Glucocorticoid receptor gene inactivation in dopamine-innervated areas selectively decreases behavioral responses to amphetamine

Behavioral changes of food allergic model mice during light and dark period

Although an animal model of food allergy has been used to investigate its progression mechanism, most researcher could not assess its symptoms for long especially under dark environment. We assessed the behavioral changes of food allergic mice using an image analysis system to track a mouse under both light and dark environments. Mice were sensitized with intraperitoneal ovalbumin (OVA) injections and challenged ten times with oral OVA administration. The OVA challenges induced weight loss and diarrhea. We assessed their behavior and found that the OVA challenges decreased their total moving distance during the dark period. We also revealed that the OVA challenges increased the inactive time of mice during the dark period. Interestingly, these changes were not observed or very small during the light period. We next assessed the location of mice in the home-cage and found that the OVA challenges increased the time when mice stayed at corners and decreased the time at the center during the dark period. These observations suggest mental abnormality of mice. Indeed, the OVA challenges increased the immobility time of mice in the tail suspension test. Thus, food allergic mice exhibited reduced activity and might exhibit psychological symptoms during dark period.

Cross-talk between the HPA axis and addiction-related regions in stressful situations

Addiction is a worldwide problem that has a negative impact on society by imposing significant costs on health care, public security, and the deactivation of the community economic cycle. Stress is an important risk factor in the development of addiction and relapse vulnerability. Here we review studies that have demonstrated the diverse roles of stress in addiction. Term searches were conducted manually in important reference journals as well as in the Google Scholar and PubMed databases, between 2010 and 2022. In each section of this narrative review, an effort has been made to use pertinent sources. First, we will provide an overview of changes in the Hypothalamus-Pituitary-Adrenal (HPA) axis component following stress, which impact reward-related regions including the ventral tegmental area (VTA) and nucleus accumbens (NAc). Then we will focus on internal factors altered by stress and their effects on drug addiction vulnerability. We conclude that alterations in neuro-inflammatory, neurotrophic, and neurotransmitter factors following stress pathways can impact related mechanisms on craving and relapse susceptibility.

Sleep Deprivation Induces Dopamine System Maladaptation and Escalated Corticotrophin-Releasing Factor Signaling in Adolescent Mice

Sleep disruption is highly associated with the pathogenesis and progression of a wild range of psychiatric disorders. Furthermore, appreciable evidence shows that experimental sleep deprivation (SD) on humans and rodents evokes anomalies in the dopaminergic (DA) signaling, which are also implicated in the development of psychiatric illnesses such as schizophrenia or substance abuse. Since adolescence is a vital period for the maturation of the DA system as well as the occurrence of mental disorders, the present studies aimed to investigate the impacts of SD on the DA system of adolescent mice. We found that 72 h SD elicited a hyperdopaminergic status, with increased sensitivity to the novel environment and amphetamine (Amph) challenge. Also, altered neuronal activity and expression of striatal DA receptors were noticed in the SD mice. Moreover, 72 h SD influenced the immune status in the striatum, with reduced microglial phagocytic capacity, primed microglial activation, and neuroinflammation. The abnormal neuronal and microglial activity were putatively provoked by the enhanced corticotrophin-releasing factor (CRF) signaling and sensitivity during the SD period. Together, our findings demonstrated the consequences of SD in adolescents including aberrant neuroendocrine, DA system, and inflammatory status. Sleep insufficiency is a risk factor for the aberration and neuropathology of psychiatric disorders.

Striatal miR-183-5p inhibits methamphetamine-induced locomotion by regulating glucocorticoid receptor signaling

MicroRNA (miRNA)-mediated striatal gene regulation may play an important role in methamphetamine (METH) addiction. This study aimed to identify changes in novel miRNAs and their target genes during METH self-administration and investigate their roles in METH-induced locomotion. RNA sequencing analysis revealed that mir-183-5p was upregulated in the striatum of METH self-administered rats, and target gene prediction revealed that the glucocorticoid receptor (GR) gene, Nr3c1, was a potential target gene for mir-183-5p. We confirmed that single and repeated METH administrations increased METH-induced locomotion and plasma corticosterone levels in rats. Additionally, increased miR-185-5p expression and decreased GR gene expression were observed only in the repeated-METH-injection group but not in the single-injection group. We then investigated the effects of miR-183-5p on METH-induced locomotion using a miR-183-5p mimic and inhibitor. Injection of a mir-183-5p mimic in the striatum of rats attenuated METH-induced locomotion, whereas injection of a miR-183-5p inhibitor enhanced the locomotor activity in METH-administered rats. Furthermore, the miR-183-5p mimic reduced the phosphorylation of tyrosine hydroxylase (TH) whereas the inhibitor increased it. Taken together, these results indicate that repeated METH injections increase striatal miR-183-5p expression and regulate METH-induced locomotion by regulating GR expression in rats, thereby suggesting a potential role of miR-183-5p as a novel regulator of METH-induced locomotion.

SWI/SNF chromatin remodeler complex within the reward pathway is required for behavioral adaptations to stress

Enduring behavioral changes upon stress exposure involve changes in gene expression sustained by epigenetic modifications in brain circuits, including the mesocorticolimbic pathway. Brahma (BRM) and Brahma Related Gene 1 (BRG1) are ATPase subunits of the SWI/SNF complexes involved in chromatin remodeling, a process essential to enduring plastic changes in gene expression. Here, we show that in mice, social defeat induces changes in BRG1 nuclear distribution. The inactivation of the Brg1/Smarca4 gene within dopamine-innervated regions or the constitutive inactivation of the Brm/Smarca2 gene leads to resilience to repeated social defeat and decreases the behavioral responses to cocaine without impacting midbrain dopamine neurons activity. Within striatal medium spiny neurons, Brg1 gene inactivation reduces the expression of stress- and cocaine-induced immediate early genes, increases levels of heterochromatin and at a global scale decreases chromatin accessibility. Altogether these data demonstrate the pivotal function of SWI/SNF complexes in behavioral and transcriptional adaptations to salient environmental challenges.

Repeated exposure to social stressors in rodents results in behavioural changes. Here the authors show that behavioural adaptations to stress are associated with nuclear organization changes through SWI/SNF chromatin remodeler in specific neuronal populations of the mesolimbic system.

Pharmacological perturbation reveals deficits in D2 receptor responses in Thap1 null mice

The primary dystonia DYT6 is caused by mutations in the transcription factor Thanatos‐associated protein 1 (THAP1). To understand THAP1’s functions, we generated mice lacking THAP1 in the nervous system. THAP1 loss causes locomotor deficits associated with transcriptional changes. Since many of the genes misregulated involve dopaminergic signaling, we pharmacologically challenged the two striatal canonical dopamine pathways: the direct, regulated by the D1 receptor, and the indirect, regulated by the D2 receptor. We discovered that depleting THAP1 specifically interferes with the D2 receptor responses, pointing to a selective misregulation of the indirect pathway in DYT6 with implications for pathogenesis and treatment.

Glucocorticoid receptor signaling in ventral tegmental area neurons increases the rewarding value of a high-fat diet in mice

The reward system, which consists of dopaminergic neurons projecting from the ventral tegmental area (VTA) to the nucleus accumbens and caudate-putamen in the striatum, has an important role in the pathogenesis of not only drug addiction but also diet-induced obesity. In the present study, we examined whether signaling through glucocorticoid receptors (GRs) in the reward system affects the rewarding value of a high-fat diet (HFD). To do so, we generated mice that lack functional GRs specifically in dopaminergic neurons (D-KO mice) or corticostriatal neurons (CS-KO mice), subjected the mice to caloric restriction stress conditions, and evaluated the rewarding value of a HFD by conditioned place preference (CPP) test. Caloric restriction induced increases in serum corticosterone to similar levels in all genotypes. While CS-KO as well as WT mice exhibited a significant preference for HFD in the CPP test, D-KO mice exhibited no such preference. There were no differences between WT and D-KO mice in consumption of HFD after fasting or cognitive function evaluated by a novel object recognition test. These data suggest that glucocorticoid signaling in the VTA increases the rewarding value of a HFD under restricted caloric stress.

A proposed role for glucocorticoids in mediating dopamine-dependent cue-reward learning

Learning to respond appropriately to one's surrounding environment is fundamental to survival. Importantly, however, individuals vary in how they respond to cues in the environment and this variation may be a key determinant of psychopathology. The ability of seemingly neutral cues to promote maladaptive behavior is a hallmark of several psychiatric disorders including, substance use disorder, post-traumatic stress disorder, eating disorders and obsessive-compulsive disorder. Thus, it is important to uncover the neural mechanisms by which such cues are able to attain inordinate control and promote psychopathological behavior. Here, we suggest that glucocorticoids play a critical role in this process. Glucocorticoids are primarily recognized as the main hormone secreted in response to stress but are known to exert their effects across the body and the brain, and to affect learning and memory, cognition and reward-related behaviors, among other things. Here we speculate that glucocorticoids act to facilitate a dopamine-dependent form of cue-reward learning that appears to be relevant to a number of psychiatric conditions. Specifically, we propose to utilize the sign-tracker/goal-tracker animal model as a means to capture individual variation in stimulus-reward learning and to isolate the role of glucocorticoid-dopamine interactions in mediating these individual differences. It is hoped that this framework will lead to the discovery of novel mechanisms that contribute to complex neuropsychiatric disorders and their comorbidity.

Experience and activity-dependent control of glucocorticoid receptors during the stress response in large-scale brain networks

The diversity of actions of the glucocorticoid stress hormones among individuals and within organs, tissues and cells is shaped by age, gender, genetics, metabolism, and the quantity of exposure. However, such factors cannot explain the heterogeneity of responses in the brain within cells of the same lineage, or similar tissue environment, or in the same individual. Here, we argue that the stress response is continuously updated by synchronized neural activity on large-scale brain networks. This occurs at the molecular, cellular and behavioral levels by crosstalk communication between activity-dependent and glucocorticoid signaling pathways, which updates the diversity of responses based on prior experience. Such a Bayesian process determines adaptation to the demands of the body and external world. We propose a framework for understanding how the diversity of glucocorticoid actions throughout brain networks is essential for supporting optimal health, while its disruption may contribute to the pathophysiology of stress-related disorders, such as major depression, and resistance to therapeutic treatments.

Augmentation of morphine-conditioned place preference by food restriction is associated with alterations in the oxytocin/oxytocin receptor in rat models

BACKGROUND

Studies indicate that food restriction (FR) reinforces the effects of morphine. The exact mechanisms by which FR influences the reward circuitry of morphine have not yet been determined.

OBJECTIVES

We hypothesized that the effects of FR on the oxytocin (OXT) system and HPA axis can be associated with substance abuse disorders. In this study, the serum levels of OXT and corticosterone, and the expression of OXT/OXT receptor (OXTR), glucocorticoid receptor (GR), and brain-derived neurotrophic factor (BDNF) in the hippocampus, prefrontal cortex, and nucleus accumbens were investigated in an FR model.

METHODS

First, the male rats (n = 8 per group) were subjected to FR for 3 weeks. Then, morphine-induced conditioned place preference (CPP) was observed using two doses of morphine (3 and 5 mg/kg). The serum concentrations of corticosterone and OXT were determined by ELISA and the expression of genes was examined by qPCR.

RESULTS

FR induced an enhanced preference in the animals for the 5 mg/kg dose of morphine compared to the controls. Serum corticosterone levels increased after FR but OXT levels decreased. Meanwhile, FR actuated downregulation of GR, BDNF, and OXT genes, while inducing the overexpression of OXTR.

CONCLUSION

We propose the inclusion of OXT and OXTR alterations in the enhancement of morphine-induced CPP and addiction vulnerability following FR. Moreover, we conclude that altered BDNF levels and HPA axis activity may be the mechanisms involved in the effects of FR on morphine-induced behavior.

The glucocorticoid receptor in the nucleus accumbens plays a crucial role in social rank attainment in rodents

Social hierarchy in social species is usually established through competitive encounters with conspecifics. It determines the access to limited resources and, thus, leads to reduced fights among individuals within a group. Despite the known importance of social rank for health and well-being, the knowledge about the processes underlying rank attainment remains limited. Previous studies have highlighted the nucleus accumbens (NAc) as a key brain region in the attainment of social hierarchies in rodents. In addition, glucocorticoids and the glucocorticoid receptor (GR) have been implicated in the establishment of social hierarchies and social aversion. However, whether GR in the NAc is involved in social dominance is not yet known. To address this question, we first established that expression levels of GR in the NAc of high anxious, submissive-prone rats are lower than that of their low anxious, dominant-prone counterparts. Furthermore, virally-induced downregulation of GR expression in the NAc in rats led to an improvement of social dominance rank. We found a similar result in a cell-specific mouse model lacking GR in dopaminoceptive neurons (i.e., neurons containing dopamine receptors). Indeed, when cohabitating in dyads of mixed genotypes, mice deficient for GR in dopaminoceptive neurons had a higher probability to become dominant than wild-type mice. Overall, our results highlight GR in the NAc and in dopaminoceptive neurons as an important regulator of social rank attainment.

Astrocytes determine conditioned response to morphine via glucocorticoid receptor-dependent regulation of lactate release

To date, neurons have been the primary focus of research on the role of glucocorticoids in the regulation of brain function and pathological behaviors, such as addiction. Astrocytes, which are also glucocorticoid-responsive, have been recently implicated in the development of drug abuse, albeit through as yet undefined mechanisms. Here, using a spectrum of tools (whole-transcriptome profiling, viral-mediated RNA interference in vitro and in vivo, behavioral pharmacology and electrophysiology), we demonstrate that astrocytes in the nucleus accumbens (NAc) are an important locus of glucocorticoid receptor (GR)-dependent transcriptional changes that regulate rewarding effects of morphine. Specifically, we show that targeted knockdown of the GR in the NAc astrocytes enhanced conditioned responses to morphine, with a concomitant inhibition of morphine-induced neuronal excitability and plasticity. Interestingly, GR knockdown did not influence sensitivity to cocaine. Further analyses revealed GR-dependent regulation of astroglial metabolism. Notably, GR knockdown inhibited induced by glucocorticoids lactate release in astrocytes. Finally, lactate administration outbalanced conditioned responses to morphine in astroglial GR knockdown mice. These findings demonstrate a role of GR-dependent regulation of astrocytic metabolism in the NAc and a key role of GR-expressing astrocytes in opioid reward processing.

The ergogenic impact of the glucocorticoid prednisolone does not translate into increased running motivation in mice

Glucocorticoids, such as prednisolone, are considered sport doping agents owing to their ergogenic properties. These are accounted for by peripheral mechanisms associated with energetic and anti-inflammatory processes. However, because glucocorticoids target brain tissues, it is likely that these ergogenic impacts are associated with central effects. One of these might be reward motivation, which relies on glucocorticoid receptor-expressing mesocorticolimbic dopaminergic neurons. In keeping with this possibility, this study has explored in mice whether repeated prednisolone administration (5 or 15 μg/ml of drinking water for 10 days) affected intrinsic motivation for running, a strong reinforcer in rodents. Running motivation was assessed by means of a cued-reward motivated instrumental task wherein wheel-running was conditioned by prior nose poke responses under fixed (FR), and then progressive (PR), ratio reinforcement schedules. Sub-chronic ingestion of prednisolone decreased the running distance covered during each rewarded sequence under FR schedules. This finding did not extend to wheel-running performances in mice provided free (i.e. unconditioned) wheel-running opportunities. Running motivation, as estimated under a PR reinforcement schedule, was found to be decreased (lowest concentration) or to remain unaffected (highest concentration) by prednisolone concentration. Lastly, an inter-individual analysis of the respective effects of prednisolone on muscular endurance (as assessed in the wire grid-hanging test) and on running motivation indicated that the former was not predictive of the latter. This observation suggests that prednisolone ergogenic impacts might occur without any concomitant increase in intrinsic exercise motivation.

Dlx5 and Dlx6 expression in GABAergic neurons controls behavior, metabolism, healthy aging and lifespan

Dlx5 and Dlx6 encode two homeobox transcription factors expressed by developing and mature GABAergic interneurons. During development, Dlx5/6 play a role in the differentiation of certain GABAergic subclasses. Here we address the question of the functional role of Dlx5/6 in the mature central nervous system. First, we demonstrate that Dlx5 and Dlx6 are expressed by all subclasses of adult cortical GABAergic neurons. Then we analyze VgatΔDlx5-6 mice in which Dlx5 and Dlx6 are simultaneously inactivated in all GABAergic interneurons. VgatΔDlx5-6 mice present a behavioral pattern suggesting reduction of anxiety-like behavior and obsessive-compulsive activities, and a lower interest in nest building. Twenty-month-old VgatΔDlx5-6 animals have the same size as their normal littermates, but present a 25% body weight reduction associated with a marked decline in white and brown adipose tissue. Remarkably, both VgatΔDlx5-6/+ and VgatΔDlx5-6 mice present a 33% longer median survival. Hallmarks of biological aging such as motility, adiposity and coat conditions are improved in mutant animals. Our data imply that GABAergic interneurons can regulate healthspan and lifespan through Dlx5/6-dependent mechanisms. Understanding these regulations can be an entry point to unravel the processes through which the brain affects body homeostasis and, ultimately, longevity and healthy aging.

Adolescent social stress and social context influence the intake of ethanol and sucrose in male rats soon and long after the stress exposures

Social instability stress in adolescent rats (SS; postnatal day 30-45, daily 1 hr isolation +new cage partner) alters behavioural responses to psychostimulants, but differences in voluntary consumption of natural and drug rewards are unknown. SS also is associated with an atypical behavioural repertoire, for example reduced social interactions. Here, we investigated whether SS rats differ from control (CTL) rats in ethanol (EtOH) or sucrose intake in experiments involving different social contexts: alone, in the presence of an unfamiliar peer, in the presence of its cage partner, or in competition against its cage partner. SS rats drank more EtOH than CTL rats irrespective of social context, although the effects were driven primarily by those tested soon after the test procedure rather than weeks later in adulthood. SS and CTL rats did not differ in sucrose intake, except in adulthood under conditions of competition for limited access (SS>CTL). Adolescent rats drank more sucrose than adults, in keeping with evidence that adolescents are more sensitive to natural rewards than adult animals. Overall, adolescent SS modified the reward value of EtOH and sucrose, perhaps through stress/glucocorticoids modifying the development of the mesocorticolimbic system.

Glucocorticoid Signaling in Health and Disease: Insights From Tissue-Specific GR Knockout Mice

Glucocorticoids are adrenally produced hormones critically involved in development, general physiology, and control of inflammation. Since their discovery, glucocorticoids have been widely used to treat a variety of inflammatory conditions. However, high doses or prolonged use leads to a number of side effects throughout the body, which preclude their clinical utility. The primary actions of glucocorticoids are mediated by the glucocorticoid receptor (GR), a transcription factor that regulates many complex signaling pathways. Although GR is nearly ubiquitous throughout the body, glucocorticoids exhibit cell- and tissue-specific effects. For example, glucocorticoids stimulate glucose production in the liver, reduce glucose uptake in the skeletal muscle, and decrease insulin secretion from the pancreatic β-cells. Mouse models represent an important approach to understanding the dynamic functions of GR signaling in normal physiology, disease, and resistance. In the absence of a viable GR null model, gene-targeting techniques utilizing promoter-driven recombination have provided an opportunity to characterize the tissue-specific actions of GR. The aim of the present review is to describe the organ systems in which GR has been conditionally deleted and summarize the functions ascribed to glucocorticoid action in those tissues.

Glucocorticoid receptor in rat nucleus accumbens: Its roles in propofol addictions

Propofol has been demonstrated as a drug of abuse in humans. Our previous study indicated that dexamethasone, a potent agonist of glucocorticoid receptor (GR), inhibited propofol-maintained rat self-administration behaviors by systematic injection. However, the direct effect of GR in the nucleus accumbens (NAc) on propofol self-administration behavior has not been explored. The propofol-maintained self-administration was established in rats after a successive 3-h daily self-administration of propofol for 14days. On day 15, 30min prior to the last training, rats received one of three doses (0.3, 1.0, or 3.0μg/site) of dexamethasone or vehicle via intra-NAc injection. The number of active nose-poke responses, propofol injections, and inactive nose-poke responses was recorded. Dopamine D1 receptor and c-Fos expressions were detected. Plasma corticosterone level was measured by enzyme-linked immunosorbent assay. Intra-NAc administration of dexamethasone (1.0 and 3.0μg/site) facilitated the active nose-poke responses, which was accompanied by the upregulation of D1 receptor and c-Fos in the NAc. Plasma corticosterone level was not changed in dexamethasone-treated groups. This study provides crucial evidence that GR in the NAc plays an important role in regulating propofol self-administration behaviors in rats, which may be mediated by changes in D1 receptor and c-Fos expressions, and this also needs further examination with GR antagonist in the future.

Glucocorticoid receptor action in metabolic and neuronal function

Glucocorticoids via the glucocorticoid receptor (GR) have effects on a variety of cell types, eliciting important physiological responses via changes in gene expression and signaling. Although decades of research have illuminated the mechanism of how this important steroid receptor controls gene expression using in vitro and cell culture–based approaches, how GR responds to changes in external signals in vivo under normal and pathological conditions remains elusive. The goal of this review is to highlight recent work on GR action in fat cells and liver to affect metabolism in vivo and the role GR ligands and receptor phosphorylation play in calibrating signaling outputs by GR in the brain in health and disease. We also suggest that both the brain and fat tissue communicate to affect physiology and behavior and that understanding this “brain-fat axis” will enable a more complete understanding of metabolic diseases and inform new ways to target them.

Impact of Early Consumption of High-Fat Diet on the Mesolimbic Dopaminergic System

Increasing evidence suggest that consumption of high-fat diet (HFD) can impact the maturation of brain circuits, such as during adolescence, which could account for behavioral alterations associated with obesity. In the present study, we used behavioral sensitization to amphetamine to investigate the effect of periadolescent HFD exposure (pHFD) in rats on the functionality of the dopamine (DA) system, a central actor in food reward processing. pHFD does not affect responding to an acute injection, however, a single exposure to amphetamine is sufficient to induce locomotor sensitization in pHFD rats. This is paralleled by rapid neurobiological adaptations within the DA system. In pHFD-exposed animals, a single amphetamine exposure induces an increase in bursting activity of DA cells in the ventral tegmental area (VTA) as well as higher DA release and greater expression of (tyrosine hydroxylase, TH) in the nucleus accumbens (NAc). Post-synaptically, pHFD animals display an increase in NAc D2 receptors and c-Fos expression after amphetamine injection. These findings highlight the vulnerability of DA system to the consumption of HFD during adolescence that may support deficits in reward-related processes observed in obesity.

HPA Axis Interactions with Behavioral Systems

Perhaps the most salient behaviors that individuals engage in involve the avoidance of aversive experiences and the pursuit of pleasurable experiences. Engagement in these behaviors is regulated to a significant extent by an individual's hormonal milieu. For example, glucocorticoid hormones are produced by the hypothalamic-pituitary-adrenocortical (HPA) axis, and influence most aspects of behavior. In turn, many behaviors can influence HPA axis activity. These bidirectional interactions not only coordinate an individual's physiological and behavioral states to each other, but can also tune them to environmental conditions thereby optimizing survival. The present review details the influence of the HPA axis on many types of behavior, including appetitively-motivated behaviors (e.g., food intake and drug use), aversively-motivated behaviors (e.g., anxiety-related and depressive-like) and cognitive behaviors (e.g., learning and memory). Conversely, the manuscript also describes how engaging in various behaviors influences HPA axis activity. Our current understanding of the neuronal and/or hormonal mechanisms that underlie these interactions is also summarized. © 2016 American Physiological Society. Compr Physiol 6:1897-1934, 2016.

Circadian clock and stress interactions in the molecular biology of psychiatric disorders

Many psychiatric disorders are characterized by circadian rhythm abnormalities, including disturbed sleep/wake cycles, changes in locomotor activity, and abnormal endocrine function. Animal models with mutations in circadian "clock genes" commonly show disturbances in reward processing, locomotor activity and novelty seeking behaviors, further supporting the idea of a connection between the circadian clock and psychiatric disorders. However, if circadian clock dysfunction is a common risk factor for multiple psychiatric disorders, it is unknown if and how these putative clock abnormalities could be expressed differently, and contribute to multiple, distinct phenotypes. One possible explanation is that the circadian clock modulates the biological responses to stressful environmental factors that vary with an individual's experience. It is known that the circadian clock and the stress response systems are closely related: Circadian clock genes regulate the physiological sensitivity to and rhythmic release of glucocorticoids (GC). In turn, GCs have reciprocal effects on the clock. Since stressful life events or increased vulnerability to stress are risk factors for multiple psychiatric disorders, including post-traumatic stress disorder (PTSD), attention deficit hyperactivity disorder (ADHD), bipolar disorder (BD), major depressive disorder (MDD), alcohol use disorder (AUD) and schizophrenia (SCZ), we propose that modulation of the stress response is a common mechanism by which circadian clock genes affect these illnesses. Presently, we review how molecular components of the circadian clock may contribute to these six psychiatric disorders, and present the hypothesis that modulation of the stress response may constitute a common mechanism by which the circadian clock affects multiple psychiatric disorders.