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Chronic social defeat up-regulates expression of the serotonin transporter in rat dorsal raphe nucleus and projection regions in a glucocorticoid-dependent manner
Abstract
Chronic stress and dysfunction of the serotonergic system in the brain have been considered as two of the major risks for development of depression. In the present study, adult Fischer 344 rats were subjected to a regimen of chronic social defeat (CSD). To mimic stressful conditions some rats were not exposed to CSD but instead treated with corticosterone (CORT) in oral solution while maintained in their home cage. Protein levels of the serotonin transporter (SERT) in the dorsal raphe nucleus (DRN), hippocampus, frontal cortex and amygdala were examined by western blotting or immunofluorescence staining. The results showed that CSD up-regulated SERT protein levels in the DRN, hippocampus, frontal cortex and amygdala regions. This upregulation was abolished or prevented by adrenalectomy, or treatment with antagonists of corticosteroid receptors mifepristone and spironolactone, alone or in combination. Similarly, up-regulated SERT protein levels in these brain regions were also observed in rats treated with oral CORT ingestion, which was analogously prevented by treatment with mifepristone and spironolactone. Furthermore, both CSD- and CORT-induced upregulation of SERT protein levels in the DRN and three brain regions were attenuated by simultaneous treatment with fluoxetine, an antidepressant that specifically inhibits serotonin reuptake. The results indicate that upregulation in SERT protein levels in the DRN and forebrain limbic structures caused by CSD regimen was mainly motivated by CORT through corticosteroid receptors. The present findings demonstrate that chronic stress is closely correlated with the serotonergic system by acting on the regulation of the SERT expression in the DRN and its projection regions, which may contribute to the development of depression. © 2012 International Society for Neurochemistry, J. Neurochem. (2012) 10.1111/jnc.12055.
... Evidence suggests an interaction between the serotonin transporter (SERT) and stress. For example, adult male rats exposed to social defeat upregulated SERT protein levels in the dorsal raphe nuclei (DRN); this effect was mimicked by oral corticosterone ingestion and was prevented by treatment with mifepristone and spironolactone (Zhang et al., 2012). Conversely, social defeat in adult male mice down-regulated the mRNA levels of the SERT gene in the raphe nuclei area (Boyarskikh et al., 2013). ...
... In mid-adolescence, adolescent defeated mice showed a higher SERT binding in both the DH and VH than control mice. It has been reported that 24 h after CSD, adult defeated rodents showed higher levels of SERT mRNA and SERT protein than controls in the raphe nuclei and its projecting regions such as the hippocampus, frontal cortex, and amygdala (Filipenko et al., 2002;Zhang et al., 2012Zhang et al., , 2017. Moreover, it has been reported that a single social defeat in rodents increases both the hippocampal 5-HT levels (Keeney et al., 2006) and c-fos expression in the DRN (Cooper et al., 2009), suggesting hyperactivity of the serotonergic system in response to perceived aggression (Hammels et al., 2015). ...
... Moreover, it has been reported that a single social defeat in rodents increases both the hippocampal 5-HT levels (Keeney et al., 2006) and c-fos expression in the DRN (Cooper et al., 2009), suggesting hyperactivity of the serotonergic system in response to perceived aggression (Hammels et al., 2015). Therefore, it has been proposed that social defeat-induced serotonergic hyperactivity could trigger feedback mechanisms responsible for the normalization of its activity, one of which could be the SERT up-regulation (Filipenko et al., 2002;Zhang et al., 2012Zhang et al., , 2017. Future studies could provide further support to this proposal. ...
Chronic stress exposure during adolescence is a significant risk factor for the development of depression. Chronic social defeat (CSD) in rodents is an animal model of depression with excellent ethological, predictive, discriminative, and face validity. Because the CSD model has not been thoroughly examined as a model of stress-induced depression within the adolescence stage, the present study analyzed the short- and long-term behavioral and neuroendocrine effects of CSD during early adolescence. Therefore, adolescent male Swiss-Webster (SW) mice were exposed to the CSD model from postnatal day (PND) 28 to PND37. Twenty-four hours (mid-adolescence) or 4 weeks (early adulthood) later, mice were tested in two models of depression; the social interaction test (SIT) and forced swimming test (FST); cognitive deficits were evaluated in the Barnes maze (BM). Finally, corticosterone and testosterone content was measured before, during, and after CSD exposure, and serotonin transporter (SERT) autoradiography was studied after CSD in adolescent and adult mice. CSD during early adolescence induced enduring depression-like behaviors as inferred from increased social avoidance and immobility behavior in the SIT and FST, respectively, which correlated in an age-dependent manner with SERT binding in the hippocampus; CSD during early adolescence also induced long-lasting learning and memory impairments in the Barnes maze (BM). Finally, CSD during early adolescence increased serum corticosterone levels in mid-adolescence and early adulthood and delayed the expected increase in serum testosterone levels observed at this age. In conclusion: (1) CSD during early adolescence induced long-lasting depression-like behaviors, (2) sensitivity of SERT density during normal brain development was revealed, (3) CSD during early adolescence induced enduring cognitive deficits, and (4) results highlight the vulnerability of the adolescent brain to social stressors on the adrenal and gonadal axes, which emphasizes the importance of an adequate interaction between both axes during adolescence for normal development of brain and behavior.
... Hyperactivity of the HPA axis has been observed in the majority of patients with depression [16,17]. Furthermore, it is also well documented that corticosteroids modulate emotional behaviours and cognition in animals and humans in a complex manner [18]. On the other hand, the serotonergic and adrenergic systems play critical roles in modulating the functional neural circuits in brain [19,20] and have been implicated in hippocampal-dependent memory. ...
... This is also accompanied by in vivo abnormalities in HPA-related hormones, the monoaminergic system, and transcriptional regulation factors (Fig. 14) such as CREB and BDNF. The above findings are consistent with the report by Zhang et al. [18], who also showed that the oral administration of CORT to rats unexposed to SDS increased SERT protein levels in the dorsal raphe nuclei, the hippocampus, the frontal cortex, and the amygdala. Furthermore, they also found that using antagonists of the glucocorticoid receptor, mifepristone and spironolactone (both alone and in combination), inhibited the increase in SERT protein levels in cerebral regions induced by SDS or orally administered CORT. ...
... Furthermore, they also found that using antagonists of the glucocorticoid receptor, mifepristone and spironolactone (both alone and in combination), inhibited the increase in SERT protein levels in cerebral regions induced by SDS or orally administered CORT. Therefore, the increase in SERT protein levels in the dorsal raphe nuclei and forebrain limbic structures induced by SDS is primarily induced by CORT via the corticosteroid receptors [18]. This links changes in HPA axis-modulating hormones to changes in monoamine neurotransmitter levels in the offspring in this study. ...
Background:
Epidemiological surveys and studies with animal models have established a relationship between maternal stress and affective disorders in their offspring. However, whether maternal depression before pregnancy influences behaviour and related neurobiological mechanisms in the offspring has not been studied.
Results:
A social defeat stress (SDS) maternal rat model was established using the resident-intruder paradigm with female specific pathogen-free Wistar rats and evaluated with behavioural tests. SDS maternal rats showed a significant reduction in sucrose preference and locomotor and exploratory activities after 4 weeks of stress. In the third week of the experiment, a reduction in body weight gain was observed in SDS animals. Sucrose preference, open field, the elevated-plus maze, light-dark box, object recognition, the Morris water maze, and forced swimming tests were performed using the 2-month-old male offspring of the female SDS rats. Offspring subjected to pre-gestational SDS displayed enhanced anxiety-like behaviours, reduced exploratory behaviours, reduced sucrose preference, and atypical despair behaviours. With regard to cognition, the offspring showed significant impairments in the retention phase of the object recognition test, but no effect was observed in the acquisition phase. These animals also showed impairments in recognition memory, as the discrimination index in the Morris water maze test in this group was significantly lower for both 1 h and 24 h memory retention compared to controls. Corticosterone, adrenocorticotropic hormone, and monoamine neurotransmitters levels were determined using enzyme immunoassays or radioimmunoassays in plasma, hypothalamus, left hippocampus, and left prefrontal cortex samples from the offspring of the SDS rats. These markers of hypothalamic-pituitary-adrenal axis responsiveness and the monoaminergic system were significantly altered in pre-gestationally stressed offspring. Brain-derived neurotrophic factor (BDNF), cyclic adenosine monophosphate response element binding protein (CREB), phosphorylated CREB (pCREB), and serotonin transporter (SERT) protein levels were evaluated using western blotting with right hippocampus and right prefrontal cortex samples. Expression levels of BDNF, pCREB, and SERT in the offspring were also altered in the hippocampus and in the prefrontal cortex; however, there was no effect on CREB.
Conclusion:
We conclude that SDS before pregnancy might induce depressive-like behaviours, cognitive deficits, and neurobiological alterations in the offspring.
... To address this hypothesis, in the present study, in situ hybridization and immunohistochemistry were performed to measure GR mRNA and protein levels in the hippocampus, amygdala, LC and raphe nuclei in rats subjected to the chronic social defeat (CSD) regimen to evaluate whether a similar stress regimen caused different alterations in GR expression. We previously reported that CSD upregulated the expression of NET and SERT via corticosteroid receptors (Chen et al., 2012;Zhang et al., 2012), However, only western blotting was performed to examine NET alterations in the LC, and there was no measurement of SERT mRNA after CSD. Considering GR changes may be different in different tissues and the alteration of protein levels of NET and SERT in the brain region may specifically depend on the sub-regions of the brain, the present study used immunohistochemistry to measure the effects of CSD on immunoreactive expression of NET and SERT in LC and DRN. ...
... Previously we reported CSD-induced up-regulations of SERT protein levels in the rat DRN and its projection regions (Zhang et al., 2012). However, SERT mRNA levels were not measured in that study. ...
... It is an essential way to keep highly physiological and pathological requirements in response to stress. Our previous studies demonstrated that CSD significantly increased mRNA and protein levels of NET and dopamine b-hydroxylase in the LC, as well as protein levels of SERT in the DRN, which could be abolished by simultaneous treatments with corticosteroid receptor antagonists mifepristone and spironolactone (Chen et al., 2012;Zhang et al., 2012;Fan et al., 2013). This stress-induced upregulation of monoaminergic phenotypes through the GR was confirmed by administration of corticosterone in vivo (Fan et al., 2014) andin vitro (Sun et al., 2010;Zha et al., 2011). ...
Our previous studies demonstrated that chronic social defeat (CSD) up-regulated expression of the serotonin transporter (SERT) and norepinephrine transporter (NET) in the brain, which was mediated by corticosteroid receptors. In the present study we first analyzed the alterations of corticosteroid receptors in different brain regions after the CSD paradigm. The results showed that CSD significantly reduced glucocorticoid receptor (GR) protein levels in the CA1 and dentate gyrus of the hippocampus, as well as in central and basolateral nuclei of the amygdala, which was accompanied by the translocation of GR from cytoplasm to nuclei. CSD also markedly reduced GR mRNA levels and MR immunoreactivity in the CA1, CA3 and dentate gyrus areas of the hippocampus. Conversely, CSD pronouncedly enhanced GR mRNA and protein levels in the dorsal raphe nucleus and locus coeruleus relative to the control. As an extension of our previous studies, in situ hybridization and immunohistochemical staining demonstrated that CSD regimen caused a notable increase of SERT mRNA levels in the dorsal raphe nucleus and increased SERT immunoreactivities in CA1 and CA3 of the hippocampus, as well as those in the basolateral nuclei of the amygdala. Likewise, CSD regimen resulted in an evident enhancement of NET immunoreactivity in the CA1 of the hippocampus and in the basolateral nuclei of the amygdala. Our current findings suggest that GR expressional alterations in response to CSD are complex and brain region-specific, which may correspond to their different functions in these regions.
... Modulation of serotoninergic neurotransmission is reported as a treatment for psychotic depression (Butler and Meegan, 2008;Zhang et al., 2012). Serotonin (5-hydroxytryptamine) is functionally implicated in a variety of behavioral responses, and plasma serotonin levels are a promising marker of major depression (Meredith et al., 2005). ...
... Animal studies indicate that serotonergic neurotransmission is affected by the stress hormone axis (Lanfumey et al., 2008). RU-486 administration prevents increases in SERT expression, caused by corticosterone in the rat dorsal raphe nucleus (Zhang et al., 2012). In humans, central SERT levels are related to the stress hormone response in patients suffering from negative mood states (Reimold et al., 2011). ...
... Considerable research suggests stress hormones play an essential role during chronic stress (Buwalda et al., 2005;Lanfumey et al., 2008;Way and Taylor, 2010;Reimold et al., 2011), and animal studies indicate that serotonergic neurotransmission may be affected by the stress hormone axis (Lanfumey et al., 2008). SERT protein up-regulation in the dorsal raphe nucleus, caused by a chronic social defeat regimen, is mainly mediated through corticosterone and its receptors (Zhang et al., 2012). In humans, central SERT levels are highly associated with the stress hormone response in patients suffering from negative mood states (Reimold et al., 2011). ...
Regulating serotonin expression can be used to treat psychotic depression. Mifepristone, a glucocorticoid receptor antagonist, is an effective candidate for psychotic depression treatment. However, the underlying mechanism related to serotonin transporter expression is poorly understood. In this study, we cloned the human brain serotonin transporter into Xenopus oocytes, to establish an in vitro expression system. Two-electrode voltage clamp recordings were used to detect serotonin transporter activity. Our results show that mifepristone attenuates serotonin transporter activity by directly inhibiting the serotonin transporter, and suggests that the serotonin transporter is a pharmacological target of mifepristone for the treatment of psychotic depression.
... Ce modèle présente, entre autres, une augmentation des taux d'ARNm de Htr1a et de Slc6a4 associée à une augmentation des taux de R-5-HT 1A dans le raphé dorsal (Carneiro-Nascimento et al., 2021;Filipenko et al., 2002;Zhang et al., 2012). Il est intéressant de noter que, dans les neurones 5-HT, la signalisation associée aux glucocorticoïdes est capable de réguler positivement la transcription du gène humain de la protéine SERT. ...
... Il est intéressant de noter que, dans les neurones 5-HT, la signalisation associée aux glucocorticoïdes est capable de réguler positivement la transcription du gène humain de la protéine SERT. En effet, la corticostérone augmente l'expression du SERT et son activité de recapture (Glatz et al., 2003;Zhang et al., 2012) Ces modifications pourraient être à l'origine d'une diminution de l'activité du système 5-HT et de la mise en place d'un phénotype dépressif, en lien avec une dérégulation de l'axe hypothalamo-hypophyso-surrénalien (axe HHS). En effet, les patients dépressifs présentent une sur-activation de l'axe HHS qui se traduit, entre autres, par une augmentation du taux de corticostérone ainsi qu'une diminution du volume de l'hippocampe (Varghese and Brown, 2001) et une perturbation du cycle circadien. ...
De nombreuses maladies psychiatriques, notamment la dépression ou la schizophrénie, sont associées à un dysfonctionnement de la signalisation sérotoninergique. Il a été précédemment montré que le récepteur 5-HT2B est exprimé par certains neurones sérotoninergiques et est nécessaire aux effets comportementaux et neurogéniques des inhibiteurs sélectifs de la recapture de la sérotonine et à la MDMA (3,4-méthylènedioxy-N-méthylamphétamine). De plus, l'activation des récepteurs 5-HT2B contrecarre les effets de l'activation des récepteurs 5-HT1A. L'objectif de la première étude est de comprendre comment le récepteur 5-HT2B interagit avec le récepteur 5-HT1A et l'impact de cette association sur leurs voies de signalisation respectives. Avec différents outils expérimentaux, nous avons démontré que les récepteurs 5-HT1A et 5-HT2B peuvent former des hétérodimères. De plus, l'expression du récepteur 5-HT2B empêche l'internalisation du récepteur 5-HT1A par sa propre stimulation, tandis que la présence du récepteur 5-HT1A imite l'effet de la stimulation sur l'expression à la surface du récepteur 5-HT2B. Ces données soutiennent un cross-talk différentiel entre les récepteurs 5-HT1A et 5-HT2B. Dans une deuxième étude, nous avons découvert que CIPP, une protéine d'échafaudage, interagit avec le récepteur 5-HT2B via son domaine PDZ et augmente la libération de calcium dendritique dépendante de la stimulation du récepteur 5-HT2B. CIPP favorise aussi l'augmentation de la densité et la maturation des épines dendritiques et réduit la colocalisation des récepteurs NMDA avec les récepteurs 5-HT2B. Par conséquent, ces données soutiennent le rôle du récepteur 5-HT2B dans la plasticité neuronale.
... DEX treatment increases SERT gene expression (30) and SERT localization on 5-HT neurons (31). During chronic social defeat, cortisol can up-regulate SERT expression via GR (32). Taken together, these studies show that 5-HT could potentially be the mediatory factor linking cortisol action to SPX1a expression. ...
... During chronic social defeat, a statistically significant upregulation of SERT was observed in Area 3, where major 5-HT neuronal populations are located. Our results are in agreement with previous studies where repeated social defeat increased SERT expression in the dorsal raphe nucleus in rats (32,39). The upregulation of SERT gene expression during chronic social defeat could lead to increased reuptake of 5-HT from the synaptic cleft and decrease the extracellular 5-HT availability (40), which reduces the inhibitory signal upon SPX1a, leading to upregulation of SPX1a gene expression. ...
Social disturbance in interpersonal relationships is the primary source of stress in humans. Spexin (SPX, SPX1a in cichlid), an evolutionarily conserved neuropeptide with diverse physiological functions, is up-regulated in the brain during chronic social defeat stress in teleost. On the other hand, repeated exposure to social stress can lead to dysregulation of the monoaminergic system and increase the vulnerability of developing depression. Since dysfunction of the serotonin (5-hydroxytryptamine, 5-HT) system is associated with social stress and the pathophysiology of depression, the present study investigated the regulatory relationship between the central 5-HT system and SPX1a in the male teleost, Nile tilapia (Oreochromis niloticus). To identify stress factors that regulate SPX1a gene expression, cortisol, dexamethasone (DEX), and 5-HT were used to treat tilapia brain primary cultures. Our study shows cortisol and DEX treatment had no effect on SPX1a gene expression, but SPX1a gene expression was down-regulated following 5-HT treatment. Anatomical localization showed a close association between 5-HT immunoreactive projections and SPX1a neurons in the semicircular torus. In addition, 5-HT receptors (5-HT2B) were expressed in SPX1a neurons. SPX1a immunoreactive neurons and SPX1a gene expression were significantly increased in socially defeated tilapia. On the other hand, citalopram (antidepressant, 5-HT antagonist) treatment to socially defeated tilapia normalized SPX1a gene expression to control levels. Taken together, the present study shows that 5-HT is an upstream regulator of SPX1a and that the inhibited 5-HT activates SPX1a during social defeat.
... Knock-out mice lacking key components of serotonergic machinery show altered stress-related behaviors (Holmes et al., 2003;Lira et al., 2003;Adamec et al., 2006;Gutknecht et al., 2015). Extracellular levels of serotonin (Kawahara et al., 1993;Mokler et al., 2007), expression of serotonin-related molecules (Adell et al., 1988;Zhang et al., 2012;Issler et al., 2014;Donner et al., 2018), serotonergic activity (Grahn et al., 1999;Paul et al., 2011;Grandjean et al., 2019), and innervation (Natarajan et al., 2017) have been shown to change in response to both acute and chronic stress. Such regulation is linked to behavioral changes including anhedonia (Berton et al., 1997;Wood et al., 2013;Lopes et al., 2016;Natarajan et al., 2017) and is altered by treatment with antidepressants and anxiolytics (Benmansour et al., 1999;Abumaria et al., 2007). ...
... Studies in rodent models have shown that serotonergic molecular machinery is upregulated in the DR after both chronic (Adell et al., 1988;Zhang et al., 2012;Donner et al., 2016) and acute stress (Donner et al., 2018). However, they did not specifically address differences between rodents that are susceptible or resilient to chronic stress-induced anhedonia, or whether this upregulation occurs in identified classes of neurons expressing specific neurotransmitters. ...
Chronic stress induces anhedonia in susceptible but not resilient individuals, a phenomenon observed in humans as well as animal models, but the molecular mechanisms underlying susceptibility and resilience are not well understood. We hypothesized that the serotonergic system, which is implicated in stress, reward and antidepressant therapy, may play a role. We found that plasticity of the serotonergic system contributes to the differential vulnerability to stress displayed by susceptible and resilient animals. Stress-induced anhedonia was assessed in adult male rats using social defeat and intracranial self-stimulation (ICSS), while changes in serotonergic phenotype were investigated using immunohistochemistry and in situ hybridization. Susceptible, but not resilient, rats displayed an increased number of neurons expressing the biosynthetic enzyme for serotonin, tryptophan-hydroxylase-2 (TPH2), in the ventral subnucleus of the dorsal raphe nucleus (DRv). Further, a decrease in the number of DRv glutamatergic (VGLUT3+) neurons was observed in all stressed rats. This neurotransmitter plasticity is activity-dependent, as was revealed by chemogenetic manipulation of the central amygdala, a stress-sensitive nucleus that forms a major input to the DR. Activation of amygdalar corticotropin releasing hormone (CRH)+ neurons abolished the increase in DRv TPH2+ neurons and ameliorated stress-induced anhedonia in susceptible rats. These findings show that activation of amygdalar CRH+ neurons induces resilience, and suppresses the gain of serotonergic phenotype in the DR that is characteristic of susceptible rats. This molecular signature of vulnerability to stress-induced anhedonia and the active nature of resilience could be targeted to develop new treatments for stress-related disorders like depression.SIGNIFICANCE STATEMENTDepression and other mental disorders can be induced by chronic or traumatic stressors. However, some individuals are resilient and do not develop depression in response to chronic stress. A complete picture of the molecular differences between susceptible and resilient individuals is necessary to understand how plasticity of limbic circuits is associated with the pathophysiology of stress-related disorders. Using a rodent model, our study identifies a novel molecular marker of susceptibility to stress-induced anhedonia, a core symptom of depression, and a means to modulate it. These findings will guide further investigation into cellular and circuit mechanisms of resilience, and the development of new treatments for depression.
... Stress also influences 5-HT 107 neurotransmission (Graeff et al., 1996;Hale et al., 2012). Alterations in brain 5-HT, 5-HT-related 108 molecular content (Kang et al., 2005), and serotonergic activity (Paul et al., 2011;Zhang et al., 2012), 109 have been observed in individuals exposed to acute or chronic stress. In behavioral experiments, 110 mice with hereditary central 5-HT deficiency are more susceptible to social stress (Sachs et al., 2015), 111 and increasing 5-HT levels with SSRIs prevents the impairment of stress adaptation (Uno et al.,112 2019). ...
Depression is a frequent and serious illness, and stress is considered the main risk factor for its onset. First-line antidepressants increase serotonin (5-hydroxytryptamine; 5-HT) levels in the brain. We previously reported that an N -acetyltransferase, Shati/Nat8l, is upregulated in the dorsal striatum (dSTR) of stress-susceptible mice exposed to repeated social defeat stress (RSDS) and that dSTR Shati/Nat8l overexpression in mice (dSTR-Shati OE) induces stress vulnerability and local reduction in 5-HT content. Male mice were used in this study, and we found that dSTR 5-HT content decreased in stress-susceptible but not in resilient mice. Moreover, vulnerability to stress in dSTR-Shati OE mice was suppressed by the activation of serotonergic neurons projecting from the dorsal raphe nucleus (dRN) to the dSTR, followed by upregulation of 5-HT content in the dSTR using designer receptors exclusively activated by designer drugs (DREADD). We evaluated the role of GABA in modulating the serotonergic system in the dRN. Stress-susceptible after RSDS and dSTR-Shati OE mice exhibited an increase in dRN GABA content. Furthermore, dRN GABA content was correlated with stress sensitivity. We found that the blockade of GABA signaling in the dRN suppressed stress susceptibility in dSTR-Shati OE mice. In conclusion, we propose that dSTR 5-HT and dRN GABA, controlled by striatal Shati/Nat8l via the dSTR-dRN neuronal circuitry, critically regulate stress sensitivity. Our study provides insights into the neural processes that underlie stress and suggests that dSTR Shati/Nat8l could be a novel therapeutic target for drugs against depression, allowing direct control of the dRN serotonergic system.
... Drugs that stimulate the serotonergic system result in the release of prolactin and CORT. In adult studies, the most commonly used drug was fenfluramine, which showed a weakened prolactin response in patients with depression compared to controls (Zhang et al., 2012). L-5-hydroxytryptamine (L-5-HTP) is a precursor of serotonin and increases serotonin turnover in the central nervous system. ...
Depression and anxiety are the most common mental illnesses affecting children and adolescents, significantly harming their well-being. Research has shown that regular physical activity can promote cognitive, emotional, fundamental movement skills, and motor coordination, as a preventative measure for depression while reducing the suicide rate. However, little is known about the potential role of physical activity in adolescent depression and anxiety. The studies reviewed in this paper suggest that exercise can be an effective adjunctive treatment to improve depressive and anxiety symptoms in adolescents, although research on its neurobiological effects remains limited.
... Their role in stress and depression models was shown in mice (10,25,72,73), rats (74)(75)(76)(77), tree shrews (62), and cpEW samples of suicide victims (73,78) further supporting the translational value of results obtained in animal studies. Both extrahypothalamic CRH systems (79, 80) and cpEW UCN1 cells (81,82) may interact with the serotonergic (5-HT) cells in the dorsal raphe nucleus (DR) that also show stress-induced activity (83,84) and PACAP mRNA expression in mice (85). The high significance of serotonergic neurotransmission in mood control in the prefrontal cortex, hippocampus and amygdala is without debate (86, 87; for review see 88, 89). ...
According to the three hit concept of depression, interaction of genetic predisposition altered epigenetic programming and environmental stress factors contribute to the disease. Earlier we demonstrated the construct and face validity of our three hit concept-based mouse model. In the present work, we aimed to examine the predictive validity of our model, the third willnerian criterion. Fluoxetine treatment was applied in chronic variable mild stress (CVMS)-exposed (environmental hit) CD1 mice carrying one mutated allele of pituitary adenylate cyclase-activating polypeptide gene (genetic hit) that were previously exposed to maternal deprivation (epigenetic hit) vs. controls. Fluoxetine reduced the anxiety level in CVMS-exposed mice in marble burying test, and decreased the depression level in tail suspension test if mice were not deprived maternally. History of maternal deprivation caused fundamental functional-morphological changes in response to CVMS and fluoxetine treatment in the corticotropin-releasing hormone-producing cells of the bed nucleus of the stria terminalis and central amygdala, in tyrosine-hydroxylase content of ventral tegmental area, in urocortin 1-expressing cells of the centrally projecting Edinger-Westphal nucleus, and serotonergic cells of the dorsal raphe nucleus. The epigenetic background of alterations was approved by altered acetylation of histone H3. Our findings further support the validity of both the three hit concept and that of our animal model. Reversal of behavioral and functional-morphological anomalies by fluoxetine treatment supports the predictive validity of the model. This study highlights that early life stress does not only interact with the genetic and environmental factors, but has strong influence also on therapeutic efficacy.
... Les altérations du système 5-HT conséquentes au modèle de défaite sociale ont été particulièrement détaillées. Ce type de protocole provoque une diminution des taux de sérotonine associée à des modifications spécifiques du RD (Keeney et al., 2006;Zhang et al., 2012). En outre, les neurones GABA du RD jouent un rôle majeur dans le comportement social des animaux, qui est altéré par cette procédure de stress, notamment en augmentant la fréquence des courants postsynaptiques inhibiteurs sur les neurones 5-HT (Challis et al., 2013;Crawford et al., 2013). ...
Les études épidémiologiques mettent en évidence que les patients atteint de diabète de type 2 (DT2) ont deux fois plus de risque de souffrir de dépression majeure (DM), un trouble mental caractérisé par une tristesse intense et/ou une anhédonie. Plus précisément, les données de la littérature indiquent que la résistance à l’insuline, qui est la caractéristique majeure du DT2, est positivement corrélée à la sévérité des symptômes dépressifs. Etant donné le rôle essentiel que joue la neurotransmission sérotoninergique (5-HT) dans la physiopathologie de la DM, nous avons émis l’hypothèse que la résistance à l’insuline sélective de ce système neuronal est responsable des troubles de l’humeur associés au DT2. En ce sens, des altérations du système 5-HT ont été observées dans un modèle de troubles émotionnels associés à un DT2. En effet, le régime obésogène utilisé dans ce modèle induit une altération significative des propriétés électrophysiologiques des neurones 5-HT du Raphé dorsal (DR) ainsi qu’une diminution des taux de sérotonine. Cette étude vise également à déterminer l’action de l’insuline cérébrale sur le comportement émotionnel et le système sérotoninergique. En utilisant une approche par électrophysiologie ex-vivo, nous avons pu observer que l’insuline modulait positivement l’activité des neurones 5-HT du RD. Nous avons également pu mettre en évidence un effet de type anxiolytique de l’action de l’insuline sur le cerveau par voie intranasale. Cet effet est accompagné de diminution des taux de sérotonine (5-HT) tissulaires dans certaines structures cérébrales impliquées dans la régulation de l’anxiété. Enfin, nous avons utilisé un modèle transgénique grâce auquel nous avons invalidé sélectivement le récepteur à l’insuline dans les neurones 5-HT. L’étude comportementale a permis de mettre en évidence une diminution du comportement de type anxieux chez ces animaux, associé à une diminution de l’activité des neurones sérotoninergiques du RD. Ensemble ces données suggèrent que l’insuline peut moduler le comportement émotionnel notamment via le système sérotoninergique. Ces éléments pourront contribuer à la possible découverte de nouveaux traitements et à la prise en charge des troubles de l’humeur chez les patients atteint de DT2.
... This activation of the dopaminergic system produces a decrease in social interaction in animals as well as depressive-like symptoms and anhedonia, amongst other effects [100,101]. The serotonin and norepinephrine systems constitute other signaling systems involved in a series of mental disorders (anxiety, depression, etc.) and are also affected by social stress [102][103][104][105]. Chronic social stress produces an upregulation of the serotonin transporter in the dorsal raphe nucleus, which translates into a deficiency of synaptic serotonin, thus contributing to the appearance of depressive symptoms that can promote the addictive process [79,106,107]. In addition, activation of the HPA axis increases the release of norepinephrine, and if this increase is prolonged, it can produce negative emotions such as anxiety and fear [108]. ...
There is huge scientific interest in the neuropeptide oxytocin (OXT) due to its putative capacity to modulate a wide spectrum of physiological and cognitive processes including motivation, learning, emotion, and the stress response. The present review seeks to increase the understanding of the role of OXT in an individual’s vulnerability or resilience with regard to developing a substance use disorder. It places specific attention on the role of social stress as a risk factor of addiction, and explores the hypothesis that OXT constitutes a homeostatic response to stress that buffers against its negative impact. For this purpose, the review summarizes preclinical and clinical literature regarding the effects of OXT in different stages of the addiction cycle. The current literature affirms that a well-functioning oxytocinergic system has protective effects such as the modulation of the initial response to drugs of abuse, the attenuation of the development of dependence, the blunting of drug reinstatement and a general anti-stress effect. However, this system is dysregulated if there is continuous drug use or chronic exposure to stress. In this context, OXT is emerging as a promising pharmacotherapy to restore its natural beneficial effects in the organism and to help rebalance the functions of the addicted brain.
... The expression of Slc6a4 in the RN was increased in CSS mice compared with CON mice, similarly to a previous study that used repeated social stress (Filipenko et al., 2002). Assuming that the increase in RN Slc6a4 mRNA predicts an increase in RN SERT protein, as observed by others (Zhang et al., 2012), 5-HT reuptake would be increased in target regions, leading to reduced synaptic levels of 5-HT (De Felice, 2016). Studies in MDD patients have yielded different findings for SERT binding: increased, decreased or unchanged levels of SERT binding have been reported, which reflects the complexity of the clinical condition and its comorbidities, the brain region studied and the methods used (Meyer, 2007). ...
Serotonin (5-HT), via its receptors expressed in discrete brain regions, modulates aversion and reward processing and is implicated in various psychiatric disorders including depression. Stressful experiences affect central serotonergic activity and act as a risk factor for depression; this can be modelled preclinically. In adult male C57BL/6J mice, 15-day chronic social stress (CSS) leads to depression-relevant behavioural states, including increased aversion and reduced reward sensitivity. Based on this evidence, here we investigated CSS effects on 5-HT1A, 5-HT2A, and 5-HT2C receptor binding in discrete brain regions using in vitro quantitative autoradiography with selective radioligands. In addition, mRNA expression of Htr1a, 2a, 2c and Slc6a4 (5-HT transporter) was measured by quantitative PCR. Relative to controls, the following effects were observed in CSS mice: 5-HT1A receptor binding was markedly increased in the dorsal raphe nucleus (136%); Htr1a mRNA expression was increased in raphe nuclei (19%), medial prefrontal cortex (35%), and hypothalamic para- and periventricular nuclei (21%) and ventral medial nucleus (38%). 5-HT2A receptor binding was decreased in the amygdala (48%) and ventral tegmental area (60%); Htr2a mRNA expression was increased in the baso-lateral amygdala (116%). 5-HT2C receptor binding was decreased in the dorsal raphe nucleus (42%). Slc6a4 mRNA expression was increased in the raphe (59%). The present findings add to the translational evidence that chronic social stress impacts on the central serotonergic system in a region- and receptor-specific manner, and that this altered state of the serotonergic system contributes to stress-induced dysfunctions in emotional processing.
... The HPA axis mobilizes energy reserves through the release of glucocorticoids, to meet an organism's need for resources to cope with and adapt to stressors. Among the glucocorticoids (primarily cortisol in humans, corticosterone in rodents; hereafter referred to as CORT) released during stress, CORT is the main hormone released by the adrenal cortex and it serves as a master in the control of neuronal and signal transduction (Zhang et al., 2012). Proper regulation of the stress response is essential to avoid an energetically-costly HPA axis hyperactivity that could disrupt neuronal circuitries and result in disease (Herman et al., 2016;Wei et al., 2019). ...
Dysregulation of the stress-induced activation of the hypothalamic-pituitary-adrenocortical axis can result in disease. Bidirectional communication exists between the brain and the gut, and alterations in these interactions appear to be involved in stress regulation and in the pathogenesis of neuropsychiatric diseases, such as depression. Serotonin (5HT) plays a crucial role in the functions of these two major organs but its direct influence under stress conditions remains unclear. To investigate the role of neuronal 5HT on chronic stress responses and its influence on the gut microbiome, mice lacking the gene for tryptophan hydroxylase-2 were treated with the stress hormone corticosterone (CORT) for 21 days. The intake of fluid and food, as well as body weights were recorded daily. CORT levels, expression of glucocorticoid receptors (GR) in the brain and the size of the adrenal gland were evaluated. Caecum was used for 16S rRNA gene characterization of the gut microbiota. Results show that 5HT depletion produced an increase in food intake and a paradoxical reduction in body weight that were enhanced by CORT. Neuronal 5HT depletion impaired the feedback regulation of CORT levels but had no putative effect on the CORT-induced decrease in hippocampal GR expression and the reduction of the adrenal cortex size. Finally, the composition and structure of the gut microbiota were significantly impacted by the absence of neuronal 5HT, and these alterations were enhanced by chronic CORT treatment. Therefore, we conclude that neuronal 5HT influences the stress-related responses at different levels involving CORT levels regulation and the gut microbiome.
... Although we did not measure the changes in the 5-HT level in the current study, previous studies have shown elevated serotonergic activity in the brain following chronic social defeat stress 42,43 . For instance, chronic social defeat experience in the rats increases the expression of both tryptophan hydroxylase 2 and serotonin transporter expression in the dorsal raphe nucleus 44,45 . Similar studies in the rainbow trout and Nile tilapia have demonstrated activation of 5-HT system, characterized by high 5-HIAA/5-HT turnover rate, following social defeat stress exposure 19,25,46 . ...
Spexin (SPX), a neuropeptide evolutionarily conserved from fish to mammals, is widely distributed in the brain and peripheral tissues and associated with various physiological functions. Recently SPX has been suggested to be involved in neurological mechanism of stress. The current study investigates the involvement of SPX in chronic social defeat stress, using male teleost, the Nile tilapia (Oreochromis niloticus) as an animal model due to its distinct social hierarchy of dominant and subordinate relationship. The tilapia genome has SPX1a and SPX1b but has no SPX2. In the Nile tilapia, we localized SPX1a and SPX1b in the brain using in-situ hybridization. Next, using qPCR we examined gene expression of SPX1a and SPX1b in chronically stress (socially defeated) fish. SPX1a expressing cells were localized in the semicircular torus of the midbrain region and SPX1b expressing cells in the telencephalon. Chronically stress fish showed elevated plasma cortisol levels; with an upregulation of SPX1a and SPX1b gene expression in the brain compared to non-stress (control) fish. Since social defeat is a source of stress, the upregulated SPX mRNA levels during social defeat suggests SPX as a potentially inhibitory neuropeptide capable of causing detrimental changes in behaviour and physiology.
... Previous studies in rodent models have shown that serotonergic molecular machinery is upregulated in the DR after both chronic (Adell et al., 1988;Zhang et al., 2012;Donner et al., 2016) and acute stress (Donner et al., 2018). However, these studies did not specifically address differences between animals that are susceptible or resilient to chronic stress-induced was not peer-reviewed) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. ...
Chronic stress induces anhedonia in susceptible, but not resilient individuals, a phenomenon observed in humans as well as animal models, but the molecular mechanisms underlying susceptibility and resilience are not well understood. We hypothesized that the serotonergic system, which is implicated in stress, reward and antidepressant therapy, may play a role. We found that plasticity of the serotonergic system contributes to the differential vulnerability to stress displayed by susceptible and resilient animals. Stress-induced anhedonia was assessed in adult male rats using social defeat and intracranial self-stimulation (ICSS), while changes in serotonergic phenotype were investigated using immunohistochemistry and in situ hybridization. Susceptible, but not resilient, rats displayed an increased number of neurons expressing the biosynthetic enzyme for serotonin, tryptophan-hydroxylase-2 (TPH2), in the ventral subnucleus of the dorsal raphe nucleus (DRv). Further, a decrease in the number of DRv glutamatergic neurons was observed in all stressed animals. This neurotransmitter plasticity is dependent on DR activity, as was revealed by chemogenetic manipulation of the central amygdala, a stress-sensitive nucleus that forms a major input to the DR. Activation of amygdalar corticotropin releasing hormone (CRH)+ neurons abolished the increase in DRv TPH2+ neurons and ameliorated stress-induced anhedonia in susceptible animals. These findings show that activation of amygdalar projections induces resilience, and suppresses the gain of serotonergic phenotype in the DR that is characteristic of susceptible animals. This molecular signature of vulnerability to stress-induced anhedonia and the active nature of resilience could be a target of new treatments for stress-related disorders like depression.
SIGNIFICANCE STATEMENT
Depression and other mental disorders can be induced by chronic or traumatic stressors. However, some individuals are resilient and do not develop depression in response to chronic stress. A complete picture of the molecular differences between susceptible and resilient individuals is necessary to understand how plasticity of limbic circuits is associated with the pathophysiology of stress-related disorders. Using a rodent model, our study identifies a novel molecular marker of susceptibility to stress-induced anhedonia, a core symptom of depression, and a means to modulate it. These findings will guide further investigation into cellular and circuit mechanisms of resilience, and the development of new treatments for depression.
... A small number of studies investigating the effects of chronic CORT treatment on SERT expression in ex vivo analysis of brain tissue are available. These reports provide evidence for increases 47 as well as decreases of SERT brain levels 48 using different CORT administration protocols. We have recently described a dramatic reduction of SERT mRNA levels in the dorsal raphe nucleus 49 in a CORT paradigm comparable to the one applied in the present study. ...
The serotonin transporter (SERT, Slc6a4) plays an important role in the regulation of serotonergic neurotransmission and its aberrant expression has been linked to several psychiatric conditions. While SERT density has been proven to be amenable to in vivo quantitative evaluation by positron emission tomography (PET) in humans, this approach is in its infancy for rodents. Here we set out to evaluate the feasibility of using small-animal PET employing [11C]DASB ([11C]-3-amino-4-(2-dimethylaminomethyl-phenylsulfanyl)-benzonitrile) as a radiotracer to measure SERT density in designated areas of the mouse brain. Using Slc6a4+/+, Slc6a4+/−, and Slc6a4−/− mice as a genetic model of different SERT expression levels, we showed the feasibility of SERT imaging in the mouse brain with [11C]DASB-PET. The PET analysis was complemented by an evaluation of SERT protein expression using western blot, which revealed a highly significant correlation between in vivo and ex vivo measurements. [11C]DASB-PET was then applied to the examination of dynamic changes of SERT levels in different brain areas in the chronic corticosterone mouse model of chronic stress. The observed significant reduction in SERT density in corticosterone-treated mice was independently validated by and correlated with western blot analysis. This is the first demonstration of a quantitative in vivo evaluation of SERT density in subregions of the mouse brain using [11C]DASB-PET. The evidenced decrease in SERT density in response to chronic corticosterone treatment adds a new dimension to the complex involvement of SERT in the pathophysiology of stress-induced mental illnesses.
... Where SERT is downregulated, less serotonin is reuptaken and thus longer 5-HT action is observed in the synaptic cleft. In contrast, upregulated SERT protein levels were observed in the chronic social defeat and ovariectomized rats exposed to chronic aversive stimuli (Zhang et al., 2012;Charoenphandhu et al., 2013). ...
In long-term stress exposure, excess glucocorticoids disturb the balance of monoamine neurotransmitters leading to mood disorders and memory impairment. Venlafaxine and Agomelatin are currently used to treat these disorders. Voluntary exercise also has beneficial effects on mental health. In this work, we analyzed 1. the time-dependent changes in stress-induced mood disorders, 2. the modulating effect of voluntary exercise on the hypothalamic pituitary adrenal axis, 3. the effectiveness of Agomelatin, Venlafaxine and exercise to prevent stress-related behaviors and 4. the localization of MT1 and MT2 receptors in transgenic reporter mice. We demonstrate that stress caused physical, emotional and behavioral abnormalities in stressed rats. Pre-treatment with Agomelatin, Venlafaxine and exercise reduced the chronic stress-related behaviors and prevented anxiety, depression and memory deficits. The mapping of MT1 and MT2 receptors identified potential sites of action of Agomelatin.
... SSRIs are second-generation antidepressants commonly used to treat both depression and anxiety disorders; they block the reuptake of serotonin and result in an increased concentration of serotonin in the synaptic cleft. Chronic stress induced CORT release and leads to the upregulation of SERT protein levels in the brain region (e.g., dorsal raphe nucleus, hippocampus, and frontal cortex) (Filipenko et al., 2002;Gardner et al., 2009;Zhang et al., 2012). In the present study, we demonstrated that CRS exposure increased SERT protein levels in both brain regions, whereas treatment with VBLW significantly reduced SERT expression in both brain regions (Figure 7). ...
The leaves of Vaccinium bracteatum Thunb. are a source of traditional herbal medicines found in East Asia. The present study aimed to evaluate the mechanisms underlying the antidepressant-like effects of water extract of V. bracteatum Thunb. leaves (VBLW) in a mouse model of chronic restraint stress (CRS) and to identify the possible molecular in vitro mechanisms of the neuroprotective effects. The CRS-exposed mice were orally administered VBLW (100 and 200 mg/kg) daily for 21 days consecutively. The behavioral effects of VBLW were assessed through the forced swim test (FST) and the open field test (OFT). The levels of serum corticosterone (CORT), corticotropin releasing hormone (CRH), and adrenocorticotropin hormone (ACTH), brain monoamines, such as serotonin, dopamine, and norepinephrine, and serotonin turnover by tryptophan hydroxylase 2 (TPH2), serotonin reuptake (SERT), and monoamine oxidase A (MAO-A) were evaluated, in addition to the extracellular signal-regulated kinases (ERKs)/protein kinase B (Akt) signaling pathway. CRS-exposed mice treated with VBLW (100 and 200 mg/kg) showed significantly reduced immobility time and increased swimming and climbing times in the FST, and increased locomotor activity in the OFT. Moreover, CRS mice treated with VBLW exhibited significantly decreased CORT and ACTH, but enhanced brain monoamine neurotransmitters. In addition, CRS mice treated with VBLW had dramatically decreased protein levels of MAO-A and SERT, but increased TPH2 protein levels in the hippocampus and the PFC. Similarly, VBLW significantly upregulated the ERKs/Akt signaling pathway in the hippocampus and the PFC. Furthermore, VBLW showed neuroprotective effects via increased CREB phosphorylation in CORT-induced cell injury that were mediated through the ERK/Akt/mTOR signaling pathways. These results suggested that the antidepressant-like effects of VBLW might be mediated by the regulation of the HPA axis, glucocorticoids, and serotonin turnover, such as TPH2, SERT, and MAO-A, as well as the concentration of monoamine neurotransmitters, and the activities of ERK and Akt phosphorylation, which were possibly associated with neuroprotective effects.
... (Slc6a4) and the enzyme tryptophan hydroxylase (Tph2) ( Fig. 2H) would be accompanied by 476 changes in the amount of serotonin in the 4Eki brain, as previously shown ( Charoenphandhu 477 et al., 2011;Zhang et al., 2012;Yohn et al., 2017). Using quantitative ELISA, we measured a 478 decrease in tissue levels of serotonin in 4Eki forebrain, as compared to wild-type ( Fig. 3B). ...
The MAPK/ERK (mitogen-activated protein kinases/extracellular signal-regulated kinase) pathway is a cardinal regulator of synaptic plasticity, learning, and memory in the hippocampus. One of major endpoints of this signaling cascade is the 5’ mRNA cap binding protein eIF4E (eukaryotic Initiation Factor 4E), which is phosphorylated on Ser 209 by MNK (MAPK-interacting protein kinases) and controlsmRNAtranslation. The precise role of phospho-eIF4E in the brain is yet to be determined. Herein, we demonstrate that ablation of eIF4E phosphorylation in male mice (4Eki mice) does not impair long-term spatial or contextual fear memory, or the late phase of LTP. Using unbiased translational profiling in mouse brain, we show that phospho-eIF4E differentially regulates the translation of a subset of mRNAs linked to inflammation, the extracellular matrix, pituitary hormones, and the serotonin pathway. Consequently, 4Eki male mice display exaggerated inflammatory responses and reduced levels of serotonin, concomitant with depression and anxiety-like behaviors. Remarkably, eIF4E phosphorylation is required for the chronic antidepressant action of the selective serotonin reuptake inhibitor fluoxetine. Finally, we propose a novel phospho-eIF4E-dependent translational control mechanism in the brain, via the GAIT complex (gamma IFN activated inhibitor of translation). In summary, our work proposes a novel translational control mechanism involved in the regulation of inflammation and depression, which could be exploited to design novel therapeutics.
... Serotonergic neurons project from the DRN to the extended amygdala, hippocampus, striatum, nucleus accumbens, and cortex [40]. Several lines of evidence have shown that transport capacity (Vmax) of cortical SERT, SERT activity and SERT protein level are enhanced in the frontal cortex of LPS-administered animal [19] and in the DRN of chronic social defect animal model [41]. In addition, serotonin level is decreased in the DRN in stressdepressed rats [42]. ...
Background
Acupuncture has been used as a common therapeutic tool in many disorders including anxiety and depression. Serotonin transporter (SERT) plays an important role in the pathology of anxiety and other mood disorders. The aim of this study was to evaluate the effects of acupuncture on lipopolysaccharide (LPS)-induced anxiety-like behaviors and SERT in the dorsal raphe nuclei (DRN). Methods
Rats were given acupuncture at ST41 (Jiexi), LI11 (Quchi) or SI3 (Houxi) acupoint in LPS-treated rats. Anxiety-like behaviors of elevated plus maze (EPM) and open field test (OFT) were measured and expressions of SERT and/or c-Fos were also examined in the DRN using immunohistochemistry. ResultsThe results showed that 1) acupuncture at ST41 acupoint, but neither LI11 nor SI3, significantly attenuated LPS-induced anxiety-like behaviors in EPM and OFT, 2) acupuncture at ST41 decreased SERT expression increased by LPS in the DRN. Conclusions
Our results suggest that acupuncture can ameliorate anxiety-like behaviors, possibly through regulation of SERT in the DRN.
... Band intensities were quantified by optical densitometry of developed autoradiographs (Scion Image software, ScionCorp, Walkersville, MD, USA) and the intensities of the bands were normalized to the loading of control β-actin (ab8227). All analyses were done using three to five animals per group [47]. ...
Methods:
The animals were divided according to experimental manipulation, Fluoxetine Group (FG): male pups received application of fluoxetine (10mg/kg, 10μL/g) and Saline Group (SG): male pups received saline application (0.9% NaCl, 10μL/g), both throughout lactation (PND1 to PND21). They evaluated body weight, food intake, SERT gene and protein expression, serotonin content in the hypothalamus. The neonatal exposure to fluoxetine promoted reduction in body weight, disturb the serotonin hypophagic response, and increase the serotonin and SERT hypothalamic in young animals. We conclude that the changes of components of the serotonergic system by neonatal exposure to fluoxetine may be responsible for disturb the inhibitory action of serotonin on food intake.
... On one side, it blocks transcription of tryptophan hydroxylase (TPH) (Clark et al., 2005) and serotonin receptor 1B (HTR1B) (Nugent et al., 2013). On the other side, GC release activates the transcription of the monoamine oxidase (MAOA) (Ahmed et al., 2013) and the serotonin transporter (SLC6A4) (Zhang et al., 2012). Overall, in response to cortisol, DRN cells: decrease the synthesis of serotonin, and increase its metabolism and transport. ...
Introduction:
Recent research demonstrates the heterogeneous etiology of psychotic disorders, where gen-environment (GxE) interaction plays a key role. Large genetic studies have linked many genetic variants with schizophrenia, but each variant is only associated with a small effect and the GxE interaction contribution has not been evaluated.
Methods:
The PEPs Project was designed to carefully collect a large amount of genetic and environmental exposure data of 335 FEP patients and 253 matched healthy controls.780single-nucleotide polymorphisms (from 159 candidate genes)and 16 environmental variables previously reported as the main psychosis non-genetic risk factors were analyzed together using entropy-based measures of information gain.
Results:
Our analyses identified an interaction between nine SNPs and the exposition to the environmental risk factors of psychosis, showing a clear enrichment of genes linked to serotonin neurotransmission and neurodevelopmental processes.
Conclusions:
This study has allowed the identification of several GxE-environment interactions involved in the risk of presenting a FEP. Our results highlight the importance of serotonin neurotransmission interacting with certain environmental stimuli. The serotoninergic system may be playing a key role in the regulatory network of stress and other systems implicated in the emergence and development of psychotic disorders.
... Concerning the 5-HT mediated regulation of anxiety, there are several discrepancies of its gene expression within the DRN and vmPFC for mood and anxiety-like behaviors. However, our results corroborate previous findings that showed increased 5-HTT expression in the DRN 42 , and reduced TPH synthesis and 5-HTT function in the vmPFC in animal models of depression 8,9 . Furthermore, the increase of TPH 43,44 , with lower levels of 5-HT and its metabolite (5-hydroxyindoleacetic acid) in the DRN (or brainstem), as well as decreased 5-HTT binding in the ventral PFC, have also been reported in patients with major depression and suicidal behaviors [44][45][46] . ...
Tetratricopeptide repeat domain 9A (TTC9A) expression is abundantly expressed in the brain. Previous studies in TTC9A knockout (TTC9A−/−) mice have indicated that TTC9A negatively regulates the action of estrogen. In this study we investigated the role of TTC9A on anxiety-like behavior through its functional interaction with estrogen using the TTC9A−/− mice model. A battery of tests on anxiety related behaviors was conducted. Our results demonstrated that TTC9A−/− mice exhibited an increase in anxiety-like behaviors compared to the wild type TTC9A+/+ mice. This difference was abolished after ovariectomy, and administration of 17-β-estradiol benzoate (EB) restored this escalated anxiety-like behavior in TTC9A−/− mice. Since serotonin is well-known to be the key neuromodulator involved in anxiety behaviors, the mRNA levels of tryptophan hydroxylase (TPH) 1, TPH2 (both are involved in serotonin synthesis), and serotonin transporter (5-HTT) were measured in the ventromedial prefrontal cortex (vmPFC) and dorsal raphe nucleus (DRN). Interestingly, the heightened anxiety in TTC9A−/− mice under EB influence is consistent with a greater induction of TPH 2, and 5-HTT by EB in DRN that play key roles in emotion regulation. In conclusion, our data indicate that TTC9A modulates the anxiety-related behaviors through modulation of estrogen action on the serotonergic system in the DRN.
... Moreover, high concentration of GC can make 5-HT transporter (5-HTT) expression increase in hippocampus, amygdala, dorsal raphe nucleus, and other brain areas by GR dependent manner. The increased 5-HTT will increase the reuptake of 5-HT in synaptic cleft, which aggravates the decrease of 5-HT concentration and the severity of the symptoms in depressed patients [42]. Stress can affect the excitability of neurons of locus coeruleus (LC), raphe nucleus, and substantia nigra by HPA axis and 5-HT and NE/DA play an important role in the change of emotion and mood [43]. ...
The aim of the present study was to investigate the antidepressant-like effects of two fractions, including petroleum ether soluble fraction (Fraction A, FA) and water-EtOH soluble fraction (Fraction B, FB) prepared from the Danzhi-xiaoyao-san (DZXYS) by using chronic unpredictable mild stress-induced depressive rat model. The results indicated that DZXYS could ameliorate the depression-like behavior in chronic stress model of rats. The inhibition of hyperactivity of HPA axis and the modulation of monoamine and amino acid neurotransmitters in the hippocampus may be the important mechanisms underlying the action of DZXYS antidepressant-like effect in chronically stressed rats.
... Chronic stress, which induces depressive-like behavior in rodents, has been shown to reduce central serotonin availability (Boyarskikh et al., 2013;Zhang et al., 2012). Moreover, changes in synaptic availability of serotonin are associated with neuronal remodeling (Sun and Schacher, 1998;Vetencourt et al., 2011). ...
Postpartum depression (PPD) is a common complication following childbirth experienced by one in every five new mothers. Although the neural basis of PPD remains unknown previous research in rats has shown that gestational stress, a risk factor for PPD, induces depressive-like behavior during the postpartum period. Moreover, the effect of gestational stress on postpartum mood is accompanied by structural modifications within the nucleus accumbens (NAc) and the medial prefrontal cortex (mPFC) - limbic regions that have been linked to PPD. Mothers diagnosed with PPD are often prescribed selective serotonin reuptake inhibitor (SSRI) antidepressant medications and yet little is known about their effects in models of PPD. Thus, here we investigated whether postpartum administration of Citalopram, an SSRI commonly used to treat PPD, would ameliorate the behavioral and morphological consequences of gestational stress. In addition, we examined the effects of gestational stress and postpartum administration of Citalopram on structural plasticity within the basolateral amygdala (BLA) which together with the mPFC and NAc forms a circuit that is sensitive to stress and is involved in mood regulation. Our results show that postpartum rats treated with Citalopram do not exhibit gestational stress-induced depressive-like behavior in the forced swim test. In addition, Citalopram was effective in reversing gestational stress-induced structural alterations in the postpartum NAc shell and mPFC. We also found that gestational stress increased spine density within the postpartum BLA, an effect which was not reversed by Citalopram treatment. Overall, these data highlight the usefulness of gestational stress as a valid and informative translational model for PPD. Furthermore, they suggest that structural alterations in the mPFC-NAc pathway may underlie stress-induced depressive-like behavior during the postpartum period and provide much needed information on how SSRIs may act in the maternal brain to treat PPD.
Copyright © 2015. Published by Elsevier Inc.
... Studies using the LH model have shown that 5-HT 2A receptors are differentially regulated and severely impaired after exposure to single or repeated stress [85,86]. Defects of 5-HT neurotransmission, including upregulation of SERT in the DRN, have also been observed in the CSD model, illustrating the importance of the serotonergic pathway in the pathophysiology of MDD [87,88]. ...
Major depressive disorder (MDD) is a heritable neuropsychiatric disease associated with severe changes at cellular and molecular levels. Its diagnosis mainly relies on the characterization of a wide range of symptoms including changes in mood and behavior. Despite the availability of antidepressant drugs, 10 to 30 % of patients fail to respond after a single or multiple treatments, and the recurrence of depression among responsive patients is very high. Evidence from the past decades suggests that the brain neurotransmitter serotonin (5-HT) is incriminated in MDD, and that a dysfunction of 5-HT receptors may play a role in the genesis of this disease. The 5-HT membrane transporter protein (SERT), which helps regulate the serotonergic transmission, is also implicated in MDD and is one of the main targets of antidepressant therapy. Although a number of behavioral tests and animal models have been developed to study depression, little is known about the neurobiological bases of MDD. Understanding the role of the serotonergic pathway will significantly help improve our knowledge of the pathophysiology of depression and may open up avenues for the development of new antidepressant drugs. The overarching goal of this review is to present recent findings from studies examining the serotonergic pathway in MDD, with a focus on SERT and the serotonin 1A (5-HT1A), serotonin 1B (5-HT1B), and serotonin 2A (5-HT2A) receptors. This paper also describes some of the main molecules involved in the internalization of 5-HT receptors and illustrates the changes in 5-HT neurotransmission in knockout mice and animal model of depression.
... High concentrations of glucocorticoids can have long-term adverse effects, which include: (1) imbalance of negative feedback in the HPA axis, including downregulation of negative feedback and dysfunction of GRs, disinhibition in the dexamethasone suppression test, and high concentrations of glucocorticoids in the blood; (2) excessive activation of GRs in its target cells in the CNS leads to neuronal apoptosis and degeneration [48] which is explained by the attenuation of BDNF expression and proliferation [70,71] . In addition, the increased glucocorticoid levels enhance the expression of 5-HT transporters in the hippocampus, the frontal cortex, the amygdala, the dorsal raphe nucleus, and other brain regions in a GR-dependent manner, resulting in reduced 5-HT in the synaptic cleft and aggravation of depressive symptoms [72] . Accordingly, the strategy for MDD treatment is either restoring the negative feedback in the HPA or blocking the over-activated GRs. ...
Major depressive disorder (MDD) is a common and devastating psychiatric disorder characterized by persistent low mood, cognitive disorder, and impaired social function. Despite its complex mechanisms, increasing evidence has identified the involvement of neurotrophic factors, inflammatory cytokines, the hypothalamus-pituitary-adrenal axis, and glutamate receptors in the pathophysiology of this illness. The present review synthesizes recent research achievements to define the network between different hypotheses of MDD and to understand which part is most pivotal for its pathogenesis. By integrating MDD-related signal pathways, we highlight brain-derived neurotrophic factor (BDNF) dysfunction and increased apoptosis as the final common cascades, and new therapeutic strategies aiming to enhance BDNF function have been shown to exert a rapid and effective antidepressant action.
Background:
Chronic aflatoxin B1 (AFB1) exposure may increase the risk of multiple neuropsychiatric disorders. Stress is considered one of the main contributors to major depressive disorder. Whether and how chronic AFB1 exposure affects vulnerability to stress is unclear.
Methods:
Mice were exposed for three weeks to AFB1 (100 µg/kg/d) and/or chronic mild stress (CMS). The vulnerability behaviors in response to stress were assessed in the forced swimming test (FST), sucrose preference test (SPT), and tail suspension test (TST). Microglial pyroptosis was investigated using immunofluorescence, enzyme-linked immunosorbent assays, and western blot assay in the hippocampus of mice. Hippocampal neurogenesis and the effects of AFB1-treated microglia on proliferation and differentiation of neural stem/precursor cells (NSPCs) were assessed via immunofluorescence in the hippocampus of mice.
Results:
Mice exposed to CMS in the presence of AFB1 exhibited markedly greater vulnerability to stress than mice treated with CMS or AFB1 alone, as indicated by reduced sucrose preference and longer immobility time in the forced swimming test. Chronic aflatoxin B1 exposure resulted in changes in the microglial morphology and increase in TUNEL+ microglia and GSDMD+ microglia in the hippocampal dentate gyrus. When mice were exposed to both CMS and AFB1, pyroptosis-related molecules (such as NLRP3, caspase-1, GSDMD-N, and interleukin-1β) were significantly upregulated in the hippocampus. These molecules were also significantly enhanced by AFB1 in primary microglial cultures. AFB1-treated mice showed decrease in the numbers of BrdU+, BrdU-DCX+, and BrdU-NeuN+ cells in the hippocampal dentate gyrus, as well as the percentages of BrdU+ cells that were NeuN+ in the presence or absence of CMS when compared with vehicle-treated mice. The combination of AFB1 and CMS exacerbated these effects to an even greater extent. The number of DCX+ cells correlated negatively with the percentage of ameboid microglia, TUNEL+ microglia and GSDMD+ microglia in the hippocampal dentate gyrus. AFB1-treated microglia suppressed the proliferation and neuronal differentiation of NSPCs in vitro.
Conclusion:
Chronic AFB1 exposure induces microglial pyroptosis, promoting an adverse neurogenic microenvironment that impairs hippocampal neurogenesis, which may render mice more vulnerable to stress.
Organic cation transporter-3 (OCT3) is widely distributed in the brain with high expression in portions of the stress axis. These high capacity, polyspecific transporters function in monoamine clearance and are sensitive to the stress hormone corticosterone. In rats, withdrawal from chronic amphetamine increases OCT3 expression in specific limbic brain regions involved anxiety and stress responses, including the ventral hippocampus, central nucleus of amygdala (CeA) and dorsomedial hypothalamus. (DMH). Previous studies show that glucocorticoid receptor (GR) agonists increase OCT1 mRNA and OCT2 mRNA expression in non-neural tissues. Thus, we hypothesized that corticosterone increases OCT3 expression in the brain by activating GRs. Male Sprague-Dawley rats were pre-treated daily with the GR antagonist mifepristone (20 mg/kg; sc.) or vehicle followed 45 min later by injections of corticosterone or vehicle for 2 weeks. Corticosterone treatment significantly increased OCT3 expression in the ventral hippocampus and increased anxiety-like behavior. However, these effects were not blocked by mifepristone. Interestingly, treatment with mifepristone alone reduced plasma corticosterone levels and increased serotonin transporter and GR expression in the ventral hippocampus but did not significantly affect OCT3 expression or behavior. No treatment effects on OCT3, serotonin transporter or GR expression were observed in the DMH, CeA or dorsal hippocampus. Our findings suggest that corticosterone increases OCT3 expression in the ventral hippocampus by a mechanism independent of GRs, and that mifepristone and corticosterone can act in an independent manner to affect HPA axis-related physiological and behavioral parameters.
Stress is associated with different emotional states, where fear and anxiety are the most commonly experienced during stressful situations. Fear plays a critical role in rapid reactions to perceived threats, preparing the organism for immediate responses to face potential dangers, including the ability to get ready to cope with adversity or to escape. It may be an adaptive emotion, but chronic and uncontrollable fear has been associated with the origin and development of anxiety, which is characterized by anticipated fear and uncertainty, associated with threatening events. Anxiety may contribute to improve adaptive responses, stimulating attention and arousal, shaping cognitive processes involved in different coping strategies. If anxiety continues longer, as it is observed during chronic stress, it may interfere with cognitive and emotional processes, which, in turn, may lead to the origin and development of chronic and severe anxiety disorders. Chronic stress, mostly produced by the impact of unavoidable and uncontrollable conditions, may lead to learned helplessness, which has been associated with the origin and development of depression. Chronic stress may lead to hyper-activation of the hypothalamic-pituitary-adrenal (HPA) axis, with the resulting increased levels of cortisol, and various aminergic systems are also involved in this process, including the serotonergic, the dopaminergic and the noradrenergic systems, which, in turn, are also interconnected with cortical and limbic structures. The amygdala plays a critical role in identifying potentially stressful stimuli and detecting present threats or imminent danger, which therefore contributes to activating the necessary adaptive responses. It represents the main structure of an adaptive neural circuit involved in cognitive and emotional processing, which includes reciprocal connections with other neural structures, such as the hippocampus, the bed nucleus of the stria terminalis (BNST) and different areas of the prefrontal cortex (PFC). Activation of the amygdala, associated with feelings of fear and anxiety, may be neutralized by the ventro-medial PFC (VM-PFC), which has been involved in decreasing learned helplessness and the resulting learned control, consolidating neural pathways involved in predictability and controllability, which are crucial for the development of resilience.KeywordsPsychoneurobiologyStressFearAnxietyDepressionVulnerability
Les études épidémiologiques estiment que le risque de dépression majeure (DM) est plus élevé chez les patients diabétiques comparé à la population générale. Des études plus spécifiques mettent en lumière des corrélations entre la dégradation de certains paramètres métaboliques et les symptômes anxio-dépressifs chez l'humain. C'est notamment le cas pour l'insulino-résistance périphérique qui est positivement corrélée à la sévérité de la DM. En revanche, les conséquences de l'insulino-résistance centrale sur les troubles dépressifs n'ont jamais été étudiés de manière approfondie non seulement en clinique mais également chez l'animal de laboratoire. Compte tenu de la présence du récepteur à l'insuline dans le cerveau, une des hypothèses serait que cette hormone module directement (ou indirectement) l'activité des systèmes monoaminergiques et notamment celle des neurones sérotoninergiques (5-HT) majoritairement regroupé dans le noyau dorsal du raphé (NDR). En effet, si l'influence de l'insuline sur le système dopaminergique et le comportement alimentaire a déjà été montré, très peu d'études se sont intéressées à son impact sur le système 5-HT pourtant clé dans la physiopathologie de la DM. Au cours de ce travail de thèse nous avons pu montrer que le récepteur à l'insuline est présent sur les neurones 5-HT du NDR. Grâce à des techniques d'électrophysiologie ex- et in-vivo et de microdialyse intracérébrale réalisées sur modèle murin, nous avons caractérisé l'effet excitateur de l'insuline sur l'activité électrique des neurones 5-HT. Ces résultats nous ont amené à tester les effets comportementaux de l'insuline et à montrer les effets anxiolytiques de son injection intra-raphé et intra-nasale chez la souris saine. Dans un second temps, afin de se placer dans un contexte pathologique et de mieux comprendre l'impact de la perturbation de la signalisation de l'insuline sur l'humeur, nous avons étudié l'activité du système 5-HT et les comportements de type anxio-dépressifs dans des modèles murins de diabète de type 1 et 2 (DT1/DT2). Dans ces deux modèles, que ce soit dans un contexte d'insulinopénie (DT1) ou d'insulino-résistance (DT2), les souris présentent un phénotype anxieux et certains traits de la DM associés à un diminution de l'activité du système sérotoninergique du NDR. Enfin, nous avons tenté d'identifier l'implication de l'apeline, une adipokine connue pour ses propriétés insulino-sensibilisatrice sur les anomalies comportementales induites par un DT2. Nos résultats montrent que les souris présentant une invalidation génétique de l'apeline, sont plus susceptibles à développer une insulino-résistance en réponse à un régime alimentaire diabétogène et des troubles comportementaux. De manière intéressante le traitement par la metformine, un antidiabétique aux propriétés insulino-sensibilisatrice, ne permet pas l'amélioration des paramètres métaboliques de ces souris mutantes mais améliore leur état anxieux. Ainsi ce travail de thèse a permis de souligner l'existence d'interactions anatomiques et fonctionnelles entre le système insulinergique et sérotoninergique central ainsi que leur importance dans l'anxiété, un trouble psychiatrique souvent annonciateur d'un épisode dépressif. [...]
Interactions between the hypothalamic-pituitary-adrenal axis and the central 5-HT system in the depressive state remain largely unknown. The present study investigated corticosterone (CORT) regulations of extracellular 5-HT in the hippocampal CA3 in a mouse model of depression. Basal dialysate 5-HT, true extracellular 5-HT, 5-HT reuptake efficiency, and time courses of dialysate 5-HT following CORT injections at 10, 20, and 40 mg/kg were determined at baseline, depressive-like state and after subsequent fluoxetine (FLX) treatment using in vivo microdialysis in male C57BL/6 mice. Behavioral tests were used to determine behavioral phenotypes and therapeutic responses to FLX. Depressed mice showed decreased extracellular 5-HT, increased 5-HT reuptake efficiency, and absence of the increase in dialysate 5-HT response to CORT injections, which were all reversed in FLX-responsive mice. Surprisingly, the FLX nonresponsive mice continued to worsen behaviorally and exhibited lower extracellular 5-HT and higher 5-HT reuptake efficiency. Our study indicates that abolished-CORT induced 5-HT response, decreased extracellular 5-HT, and increased 5-HT reuptake efficiency might be the signature features associated with depressive-like state. Increased 5-HT reuptake efficiency was one of the underlying mechanisms, with target effectors remaining to be explored. The findings in the FLX nonresponsive mice suggest distinct neuromechanisms, which might be genetically predetermined.
Major depressive disorder is a major psychiatric disorder and a leading cause of disability around the world. Females have about twice as high an incidence of depression as males. However, preclinical animal models of depression have seldom investigated the molecular alterations associated with higher depression risk in females. In this study, adopting the early-life stress (ELS) paradigm of limited bedding and nesting material, we found that ELS induced depression-like behaviors only in adult female mice, as evaluated by sucrose preference and tail suspension tests. We then examined the ELS effects on monoamine neurotransmission (transporters for monoamine reuptake and release) in depression-related brain regions in female mice. We found that ELS resulted in widespread changes of the expression levels of these transporters in four brain regions. Moreover, systemic 21-day treatment with vortioxetine, a novel multimodal antidepressant, successfully reversed depression-like behaviors and normalized some molecular changes, including that of the norepinephrine transporter in the medial prefrontal cortex, vesicular monoamine transporter 2 in nucleus accumbens core, and serotonin transporter in amygdala. Collectively, these results provide evidence for the validity of using the limited bedding and nesting material paradigm to investigate sex differences in depression and demonstrate that the region-specific alterations of monoamine neurotransmission may be associated with depression-like behaviors in female mice.
This article is part of the special issue on ‘Stress, Addiction and Plasticity’.
Prenatal stress (PNS) influences offspring neurodevelopment, inducing anxiety-like behavior and memory deficits. We investigated whether pretreatment of Bacopa monnieri extract (CDRI-08/BME) ameliorates PNS-induced changes in signaling molecules, and changes in the behavior of Wistar rat offspring. Pregnant rats were randomly assigned into control (CON)/prenatal stress (PNS)/PNS and exposed to BME treatment (PNS + BME). Dams were exposed to stress by placing them in a social defeat cage, where they observed social defeat from gestational day (GD)-16–18. Pregnant rats in the PNS + BME group were given BME treatment from GD-10 to their offspring’s postnatal day (PND)-23, and to their offspring from PND-15 to -30. PNS led to anxiety-like behavior; impaired memory; increased the level of corticosterone (CORT), adrenocorticotropic hormone, glucocorticoid receptor, pro-apoptotic Casepase-3, and 5-HT2C receptor; decreased anti-apoptotic Bcl-2, synaptic proteins (synaptophysin, synaptotagmin-1), 5-HT1A, receptor, phosphorylation of calmodulin-dependent protein kinase II/neurogranin, N-methyl-D-aspartate receptors (2A,2B), postsynaptic density protein 95; and conversion of pro and mature brain derived neurotropic factor in their offspring. The antioxidant property of BME possibly inhibiting the PNS-induced changes in observed molecules, anxiety-like behavior, and memory deficits. The observed results suggest that pretreatment of BME could be an effective coping strategy to prevent PNS-induced behavioral impairments in their offspring.
Selective serotonin reuptake inhibitors are the first-line antidepressants for treating major depressive and post-traumatic stress disorders. These inhibitors directly bind to the serotonin transporter (SERT). Protein kinase C (PKC) is a key regulator of SERT functions as it can attenuate SERT activity through phosphorylation and its subsequent internalization. However, whether PKC-regulated SERT functions are involved in emotional impairment in a mouse model of stress remains unclear. Using a mouse model of swim-induced stress, we investigated whether the PKC-SERT system is involved in emotional impairment and tried to identify the PKC isoforms involved in this mechanism. Mice exposed to swim stress showed enhanced immobility and decreased social interaction times compared to those in swim stress-naive mice. Moreover, significant decreases in phosphorylated PKCβI and SERT levels were observed in the prefrontal cortex of stressed mice compared to those of swim stress-naive mice. No changes in levels of other phosphorylated PKC isoforms were observed between the two groups. Phorbol 12-myristate 13-acetate (a PKC activator) administration significantly attenuated enhanced immobility and decreased social interaction time in stressed mice and increased the serotonin turnover. Further, the PKC activator increased levels of phosphorylated PKCβI or SERT and decreased cell surface localization of SERT in stressed mice. Contrary to this, chelerythrine (a PKC inhibitor) administration exacerbated the immobility and sociality of mice exposed to mild stress. Our results suggest that PKCβI activation attenuates emotional impairment by suppressing SERT function in stressed mice. Thus, PKCβI may be a key target for the development of new treatment strategies for emotional impairment in stress-related disorders.
Propofol is the most common intravenous anesthetic agent for induction and maintenance of anesthesia, and has been used clinically for more than 30 years. However, the mechanism by which propofol induces loss of consciousness (LOC) remains largely unknown. The adenosine A 2A receptor (A 2A R) has been extensively proven to have an effect on physiological sleep. It is, therefore, important to investigate the role of A 2A R in the induction of LOC using propofol. In the present study, the administration of the highly selective A 2A R agonist (CGS21680) and antagonist (SCH58261) was utilized to investigate the function of A 2A R under general anesthesia induced by propofol by means of animal behavior studies, resting‐state magnetic resonance imaging and c ‐Fos immunofluorescence staining approaches. Our results show that CGS21680 significantly prolonged the duration of LOC induced by propofol, increased the c ‐Fos expression in nucleus accumbens (NAc) and suppressed the functional connectivity of NAc‐dorsal raphe nucleus (DR) and NAc‐cingulate cortex (CG). However, SCH58261 significantly shortened the duration of LOC induced by propofol, decreased the c ‐Fos expression in NAc, increased the c ‐Fos expression in DR, and elevated the functional connectivity of NAc‐DR and NAc‐CG. Collectively, our findings demonstrate the important roles played by A 2A R in the LOC induced by propofol and suggest that the neural circuit between NAc‐DR maybe controlled by A 2A R in the mechanism of anesthesia induced by propofol.
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Chronic restraint stress (CRS) magnifies restraint-induced corticosterone secretion through a mechanism involving increased adrenocortical 5-HT content and turnover. We analysed the impact of CRS on serotonin transporter (SERT) expression and distribution in rat adrenal glands. Male Wistar rats were submitted to CRS (20 min/day) or undisturbed control conditions for 14 days. Exposure to CRS induced a remarkable increase in SERT-like immunoreactivity in the adrenal cortex, which closely matched that of chromogranin A immunostaining, along with a significant increase in SERT protein and mRNA levels in whole adrenals as determined by immunohistochemistry, Western blot and RT-PCR assays, respectively; all these CRS-induced changes occurred almost exclusively in left adrenals. Closely similar results were obtained in animals that received a 14-day chronic corticosterone treatment. These results unravel an interesting association between chronic stress exposure and SERT expression in adrenocortical chromogranin A-positive cells, which seems to be a glucocorticoid-dependent phenomenon.
Background
The activity of the hypothalamic-pituitary-adrenal (HPA) axis is commonly dysregulated in stress-related psychiatric disorders. Annexin A1 (ANXA1), an endogenous ligand of formyl peptide receptor (FPR) 2/3, is a member of the family of phospholipid- and calcium-binding proteins with a well-defined role in the delayed early inhibitory feedback of glucocorticoids (GC) in the pituitary gland and implicated in the occurrence of behavioural disorders such as anxiety.
Objective
The present study aimed to evaluate the potential role of ANXA1 and its main receptor, as a cellular mediator of behavioural disorders, in a model of corticosterone (CORT)-induced depression and subsequently the possible correlation between the depressive state and impairment of hippocampal memory.
Methods
To induce the depression model, wild-type (WT), ANXA1 knockout (KO), and FPR2/3 KO mice were exposed to orally administration of CORT for 28 days dissolved in drinking water. Histological, biochemical and behavioural analyses were performed.
Results
FPR2/3 KO and ANXA1 KO mice showed improvement in anxiety and depression-like behaviour compared with WT mice after CORT administration. In addition, FPR2/3 KO and ANXA1 KO mice showed a reduction in histological alterations and neuronal death in hippocampal sections. Moreover, CORT+ FPR2/3 KO and ANXA1 KO, exhibited an higher expression of brain derived neurotrophic factor (BDNF), phospho-ERK, cAMP response element-binding protein (pCREB) and a decrease of serotonin transporter expression (SERT) compared to WT(CORT+) mice.
Conclusion
In conclusion, the absence of the ANXA1 protein, even more than the absence of its main receptor (FPR 2/3), was fundamental to the inhibitory action of GC on the HPA axis; it also maintained the hippocampal homeostasis by preventing neuronal damage associated with depression.
In this study, we examined whether the presence of mother suppresses early-life stressful social experience (SSE)-induced anxiety-like behavior and impairment of short-term memory later in life. On postnatal day (PND)-5, mothers with pups were grouped as follows: (i) control; (ii) maternal separation (MS); (iii) pups with mother experience the presence of a stranger (M+P-ST); and (iv) maternal separated pups experience the presence of a stranger (MSP-ST). Individuals were subjected to light-dark box and spontaneous alternation from PND-29 to 32. We observed that the MSP-ST group exhibits anxiety-like behavior and impairment in short-term memory. Further, SSE significantly elevated the adrenocorticotropic hormone, corticosterone and expression of glucocorticoid receptor (GR) in MSP-ST pups. Similarly, serotonin (5-hydroxytryptamine; 5-HT), dopamine, noradrenaline and expression of serotonin transporter levels were significantly elevated in MSP-ST pups. These observations suggest that during early postnatal days, the pups may recognize strangers by the sense of smell, and the presence of mother reduces the SSE-induced stress.
The present study evaluates the anti-oxidative stress activity of Vaccinium bracteatum Thunb. fruit extract (VBFW) to identify the mechanisms responsible for its antidepressant-like effects. To evaluate the antidepressant and anti-oxidant effects of VBFW, malondialdehyde (MDA), serotonin transporter (SERT), and monoamine oxidase A (MAO-A) levels were measured in a mouse model of chronic restraint stress (CRS). The underlying mechanisms preventing oxidative stress and neuronal apoptosis were investigated using in vitro models of hydrogen peroxide (H2O2)-induced neuronal damage. The results showed that VBFW treatment (200mg/kg) significantly reduced MDA, SERT, and MAO-A levels in the prefrontal cortex of CRS mice. Furthermore, VBFW (30μg/mL) exhibited protective effects against H2O2-induced cell death via inhibition of the H2O2-induced increase in Bax and decrease in Bcl-2 levels within the mitochondria of SH-SY5Y cells. Furthermore, VBFW (10 and 30μg/mL) exerted protective effects against H2O2-induced cell death through inhibition of key mitochondria-associated apoptotic proteins such as cytochrome c, caspase-3 and PARP. Additionally, VBFW (10 and 30μg/mL) could improve the activity of anti-oxidant enzymes (such as SOD and catalase) in H2O2-treated SH-SY5Y cells. These results suggest that the antidepressant and anti-oxidant effects of VBFW might be mediated by the regulation of SERT and MAO-A, and possibly associated with regulation of oxidative stress-induced apoptosis.
Dominance hierarchies are common across the animal kingdom and have important consequences for reproduction and survival. Animals of lower social status cope with repeated social defeat using proactive and reactive behaviours. However, there remains a paucity of information on how an individual's coping behaviours changes over time or what neural mechanisms are involved. We used a resident-intruder paradigm in the African cichlid fish Astatotilapia burtoni to investigate the neural correlates of these two opposing behaviour groups. Fish initially used both proactive and reactive behaviours, but had a dramatic increase in use of proactive behaviours during the third interaction, and this was followed by cessation of proactive behaviours and exclusive use of reactive coping. By quantifying neural activation in socially-relevant brain regions, we identify a subset of brain nuclei, including those homologous to the mammalian amygdala, showing higher activation in fish displaying proactive but not reactive behaviours. Fish displaying reactive behaviours had greater neural activation in the superior raphe, suggesting a possible conserved function during social defeat across vertebrates. These data provide the first evidence on the involvement of specific brain regions underlying proactive and reactive coping in fishes, indicating that these nuclei have conserved functions during social defeat across taxa.
Adverse juvenile experiences, including physical abuse, often have negative health consequences later in life. We investigated the influence of social defeat stress exposure as juveniles on neuropsychological behaviors, and the causal role of glucocorticoids in abnormal behaviors and impairment of neurogenesis in mice exposed to the stress. The juvenile (24-day-old) and adult (70-day-old) male C57BL/6J mice were exposed to social defeat stress induced by an aggressive ICR mouse. Social defeat stress exposure as juveniles, even for 1 day, induced persistent social avoidance to the unfamiliar ICR mouse in the social interaction test, but that was not observed in mice exposed to the stress as adults. Social avoidance by the stress exposure as juveniles for 10 consecutive days was observed, when the target mouse was not only unfamiliar ICR but also another C57BL/J mouse, but not an absent or an anesthetized ICR mouse. The stress exposure did not induce anxiety- and depression-like behavior in spontaneous locomotor activity, elevated plus-maze test, marble-burying test, forced swimming test, or sucrose preference test. Serum corticosterone levels increased immediately after the stress exposure. The hippocampal neurogenesis was suppressed 1 day and 4 weeks after the stress exposure. Administration of mifepristone, a glucocorticoid receptor antagonist, prior to each stress exposure, blocked the persistent social avoidance and suppression of neurogenesis. In conclusion, social avoidance induced by social defeat stress exposure as juveniles are more persistent than that as adults. These social avoidances are associated with suppression of hippocampal neurogenesis via glucocorticoid receptors.
Chronic stress enhances risk for psychiatric disorders, and in animal models is known to evoke depression-like behavior accompanied by perturbed neurohormonal, metabolic, neuroarchitectural and transcriptional changes. Serotonergic neurotransmission, including serotonin2A (5-HT2A) receptors, have been implicated in mediating specific aspects of stress-induced responses. Here we investigated the influence of chronic unpredictable stress (CUS) on depression-like behavior, serum metabolic measures, and gene expression in stress-associated neurocircuitry of the prefrontal cortex (PFC) and hippocampus in 5-HT2A receptor knockout (5-HT2A−/−) and wild-type mice of both sexes. While 5-HT2A−/− male and female mice exhibited a baseline reduced anxiety-like state, this did not alter the onset or severity of behavioral despair during and at the cessation of CUS, indicating that these mice can develop stress-evoked depressive behavior. Analysis of metabolic parameters in serum revealed a CUS-evoked dyslipidemia, which was abrogated in 5-HT2A−/− female mice with a hyperlipidemic baseline phenotype. 5-HT2A−/− male mice in contrast did not exhibit such a baseline shift in their serum lipid profile. Specific stress-responsive genes (Crh, Crhr1, Nr3c1, and Nr3c2), trophic factors (Bdnf, Igf1) and immediate early genes (IEGs) (Arc, Fos, Fosb, Egr1-4) in the PFC and hippocampus were altered in 5-HT2A−/− mice both under baseline and CUS conditions. Our results support a role for the 5-HT2A receptor in specific metabolic and transcriptional, but not behavioral, consequences of CUS, and highlight that the contribution of the 5-HT2A receptor to stress-evoked changes is sexually dimorphic.
Depression and substance use disorders are often comorbid, but the reasons for this are unclear. In human studies, it is difficult to determine how one disorder may affect predisposition to the other and what the underlying mechanisms might be. Instead, animal studies allow experimental induction of behaviors relevant to depression and drug-taking, and permit direct interrogation of changes to neural circuits and molecular pathways. While this field is still new, here we review animal studies that investigate whether depression-like states increase vulnerability to drug-taking behaviors. Since chronic psychosocial stress can precipitate or predispose to depression in humans, we review studies that use psychosocial stressors to produce depression-like phenotypes in animals. Specifically, we describe how postweaning isolation stress, repeated social defeat stress, and chronic mild (or unpredictable) stress affect behaviors relevant to substance abuse, especially operant self-administration. Potential brain changes mediating these effects are also discussed where available, with an emphasis on mesocorticolimbic dopamine circuits. Postweaning isolation stress and repeated social defeat generally increase acquisition or maintenance of drug self-administration, and alter dopamine sensitivity in various brain regions. However, the effects of chronic mild stress on drug-taking have been much less studied. Future studies should consider standardizing stress-induction protocols, including female subjects, and using multi-hit models (e.g. genetic vulnerabilities and environmental stress).
Depression is a heterogeneous disorder characterized by alterations at psychological, behavioural, physiological, neurophysiological, and neurochemical levels. Social stress is a prevalent stress in man, and the repeated social defeat stress model in rats has been proposed as being the rodent equivalent to loss of control, which in subordinate animals produces alterations that resemble several of the cardinal symptoms found in depressed patients. Here, rats followed a resident-intruder protocol for 4 consecutive days during which behavioural, physiological, and electroencephalographic (EEG) parameters were simultaneously monitored in subordinate rats. On day 5, prefrontal dopamine (DA) and hippocampal serotonin (5-HT) as well as corticosterone were measured in submissive rats that had visual, acoustic, and olfactory (but no physical) contact with a dominant, resident conspecific rat. Socially defeated rats demonstrated increases in ultrasonic vocalizations (20-25 KHz), freezing, submissive defensive behaviour, inactivity, and haemodynamic response, while decreases were found in repetitive grooming behaviour and body weight. Additionally, alterations in the sleep-wake architecture were associated with reduced active waking, enhanced light sleep, and increased frequency of transitions from light sleep to quiet wakefulness, indicating sleep instability. Moreover, the attenuation of EEG power over the frequency range of 4.2-30 Hz, associated with a sharp transient increase in delta oscillations, appeared to reflect increased brain activity and metabolism in subordinate animals. These EEG changes were synchronous with a marked increase in body temperature and a decrease in locomotor activity. Furthermore, psychosocial stress consistently increased 5-HT, DA, and corticosterone levels. The increased levels of cortical DA and hippocampal 5-HT during social threat may reflect a coping mechanism to promote alertness and psychological adaptation to provocative and threatening stimuli. These neurophysiological changes are hypothesized to be the consequence of dynamics in monoamine systems, which could be useful markers for disease progression in the aetiology of depression.
We report the case of a woman with longstanding refractory depression and psychotic features who was eventually diagnosed with Cushing disease. After surgical treatment of a pituitary adenoma, she experienced gradual psychiatric recovery and was eventually able to discontinue all psychotropic medication. We review the psychiatric components of Cushing disease, implications of psychiatric illnesses for the treatment and prognosis of Cushing disease, and potential pathophysiological mechanisms linking glucocorticoid excess to psychiatric illness.
A large body of data suggests that the activation of α1 receptors by a tonic noradrenergic input might be responsible for the tonic discharge of the serotonergic neurons of the dorsal raphe nucleus (DRN). To test this hypothesis, it was necessary to determine the origin of the noradrenergic and adrenergic innervation of these neurons. For this purpose, we combined small iontophoretic injections of the sensitive retrograde tracer cholera toxin b subunit (CTb) in the different subdivisions of the DRN with tyrosine hydroxylase immunohistochemistry. After CTb injections in the ventral or dorsal parts of the central DRN, a small number of double-labeled cells was observed in the locus coeruleus (A6 noradrenergic cell group), the A5 noradrenergic group, the dorsomedial medulla (C3 adrenergic cell group), and the lateral paragigantocellular nucleus (C1 adrenergic cell group). After CTb injections in the lateral wings or the dorsal part of the rostral DRN, a similar number of double-labeled cells was seen in C3. Slightly more double-labeled cells were seen in A6 and A5. In addition, a substantial to large number of double-labeled cells appeared in C1, the commissural part of the nucleus of the solitary tract (A2 noradrenergic cell group) and the caudoventrolateral medulla (A1 noradrenergic cell group). These results indicate that the noradrenergic and adrenergic inputs to the DRN arise from all the catecholaminergic cell groups of the lower brainstem except the A7 noradrenergic group. They further reveal the existence of a topographical organization of these afferents to the different subdivisions of the DRN.
New genetic models that target the serotonin system show that transient alterations in serotonin homeostasis cause permanent changes to adult behaviour and modify the fine wiring of brain connections. These findings have revived a long-standing interest in the developmental role of serotonin. Molecular genetic approaches are now showing us that different serotonin receptors, acting at different developmental stages, modulate different developmental processes such as neurogenesis, apoptosis, axon branching and dendritogenesis. Our understanding of the specification of the serotonergic phenotype is improving. In addition, studies have revealed that serotonergic traits are dissociable, as there are populations of neurons that contain serotonin but do not synthesize it.
The function of the central cannabinoid receptor (CB1) was investigated by invalidating its gene. Mutant mice did not respond to cannabinoid drugs, demonstrating the exclusive
role of the CB1 receptor in mediating analgesia, reinforcement, hypothermia, hypolocomotion, and hypotension. The acute effects of opiates
were unaffected, but the reinforcing properties of morphine and the severity of the withdrawal syndrome were strongly reduced.
These observations suggest that the CB1 receptor is involved in the motivational properties of opiates and in the development of physical dependence and extend the
concept of an interconnected role of CB1 and opiate receptors in the brain areas mediating addictive behavior.
While females are considered more susceptible to depressive behavior, this assertion is not strongly supported by the experimental
literature. Since stress contributes to depressive behavior, male and female Wistar Kyoto (WKY) rats were exposed to either
one session (acute stress) or 5 sessions (chronic stress) of restraint plus cold in order to study depressive behavior in
male and female rats. After their respective treatment exposure, rats were tested in the open field test (OFT) and for retention
of a passive-avoidance (P-A) task. One stress session resulted in significant immobility in the OFT for males, whereas 5 sessions
were required to produce similar immobility in female rats. Acute stress interfered with the retention of the P-A response
for males, while both acute and chronic stress produced poor P-A responses in female rats. Food consumption decresed, progressively,
as a function of stress sessions, in female rats, whereas feeding in males returned to control levels after five stress days.
Both acute and chronic stress exacerbated the stress ulcer response in male rats, but not in female rats. Chronic, but not
acute, stress resulted in an increase in serotonin transporter mRNA levels in the dorsal raphe nucleus of both male and, female
rats. The general consensus from these data suggested that female rats were more vulnerable to chronic stress and consequently
supported the notion that females may be more susceptible to stress induced behavioral depression.
Key WordsWKY rats–acute and chronic stress–gender–passive avoidance–open field behavior–stress-ulcer–adrenal weight–serotonin–dorsal raphe nucleus
Both hypothalamic-pituitary-adrenal (HPA) axis activity and serotonergic systems are commonly dysregulated in stress-related psychiatric disorders. We describe here a non-invasive rat model for hypercortisolism, as observed in major depression, and its effects on physiology, behavior, and the expression of tph2, the gene encoding tryptophan hydroxylase 2, the rate-limiting enzyme for brain serotonin (5-hydroxytryptamine; 5-HT) synthesis. We delivered corticosterone (40 μg/ml, 100 μg/ml or 400 μg/ml) or vehicle to adrenal-intact adult, male rats via the drinking water for 3 weeks. On days 15, 16, 17 and 18, respectively, the rats' emotionality was assessed in the open-field (OF), social interaction (SI), elevated plus-maze (EPM), and forced swim tests (FST). On day 21, half of the rats in each group were killed 2h into the dark phase of a 12/12 h reversed light/dark cycle; the other half were killed 2h into the light phase. We then measured indices of HPA axis activity, plasma glucose and interleukin-6 (IL-6) availability, and neuronal tph2 expression at each time point. Chronic corticosterone intake was sufficient to cause increased anxiety- and depressive-like behavior in a dose-dependent manner. It also disrupted the diurnal pattern of plasma adrenocorticotropin (ACTH), corticosterone, and glucose concentrations, caused adrenal atrophy, and prevented regular weight gain. No diurnal or treatment-dependent changes were found for plasma concentrations of IL-6. Remarkably, all doses of corticosterone treatment abolished the diurnal variation of tph2 mRNA expression in the brainstem dorsal raphe nucleus (DR) by elevating the gene's expression during the animals' inactive (light) phase. Our data demonstrate that chronic elevation of corticosterone creates a vulnerability to a depression-like syndrome that is associated with increased tph2 expression, similar to that observed in depressed patients.
Data suggest that the serotonin (5-hydroxytryptamine, 5-HT) system is implicated in the pathogenesis of multiple neuropsychiatric disorders and may also be involved in smoking behaviour since nicotine increases brain serotonin secretion. It is known that smoking behaviour is influenced by both genetic and environmental factors. The present review examines the role of the serotonin transporter gene (5-HTT) in smoking behaviour and investigating studies that showed association of 5-HTT gene with smoking. This study discusses a polymorphism which has been investigated by many researchers, as the bi-allelic insertion/deletion polymorphism in the 5'- flanking promoter region (5-HTTLPR). This gene has received considerable attention in attempts to understand the molecular determinants of smoking. Therefore, in the present study, the relationship between genetic polymorphism of serotonin transporter in smoking behaviour is reviewed considering the interactive effect of genetic factors.
MicroRNA-16 and Depression
Signal transmission between neurons is effected by neurotransmitters such as serotonin. Membrane-bound transporters remove excess neurotransmitters. Disruption of the delicate balance between neurotransmitter release and removal can lead to larger disruptions in neuronal circuitry. Depression and anxiety may be linked to dysfunction of some of these circuits. Uptake inhibitors can be used to treat depression, but the molecular pathways affected have been unclear. Baudry et al. (p. 1537 ) now show that microRNA-16 controls synthesis of the serotonin transporter and that the amount of microRNA-16 can be controlled by the same uptake inhibitors used to treat depression.
Numerous clinical and experimental studies have linked stress to changes in risk factors associated with the development of physiological syndromes, including metabolic disorders. How different mediators of the stress response, such as corticosterone (CORT), influence these changes in risk remains unclear. Although CORT has beneficial short-term effects, long-term CORT exposure can result in damage to the physiological systems it protects acutely. Disruption of this important physiologic signal is observed in numerous disparate disorders, ranging from depression to Cushing's syndrome. Thus, understanding the effects of chronic high CORT on metabolism and physiology is of key importance. We explored the effects of 4-wk exposure to CORT dissolved in the drinking water on the physiology and behavior of male mice. We used this approach as a noninvasive way of altering plasma CORT levels while retaining some integrity in the diurnal rhythm present in normal animals. This approach has advantages over methods involving constant CORT pellets, CORT injections, or adrenalectomy. We found that high doses of CORT (100 microg/ml) result in rapid and dramatic increases in weight gain, increased adiposity, elevated plasma leptin, insulin and triglyceride levels, hyperphagia, and decreased home-cage locomotion. A lower dose of CORT (25 microg/ml) resulted in an intermediate phenotype in some of these measures but had no effect on others. We propose that the physiological changes observed in the high-CORT animals approximate changes observed in individuals suffering from the metabolic syndrome, and that they potentially serve as a model for hypercortisolemia and stress-related obesity.
Anxiety disorders, depression and animal models of vulnerability to a depression-like syndrome have been associated with dysregulation of serotonergic systems in the brain. To evaluate the effects of early life experience, adverse experiences during adulthood, and potential interactions between these factors on serotonin transporter (slc6a4) mRNA expression, we investigated in rats the effects of maternal separation (180 min/day from days 2 to 14 of life; MS180), neonatal handing (15 min/day from days 2 to 14 of life; MS15), or normal animal facility rearing (AFR) control conditions with or without subsequent exposure to adult social defeat on slc6a4 mRNA expression in the dorsal raphe nucleus (DR) and caudal linear nucleus. At the level of specific subdivisions of the DR, there were no differences in slc6a4 mRNA expression between MS15 and AFR rats. Among rats exposed to a novel cage control condition, increased slc6a4 mRNA expression was observed in the dorsal part of the DR in MS180 rats, relative to AFR control rats. In contrast, MS180 rats exposed to social defeat as adults had increased slc6a4 mRNA expression throughout the DR compared to both MS15 and AFR controls. Social defeat increased slc6a4 mRNA expression, but only in MS180 rats and only in the "lateral wings" of the DR. Overall these data demonstrate that early life experience and stressful experience during adulthood interact to determine slc6a4 mRNA expression. These data support the hypothesis that early life experience and major stressful life events contribute to dysregulation of serotonergic systems in stress-related neuropsychiatric disorders.
Major depression is associated with both dysregulation of the hypothalamic pituitary adrenal axis and serotonergic deficiency, not the least of the 5-HT2A receptor. However, how these phenomena are linked to each other, and whether a low 5-HT2A receptor level is a state or a trait marker of depression is unknown. In mice with altered glucocorticoid receptor (GR) expression we investigated 5-HT2A receptor levels by Western blot and 3H-MDL100907 receptor binding. Serotonin fibre density was analyzed by stereological quantification of serotonin transporter immunopositive fibers. To establish an effect of GR activation on 5-HT2A levels, mature organotypic hippocampal cultures were exposed to corticosterone with or without GR antagonist mifepristone and mineralocorticoid receptor (MR) antagonist spironolactone. In GR under-expressing mice, hippocampal 5-HT2A receptor protein levels were decreased (26.3 +/- 1.6%, p < 0.05) and frontal 5-HT2A receptor binding was decreased (20 +/- 15%, p < 0.01) as compared to wild-type mice. Conversely, in over-expressing GR mice hippocampal 5-HT2A receptor protein levels were increased (60.8 +/- 4.0%, p = 0.0001) and 5-HT2A receptor binding was increased in dorsal hippocampus (77 +/- 35%, p < 0.05) as compared to wild-type mice. No difference in serotonin fibre density was observed in the GR over-expressing mice, while the GR under-expressing mice showed lower serotonergic innervation in the frontal cortex area. An effect of GR activation on 5-HT2A receptor levels was further corroborated by the culture studies as long-term exposure of 3 microM corticosterone to organotypic hippocampal cultures increased 5-HT2A receptor levels (p < 0.05). The corticosterone-induced 5-HT2A receptor up-regulation was blocked by addition of either spironolactone or mifepristone.
Although previous studies have examined the extent to which adrenocorticotropic hormone (ACTH) secretion depends on endogenous glucocorticoid levels, few have examined the parallel glucocorticoid dependency of gene expression within the corticotropin releasing hormone (CRH) neuron containing subregion of the hypothalamic paraventricular nucleus (PVN). This study examined resting and stress-induced expression of three immediate early genes (c-fos, zif268, and NGFI-B mRNAs) and two phenotypic restricted immediate early genes that code for ACTH secretagogues (CRH and arginine vasopressin [AVP] hnRNAs) in the PVN of adrenalectomized (ADX) rats given either 0.9% saline to drink for 5 days or saline with corticosterone (CORT; 25 microg/ml). CORT-containing saline was replaced with saline 18 h before testing to ensure clearance of CORT at the time of testing. Dependent measures were examined 0, 15, 30, 60, or 120 min after 30 min restraint. Compared to sham surgery, ADX produced a large upregulation of basal ACTH secretion but only a trend for an increase in basal PVN CRH and parvocellular (mp) PVN AVP hnRNA expression, and a marked augmentation of restraint-induced ACTH secretion and the expression of all five genes examined. CORT containing saline partially normalized basal and restraint-induced ACTH secretion and restraint-induced AVP hnRNA, c-fos mRNA, and zif268 mRNA in the PVN in ADX rats. In contrast, expression patterns of restraint-induced PVN CRH hnRNA and NGFI-B mRNA were not different between ADX rats with or without CORT replacement. Given that there was no circulating CORT present at the time of restraint challenge in either group of ADX rats, the differential impact of CORT replacement on restraint-induced PVN gene expression must reflect differential dependency of the expression of these genes in the PVN on the prior presence of CORT.
High affinity [3H]imipramine binding, endogenous levels of serotonin and noradrenaline, and serotonin uptake were determined in brain regions of rats with selective destruction of serotonergic neurons by 5,7-dihydroxytryptamine (5,7-DHT), of adrenergic neurons by 6-hydroxydopamine (6-OHDA), and of rats treated with reserpine. Neonatal treatment with 5,7-DHT resulted in a significant decrease of both serotonin levels and density (Bmax) of high affinity [3H]imipramine binding sites in the hippocampus. In contrast, an elevation of serotonin levels and an increase in Bmax of [3H]imipramine binding were noted in the pons--medulla region. No changes were observed in the noradrenaline content in either of these regions. Intracerebral 6-OHDA lesion produced a drastic suppression of noradrenaline levels in cerebral cortex but failed to alter the binding affinity (KD) or density (Bmax) of [3H]imipramine recognition sites. A single injection of reserpine (2.5 mg/kg) resulted in marked depletion of both serotonin (by 57%) and noradrenaline (by 86%) content and serotonin uptake (by 87%) in the cerebral cortex but had no significant influence of the parameters of high affinity [3H]imipramine binding in this brain region. The results suggest that high affinity [3H]imipramine binding in the brain is directly related to the integrity of serotonergic neurons but not to the magnitude of the uptake or the endogenous levels of the transmitter, and is not affected by damage to noradrenergic neurons or by low levels of noradrenaline.
A large body of data suggests that the activation of alpha 1 receptors by a tonic noradrenergic input might be responsible for the tonic discharge of the serotonergic neurons of the dorsal raphe nucleus (DRN). To test this hypothesis, it was necessary to determine the origin of the noradrenergic and adrenergic innervation of these neurons. For this purpose, we combined small iontophoretic injections of the sensitive retrograde tracer cholera toxin b subunit (CTb) in the different subdivisions of the DRN with tyrosine hydroxylase immunohistochemistry. After CTb injections in the ventral or dorsal parts of the central DRN, a small number of double-labeled cells was observed in the locus coeruleus (A6 noradrenergic cell group), the A5 noradrenergic group, the dorsomedial medulla (C3 adrenergic cell group), and the lateral paragigantocellular nucleus (C1 adrenergic cell group). After CTb injections in the lateral wings or the dorsal part of the rostral DRN, a similar number of double-labeled cells was seen in C3. Slightly more double-labeled cells were seen in A6 and A5. In addition, a substantial to large number of double-labeled cells appeared in C1, the commissural part of the nucleus of the solitary tract (A2 noradrenergic cell group) and the caudoventrolateral medulla (A1 noradrenergic cell group). These results indicate that the noradrenergic and adrenergic inputs to the DRN arise from all the catecholaminergic cell groups of the lower brainstem except the A7 noradrenergic group. They further reveal the existence of a topographical organization of these afferents to the different subdivisions of the DRN.
Alterations in multiple biological functions, such as transcription factor activity, are implicated in the neurobiology of depression, based primarily on the characterization of antidepressant efficacy in naïve rodents rather than on models that capture the protracted feelings of anhedonia and helplessness that typify depression. This unit presents rat and mouse models of depression that involve chronic oral exposure to the stress-associated adrenal hormone, corticosterone (CORT), resulting in anhedonic- and helplessness-like behaviors that are persistent yet reversible by chronic antidepressant treatment. Prior CORT exposure also chronically influences molecular targets hypothesized to contribute to negative mood. One example is phosphorylation of cAMP response element binding protein in the hippocampus and nucleus accumbens. Prior chronic CORT exposure provides an alternative method to chronic mild stress models of depression that is easily replicable and persists well beyond the CORT exposure period, thereby modeling the persistent depressive-like state in humans.
Cell bodies in the hypothalamic paraventricular nucleus (PVN) mediate stress-induced increases in renin and corticosterone secretion. Since the PVN has an extensive catecholaminergic innervation, we wanted to determine the role of catecholamines in the neuroendocrine response to stress. The stressor was a conditioned emotional (fear) response paradigm (CER). The catecholamine neurotoxin, 6-hydroxydopamine (6-OHDA), was injected into the PVN 14 days before the rats were subjected to the CER procedure. Damage to noradrenergic nerve terminals was verified immunocytochemically, using an antibody against dopamine β-hydroxylase. Injection of 6-OHDA into the PVN prevented the stress-induced increase in plasma renin activity (PRA), plasma renin concentration (PRC) and plasma corticosterone concentration, suggesting that intact catecholaminergic innervation of neurons in the PVN is necessary for the stress-induced increase in renin and corticosterone secretion. To determine if β-adrenoceptors in the PVN mediate the effect of stress on renin and corticosterone secretion, the β-adrenoceptor antagonist sotalol was injected into the PVN through chronically implanted bilateral cannulae. The injection was performed on the 4th day of the CER paradigm, just before the rats were placed into the CER chamber. Sotalol prevented the stress-induced increase in corticosterone concentration, but did not diminish the stress-induced increase in PRA and PRC. These results suggest that the stress-induced increase in corticosterone concentration is influenced by β-adrenoceptors in the PVN. The stress-induced increase in PRA and PRC is mediated by different receptors whose ligands might be catecholamines acting at non-β-receptors or other neuroactive substances colocalized in catecholaminergic nerve terminals.
In situ hybridization histochemistry and quantitative autoradiography were used to evaluate the effects of repeated administration of the serotonin reuptake enhancer, tianeptine. Tianeptine (10 mg/kg twice daily, for 14 days) significantly reduced both the expression of serotonin transporter mRNA and serotonin transporter binding sites labeled by [3H]paraxetine in rat dorsal raphe nucleus. In median raphe nucleus, tianeptine did not change either expression of serotonin transporter mRNA or binding. This effect, which is similar to a reported effect for serotonin reuptake inhibitors, may help to explain the antidepressant effect of tianeptine.
The monoamines, serotonin, dopamine, norepinephrine, epinephrine and histamine, play a critical role in the function of the hypothalamic–pituitary–adrenal axis and in the integration of information in sensory, limbic, and motor systems. The primary mechanism for termination of monoaminergic neurotransmission is through reuptake of released neurotransmitter by Na+,CI-dependent plasma membrane transporters. A second family of transporters packages monoamines into synaptic and secretory vesicles by exchange of protons. Identification of those cells which express these two families of neurotransmitter transporters is an initial step in understanding what adaptive strategies cells expressing monoamine transporters use to establish the appropriate level of transport activity and thus attain the appropriate efficiency of monoamine storage and clearance. The most recent advances in this field have yielded several surprises about their function, cellular and subcellular localization, and regulation, suggesting that these molecules are not static and most likely are the most important determinants of extracellular levels of monoamines. Here, information on the localization of mRNAs for these transporters in rodent and human brain is summarized along with immunohistochemical information at the light and electron microscopic levels. Regulation of transporters at the mRNA level by manipulation in rodents and differences in transporter site densities by tomographic techniques as an index of regulation in human disease and addictive states are also reviewed. These studies have highlighted the presence of monoamine neurotransmitter transporters in neurons but not in gliain situ.The norepinephrine transporter is present in all cells which are both tyrosine hydroxylase (TH)- and dopamine β-hydroxylase-positive but not in those cells which are TH- and phenyl-N-methyltransferase-positive, suggesting that epinephrine cells may have their own, unique transporter. In most dopaminergic cells, dopamine transporter mRNA completely overlaps with TH mRNA-positive neurons. However, there are areas in which there is a lack of one to one correspondence. The serotonin transporter (5-HTT) mRNA is found in all raphe nuclei and in the hypothalamic dorsomedial nucleus where the 5-HTT mRNA is dramatically reduced following immobilization stress. The vesicular monoamine transporter 2 (VMAT2) is present in all monoaminergic neurons including epinephrine- and histamine-synthesizing cells. Immunohistochemistry demonstrates that the plasma membrane transporters are present along axons, soma, and dendrites. Subcellular localization of DAT by electron microscopy suggests that these transporters are not at the synaptic density but are confined to perisynaptic areas, implying that dopamine diffuses away from the synapse and that contribution of diffusion to dopamine signalling may vary between brain regions. Interestingly, the presence of VMAT2 in vesicles underlying dendrites, axons, and soma suggests that monoamines may be released at these cellular domains. An understanding of the regulation of transporter function may have important therapeutic consequences for neuroendocrine function in stress and psychiatric disorders.
Stress has been reported to activate the locus coeruleus (LC)-noradrenergic system. However, the molecular link between chronic stress and noradrenergic neurons remains to be elucidated. In the present study adult Fischer 344 rats were subjected to a regimen of chronic social defeat (CSD) for 4weeks. Measurements by in situ hybridization and Western blotting showed that CSD significantly increased mRNA and protein levels of the norepinephrine transporter (NET) in the LC region and NET protein levels in the hippocampus, frontal cortex and amygdala. CSD-induced increases in NET expression were abolished by adrenalectomy or treatment with corticosteroid receptor antagonists, suggesting the involvement of corticosterone and corticosteroid receptors in this upregulation. Furthermore, protein levels of protein kinase A (PKA), protein kinase C (PKC), and phosphorylated cAMP-response element binding (pCREB) protein were significantly reduced in the LC and its terminal regions by the CSD paradigm. Similarly, these reduced protein levels caused by CSD were prevented by adrenalectomy. However, effects of corticosteroid receptor antagonists on CSD-induced down-regulation of PKA, PKC, and pCREB proteins were not consistent. While mifeprestone and spironolactone, either alone or in combination, totally abrogate CSD effects on these protein levels of PKA, PKC and pCREB in the LC and those in the hippocampus, frontal cortex and amygdala, their effects on PKA and PKC in the hippocampus, frontal cortex and amygdala were region-dependent. The present findings indicate a correlation between chronic stress and activation of the noradrenergic system. This correlation and CSD-induced alteration in signal transduction molecules may account for their critical effects on the development of symptoms of major depression.
Limbic endocannabinoid signaling is known to be sensitive to chronic stress; however, studies investigating the impact of prolonged exposure to glucocorticoid hormones have been limited by the concurrent exposure to the stress of daily injections. The present study was designed to examine the effects of a noninvasive approach to alter plasma corticosterone (CORT) on the endocannabinoid system. More precisely, we explored the effects of a 4-week exposure to CORT dissolved in the drinking water of mice (100 μg/ml) and measured cannabinoid CB(1) receptor binding, endocannabinoid content, activity of the endocannabinoid degrading enzyme fatty acid amide hydrolase (FAAH), and mRNA expression of both the CB(1) receptor and FAAH in both the hippocampus and amygdala. Our data demonstrate that CORT decreases CB(1) receptor binding site density in both the hippocampus and amygdala and also reduced anandamide (AEA) content and increased FAAH activity within both structures. These changes in both CB(1) receptor binding and FAAH activity were not accompanied by changes in mRNA expression of either the CB(1) receptor or FAAH in either brain region. Interestingly, our CORT delivery regimen significantly increased 2-AG concentrations within the hippocampus, but not the amygdala. Collectively, these data demonstrate that the confounder of injection stress is sufficient to conceal the ability of protracted exposure to glucocorticoids to reduce CB(1) receptor density and augment AEA metabolism within limbic structures.
Degeneration of the noradrenergic locus coeruleus (LC) in aging and neurodegenerative diseases is well documented. Slowing or reversing this effect may have therapeutic implications. Phox2a and Phox2b are homeodomain transcriptional factors that function as determinants of the noradrenergic phenotype during embryogenesis. In the present study, recombinant lentiviral eGFP-Phox2a and -Phox2b (vPhox2a and vPhox2b) were constructed to study the effects of Phox2a/2b over-expression on dopamine β-hydroxylase (DBH) and norepinephrine transporter (NET) levels in central noradrenergic neurons. Microinjection of vPhox2 into the LC of adult rats significantly increased Phox2 mRNA levels in the LC region. Over-expression of either Phox2a or Phox2b in the LC was paralleled by significant increases in mRNA and protein levels of DBH and NET in the LC. Similar increases in DBH and NET protein levels were observed in the hippocampus following vPhox2 microinjection. In the frontal cortex, only NET protein levels were significantly increased by vPhox2 microinjection. Over-expression of Phox2 genes resulted in a significant increase in BrdU-positive cells in the hippocampal dentate gyrus. The present study demonstrates an upregulatory effect of Phox2a and Phox2b on the expression of DBH and NET in noradrenergic neurons of rat brains, an effect not previously shown in adult animals. Phox2 genes may play an important role in maintaining the function of the noradrenergic neurons after birth, and regulation of Phox2 gene expression may have therapeutic utility in aging or disorders involving degeneration of noradrenergic neurons.
Drugs that selectively inhibit the serotonin transporter (SERT) are widely prescribed for treatment of depression and a range of anxiety disorders. We studied the time course of changes in tryptophan hydroxylase (TPH) in four raphe nuclei after initiation of two different SERT inhibitors, citalopram and fluoxetine. In the first experiment, groups of Sprague-Dawley rats received daily meals of rice pudding either alone (n=9) or mixed with citalopram 5 mg/kg/day (n=27). Rats were sacrificed after 24 h, 7 days or 28 days of treatment. Sections of dorsal raphe nucleus (DRN), median raphe nucleus (MRN), raphe magnus nucleus (RMN) and caudal linear nucleus (CLN) were processed for TPH immunohistochemistry. Citalopram induced a significant reduction in DRN TPH-positive cell counts at 24 h (41%), 7 days (38%) and 28 days (52%). Similar reductions in TPH-positive cell counts were also observed at each timepoint in the MRN and in the RMN. In the MRN, citalopram resulted in significant reductions at 24 h (26%), 7 days (16%) and 28 days (23%). In the RMN, citalopram induced significant reductions of TPH-positive cell counts at 24 h (45%), 7 days (34%) and 28 days (43%). By contrast, no significant differences between control and treatment groups were observed in the CLN at any of the time points that we studied. To investigate whether these changes would occur with other SERT inhibitors, we conducted a second experiment, this time with a 28-day course of fluoxetine. As was observed with citalopram, fluoxetine induced significant reductions of TPH cell counts in the DRN (39%), MRN (38%) and RMN (41%), with no significant differences in the CLN. These results indicate that SERT inhibition can alter the regulation of TPH, the rate limiting enzyme for serotonin biosynthesis. This persistent and regionally specific downregulation of serotonin biosynthesis may account for some of the clinical withdrawal symptoms associated with drugs that inhibit SERT.
Major depressive disorder is a heritable psychiatric syndrome that appears to be associated with subtle cellular and molecular alterations in a complex neural network. The affected brain regions display dynamic neuroplastic adaptations to endocrine and immunologic stimuli arising from within and outside the CNS. Depression's clinical and etiological heterogeneity adds a third level of complexity, implicating different pathophysiological mechanisms in different patients with the same DSM diagnosis. Current pharmacological antidepressant treatments improve depressive symptoms through complex mechanisms that are themselves incompletely understood. This review summarizes the current knowledge of the neurobiology of depression by combining insights from human clinical studies and molecular explanations from animal models. The authors provide recommendations for future research, with a focus on translating today's discoveries into improved diagnostic tests and treatments.
Hyperactivity of the hypothalamus-pituitary-adrenal (HPA) axis and increased levels of glucocorticoid hormones in patients with depression have mostly been ascribed to impaired feedback regulation of the HPA axis, possibly caused by altered function of the receptor for glucocorticoid hormones, the glucocorticoid receptor (GR). Antidepressants, in turn, ameliorate many of the neurobiological disturbances in depression, including HPA axis hyperactivity, and thereby alleviate depressive symptoms. There is strong evidence for the notion that antidepressants exert these effects by modulating the GR. Such modulations, however, can be manifold and range from regulation of receptor expression to post-translational modifications, which may result in differences in GR nuclear translocation and GR-dependent gene transcription. The idea that the therapeutic action of antidepressants is mediated, at least in part, by restoring GR function, is consistent with studies showing that decreased GR function contributes to HPA axis hyperactivity and to the development of depressive symptoms. Conversely, excessive glucocorticoid signalling, which requires an active GR, is associated with functional impairments in the depressed brain, especially in the hippocampus, where it results in reduced neurogenesis and impaired neuroplasticity. In this review, we will focus on the GR as a key player in the precipitation, development and resolution of depression. We will discuss potential explanations for the apparent controversy between glucocorticoid resistance and the detrimental effects of excessive glucocorticoid signalling. We will review some of the evidence for modulation of the GR by antidepressants and we will provide further insight into how antidepressants may regulate the GR to overcome depressive symptoms.
Based on electrophysiological, neurochemical, genetic and neuropharmacological approaches it is currently accepted that serotonin (5-HT) functions to promote waking (W) and to inhibit rapid-eye movement sleep (REMS). The serotonin-containing neurons of the dorsal raphe nucleus (DRN) provide part of the serotonergic innervation of the telencephalon, diencephalon, mesencephalon and rhombencephalon of laboratory animals and man. The DRN has been subdivided into several clusters on the basis of differences in cellular morphology, expression of other neurotransmitters and afferent and efferent connections. These differences among subpopulations of 5-HT neurons may have important implications for neural mechanisms underlying 5-HT modulation of sleep and waking. The DRN contains 5-HT and non-5-HT neurons. The latter express a variety of substances including dopamine, γ-aminobutyric acid (GABA) and glutamate. In addition, nitric oxide and a number of neuropeptides have been characterized in the DRN. Available evidence tends to indicate that non-5-HT cells contribute to the regulation of the activity of 5-HT neurons during the sleep-wake cycle through local circuits and/or their mediation of the effects of afferent inputs. Mutant mice that do not express 5-HT(1A) or 5-HT(1B) receptor exhibit greater amounts of REMS than their wild-type couterparts. 5-HT(2A) and 5-HT(2C) receptor knockout mice show a significant increase of W and a reduction of slow wave sleep that is related, at least in part, to the increased release of norepinephrine and dopamine. A normal circadian sleep pattern is observed in 5-HT(7) receptor knockout mice; however, the mutants spend less time in REMS. Local microinjection of 5-HT(1B), 5-HT(2A/2C), 5-HT(3) and 5-HT(7) receptor agonists into the DRN selectively suppresses REMS in the rat. In contrast, microinjection of 5-HT(1A) receptor agonists promotes REMS. Similarly, local administration of the melanin-concentrating hormone or the GABA(A) receptor agonist muscimol produces an increase of REMS in the rat. Presently, there are no data on the effect of local infusion into the DRN of noradrenergic, dopaminergic, histaminergic, orexinergic and cholinergic agonists on sleep variables in laboratory animals.
Serotonergic (5-HT) cells in the rat dorsal raphe nucleus (DRN) appear in topographically organized groups. Based on cellular morphology, expression of other neurotransmitters, afferent and efferent connections and functional properties, 5-HT neurons of the DRN have been grouped into six cell clusters. The subdivisions comprise the rostral, ventral, dorsal, lateral, caudal and interfascicular parts of the DRN. In addition to 5-HT cells, neurons containing γ-aminobutyric acid (GABA), glutamate, dopamine, nitric oxide and the neuropeptides corticotropin-releasing factor, substance P, galanin, cholecystokinin, neurotensin, somatostatin, vasoactive intestinal peptide, neuropeptide Y, thyrotropin-releasing hormone, growth hormone, leu-enkephalin, met-enkephalin and gastrin have been characterized in the DRN. Moreover, numerous brain areas have neurons that project to the DRN and express monoamines (norepinephrine, histamine), amino acids (GABA, glutamate), acetylcholine or neuropeptides (orexin, melanin-concentrating hormone, corticotropin-releasing factor and substance P) that directly or indirectly, through local circuits, regulate the activity of 5-HT cells. The 5-HT cells predominate along the midline of the rostral, dorsal and ventral subdivisions of the DRN and outnumber the non-5-HT cells occurring in the raphe nucleus. The GABAergic and glutamatergic neurons are clustered mainly in the lateral and dorsal subdivisions of the DRN, respectively. The 5-HT(1A) receptor is located on the soma and the dendrites of 5-HT neurons and at postsynaptic sites (outside the DRN). It is expressed, in addition, by non-5-HT cells of the DRN. The 5-HT(1B) receptor is located at presynaptic and postsynaptic sites (outside the boundaries of the DRN). It has been described also in the ventromedial DRN where it is expressed by non-5-HT cells. The 5-HT(2A) and 5-HT(2C) receptors are located within postsynaptic structures. At the level of the DRN the 5-HT(2A) and 5-HT(2C) receptor-containing cells are predominantly GABAergic interneurons and projection neurons. Within the boundaries of the DRN the 5-HT(3) receptor is expressed by, among others, glutamatergic interneurons. 5-HT(7) receptors in the DRN are not localized to serotonergic neurons but, at least in part, to GABAergic cells and terminals. The complex structure of the DRN may have important implications for neural mechanisms underlying 5-HT modulation of wakefulness and REM sleep.
Spine date: 1990. Thesis (Ph. D.)--Loyola University of Chicago, 1989. Includes bibliographical references (leaves 147-187).
Alterations in multiple biological functions, such as transcription factor activity, are implicated in the neurobiology of depression, based primarily on the characterization of antidepressant efficacy in naïve rodents rather than on models that capture the protracted feelings of anhedonia and helplessness that typify depression. This unit presents rat and mouse models of depression that involve chronic oral exposure to the stress-associated adrenal hormone, corticosterone (CORT), resulting in anhedonic- and helplessness-like behaviors that are persistent yet reversible by chronic antidepressant treatment. Prior CORT exposure also chronically influences molecular targets hypothesized to contribute to negative mood. One example is phosphorylation of cAMP response element binding protein in the hippocampus and nucleus accumbens. Prior chronic CORT exposure provides an alternative method to chronic mild stress models of depression that is easily replicable and persists well beyond the CORT exposure period, thereby modeling the persistent depressive-like state in humans.
Descending projections arising from brainstem serotonergic (5HT) neurons contribute to both facilitatory and inhibitory controls of spinal cord "pain" transmission neurons. Unclear, however, are the brainstem networks that influence the output of these 5HT neurons. To address this question, here we used a novel neuroanatomical tracing method in a transgenic line of mice in which Cre recombinase is selectively expressed in 5HT neurons (ePet-Cre mice). Specifically, we injected the conditional pseudorabies virus recombinant (BA2001) that can replicate only in Cre-expressing neurons. Because BA2001 transports exclusively in a retrograde manner, we were able to reveal a subset of the neurons and circuits that are located upstream of the Cre-expressing 5HT neurons. We show that diverse brainstem regions differentially target the 5HT neurons of the dorsal raphe (DR) and the nucleus raphe magnus of the rostroventral medulla (RVM). Among these are several catecholaminergic and cholinergic cell groups, the periaqueductal gray, several brainstem reticular nuclei, and the nucleus of the solitary tract. We conclude that a brainstem 5HT network integrates somatic and visceral inputs arising from various areas of the body. We also identified a circuit that arises from projection neurons of deep spinal cord laminae V-VIII and targets the 5HT neurons of the NRM, but not of the DR. This spinoreticular pathway constitutes an anatomical substrate through which a noxious stimulus can activate 5HT neurons of the NRM and in turn could trigger descending serotonergic antinociceptive controls.
In a previous study we showed that selective occupation of the mineralocorticoid receptor (MR) in hippocampal slices from adrenalectomized (ADX) rats attenuates the membrane hyperpolarization and resistance decrease induced in CA1 pyramidal neurons by serotonin (5HT). In the present study we established responses to 5HT in the hippocampal slice when not only MRs but also glucocorticoid receptors (GRs) were occupied, using either a combination of selective MR and GR ligands or different concentrations of the endogenous mixed agonist corticosterone. We observed that the GR agonist RU 28362 blocks the attenuating action of the MR agonist aldosterone on responses to 3, 10 and 30 microM 5HT; RU 28362 by itself did not affect 5HT responses. If a low concentration of the mixed agonist corticosterone (0.5 nM, close to the Kd for the MR) was continuously perfused in vitro, 5HT responses were steadily depressed with a delay of 2 h, while high levels of corticosterone (5 nM, around Kd for GR) only temporarily reduced 5HT responses. Finally, 5HT responses in slices from sham-operated rats (with relatively high plasma corticosterone levels) were similar to the responses obtained in slices from ADX rats. These data suggest that the previously reported MR-mediated attenuation of 5HT responses may be limited to conditions of low adrenocortical activity or pathophysiological conditions where the balance of MR- and GR-mediated effects is disturbed.
The aim of the present study was to explore in male rats the role of the catecholaminergic innervation of the hypothalamus in corticotropic and adrenal responses to different kinds of stress conditions. For this purpose, 6-hydroxydopamine (3 micrograms in 0.2 microliter saline) was stereotaxically and bilaterally infused at two levels of the main noradrenergic ascending brain stem bundle (NAB-X). The efficiency of catecholaminergic denervation of the hypothalamus was checked by measuring noradrenaline concentrations in paraventricular nuclei punches by HPLC and was confirmed by a 86% fall in noradrenaline levels of NAB-X rats killed after the stress experiments. Seven days after lesioning the NAB, sham operated controls and NAB-X lesioned animals were divided into 4 groups and submitted to 4 different stressors, i.e.: 2 min ether vapors (n = 5), 1 h immobilization (n = 7), i.v. histamine (2 mg/kg; n = 7) or i.v. insuline (10 I.U./kg; n = 8) injections. ACTH and corticosterone were measured in blood samples sequentially taken from a chronic carotid cannula, before stress and at short intervals over the 2 following hours. In comparison to the respective control groups, NAB-X dramatically reduced the ACTH response to ether (-78%) and to restraint (-53%) stress whereas the corticosterone response was affected to a lesser extent. In contrast, NAB-X slightly altered these responses in the histamine-treated group, although, surprisingly, the ACTH response tended to decrease and that of corticosterone to increase. Finally, NAB-X provoked a biphasic response to insuline-induced hypoglycemia, with a very early (5 min) rise in ACTH and corticosterone in comparison to the control group, followed by a trend to low hormonal levels up to 120 min. These results strongly suggest a differential involvement of the hypothalamic noradrenergic innervation upon the hypothalamic-pituitary-adrenal axis according to the nature of stress conditions.
Local application of the selective 5-HT1A agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) in the median raphe of rats caused locomotor stimulation. In contrast, dorsal raphe application of the compound induced flat body posture, which was discontinuous and not dose-dependent, and therefore distinct from that characteristic for postsynaptic 5-HT receptor-mediated behaviour. Injection of 8-OH-DPAT into the dorsal raphe or median raphe caused neither forepaw treading nor head-weaving; stiff tail and sniffing occurred inconsistently. By activating somatodendritic 5-HT1A autoreceptors in the median raphe, 8-OH-DPAT may disinhibit locomotor-enforcing neural pathways that receive 5-HT afferents from this nucleus. The data suggest that median raphe and dorsal raphe 5-HT neurons have different roles in motor control.
Glucocorticoids are known to induce the transcription of integrated proviral mouse mammary tumour virus (MMTV) genes in a variety of cell lines derived from mouse mammary tumours. Chimaeric genes in which selectable markers are linked to the long terminal repeat (LTR) region of MMTV can be induced by the synthetic glucocorticoid dexamethasone after introduction into mouse fibroblasts. This suggests that the regulatory elements required for hormonal induction are located within the cloned LTR fragments. The idea is supported by the observation that glucocorticoid receptors bind to certain cloned fragments of MMTV DNA in vitro. Using filter binding studies and monoclonal antibodies to the glucocorticoid receptor we have now delimited the receptor binding region to a DNA segment of 152 base pairs (bp) that has been shown to be relevant for hormonal induction. In nuclease protection experiments we have identified partially homologous receptor binding sequences located in this region, all of which share the hexanucleotide 5'-TGTTCT-3'.
The distribution of monoaminergic cell bodies in the brainstem of the cat has been examined with Falck‐Hillarp fluorescence histochemical technique. Quantitative determinations indicate that the cat brainstem contains about 60,300 indolaminergic (IA) cells. The majority of these (about 46,700, or 77.5%) are located within raphe nuclei. The largest number is contained within nucleus raphe dorsalis (RD), accounting for around 24,300 IA cells, while raphe pallidus (RP) holds about 8,000, raphe centralis superior (RCS) 7,400, raphe magnus (RM) 2,400, raphe obscurus (RO) 2,300, linearis intermedius (LI) 2,100, and the raphe pontis (RPo) only some 280 IA cells. The IA cells represent, however, only part of the neuronal population of raphe nuclei, which, in addition, hold varying numbers of other medium‐sized and small‐sized neurons. Thus, quantifications in Nissl‐stained material indicate that the IA cells make up about 70% of the medium‐sized cells in RD, 50% in RP, 35% in RCS and RO, 25% in LI, 15% in RM, and only 10% in RPo. The substantial numbers of small‐sized perikarya observed in all raphe nuclei may represent interneurons.
Significant numbers of IA cells were consistently located outside the raphe nuclei at all brainstem levels. In all, these amounted to approximately 13,600, or 22.5% of the total number of IA cells. Thus, IA cells occurred in the myelinated bundles, and sometimes in reticular formation, bordering the raphe nuclei; in the ventral brainstem forming a lateral extension from the ventral raphe (RP, RM, RPo, RCS, and LI) to the position of the rubrospinal bundle; in the periventricular gray and subjacent tegmentum of dorsal pons and caudal mesencephalon; in the locus coeruleus (LC) complex; around the motor trigeminal nucleus; caudal to the red nucleus; and in the interpeduncular and interfascicular nuclei. The wide distribution of IA cells leads to a considerable mixing with catecholaminergic (CA) cell groups.
Our observations on CA cell distribution are essentially in accordance with previous reports. Quantifications indicate that the LC complex contains about 9,150 CA cells, unilaterally. A previously unnoticed group of scattered CA cells was found in relation to the vestibular nuclei and extending dorsally toward the deep cerebellar nuclei.
Expression of serotonin (5-hydroxytryptamine, 5-HT) transporter mRNA in the rat brain was examined by in situ hybridization histochemistry with a synthetic oligonucleotide probe. 5-HT transporter mRNA was expressed in neurons in most of the raphe nuclei. The dorsal and median raphe nuclei contained intensely labeled neurons, while the caudal linear nucleus, raphe magnus nucleus, raphe pontis nucleus, raphe pallidus nucleus and the raphe obscurus nucleus contained weakly or moderately labeled neurons. The localization pattern of the 5-HT transporter mRNA-positive neurons coincides fairly well with that of 5-HT-immunoreactive neurons, indicating that 5-HT transporter is primarily located in serotonergic neurons.
In this study, we have investigated the effect of classical antidepressant on 5-HTt gene expression in rat brain by in situ hybridization histochemistry, a procedure that allows to quantify specific mRNA molecules in their neuroanatomical context
By means of in situ hybridization and immunocytochemical techniques it has been possible to follow the prenatal development of glucocorticoid receptor (GR) messenger RNA (mRNA) expression and GR immunoreactivity (IR) in the rat brain from embryonic day (E) 15 to 22. A 700-base-pair GR cDNA fragment was used for RNA probe generation. In the immunocytochemical analysis a mouse monoclonal antibody (IgG2a) against the rat liver GR was used in combination with the indirect fluorescence technique or the avidin-biotin immunoperoxidase method. At E15 till E22 a moderate to strong GR mRNA signal was observed within the neuro-epithelium from the medulla oblongata to the telencephalon. A moderate to strong labelling was also present within the paraventricular hypothalamic nucleus, the arcuate nucleus, the nucleus raphe magnus, the nucleus raphe obscurus and the locus coeruleus. In these areas a weak to moderate nuclear GR IR developed in nerve cells 1 or 2 days after the appearance of the GR mRNA signal. From E15 the adenohypophysis showed the strongest expression of GR mRNA. At E17 a strong GR IR was especially demonstrated in the nuclei of many pituitary cells, some exhibiting adrenocorticotropin IR. The results open up the possibility that there exist active GR in embryonic life capable of regulating proliferation events within the adenohypophysis and the neuro-epithelia of the brain. This embryonic GR may modulate the development of inter alia neuro-endocrine areas such as the paraventricular and arcuate nuclei and arousal-related areas such as the central 5-hydroxytryptamine and noradrenaline neuronal systems. Provided that this embryonic GR is capable of becoming activated by glucocorticoids in fetal life, it may mediate several neurochemical and behavioural impairments caused by prenatal stress.
Regional expression and antidepressant drug-induced regulation of mRNA encoding the serotonin (5-HT) transporter were studied in rat brain. While 5-HT transporter mRNA is abundantly expressed in the midbrain raphe complex, lower concentrations were also found in frontal cortex, hippocampus, and neostriatum using a combination of reverse transcriptase-polymerase chain reaction (RT-PCR), Southern hybridization, and sequence analysis. Long-term administration of antidepressants which inhibit 5-HT reuptake, but not monoamine oxidase inhibitors or 5-HT receptor agonists, decrease 5-HT transporter mRNA steady-state concentrations. Based on these observations, we conclude that (1) mRNA coding for the 5-HT transporter is present in several brain areas associated with ascending HT pathways, and (2) chronic treatment with reuptake inhibiting antidepressants may be associated with regulation of the 5-HT transporter at the level of gene expression which may contribute to the neuroadaptive mechanisms that likely underlie their therapeutic efficacy.
We found a 38% lower maximal prolactin response to an oral challenge dose of 60 mg of dl-fenfluramine relative to placebo in younger (< 30 years) depressed inpatients compared with the response in age-matched healthy controls (p < .03). Severity of depression did not correlate with prolactin response. Prolactin responses in older depressed patients (> or = 30 years) did not differ from older controls. Younger depressed patients differed from older depressed patients in terms of earlier age of onset of first lifetime episode of major depression, greater degree of suicidal intent during a recent suicide attempt, double the level of hopelessness on admission to hospital, and a higher rate of comorbid borderline personality disorder. A blunted prolactin response to fenfluramine may be interpreted as evidence for reduced serotonergic function in younger depressed patients and may underlie their observed greater suicidality and hopelessness.
Estimates of 5-hydroxytryptamine (5-HT) turnover in response to 30 min of inescapable, randomly presented, loud sound (sound stress) were obtained for regions of rat brain containing 5-HT perikarya by means of 5-hydroxytryptophan (5-HTP) accumulation after administration of an inhibitor of aromatic amino acid decarboxylase (100 mg/kg i.p., m-hydroxybenzylhydrazine, NSD 1015). Sound stress increased 5-HTP accumulation in the median raphe nucleus (MRN) twofold over that from sham-stressed controls, but did not change 5-HTP accumulation significantly in dorsal raphe nucleus (DRN) or hindbrain. These findings indicate that the 5-HT perikarya of the MRN but not those of the DRN or hindbrain are activated by sound stress, thus, provide further evidence for a functional distinction between the 5-HT neurons of these two midbrain nuclei.
Several recent studies of humans correlate stress with atrophy of the hippocampus, an area of the brain required for memory and cognition. In his Perspective, Sapolsky argues that the underlying causal agent may be glucocorticoids secreted in abnormally high amounts under stressful conditions.