whereas those in the stomach showed a net decrease. Thirty-seven mucosal receptors from the corpus, antrum, duodenum and jejunum showed responses to luminal stimuli: predominantly light stroking, acidity and hypertonicity as has been previously described. No responses to glucose or amino-acid infusions could be evoked. However, mucosal fibres showed a strong sensitivity to close-intraarterially injected CCK-8 (3-200 pmol) in 19/26 fibres tested. These responses were unaffected by cholinergic blockade when tested. The data strongly suggest that in the ferret only vagal mucosal receptors are directly sensitive to CCK-8. These fibres are therefore likely candidates for mediating some of the reflex and behavioural effects of CCK when it is released from the gastrointestinal tract and acts directly on vagal sensory endings.
An antibody specific for the C-terminus of rat alpha calcitonin gene-related peptide has been used in radioimmunoassay to measure concentrations of immunoreactive peptide in the upper gastrointestinal tract of capsaicin-treated and coeliac ganglionectomized rats, and to measure axonal transport velocities in the vagus and splanchnic nerves. In adult rats that had been treated soon after birth with capsaicin, immunoreactive calcitonin gene-related peptide in the stomach and duodenum was undetectable (less than 0.1 pmol/g) compared with 4-10 pmol/g in control rats. Removal of the coeliac ganglion also reduced concentrations of immunoreactive calcitonin gene-related peptide by 5-fold, but Leu-enkephalin and Met-enkephalin Arg6Gly7Leu8-immunoreactivities (which are thought to occur in intrinsic gut neurons) were unchanged by coeliac ganglionectomy. Concentrations of calcitonin gene-related peptide immunoreactivity in coeliac ganglia were depressed by 90% in capsaicin-treated rats but concentrations of opioid peptide immunoreactivity were similar to control. The results suggest calcitonin gene-related peptide-immunoreactivity in the upper gastrointestinal tract in the rat is predominantly of extrinsic afferent origin. Chromatographic separation on Sephadex G50, or high-performance liquid chromatography revealed that the major immunoreactive form in stomach extracts corresponded to intact calcitonin gene-related peptide, although there was evidence of smaller, less hydrophobic C-terminal fragments. Direct evidence of transport of calcitonin gene-related peptide toward the gut was obtained by ligation of the cervical vagus and greater splanchnic nerves. There was accumulation on the central side of ligatures, which suggested axonal transport velocities in the vagus of about 1.5 mm/h and 0.7 mm/h in splanchnic nerves.(ABSTRACT TRUNCATED AT 250 WORDS)
Rats were surgically prepared to allow perfusions of anatomically limited portions of the gastrointestinal (GI) surface during test meals. The results demonstrated that at least one potent satiety signal was generated when ingested food accumulated in the stomach and did not enter the small intestine. This gastric satiety signal did not require the vagus nerve for its operation. In addition, at least one other potent satiety signal was generated when food perfused the small intestine. This intestinal satiety signal did not require gastric distension for its operation. We tested a variety of GI peptides to determine whether any met the criteria imposed by this evidence for regionally specific satiety signals. Bombesin (BBS), a peptide present in high concentration in the stomach, was a potent and behaviorally specific inhibitor of food intake. Its satiating effect was not altered by subdiaphragmatic vagotomy. Cholecystokinin (CCK), a peptide hormone that is released from the small intestine by food, was also a potent and behaviorally specific inhibitor of food intake; its satiating effect did not require gastric distension for its expression, but its satiating effect was markedly reduced or abolished by subdiaphragmatic vagotomy. Thus, BBS and CCK may mediate at least part of the satiating effect of food acting in the stomach and in the small intestine, respectively.
Cholecystokinin (CCK) receptors have been detected in the rat vagus nerve. Ligation experiments have revealed a time dependent build up of the receptors at the ligature which is blocked by colchicine. Thus, at least a fraction of the receptors are being transported peripherally, presumably by fast flow. The possible involvement of these vagal CCK receptors with the ability of CCK to induce satiety is discussed.
Signals for meal termination are traced to the stomach rather than duodenum or mouth when rats eat familiar food. Two types of signal occur, one measuring amount of nutrient independent of volume or dilution, the other gastric distention. The signals concerning the second ascend the vagus. Nutrient content is measured by some product of the digestive breakdown of the nutrient. The nutrient signals have to be calibrated through a process of learning. The gastric signals generated by food with a novel flavor are disregarded and oropharyngeal cues assume control instead. Finally, evidence against the role of cholecystokinin and bombesin in satiety is presented.
The present study used in vitro autoradiography to assess whether high affinity D2 binding sites are present on sections of human inferior vagal ganglia, where arterial baroreceptor primary afferent cell bodies are located. Incubation of tissue sections with [125I]NCQ 298 (0.5 nM) revealed dense but non-uniform binding, with a well-defined topography, consistent with the localization of binding sites over cell bodies rather than nerve axons. Coincubation with the D2 antagonist raclopride (10 microM) completely abolished binding of [125I]NCQ 298. Densitometric quantification of autoradiograms estimated 82 +/- 4% specific binding for [125I]NCQ 298 (0.5 nM). These observations indicate the presence of D2 binding sites on sensory ganglia involved in cardiovascular control pathways in the human, and may help to explain some of the documented cardiovascular effects of dopamine.
We have established a method to investigate the range of mechanical, nutrient chemical and peptidergic meal-related stimuli t hat may generate vagal afferent neurophysiological signals critical to the negative feedback control of food intake in the rat. We have identified populations of fibers that respond with increased neurophysiological discharge rates to gastric loads, duodenal loads, and close celiac arterial administration of a brain-gut peptide, cholecystokinin. Load-sensitive fibers with gastric and duodenal mechanoreceptive fields are able to integrate information arising from mechanical and peptidergic stimulation, where cholecystokinin octapeptide (CCK) administration potentiates subsequent responses to distending loads, and synergizes with distending loads to produce greater excitation than either load stimulus alone or peptide stimulation alone. In addition, we have identified situations where the duodenal presence of nutrients modifies the vagal afferent activity of gastric load-sensitive fibers. Thus, our approach can mimic the temporal and spatial distribution of meal-related stimuli in the gut, and reveals the potential for nutrients in one gastrointestinal compartment to affect neutral signals arising from another gut compartment.
1. Extracellular recordings from rat mesenteric paravascular nerve bundles were made in order to characterize the responses of different populations of afferents supplying the small intestine to intravenous cholecystokinin (CCK; in the form of sulphated CCK8). 2. Approximately 70% of mesenteric nerve bundles contained CCK-sensitive afferent fibres. Responsive afferents had low spontaneous discharge (1.6 +/- 0.3 impulses s-1) and showed a 14-fold increase in firing at the peak of the response to 50 pmol CCK with the overall response lasting several minutes. The onset of the response occurred after a latency of (3.9 +/- 0.1 s) following i.v. administration of CCK, which corresponds largely to the circulation delay in these animals. The threshold dose of CCK was < 5 pmol. 3. The response to 100 pmol CCK was completely abolished by devazepide (0.5 mg kg-1) and by chronic subdiaphragmatic vagotomy performed 10-14 days prior to experimentation, indicating that CCK sensitivity was via CCKA receptors and exclusively mediated via vagal afferents rather than splanchnic or enteric afferents. 4. Evidence that CCK-sensitive afferents had mucosal receptive fields was indicated by the lack of any response to luminal distension and the sensitivity of the CCK response to luminal anaesthesia. Furthermore, CCK-sensitive afferents responded to luminal hydrochloric acid (50 mM) in a slowly adapting manner. The response to acid was significantly reduced (P < 0.005), but not abolished, by devazepide at a time when the response to exogenous CCK had been completely eliminated. 5. The exquisite sensitivity of some vagal mucosal afferents to CCK suggests that they may play a physiological role in the reflex and behavioural consequences of CCK release from the small intestine, possibly acting in a paracrine fashion. However, this sensitivity to CCK represents only one aspect of the broad chemosensitivity of these mucosal afferents and is not an obligatory component of the signal transduction pathway.
The cholecystokinin receptors expressed by vagal afferent neurons mediate the effect of cholecystokinin in inhibiting food intake and gastric emptying. We have determined the relative abundance of cholecystokininA, gastrin-cholecystokininB and gastrin-cholecystokininC receptor populations in the rat vagus by autoradiography using [125I]Bolton Hunter-cholecystokinin-8, [125I]Bolton Hunter-heptadecapeptide gastrin and [125I]Leu(15)2-17Glycine-extended heptadecapeptide gastrin, together with the selective antagonists devazepide and L-740093. The results indicate approximately three-fold higher abundance of cholecystokininA compared with gastrin-cholecystokininB receptors, and no significant representation of gastrin-cholecystokininC receptors. Topical capsaicin applied to the vagal nerve trunk abolished the accumulation of sites binding both [125I]Bolton Hunter-labelled cholecystokinin-8 and heptadecapeptide gastrin indicating that both cholecystokininA and gastrin-cholecystokininB receptor populations were present on afferent fibres. The molecular identity of the receptors expressed by rat and human nodose ganglia was examined using the reverse transcription polymerase chain reaction. Products of the predicted size for the cholecystokininA and gastrin-cholecystokininB receptors were identified. The human and rat cholecystokininA receptor products were cloned and the sequences were found to be 99% homologous to those published for receptors expressed by rat pancreas and human gall bladder. We conclude that cholecystokininA and gastrin-colecystokininB receptors are synthesized by nodose ganglion cells, and that the receptor proteins are transported to the periphery along afferent fibres. While there is a clear role for vagal cholecystokininA receptors, the function of vagal afferent gastrin-cholecystokininB receptors remains to be determined.
In vitro gastric vagal afferents' (GVAs) unit activities were recorded from the ventral GVA nerve strands in rats. The responsiveness of 16 GVA terminals to close intra-arterial injection of vehicle (0.1 ml), leptin (350 pmol), and cholecystokinin (CCK)-8 (10 pmol) was analyzed to generate a spike count-versus-time histogram. Data of 5-min spike counts before and after each treatment were normalized by dividing the latter by the former. A quotient (Q) > 1 indicates an excitatory effect, Q < 1 indicates an inhibitory effect, and Q close to 1 indicates no effect. Two types of GVA terminals were identified. Type 1 (n = 8) responded to leptin with Q > 1; CCK-8 pretreatment did not consistently alter leptin sensitivity. In contrast, Type 2 (n = 8) responded to leptin with Q < 1 or close to 1, and CCK-8 pretreatment increased the leptin sensitivity so that the terminals responded to subsequent leptin with Q > 1. These data suggest that Type 1 and Type 2 GVA terminals may provide afferent neural signals, which, in turn, will be involved in body weight and food intake control systems, respectively.
The hypothalamus plays a central role in the integrated control of feeding and energy homeostasis. We have identified two novel neuropeptides, both derived from the same precursor by proteolytic processing, that bind and activate two closely related (previously) orphan G protein-coupled receptors. These peptides, termed orexin-A and -B, have no significant structural similarities to known families of regulatory peptides. prepro-orexin mRNA and immunoreactive orexin-A are localized in neurons within and around the lateral and posterior hypothalamus in the adult rat brain. When administered centrally to rats, these peptides stimulate food consumption. prepro-orexin mRNA level is up-regulated upon fasting, suggesting a physiological role for the peptides as mediators in the central feedback mechanism that regulates feeding behavior.
The present study has employed in vitro electrophysiology to characterise the ability of bradykinin to depolarise the rat isolated nodose ganglion preparation, containing the perikarya of vagal afferent neurons. Both bradykinin and kallidin elicited a concentration-dependent (1-100 nM) depolarisation when applied to the superfusate bathing the nodose ganglia, whereas the bradykinin B1 receptor agonist, des-Arg9-bradykinin, was only effective in the micromolar range. Furthermore, the electrophysiological response to bradykinin was antagonised by the bradykinin B2 receptor antagonist, D-arginyl-L-arginyl-L-prolyl-trans-4-hydroxy-L-prolylglycyl-3-(2-t hienyl)-L-alanyl-L-seryl-D-1,2,3,4-tetrahydro-3-isoquinolinecarbonyl+ ++-L-(2alpha,3beta,7abeta)-octahydro-1H-indole-2-carbonyl-L- arginine (Hoe 140), in a concentration-related manner. To determine the anatomical location of functional bradykinin B2 receptors, in vitro autoradiography with [125I]para-iodophenyl Hoe 140 was performed on sections of rat and human inferior vagal (nodose) ganglia and confirmed the presence of binding over vagal perikarya. Collectively, these data provide evidence for functionally relevant bradykinin B2 receptors on vagal afferent neurons, which are apparently also present on human vagal perikarya.
The circulating peptide leptin, which is the product of the ob gene, provides feedback information on the size of fat stores to central Ob receptors that control food intake and body-weight homeostasis. Leptin has so far been reported to be secreted only by adipocytes and the placenta. Here we show that leptin messenger RNA and leptin protein are present in rat gastric epithelium, and that cells in the glands of the gastric fundic mucosa are immunoreactive for leptin. The physiological function of this previously unsuspected source of leptin is unknown. However, both feeding and administration of CCK-8 (the biologically active carboxy-terminal end of cholecystokinin) result in a rapid and large decrease in both leptin cell immunoreactivity and the leptin content of the fundic epithelium, with a concomitant increase in the concentration of leptin in the plasma. These results indicate that gastric leptin may be involved in early CCK-mediated effects activated by food intake, possibly including satiety.
This electrophysiological study was performed to elucidate the interactions of serotonin (5-hydroxytryptamine, 5-HT) and cholecystokinin (CCK) on mesenteric afferents supplying the rat jejunum. 5-HT and CCK produced characteristic responses in multi-unit recordings of mesenteric afferents. Waveform analysis to extract single units from the whole nerve recording identified populations of single afferents that were sensitive to either 5-HT or CCK, but not both. Furthermore, devazepide (0.5 mg/kg) completely abolished the response to CCK without altering the response to 5-HT while granisetron (0.5 mg/kg) abolished the response to 5-HT with no effect on the response to CCK. These results suggest that there are discrete, noninteractive populations of jejunal afferents that possess either 5-HT3 or CCK-A receptors but not both.
Fatty acids induce cholecystokinin (CCK) secretion and modify gastric motility, but the chain length requirements for these effects are not known. Nor is it clear whether the effects of fatty acids on gastric motility in humans are CCK mediated or directly exerted. The aim of this study was to determine the role of fatty acyl chain length in CCK secretion and in influencing gastric motility.
Fatty acids were infused into the upper gut in healthy volunteers; plasma CCK was determined by radioimmunoassay. Effects of fatty acids on antral contractility were determined by percutaneous ultrasonography; effects on proximal gastric tone were studied during fundal distention.
Plasma CCK concentration was consistently and similarly elevated by fatty acids with a chain of 12 carbon atoms or longer, whereas those of 11 or fewer carbon atoms failed to increase plasma CCK. A 12-carbon but not a 10-carbon-long chain fatty acid reduced antral contractile amplitude, an effect that was abolished by loxiglumide (a specific CCK-A receptor antagonist). The 12-carbon fatty acid also reduced proximal gastric tone more than the 10-carbon fatty acid.
A highly specific, chain length-sensitive fatty acid recognition system exists in the proximal gut mediating CCK secretion and gastric motility. An additional, probably CCK-independent, effect of fatty acid also regulates proximal gastric tone.
Two distinct receptors, cholecystokinin (CCK)-A and CCK-B, mediate CCK effects in the digestive system. The aim of this study was to elucidate the cellular sites of expression of CCK-A receptor in the rat stomach and small intestine.
We developed and characterized an antibody to the N-terminal region (LDQPQPSKEWQSA) of rat CCK-A receptor and used it for localization studies with immunohistochemistry.
Specificity of the antiserum was demonstrated by (1) detection of a broad band at 85-95 kilodaltons in Western blots of membranes from CCK-A receptor CHO-transfected cells; (2) cell surface staining of CCK-A receptor-transfected cells, (3) translocation of CCK-A receptor immunostaining in CCK-A receptor-transfected cells after exposure to CCK; and (4) abolition of tissue immunostaining by preadsorbtion of the antibody with the peptide used for immunization. CCK-A receptor immunoreactivity was localized to myenteric neurons and to fibers in the muscle and mucosa. In the stomach, myenteric neurons and mucosal fibers were abundant. Many CCK-A receptor myenteric neurons contained the inhibitory transmitter vasoactive intestinal polypeptide, and some were immunoreactive for the excitatory transmitter substance P. Subdiaphragmatic vagotomy reduced the density of CCK-A receptor fibers in the gastric mucosa by approximately 50%, whereas celiac/superior mesenteric ganglionectomy had no detectable effect on fiber density.
CCK-A receptor is expressed in functionally distinct neurons of the gastrointestinal tract. CCK-A receptor may mediate reflexes stimulated by CCK through the release of other transmitters from neurons bearing the receptor.
The circulating peptide leptin produced by fat cells acts on central receptors to control food intake and body weight homeostasis. Contrary to initial reports, leptin expression has also been detected in the human placenta, muscles, and recently, in rat gastric chief cells. Here we investigate the possible presence of leptin and leptin receptor in the human stomach.
Leptin and leptin receptor expression were assessed by immunohistochemistry, reverse transcriptase-polymerase chain reaction (RT-PCR), and western blot analysis on biopsy samples from 24 normal individuals. Fourteen (10 healthy volunteers and four patients with non-ulcer dyspepsia and normal gastric mucosa histology) were analysed for gastric secretions. Plasma and fundic mucosa leptin content was determined by radioimmunoassay.
In fundic biopsies from normal individuals, immunoreactive leptin cells were found in the lower half of the fundic glands. mRNA encoding ob protein was detected in the corpus of the human stomach. The amount of fundic leptin was 10.4 (3.7) ng leptin/g mucosa, as determined by radioimmunoassay. Intravenous infusions of pentagastrin or secretin caused an increase in circulating leptin levels and leptin release into the gastric juice. The leptin receptor was present in the basolateral membranes of fundic and antral gastric cells. mRNA encoding Ob-RL was detected in both the corpus and antrum, consistent with a protein of approximately 120 kDa detected by immunoblotting.
These data provide the first evidence of the presence of leptin and leptin receptor proteins in the human stomach and suggest that gastric epithelial cells may be direct targets for leptin. Therefore, we conclude that leptin may have a physiological role in the human stomach, although much work is required to establish this.
Leptin administered (either intracerebroventricularly, icv, or intraperitoneally, ip) acts in synergy with CCK to suppress food intake and body weight in lean mice or rats. The potentiating effect induced by the co-injection of ip CCK and leptin to inhibit food consumption in mice is mediated by the CCK-A receptor and capsaicin sensitive afferents. In vitro, studies in rats showed that a subset of gastric vagal afferent fibers responded to leptin injected directly into the gastric artery only after a prior intra-arterial CCK injection. Moreover, the tonic activity of gastric-related neurons in the nucleus tractus solitarius (NTS) increased when leptin was delivered into the gastric chamber of an in vitro stomach-brainstem preparation. CCK co-injected with leptin potentiated Fos expression selectively in the area postrema, NTS and paraventricular nucleus of the hypothalamus (PVN), which points to the PVN as part of the afferent and efferent limbs of the circuitry involved in the synergistic interaction between leptin and CCK. The dampening of CCK or leptin inhibitory action on ingestive behavior when either factor is not present or their receptors are non functional supports the notion that such leptin-CCK interaction may have a physiological relevance. These observations provide a mean through which leptin and CCK integrate short- and mid-term meal-related input signals into long-term control of energy balance.
: Ghrelin, an endogenous ligand for growth hormone secretagogue receptor, was recently identified in the rat stomach. We examined the effects of the gastric peptide ghrelin on energy balance in association with leptin and vagal nerve activity.
: Food intake, oxygen consumption, gastric emptying, and hypothalamic neuropeptide Y (NPY) messenger RNA expression were measured after intra-third cerebroventricular or intraperitoneal injections of ghrelin in mice. The gastric vagal nerve activity was recorded after intravenous administration in rats. Gastric ghrelin gene expression was assessed by Northern blot analysis. Repeated coadministration of ghrelin and interleukin (IL)-1 beta was continued for 5 days.
: Ghrelin exhibited gastroprokinetic activity with structural resemblance to motilin and potent orexigenic activity through action on the hypothalamic neuropeptide Y (NPY) and Y(1) receptor, which was lost after vagotomy. Ghrelin decreased gastric vagal afferent discharge in contrast to other anorexigenic peptides that increased the activity. Ghrelin gene expression in the stomach was increased by fasting and in ob/ob mice, and was decreased by administration of leptin and IL-1 beta. Peripherally administered ghrelin blocked IL-1 beta-induced anorexia and produced positive energy balance by promoting food intake and decreasing energy expenditure.
: Ghrelin, which is negatively regulated by leptin and IL-1 beta, is secreted by the stomach and increases arcuate NPY expression, which in turn acts through Y(1) receptors to increase food intake and decrease energy expenditure. Gastric peptide ghrelin may thus function as part of the orexigenic pathway downstream from leptin and is a potential therapeutic target not only for obesity but also for anorexia and cachexia.
Orexins-A and -B are neuropeptides derived from a single precursor prepro-orexin. The mature peptides are mainly expressed in the lateral hypothalamic and perifornical areas. The orexins have been implicated in the control of arousal and appear to be important messengers in the regulation of food intake. Two receptors for orexins have been characterised so far: orexin-1 and -2 receptors. To gain a further understanding of the biology of orexins, we studied the distribution of the orexin-1 receptor messenger RNA and protein in the rat nervous system. We first assessed the expression profile of the orexin-1 receptor gene (ox-r1) in different regions by using quantitative reverse transcription followed by polymerase chain reaction. Using immunohistochemical techniques, we investigated the distribution of orexin-1 receptor protein in the rat brain using a rabbit affinity-purified polyclonal antiserum raised against an N-terminal peptide. The orexin-1 receptor was widely and strongly expressed in the brain. Thus, immunosignals were observed in the cerebral cortex, basal ganglia, hippocampal formation, and various other subcortical nuclei in the hypothalamus, thalamus, midbrain and reticular formation. In particular, robust immunosignals were present in many hypothalamic and thalamic nuclei, as well as in the locus coeruleus. The distribution of the receptor protein was generally in agreement with the distribution of the receptor messenger RNA in the brain as reported previously by others and confirmed in the present study. In addition, we present in situ hybridisation and immunohistochemical data showing the presence of orexin-1 receptor messenger RNA and protein in the spinal cord and the dorsal root ganglia. Finally, due to the shared anatomical and functional similarities between orexins and melanin-concentrating hormone, we present a comparison between the neuroanatomical distribution of the orexin-1 receptor and melanin-concentrating hormone receptor protein-like immunoreactivities in the rat central nervous system, and discuss some functional implications. In conclusion, our neuroanatomical data are consistent with the biological effects of orexins on food intake and regulation of arousal. In addition, the data suggest other physiological roles for orexins mediated through the orexin-1 receptor.
Cholecystokinin (CCK) is an important satiety factor, acting via the vagus nerve to influence central feeding centers. CCK binding sites have been demonstrated in the vagal sensory nodose ganglion and within the nerve proper. Using in situ hybridization, expression of the CCK(A) and (B) receptors (Rs), as well as of CCK itself, was studied in the normal nodose ganglion (NG), and after vagotomy, starvation and high-fat diet. CCK(A)-R mRNA expression in dorsal root ganglia (DRGs) was also explored. In the NG, 33% of the neuron profiles (NPs) contained CCK(A)-R mRNA and in 9% we observed CCK(B)-R mRNA. CCK mRNA was not found in normal NGs. Peripheral vagotomy decreased the number of CCK(A)-R mRNA-expressing NPs, dramatically increased the number of CCK(B)-R mRNA, and induced CCK mRNA and preproCCK-like immunoreactivity in nodose NPs. No significant differences in the number of NPs labelled for either mRNA species were detected following 48 h food deprivation or in rats fed a high-fat content diet. In DRGs, 10% of the NPs expressed CCK(A)-R mRNA, a number that was not affected by either axotomy or inflammation. This cell population was distinct from neurons expressing calcitonin gene-related peptide mRNA. These results demonstrate that the CCK(A)-R is expressed by both viscero- and somatosensory primary sensory neurons, supporting a role for this receptor as a mediator both of CCK-induced satiety and in sensory processing at the spinal level. The stimulation of CCK and CCK(B)-R gene expression following vagotomy suggests a possible involvement in the response to injury for these molecules.
The role of cholecystokinin (CCK) in the effect of dietary lipid on proximal gastrointestinal function and satiety is controversial. Recent work suggests that fatty acid chain length may be a determining factor. We investigated the mechanism by which long- and short-chain fatty acids activate jejunal afferent nerves in rats. Whole mesenteric afferent nerve discharge was recorded in anaesthetized male Wistar rats during luminal perfusion of saline, sodium oleate, and sodium butyrate (both 10 mM). Both fatty acids evoked characteristic afferent nerve responses, distinct from the mechanical response to saline, that were abolished in rats following chronic subdiaphragmatic vagotomy. The effect of oleate was abolished by the CCK-A receptor antagonist Devazepide (0.5 mg/kg), whereas the effect of butyrate persisted despite pretreatment with either Devazepide or a combination of the calcium channel inhibitors nifedipine (1 mg/kg) and the omega-conotoxins GVIA and SVIB (each 25 microg/kg). In summary, long- and short-chain fatty acids activate intestinal vagal afferents by different mechanisms; oleate acts via a CCK-mediated mechanism and butyrate appears to have a direct effect on afferent terminals.
GABA(B)-receptor (GABA(B)R) agonists reduce transient lower esophageal sphincter relaxation (TLESR) and reflux episodes through an action on vagal pathways. In this study, we determined whether GABA(B)R are expressed on vagal afferent neurones and whether they modulate distension-evoked discharge of vagal afferents in the isolated stomach. Vagal mehanoreceptor activity was recorded following distensions of the isolated ferret proximal stomach before and after perfusion with the GABA(B)R-selective agonists baclofen and 3-aminopropylphosphinic acid (3-APPiA). Retrograde labeling and immunohistochemistry were used to identify GABA(B)R located on vagal afferent neurones in the nodose ganglia. Vagal afferent fibers responded to isovolumetric gastric distension with an increase in discharge. The GABA(B)-receptor agonists baclofen (5 x 10(-5) M) and 3-APPiA (10(-6) to 10(-5) M) but not muscimol (GABA(A)-selective agonist: 1.3 x 10(-5) M) significantly decreased afferent distension-response curves. The effect of baclofen (5 x 10(-5) M) was reversed by the GABA(B)-receptor antagonist CGP 62349 (10(-5) M). Over 93% of retrogradely labeled gastric vagal afferents in the nodose ganglia expressed immunoreactivity for the GABA(B)R. GABA(B)R expressed on vagal afferent fibers directly inhibit gastric mechanosensory activity. This is likely a contributing mechanism to the efficacy of GABA(B)-receptor agonists in reducing TLESR and reflux episodes in vivo.
There is evidence for interactions between leptin and cholecystokinin in controlling food intake. Since cholecystokinin acts on vagal afferent neurones, we asked whether the leptin receptor was also expressed by these neurones. Primers for different forms of the leptin receptor were used in reverse transcriptase-polymerase chain reaction (RT-PCR) of rat and human nodose ganglia. RT-PCR yielded products corresponding to the long (functional) form as well as short forms of the rat leptin receptor. Moreover, RT-PCR revealed the long form of the leptin receptor in a human nodose ganglion. The identities of RT-PCR products were confirmed by sequencing. Primers corresponding to leptin itself did not give RT-PCR products in nodose ganglia. Immunocytochemical studies revealed leptin-receptor immunoreactivity in neuronal cell bodies. Many neurones co-expressed the leptin and cholecystokinin type A receptors, or leptin receptor and cocaine- and amphetamine-related transcript. We conclude that vagal afferent neurones that express the cholecystokinin type A receptor and cocaine- and amphetamine-related transcript, may also express the long form of the leptin receptor providing a neurochemical basis for observations of interactions between cholecystokinin and leptin.
Orexin-A and -B are neuropeptides mainly expressed in the lateral hypothalamic area (LHA). A role for orexins was first demonstrated in the regulation of feeding behaviour. Subsequently, the peptides have been implicated in the control of arousal. To date, two receptors for orexins have been characterised: orexin-1 and -2 receptors (OX-R1 and OX-R2). Both receptor genes are widely expressed within the rat brain. Particularly high expression of both receptor genes in certain hypothalamic and pons nuclei could be responsible for the orexigenic and arousal properties of the peptides. It is, however, presently unclear if one given receptor subtype or both subtypes may mediate a specific biological effect of orexins such as an increase in food intake. We have recently reported the distribution of the OX-R1 protein in the rat nervous system. In this study, we report the distribution of the OX-R2 protein in the rat brain and spinal cord using specific anti-peptide antisera raised against the OX-R2 protein. We also assess the expression profile of the OX-R2 gene in different brain regions. Immunolabelling for the OX-R2 protein was observed in brain regions that exhibited OX-R1-like immunoreactivity (cerebral neocortex, basal ganglia, hippocampal formation, and many other regions in the hypothalamus, thalamus, midbrain and reticular formation). Differences in the OX-R1 and OX-R2 distribution were, however, noticed in the hippocampus, hypothalamus and dorso-lateral pons.
Fatty acid chain length determines CCK secretion and effect on human gastric motility
- J T Mclaughlin
- M G Luca
- M N Jones
- D 'amato
- M Dockray
- G J Thompson
McLaughlin JT, Luca MG, Jones MN, D'Amato M, Dockray GJ,
Thompson DG. Fatty acid chain length determines CCK secretion
and effect on human gastric motility. Gastroenterology 1998;
116:46 -53.
Messenger plasticity in primary sensory neurons
- Hokfelt
- Z Xu
- V Verge
- M Villar
- R Elde
- X J Xu
- Z Wiesenfeld-Hallin
Hokfelt, Xu Z, Verge V, Villar M, Elde R, Xu XJ, Wiesenfeld-Hallin
Z. Messenger plasticity in primary sensory neurons. In: Hokfelt T,
Schaible HG, Schmidt RF, eds. Neurooeotides, nociception, and
pain. Weinheim: Chapman & Hall, 1994:71-84.
Address reprint requests to: Graham J. Dockray, Physiological Lab-oratory Crown Street, P.O. Box 147, Liverpool L69 3BX England. e-mail: g.j.dockray@liverpool.ac.uk; fax: (44) 0151-794-5315. Supported by grants from BBSRC and MRC. Dr. Lal is an MRC Clinical Research Training Fellow
- Orexin Gut
- Brain
- Signaling
Received July 12, 2002. Accepted September 19, 2002. Address reprint requests to: Graham J. Dockray, Physiological Lab-oratory, University of Liverpool, Crown Street, P.O. Box 147, Liverpool L69 3BX England. e-mail: g.j.dockray@liverpool.ac.uk; fax: (44) 0151-794-5315. Supported by grants from BBSRC and MRC. Dr. Lal is an MRC Clinical Research Training Fellow. January 2003 OREXIN AND GUT–BRAIN SIGNALING 139
Address reprint requests to
- Crown Street
Received July 12, 2002. Accepted September 19, 2002.
Address reprint requests to: Graham J. Dockray, Physiological Laboratory, University of Liverpool, Crown Street, P.O. Box 147, Liverpool
L69 3BX England. e-mail: g.j.dockray@liverpool.ac.uk; fax: (44) 0151-
794-5315.
Supported by grants from BBSRC and MRC. Dr. Lal is an MRC
Clinical Research Training Fellow.
Glucagon-like peptide-1: a potent regulator of food intake in humans
- Gutzwiller
Messenger plasticity in primary sensory neurons
- Hokfelt
Gene expression and protein distribution of the orexin-1 receptor in the rat brain and spinal cord
- Hervieu
Glucagon-like peptide 1 promotes satiety and suppresses energy intake in humans
- Flint