Chronic social defeat downregulates the 5-HT1A receptor but not Freud-1 or NUDR in the rat prefrontal cortex

Molecular and network-level mechanisms explaining individual differences in autism spectrum disorder

The mechanisms underlying phenotypic heterogeneity in autism spectrum disorder (ASD) are not well understood. Using a large neuroimaging dataset, we identified three latent dimensions of functional brain network connectivity that predicted individual differences in ASD behaviors and were stable in cross-validation. Clustering along these three dimensions revealed four reproducible ASD subgroups with distinct functional connectivity alterations in ASD-related networks and clinical symptom profiles that were reproducible in an independent sample. By integrating neuroimaging data with normative gene expression data from two independent transcriptomic atlases, we found that within each subgroup, ASD-related functional connectivity was explained by regional differences in the expression of distinct ASD-related gene sets. These gene sets were differentially associated with distinct molecular signaling pathways involving immune and synapse function, G-protein-coupled receptor signaling, protein synthesis and other processes. Collectively, our findings delineate atypical connectivity patterns underlying different forms of ASD that implicate distinct molecular signaling mechanisms.

Possible role of transcriptional regulation of 5-HT1A receptor in the midbrain on unadaptation to stress in mice

The ability to adapt to stress is an essential defensive function of a living body, and disturbance of this ability in the brain may contribute to the development of affective illness. Previously, we reported that mice exposed to unadaptable restraint stress show emotional abnormality. Moreover, this emotional abnormality was alleviated by chronic treatment with flesinoxan, a serotonin (5-HT)_1A receptor agonist. 5-HT_1A receptor expression is regulated by several transcription factors such as nuclear deformed epidermal autoregulatory factor (NUDR/Deaf-1) and five prime repressors under dual repression binding protein 1 (Freud-1). The present study was designed to investigate the expression levels of 5-HT_1A receptor and its transcription factors in the midbrain and hippocampus of stress-adaptive and -unadaptive mice. Mice were exposed to 14 days of repeated adaptable (1 h/day) or repeated unadaptable (4 h/day) restraint stress, or were left in their home cage (non-stressed groups). In a western blot analysis, a significant increase in the expression levels of 5HT_1A receptor protein were observed in the hippocampal membrane fraction in stress-adaptive mice. In contrast, the expression levels of 5-HT_1A receptor protein in stress-unadaptive mice were significantly increased in both cytoplasmic and membrane fraction of the midbrain. Furthermore, real-time PCR analysis revealed that, in the midbrain of stress-unadaptive mice, the expression levels of 5-HT_1A receptor mRNA and Freud-1 or NUDR mRNA were significantly increased and decreased, respectively. These results suggest that increased expression of 5-HT_1A receptor due to decrease in the expression of Freud-1 and NUDR in the midbrain may play a pivotal role in the emotional abnormality of stress-unadaptive mice.

Hypericum perforatum L. prevents the acquisition of and promotes resilience against stress-induced reinstatement of the conditioned place preference induced by cocaine

Cocaine use disorder is a serious problem worldwide, and there are no approved medications for its treatment. A novel approach to the treatment of drug addiction is the use of natural products, and, in this context, preclinical evidence suggests that Hypericum perforatum L. (Hypericum) is effective against alcohol and other substance use disorders. We hypothesised that Hypericum could also be useful as a treatment for cocaine use disorder, and so we set out to test its effectiveness in a mice model of cocaine addiction. In the first experiment we evaluated its effects on the acquisition of cocaine-induced conditioned place preference (CPP). Adult male mice were conditioned with cocaine (25 mg/kg), cocaine with Hypericum (75, 150 or 300 mg/kg) or the plant extract alone (300 mg/kg). In the second experiment, we tested the effects of Hypericum on stress-induced reinstatement of cocaine CPP. All the mice were conditioned with cocaine (25 mg/kg) and, after extinction of CPP, the reinstating effects of social defeat (alone or with 75, 150 or 300 mg/kg of Hypericum) were evaluated. All the doses of Hypericum prevented the acquisition of cocaine-induced CPP. Furthermore, the plant extract dose-dependently reduced the reinstating effects of social defeat. Therefore, Hypericum is effective in reducing the rewarding effects of cocaine and prevents the stress-induced reinstatement of cocaine CPP in mice. The mechanisms underlying these positive effects of Hypericum perforatum L. need to be determined by future research. Our results endorse Hypericum as a natural treatment for cocaine dependence.

5-HT4 Receptors Are Not Involved in the Effects of Fluoxetine in the Corticosterone Model of Depression

Clinical and preclinical studies report the implication of 5-hydroxytryptamine 4 receptors (5-HT₄Rs) in depression and anxiety. Here, we tested whether the absence of 5-HT4Rs influences the response to the antidepressant fluoxetine in mice subjected to chronic corticosterone administration, an animal model of depression and anxiety. Therefore, the effects of chronic administration of fluoxetine in corticosterone-treated wild-type (WT) and 5-HT₄R knockout (KO) mice were evaluated in the open-field and novelty suppressed feeding tests. As 5-HT_1A receptor (5-HT_1AR) and brain-derived neurotrophic factor (BDNF) are critically involved in depression and anxiety, we further evaluated 5-HT_1A receptor functionality by [³⁵S]GTPγS autoradiography and BDNF mRNA expression by in situ hybridization techniques. We found that 5-HT₄R KO and WT mice displayed anxiety- and depressive-like behavior following chronic administration of corticosterone, as evidenced in the open-field and novelty suppressed feeding tests. In the open-field, a decreased central activity was observed in naïve and corticosterone-treated mice of both genotypes following chronic fluoxetine administration. In the novelty suppressed feeding test, a predictive paradigm of antidepressant activity, chronic treatment with fluoxetine reverted the latency to eat in both genotypes. The antidepressant also potentiated the corticosterone-induced desensitization of the 5-HT_1AR in the dorsal raphe nucleus. Further, chronic fluoxetine increased BDNF mRNA expression in the dentate gyrus of the hippocampus in corticosterone-treated mice of both genotypes. Therefore, our findings indicate that the behavioral effects of fluoxetine in the corticosterone model of depression and anxiety appear not to be dependent on 5-HT₄Rs.

Serotonin Signals Overcome Loser Mentality in Drosophila

Traumatic experiences generate stressful neurological effects in the exposed persons and animals. Previous studies have demonstrated that in many species, including Drosophila, the defeated animal has a higher probability of losing subsequent fights. However, the neural basis of this “loser effect” is largely unknown. We herein report that elevated serotonin (5-HT) signaling helps a loser to overcome suppressive neurological states. Coerced activation of 5-HT neurons increases aggression in males and promotes losers to both vigorously re-engage in fights and even defeat the previous winners and regain mating motivation. P1 neurons act upstream and 5-HT1B neurons in the ellipsoid body act downstream of 5-HT neurons to arouse losers. Our results demonstrate an ancient neural mechanism of regulating depressive behavioral states after distressing events.

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Activating a small subset of serotonin neurons promotes losers to fight

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Serotonin is necessary and sufficient for modulating aggression in losers

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The neural circuit for motivating losers includes P1, 5-HT, and 5-HT1B neurons

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Elevating 5-HT signaling overcomes the depressive behavioral state in losers

Medial PFC AMPA receptor and BDNF signaling are required for the rapid and sustained antidepressant-like effects of 5-HT1A receptor stimulation

We previously reported that the serotonergic system is important for the antidepressant-like effects of ketamine, a non-competitive N-methyl-D-aspartate receptor antagonist, which produces rapid and long-lasting antidepressant effects in patients with major depressive disorder (MDD). In particular, selective stimulation of the 5-HT_1A receptor in the medial prefrontal cortex (mPFC), as opposed to the somatic 5-HT_1A autoreceptor, has been shown to play a critical role in the antidepressant-like actions of ketamine. However, the detailed mechanisms underlying mPFC 5-HT_1A receptor-mediated antidepressant-like effects are not fully understood. Here we examined the involvement of the glutamate AMPA receptor and brain-derived neurotrophic factor (BDNF) in the antidepressant-like effects of 5-HT_1A receptor activation in the mPFC. The results show that intra-mPFC infusion of the 5-HT_1A receptor agonist 8-OH-DPAT induces rapid and long-lasting antidepressant-like effects in the forced swim, novelty-suppressed feeding, female urine sniffing, and chronic unpredictable stress tests. In addition, the results demonstrate that the antidepressant-like effects of intra-mPFC infusion of 8-OH-DPAT are blocked by co-infusion of an AMPA receptor antagonist or an anti-BDNF neutralizing antibody. In addition, mPFC infusion of 8-OH-DPAT increased the phosphorylation of signaling proteins downstream of BDNF, including mTOR, ERK, 4EBP1, and p70S6K. Finally, selective stimulation of the 5-HT_1A receptor increased levels of synaptic proteins and synaptic function in the mPFC. Collectively, these results indicate that selective stimulation of 5-HT_1A receptor in the mPFC exerts rapid and sustained antidepressant-like effects via activation of AMPA receptor/BDNF/mTOR signaling in mice, which subsequently increase synaptic function in the mPFC, and provide evidence for the 5-HT_1A receptor as a target for the treatment of MDD.

Exploring the impact of trauma type and extent of exposure on posttraumatic alterations in 5-HT1A expression

The long-term behavioral, psychological, and neurobiological effects of exposure to potentially traumatic events vary within the human population. Studies conducted on trauma-exposed human subjects suggest that differences in trauma type and extent of exposure combine to affect development, maintenance, and treatment of a variety of psychiatric syndromes. The serotonin 1-A receptor (5-HT1A) is an inhibitory G protein-coupled serotonin receptor encoded by the HTR1A gene that plays a role in regulating serotonin release, physiological stress responding, and emotional behavior. Studies from the preclinical and human literature suggest that dysfunctional expression of 5-HT1A is associated with a multitude of psychiatric symptoms commonly seen in trauma-exposed individuals. Here, we synthesize the literature, including numerous preclinical studies, examining differences in alterations in 5-HT1A expression following trauma exposure. Collectively, these findings suggest that the impact of trauma exposure on 5-HT1A expression is dependent, in part, on trauma type and extent of exposure. Furthermore, preclinical and human studies suggest that this observation likely applies to additional molecular targets and may help explain variation in trauma-induced changes in behavior and treatment responsivity. In order to understand the neurobiological impact of trauma, including the impact on 5-HT1A expression, it is crucial to consider both trauma type and extent of exposure.

Serotonin Signaling Trough Prelimbic 5-HT1A Receptors Modulates CSDS-Induced Behavioral Changes in Adult Female Voles

BACKGROUND

Most previous studies have focused on the effects of social defeat in male juvenile individuals. Whether chronic social defeat stress in adulthood affects female emotion and the underlying mechanisms remains unclear.

METHODS

Using highly aggressive adult female mandarin voles (Microtus mandarinus), the present study aimed to determine the effects of chronic social defeat stress on anxiety- and depression-like behaviors in adult female rodents and investigate the neurobiological mechanisms underlying these effects.

RESULTS

Exposure of adult female voles to social defeat stress for 14 days reduced the time spent in the central area of the open field test and in the open arms of the elevated plus maze and lengthened the immobility time in the tail suspension and forced swimming tests, indicating increased anxiety- and depression-like behaviors. Meanwhile, defeated voles exhibited increased neural activity in the prelimbic cortex of the medial prefrontal cortex. Furthermore, chronic social defeat stress reduced serotonin projections and levels of serotonin 1A receptors in the medial prefrontal cortex-prelimbic cortex. Intra-prelimbic cortex microinjections of the serotonin 1A receptor agonist 8-OH-DPAT reversed the alterations in emotional behaviors, whereas injections of the serotonin 1A receptor antagonist WAY-100635 into the prelimbic cortex of control voles increased the levels of anxiety- and depression-like behaviors.

CONCLUSIONS

Taken together, our results demonstrated that chronic social defeat stress increased anxiety- and depression-like behaviors in adult female voles, and these effects were mediated by the action of serotonin on the serotonin 1A receptors in the prelimbic cortex. The serotonin system may be a promising target to treat emotional disorders induced by chronic social defeat stress.

Activation of kappa opioid receptors in the dorsal raphe have sex dependent effects on social behavior in California mice

Kappa opioid receptor activation has been linked to stress and anxiety behavior, thus leading to kappa antagonists being popularized in research as potential anxiolytics. However, while these findings may hold true in standard models, the neuromodulatory effects of social defeat may change the behavioral outcome of kappa opioid receptor activation. Previous research has shown that social defeat can lead to hyperactivity of serotonergic neurons in the dorsal raphe nucleus, and that inhibition of this increase blocks the social deficits caused by defeat. Kappa opioid receptor activation in the dorsal raphe nucleus works to decrease serotonergic activity. We injected the kappa opioid receptor U50,488 directly into the dorsal raphe nucleus of male and female, defeat and control adult California mice. Here we show evidence that U50,488 induces anxiety behavior in control male California mice, but helps relieve it in defeated males. Consistent with previous literature, we find little effect in females adding evidence that there are marked and important sex differences in the kappa opioid system.

Treadmill exercise improves depression-like symptoms by enhancing serotonergic function through upregulation of 5-HT1A expression in the olfactory bulbectomized rats

The olfactory bulbectomy (OBX) is a well-known method inducing animal model of depression. Depression is associated with dysfunction of serotonin (5-hydroxytryptamine, 5-HT) system. In the present study, antidepressive effect of treadmill exercise was investigated using olfactory bulbectomized rats. After bilateral bulbectomy, the rats in the treadmill exercise groups were subjected to run on a treadmill for 30 min once a day during 28 days. Increased immobility time and decreased fast time in the forced swim test were observed in the olfactory bulbectomized rats. Sucrose preference in the sucrose preference test was decreased and activity in the open field test was also increased in the olfactory bulbectomized rats. Treadmill exercise decreased immobility time and activity and increased fast time and sucrose preference in the olfactory bulbectomized rats. Expressions of 5-HT and tryptophan hydroxylase (TPH) in the dorsal raphe of rats were suppressed by OBX and treadmill exercise increased the expressions of 5-HT and TPH in the olfactory bulbectomized rats. Serotonin receptor type 1A (5-HT1A) expression in the dorsal raphe was reduced by OBX and treadmill exercise increased 5-HT1A expression in the olfactory bulbectomized rats. In the present study, treadmill exercise ameliorated OBX-induced depressive symptoms. The antidepressive effect of treadmill exercise might be ascribed to the enhancement of serotonergic function through upregulation of 5-HT1A expression in the dorsal raphe.

Social defeat protocol and relevant biomarkers, implications for stress response physiology, drug abuse, mood disorders and individual stress vulnerability: a systematic review of the last decade

INTRODUCTION

Social defeat (SD) in rats, which results from male intraspecific confrontations, is ethologically relevant and useful to understand stress effects on physiology and behavior.

METHODS

A systematic review of studies about biomarkers induced by the SD protocol and published from 2002 to 2013 was carried out in the electronic databases PubMed, Web of Knowledge and ScienceDirect. The search terms were: social defeat, rat, neurotrophins, neuroinflammatory markers, and transcriptional factors.

RESULTS

Classical and recently discovered biomarkers were found to be relevant in stress-induced states. Findings were summarized in accordance to the length of exposure to stress: single, repeated, intermittent and continuous SD. This review found that the brain-derived neurotrophic factor (BDNF) is a distinct marker of stress adaptation. Along with glucocorticoids and catecholamines, BDNF seems to be important in understanding stress physiology.

CONCLUSION

The SD model provides a relevant tool to study stress response features, development of addictive behaviors, clinic depression and anxiety, as well as individual differences in vulnerability and resilience to stress.

The absence of 5-HT4 receptors modulates depression- and anxiety-like responses and influences the response of fluoxetine in olfactory bulbectomised mice: Adaptive changes in hippocampal neuroplasticity markers and 5-HT1A autoreceptor

Preclinical studies support a critical role of 5-HT₄ receptors (5-HT₄Rs) in depression and anxiety, but their influence in depression- and anxiety-like behaviours and the effects of antidepressants remain partly unknown. We evaluated 5-HT₄R knockout (KO) mice in different anxiety and depression paradigms and mRNA expression of some neuroplasticity markers (BDNF, trkB and Arc) and the functionality of 5-HT_1AR. Moreover, the implication of 5-HT₄Rs in the behavioural and molecular effects of chronically administered fluoxetine was assessed in naïve and olfactory bulbectomized mice (OBX) of both genotypes. 5-HT₄R KO mice displayed few specific behavioural impairments including reduced central activity in the open-field (anxiety), and decreased sucrose consumption and nesting behaviour (anhedonia). In these mice, we measured increased levels of BDNF and Arc mRNA and reduced levels of trkB mRNA in the hippocampus, and a desensitization of 5-HT_1A autoreceptors. Chronic administration of fluoxetine elicited similar behavioural effects in WT and 5-HT₄R KO mice on anxiety-and depression-related tests. Following OBX, locomotor hyperactivity and anxiety were similar in both genotypes. Interestingly, chronic fluoxetine failed to reverse this OBX-induced syndrome in 5-HT₄R KO mice, a response associated with differential effects in hippocampal neuroplasticity biomarkers. Fluoxetine reduced hippocampal Arc and BDNF mRNA expressions in WT but not 5-HT₄R KO mice subjected to OBX. These results demonstrate that the absence of 5-HT₄Rs triggers adaptive changes that could maintain emotional states, and that the behavioural and molecular effects of fluoxetine under pathological depression appear to be critically dependent on 5-HT₄Rs.

Serotonergic Neuroplasticity in Alcohol Addiction

Alcohol addiction is a debilitating disorder producing maladaptive changes in the brain, leading drinkers to become more sensitive to stress and anxiety. These changes are key factors contributing to alcohol craving and maintaining a persistent vulnerability to relapse.

Serotonin (5-Hydroxytryptamine, 5-HT) is a monoamine neurotransmitter widely expressed in the central nervous system where it plays an important role in the regulation of mood. The serotonin system has been extensively implicated in the regulation of stress and anxiety, as well as the reinforcing properties of all of the major classes of drugs of abuse, including alcohol. Dysregulation within the 5-HT system has been postulated to underlie the negative mood states associated with alcohol use disorders.

This review will describe the serotonergic (5-HTergic) neuroplastic changes observed in animal models throughout the alcohol addiction cycle, from prenatal to adulthood exposure. The first section will focus on alcohol-induced 5-HTergic neuroadaptations in offspring prenatally exposed to alcohol and the consequences on the regulation of stress/anxiety. The second section will compare alterations in 5-HT signalling induced by acute or chronic alcohol exposure during adulthood and following alcohol withdrawal, highlighting the impact on the regulation of stress/anxiety signalling pathways. The third section will outline 5-HTergic neuroadaptations observed in various genetically-selected ethanol preferring rat lines. Finally, we will discuss the pharmacological manipulation of the 5-HTergic system on ethanol- and anxiety/stress-related behaviours demonstrated by clinical trials, with an emphasis on current and potential treatments.

Depression and substance use comorbidity: What we have learned from animal studies

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).

The roles of CC2D1A and HTR1A gene expressions in autism spectrum disorders

Classical autism belongs to a group of heterogeneous disorders known as autism spectrum disorders (ASD). Autism is defined as a neurodevelopmental disorder, characterized by repetitive stereotypic behaviors or restricted interests, social withdrawal, and communication deficits. Numerous susceptibility genes and chromosomal abnormalities have been reported in association with autism but the etiology of this disorder is unknown in many cases. CC2D1A gene has been linked to mental retardation (MR) in a family with a large deletion before. Intellectual disability (ID) is a common feature of autistic cases. Therefore we aimed to investigate the expressions of CC2D1A and HTR1A genes with the diagnosis of autism in Turkey. Forty-four autistic patients (35 boys, 9 girls) and 27 controls were enrolled and obtained whole blood samples to isolate RNA samples from each participant. CC2D1A and HTR1A gene expressions were assessed by quantitative Real-Time PCR (qRT-PCR) in Genome and Stem Cell Center, Erciyes University. Both expressions of CC2D1A and HTR1A genes studied on ASD cases and controls were significantly different (p < 0.001). The expression of HTR1A was undetectable in the ASD samples. Comparison of ID and CC2D1A gene expression was also found statistically significant (p = 0.028). CC2D1A gene expression may be used as a candidate gene for ASD cases with ID. Further studies are needed to investigate the potential roles of these CC2D1A and HTR1A genes in their related pathways in ASD.

5-HT1A receptor gene silencers Freud-1 and Freud-2 are differently expressed in the brain of rats with genetically determined high level of fear-induced aggression or its absence

Serotonin 5-HT1A receptor is known to play a crucial role in the mechanisms of genetically defined aggression. In its turn, 5-HT1A receptor functional state is under control of multiple factors. Among others, transcriptional factors Freud-1 and Freud-2 are known to be involved in the repression of 5-HT1A receptor gene expression. However, implication of these factors in the regulation of behavior is unclear. Here, we investigated the expression of 5-HT1A receptor and silencers Freud-1 and Freud-2 in the brain of rats selectively bred for 85 generations for either high level of fear-induced aggression or its absence. It was shown that Freud-1 and Freud-2 levels were different in aggressive and nonaggressive animals. Freud-1 protein level was decreased in the hippocampus, whereas Freud-2 protein level was increased in the frontal cortex of highly aggressive rats. There no differences in 5-HT1A receptor gene expression were found in the brains of highly aggressive and nonaggressive rats. However, 5-HT1A receptor protein level was decreased in the midbrain and increased in the hippocampus of highly aggressive rats. These data showed the involvement of Freud-1 and Freud-2 in the regulation of genetically defined fear-induced aggression. However, these silencers do not affect transcription of the 5-HT1A receptor gene in the investigated rats. Our data indicate the implication of posttranscriptional rather than transcriptional regulation of 5-HT1A receptor functional state in the mechanisms of genetically determined aggressive behavior. On the other hand, the implication of other transcriptional regulators for 5-HT1A receptor gene in the mechanisms of genetically defined aggression could be suggested.

Sex differences in sleep, anhedonia, and HPA axis activity in a rat model of chronic social defeat

Repeated bouts of a major stressor such as social defeat are well known to induce a depression phenotype in male rats. Despite strong evidence and acknowledgement that women have a two-fold lifetime greater risk of developing major depression compared to men, the inclusion of female rats in studies employing social defeat are very rare; their absence is attributed to less aggressive interactions. This study sought to compare in male and female rats the impact of repeated social defeat, three times per week for four weeks, on the development of changes in sleep architecture and continuity, sucrose preference as a measure of anhedonia, changes in body weight, and basal plasma corticosterone levels. We found significant reductions in rapid eye movement sleep (REMS) during the light phase in both females and males, and significant increases in numbers of vigilance state transitions during the early dark phase in females but not in males. Additionally, females exhibited significantly greater reductions in sucrose intake than males. On the other hand, no sex differences in significantly elevated basal corticosterone levels were evident, and only the males exhibited changes in body weight. Taken together these findings suggest that the inclusion of female rats in studies of social defeat may offer greater insights in studies of stress and depression.

Chronic mild stress and antidepressant treatment alter 5-HT1A receptor expression by modifying DNA methylation of a conserved Sp4 site

The serotonin 1A receptor (5-HT1A), a critical regulator of the brain serotonergic tone, is implicated in major depressive disorder (MDD) where it is often found to be dys-regulated. However, the extent to which stress and antidepressant treatment impact 5-HT1A expression in adults remains unclear. To address this issue, we subjected adult male BALB/c mice to unpredictable chronic mild stress (UCMS) to induce a depression-like phenotype that was reversed by chronic treatment with the antidepressant imipramine. In prefrontal cortex (PFC) and midbrain tissue, UCMS increased 5-HT1A RNA and protein levels, changes that are expected to decrease the brain serotonergic activity. The stress-induced increase in 5-HT1A expression was paralleled by a specific increase in DNA methylation of the conserved -681 CpG promoter site, located within a Sp1-like element. We show that the -681 CpG site is recognized and repressed by Sp4, the predominant neuronal Sp1-like factor and that Sp4-induced repression is attenuated by DNA methylation, despite a stress-induced increase in PFC Sp4 levels. These results indicate that adult life stress induces DNA methylation of a conserved promoter site, antagonizing Sp4 repression to increase 5-HT1A expression. Chronic imipramine treatment fully reversed the UCMS-induced increase in methylation of the -681 CpG site in the PFC but not midbrain of stressed animals and also increased 5-HT1A expression in the PFC of control animals. Incomplete reversal by imipramine of stress-induced changes in 5-HT1A methylation and expression indicates a persistence of stress vulnerability, and that sustained reversal of behavioral impairments may require additional pathways.

Chronic Social Stress and Ethanol Increase Expression of KLF11, a Cell Death Mediator, in Rat Brain

Major depressive disorder and alcoholism are significant health burdens that can affect executive functioning, cognitive ability, job responsibilities, and personal relationships. Studies in animal models related to depression or alcoholism reveal that the expression of Krüppel-like factor 11 (KLF11, also called TIEG2) is elevated in frontal cortex, which suggests that KLF11 may play a role in stress- or ethanol-induced psychiatric conditions. KLF11 is a transcriptional activator of monoamine oxidase A and B, but also serves other functions in cell cycle regulation and apoptotic cell death. In the present study, immunohistochemistry was used to quantify intensity of nuclear KLF11, combined with an unbiased stereological approach to assess nuclei in fronto-limbic, limbic, and other brain regions of rats exposed chronically to social defeat or ethanol. KLF11 immunoreactivity was increased significantly in the medial prefrontal cortex, frontal cortex, and hippocampus of both stressed rats and rats fed ethanol. However, expression of KLF11 protein was not significantly affected in the thalamus, hypothalamus, or amygdala in either treatment group compared to respective control rats. Triple-label immunofluorescence revealed that KLF11 protein was localized in nuclei of neurons and astrocytes. KLF11 was also co-localized with the immunoreactivity of cleaved caspase-3. In addition, Western blot analysis revealed a significant reduction in anti-apoptotic protein, Bcl-xL, but an increase of caspase-3 expression in the frontal cortex of ethanol-treated rats compared to ethanol-preferring controls. Thus, KLF11 protein is up-regulated following chronic exposure to stress or ethanol in a region-specific manner and may contribute to pro-apoptotic signaling in ethanol-treated rats. Further investigation into the KLF11 signaling cascade as a mechanism for neurotoxicity and cell death in depression and alcoholism may provide novel pharmacological targets to lessen brain damage and maximize neuroprotection in these disorders.

Stress-induced alterations in 5-HT1A receptor transcriptional modulators NUDR and Freud-1

The effect of stress on the mRNA and protein level of the 5-HT1A receptor and two of its key transcriptional modulators, NUDR and Freud-1, was examined in the prefrontal cortex (PFC) and hippocampus (Hp) using rodent models: olfactory bulbectomy (OB) and prenatal stress (PS) in male and female rats; chronic mild stress in male rats (CMS) and pregnancy stress. In PFC, CMS induced the most widespread changes, with significant reduction in both mRNA and protein levels of NUDR, 5-HT1A receptor and in Freud-1 mRNA; while in Hp 5-HT1A receptor and Freud-1 protein levels were also decreased. In male, but not female OB rats PFC Freud-1 and 5-HT1A receptor protein levels were reduced, while in Hp 5-HT1A receptor, Freud-1 and NUDR mRNA's but not protein were reduced. In PS rats PFC 5-HT1A receptor protein was reduced more in females than males; while in Hp Freud-1 protein was increased in females. In pregnancy stress, PFC NUDR, Freud-1 and 5-HT1A protein receptor levels were reduced, and in HP 5-HT1A receptor protein levels were also reduced; in HP only NUDR and Freud-1 mRNA levels were reduced. Overall, CMS and stress during pregnancy produced the most salient changes in 5-HT1A receptor and transcription factor expression, suggesting a primary role for altered transcription factor expression in chronic regulation of 5-HT1A receptor expression. By contrast, OB (in males) and PS (in females) produced gender-specific reductions in PFC 5-HT1A receptor protein levels, suggesting a role for post-transcriptional regulation. These and previous data suggest that chronic stress might be a key regulator of NUDR/Freud-1 gene expression.

Krüppel-like factors are effectors of nuclear receptor signaling

Binding of steroid and thyroid hormones to their cognate nuclear receptors (NRs) impacts virtually every aspect of postembryonic development, physiology and behavior, and inappropriate signaling by NRs may contribute to disease. While NRs regulate genes by direct binding to hormone response elements in the genome, their actions may depend on the activity of other transcription factors (TFs) that may or may not bind DNA. The Krüppel-like family of transcription factors (KLF) is an evolutionarily conserved class of DNA-binding proteins that influence many aspects of development and physiology. Several members of this family have been shown to play diverse roles in NR signaling. For example, KLFs (1) act as accessory transcription factors for NR actions, (2) regulate expression of NR genes, and (3) as gene products of primary NR response genes function as key players in NR-dependent transcriptional networks. In mouse models, deletion of different KLFs leads to aberrant transcriptional and physiological responses to hormones, underscoring the importance of these proteins in the regulation of hormonal signaling. Understanding the functional relationships between NRs and KLFs will yield important insights into mechanisms of NR signaling. In this review we present a conceptual framework for understanding how KLFs participate in NR signaling, and we provide examples of how these proteins function to effect hormone action.

Activation of prelimbic 5-HT1A receptors produces antidepressant-like effects in a unilateral rat model of Parkinson's disease

Depression is a common symptom in Parkinson's disease (PD), but its pathophysiology remains unclear. Several lines of studies have revealed that the prelimbic (PrL) sub-region of the ventral medial prefrontal cortex and 5-HT1A receptors are involved in the regulation of depression. In this study, we examined whether complete unilateral lesions of the medial forebrain bundle (MFB) using 6-hydroxydopamine in rats are able to induce depressive-like behaviors, the role of PrL 5-HT1A receptors in the regulation of these behaviors, and co-localization of 5-HT1A receptor and neuronal glutamate transporter EAAC1-immunoreactive (EAAC1-ir) neurons in the PrL. The MFB lesions induced depressive-like responses as measured by the sucrose preference and forced swim tests when compared to sham-operated rats. The intra-PrL injection of 5HT1A receptor agonist 8-OH-DPAT (50, 100, and 500ng/rat) increased sucrose consumption, and decreased immobility time in both sham-operated and the lesioned rats, indicating the induction of antidepressant effects. Furthermore, the intra-PrL injection of 5HT1A receptor antagonist WAY-100635 (60, 120, and 240ng/rat) showed a decrease in sucrose consumption, and an increase in immobility time, indicating the induction of depressive-like responses. However, the effective doses in the lesioned rats were higher than those in sham-operated rats, which attribute to down-regulation of 5-HT1A receptor expression on EAAC1-ir neurons in the PrL of the lesioned rats. These findings suggest that unilateral lesions of the MFB in rats may induce depressive-like behaviors, and 5-HT1A receptors of the PrL play an important role in the regulation of these behaviors.

Vagal modulation of resting heart rate in rats: the role of stress, psychosocial factors, and physical exercise

In humans, there are large individual differences in the levels of vagal modulation of resting heart rate (HR). High levels are a recognized index of cardiac health, whereas low levels are considered an important risk factor for cardiovascular morbidity and mortality. Several factors are thought to contribute significantly to this inter-individual variability. While regular physical exercise seems to induce an increase in resting vagal tone, chronic life stress, and psychosocial factors such as negative moods and personality traits appear associated with vagal withdrawal. Preclinical research has been attempting to clarify such relationships and to provide insights into the neurobiological mechanisms underlying vagal tone impairment/enhancement. This paper focuses on rat studies that have explored the effects of stress, psychosocial factors and physical exercise on vagal modulation of resting HR. Results are discussed with regard to: (i) individual differences in resting vagal tone, cardiac stress reactivity and arrhythmia vulnerability; (ii) elucidation of the neurobiological determinants of resting vagal tone.

A zebrafish model of glucocorticoid resistance shows serotonergic modulation of the stress response

One function of glucocorticoids is to restore homeostasis after an acute stress response by providing negative feedback to stress circuits in the brain. Loss of this negative feedback leads to elevated physiological stress and may contribute to depression, anxiety, and post-traumatic stress disorder. We investigated the early, developmental effects of glucocorticoid signaling deficits on stress physiology and related behaviors using a mutant zebrafish, gr(s357), with non-functional glucocorticoid receptors (GRs). These mutants are morphologically inconspicuous and adult-viable. A previous study of adult gr(s357) mutants showed loss of glucocorticoid-mediated negative feedback and elevated physiological and behavioral stress markers. Already at 5 days post-fertilization, mutant larvae had elevated whole body cortisol, increased expression of pro-opiomelanocortin (POMC), the precursor of adrenocorticotropic hormone (ACTH), and failed to show normal suppression of stress markers after dexamethasone treatment. Mutant larvae had larger auditory-evoked startle responses compared to wildtype sibling controls (gr(wt)), despite having lower spontaneous activity levels. Fluoxetine (Prozac) treatment in mutants decreased startle responding and increased spontaneous activity, making them behaviorally similar to wildtype. This result mirrors known effects of selective serotonin reuptake inhibitors (SSRIs) in modifying glucocorticoid signaling and alleviating stress disorders in human patients. Our results suggest that larval gr(s357) zebrafish can be used to study behavioral, physiological, and molecular aspects of stress disorders. Most importantly, interactions between glucocorticoid and serotonin signaling appear to be highly conserved among vertebrates, suggesting deep homologies at the neural circuit level and opening up new avenues for research into psychiatric conditions.

Differential distribution of serotonin receptor subtypes in BNST(ALG) neurons: modulation by unpredictable shock stress

The bed nucleus of the stria terminalis (BNST) plays a critical role in regulating the behavioral response to stress. Stressors that activate the BNST also activate serotonergic (5-HT) systems. Hence, maladaptive changes of 5-HT receptor expression may contribute to stress-induced anxiety disorders. The BNST contains three neuronal types, Type I-III neurons. However, little is known about 5-HT receptor subtypes mRNA expression in these neurons, or whether it can be modulated by stress. Whole-cell patch clamp recording from Type I-III neurons was used in conjunction with single cell reverse transcriptase polymerase chain reaction (RT-PCR) to characterize 5-HT receptor mRNA expression, and examine the effects of stress on this expression. We report that Type I neurons expressed mRNA transcripts predominantly for 5-HT(1A) and 5-HT(7) receptors. Type II neurons expressed transcripts for every 5-HT receptor except the 5-HT(2C) receptor. Type II neurons were divided into three sub-populations: Type IIA in which transcripts for 5-HT(3) and 5-HT(7) receptors predominate, Type IIB that mainly express 5-HT(1B) and 5-HT(4) receptor transcripts, and Type IIC in which transcripts for 5-HT(1A) and 5-HT(2A) receptors predominate. Type III neurons were also subdivided into two sub-populations; one that predominantly expressed transcripts for 5-HT(1A), 5-HT(1B) and 5-HT(2A) receptors, and another that mainly expressed transcripts for 5-HT(2C) receptor. Unpredictable shock stress (USS) caused a long-lasting increase in anxiety-like behavior, and a concomitant decrease in 5-HT(1A) transcript expression in Type I-III neurons, as well as an up-regulation of a transcriptional repressor of 5-HT(1A) gene expression, deformed epidermal autoregulatory factor 1 (Deaf-1). Significantly USS decreased 5-HT(1A) protein level, and increased the level of Deaf-1. USS also increased 5-HT(1B) transcript expression in Type III neurons, as well as 5-HT(7) expression in Type I and II neurons. These data suggest that cell type-specific disruption of 5-HT receptor expression in BNST(ALG) neurons may contribute to stress-induced anxiety disorders.

Ingestion of theanine, an amino acid in tea, suppresses psychosocial stress in mice

The antistress effect of theanine (γ-glutamylethylamide), an amino acid in tea, was investigated using mice that were psychosocially stressed from a conflict among male mice in conditions of confrontational housing. Two male mice were housed in the same cage separated by a partition to establish a territorial imperative. When the partition was removed, the mice were co-housed confrontationally. As a marker for the stress response, changes in the adrenal gland were studied in comparison to group-housed control mice (six mice in a cage). Significant adrenal hypertrophy was observed in mice during confrontational housing, which was developed within 24 h and persisted for at least 1 week. The size of cells in the zona fasciculata of the adrenal gland, from which glucocorticoid is mainly secreted, increased (∼1.11-fold) in mice during confrontational housing, which was accompanied by a flattened diurnal rhythm of corticosterone and ACTH in blood. The ingestion of theanine (>5 μg ml(-1)) prior to confrontational housing significantly suppressed adrenal hypertrophy. An antidepressant, paroxetin, suppressed adrenal hypertrophy in a similar manner in mice during confrontational housing. In mice that ingested theanine, behavioural depression was also suppressed, and a diurnal rhythm of corticosterone and ACTH was observed, even in mice that were undergoing confrontational housing. Furthermore, the daily dose of theanine (40 μg ml(-1)) blocked the counteracting effects of caffeine (30 μg ml(-1)) and catechin (200 μg ml(-1)). The present study demonstrated that theanine prevents and relieves psychosocial stress through the modulation of hypothalamic-pituitary-adrenal axis activity.

Mechanistic role for a novel glucocorticoid-KLF11 (TIEG2) protein pathway in stress-induced monoamine oxidase A expression

Chronic stress is a risk factor for psychiatric illnesses, including depressive disorders, and is characterized by increased blood glucocorticoids and brain monoamine oxidase A (MAO A, which degrades monoamine neurotransmitters). This study elucidates the relationship between stress-induced MAO A and the transcription factor Kruppel-like factor 11 (KLF11, also called TIEG2, a member of the Sp/KLF- family), which inhibits cell growth. We report that 1) a glucocorticoid (dexamethasone) increases KLF11 mRNA and protein levels in cultured neuronal cells; 2) overexpressing KLF11 increases levels of MAO A mRNA and enzymatic activity, which is further enhanced by glucocorticoids; in contrast, siRNA-mediated KLF11 knockdown reduces glucocorticoid-induced MAO A expression in cultured neurons; 3) induction of KLF11 and translocation of KLF11 from the cytoplasm to the nucleus are key regulatory mechanisms leading to increased MAO A catalytic activity and mRNA levels because of direct activation of the MAO A promoter via Sp/KLF-binding sites; 4) KLF11 knockout mice show reduced MAO A mRNA and catalytic activity in the brain cortex compared with wild-type mice; and 5) exposure to chronic social defeat stress induces blood glucocorticoids and activates the KLF11 pathway in the rat brain, which results in increased MAO A mRNA and enzymatic activity. Thus, this study reveals for the first time that KLF11 is an MAO A regulator and is produced in response to neuronal stress, which transcriptionally activates MAO A. The novel glucocorticoid-KLF11-MAO A pathway may play a crucial role in modulating distinct pathophysiological steps in stress-related disorders.

The New Inhibitor of Monoamine Oxidase, M30, has a Neuroprotective Effect Against Dexamethasone-Induced Brain Cell Apoptosis

Stress detrimentally affects the brain and body and can lead to or be accompanied by depression. Although stress and depression may contribute to each other, the exact molecular mechanism underlying the effects is unclear. However, there is a correlation between stress and an increase in glucocorticoid secretion which causes a subsequent increase in monoamine oxidase (MAO) activity during stress. Consequently, MAO inhibitors have been used as traditional antidepressant drugs. Cellular treatment with the synthetic glucocorticoid, dexamethasone (a cellular stressor), has been reported to markedly increase both MAO A and MAO B catalytic activities, as well as apoptosis. This study compares the neuroprotective abilities of M30 (a new generation inhibitor of both MAO A and MAO B) with rasagiline (Azilect^®, another new MAO B inhibitor) and selegiline (Deprenyl^®, a traditional MAO B inhibitor) in the prevention of dexamethasone-induced brain cell death and MAO activity in human neuroblastoma cells, SH-SY5Y. M30 demonstrated the highest inhibitory effect on MAO A; however, M30 showed the lowest inhibitory effect on MAO B enzymatic activity in comparison to rasagiline and selegiline. Although, M30 exhibited the greatest neuroprotective effect by decreasing cell death rates and apoptotic DNA damage compared to rasagiline and selegiline, these neuroprotective effects of M30 were, overall, similar to rasagiline. Summarily, M30 has a generally greater impact on neuroprotection than the MAO B inhibitors, selegiline and rasagiline. Our results suggest that M30 may have great potential in alleviating disorders involving increases in both MAO A and MAO B, such as stress-induced disorders.

Chronic corticosterone administration down-regulates metabotropic glutamate receptor 5 protein expression in the rat hippocampus

Several lines of evidence suggest a dysfunctional glutamate system in major depressive disorder (MDD). Recently, we reported reduced levels of metabotropic glutamate receptor subtype 5 (mGluR5) in postmortem brains in MDD, however the neurobiological mechanisms that induce these abnormalities are unclear. In the present study, we examined the effect of chronic corticosterone (CORT) administration on the expression of mGluR5 protein and mRNA in the rat frontal cortex and hippocampus. Rats were injected with CORT (40 mg/kg s.c.) or vehicled once daily for 21 days. The expression of mGluR5 protein and mRNA was assessed by Western blotting and quantitative real-time PCR (qPCR). In addition, mGluR1 protein was measured in the same animals. The results revealed that while there was a significant reduction (-27%, P=0.0006) in mGluR5 protein expression in the hippocampus from CORT treated rats, mRNA levels were unchanged. Also unchanged were mGluR5 mRNA and protein levels in the frontal cortex and mGluR1 protein levels in both brain regions. Our findings provide the first evidence that chronic CORT exposure regulates the expression of mGluR5 and are in line with previous postmortem and imaging studies showing reduced mGluR5 in MDD. Our findings suggest that elevated levels of glucocorticoids may contribute to impairments in glutamate neurotransmission in MDD.