Forebrain glucocorticoid receptors modulate anxiety-associated locomotor activation and adrenal responsiveness

Resveratrol Ameliorates the Depressive-Like Behaviors and Metabolic Abnormalities Induced by Chronic Corticosterone Injection

Chronic glucocorticoid exposure is known to cause depression and metabolic disorders. It is critical to improve abnormal metabolic status as well as depressive-like behaviors in patients with long-term glucocorticoid therapy. This study aimed to investigate the effects of resveratrol on the depressive-like behaviors and metabolic abnormalities induced by chronic corticosterone injection. Male ICR mice were administrated corticosterone (40 mg/kg) by subcutaneous injection for three weeks. Resveratrol (50 and 100 mg/kg), fluoxetine (20 mg/kg) and pioglitazone (10 mg/kg) were given by oral gavage 30 min prior to corticosterone administration. The behavioral tests showed that resveratrol significantly reversed the depressive-like behaviors induced by corticosterone, including the reduced sucrose preference and increased immobility time in the forced swimming test. Moreover, resveratrol also increased the secretion of insulin, reduced serum level of glucose and improved blood lipid profiles in corticosterone-treated mice without affecting normal mice. However, fluoxetine only reverse depressive-like behaviors, and pioglitazone only prevent the dyslipidemia induced by corticosterone. Furthermore, resveratrol and pioglitazone decreased serum level of glucagon and corticosterone. The present results indicated that resveratrol can ameliorate depressive-like behaviors and metabolic abnormalities induced by corticosterone, which suggested that the multiple effects of resveratrol could be beneficial for patients with depression and/or metabolic syndrome associated with long-term glucocorticoid therapy.

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.

Regulation of the Hypothalamic-Pituitary-Adrenocortical Stress Response

The hypothalamo-pituitary-adrenocortical (HPA) axis is required for stress adaptation. Activation of the HPA axis causes secretion of glucocorticoids, which act on multiple organ systems to redirect energy resources to meet real or anticipated demand. The HPA stress response is driven primarily by neural mechanisms, invoking corticotrophin releasing hormone (CRH) release from hypothalamic paraventricular nucleus (PVN) neurons. Pathways activating CRH release are stressor dependent: reactive responses to homeostatic disruption frequently involve direct noradrenergic or peptidergic drive of PVN neurons by sensory relays, whereas anticipatory responses use oligosynaptic pathways originating in upstream limbic structures. Anticipatory responses are driven largely by disinhibition, mediated by trans-synaptic silencing of tonic PVN inhibition via GABAergic neurons in the amygdala. Stress responses are inhibited by negative feedback mechanisms, whereby glucocorticoids act to diminish drive (brainstem) and promote transsynaptic inhibition by limbic structures (e.g., hippocampus). Glucocorticoids also act at the PVN to rapidly inhibit CRH neuronal activity via membrane glucocorticoid receptors. Chronic stress-induced activation of the HPA axis takes many forms (chronic basal hypersecretion, sensitized stress responses, and even adrenal exhaustion), with manifestation dependent upon factors such as stressor chronicity, intensity, frequency, and modality. Neural mechanisms driving chronic stress responses can be distinct from those controlling acute reactions, including recruitment of novel limbic, hypothalamic, and brainstem circuits. Importantly, an individual's response to acute or chronic stress is determined by numerous factors, including genetics, early life experience, environmental conditions, sex, and age. The context in which stressors occur will determine whether an individual's acute or chronic stress responses are adaptive or maladaptive (pathological).

Genetic Approaches to Hypothalamic-Pituitary-Adrenal Axis Regulation

The normal function of the hypothalamic-pituitary-adrenal (HPA) axis, and resultant glucocorticoid (GC) secretion, is essential for human health. Disruption of GC regulation is associated with pathologic, psychological, and physiological disease states such as depression, post-traumatic stress disorder, hypertension, diabetes, and osteopenia, among others. As such, understanding the mechanisms by which HPA output is tightly regulated in its responses to environmental stressors and circadian cues has been an active area of investigation for decades. Over the last 20 years, however, advances in gene targeting and genome modification in rodent models have allowed the detailed dissection of roles for key molecular mediators and brain regions responsible for this control in vivo to emerge. Here, we summarize work done to elucidate the function of critical neuropeptide systems, GC-signaling targets, and inflammation-associated pathways in HPA axis regulation and behavior, and highlight areas for future investigation.

An analysis of gene expression in PTSD implicates genes involved in the glucocorticoid receptor pathway and neural responses to stress

We examined the association between posttraumatic stress disorder (PTSD) and gene expression using whole blood samples from a cohort of trauma-exposed white non-Hispanic male veterans (115 cases and 28 controls). 10,264 probes of genes and gene transcripts were analyzed. We found 41 that were differentially expressed in PTSD cases versus controls (multiple-testing corrected p<0.05). The most significant was DSCAM, a neurological gene expressed widely in the developing brain and in the amygdala and hippocampus of the adult brain. We then examined the 41 differentially expressed genes in a meta-analysis using two replication cohorts and found significant associations with PTSD for 7 of the 41 (p<0.05), one of which (ATP6AP1L) survived multiple-testing correction. There was also broad evidence of overlap across the discovery and replication samples for the entire set of genes implicated in the discovery data based on the direction of effect and an enrichment of p<0.05 significant probes beyond what would be expected under the null. Finally, we found that the set of differentially expressed genes from the discovery sample was enriched for genes responsive to glucocorticoid signaling with most showing reduced expression in PTSD cases compared to controls.

Ontogeny of hypothalamic glucocorticoid receptor-mediated inhibition of the hypothalamic-pituitary-adrenal axis in mice

Glucocorticoid receptors (GR) in the paraventricular nucleus of the hypothalamus (PVN) are important regulators of negative feedback regulation of the hypothalamic-pituitary-adrenal (HPA) axis. Previous evaluation of endogenous PVN GR function in adult mice demonstrated that mice with loss of GR exon 3 in the PVN (Sim1Cre-GRe3Δ) have a hyperactive HPA axis, growth impairment and metabolic disruptions. Here, we hypothesized that lack of negative feedback inhibition of the HPA axis through PVN GR, as demonstrated through loss of PVN GR early in life, will have developmental-stage-specific consequences. Immunofluorescence revealed that Sim1Cre-GRe3Δ mice display PVN GR loss as early as post-natal day 2 compared to control mice. Sim1Cre-GRe3Δ mice compared to controls also displayed increased corticotropin-releasing hormone (CRH) mRNA in the PVN at post-natal day 10, as shown by in situ hybridization. Corticosterone radioimmunoassay revealed that the disruptions in PVN GR and CRH expression led to elevated basal corticosterone secretion in male Sim1Cre-GRe3Δ mice by early adolescence and increased stress-induced (restraint) corticosterone secretion in late adolescence into adulthood. In comparison, female Sim1Cre-GRe3Δ mice did not display corticosterone disruption until adulthood. Circadian rhythmicity of corticosterone secretion was normal for male and female mice at all age groups regardless of genotype with one exception. In late adolescence, female Sim1Cre-GRe3Δ mice had disrupted circadian corticosterone secretion due to significantly elevated circulating levels at nadir. We conclude that PVN GR function matures at an earlier developmental time point in male than in female mice and thus leads to later differential stress responsiveness between sexes.

Genomic and non-genomic effects of glucocorticoids: implications for breast cancer

Glucocorticoids (GC) are essential steroid hormones for human life. They regulate a series of important processes by binding with three glucocorticoid receptors (GR) and activating genomic and non-genomic pathways. Activated cytoplasmic GR can directly bind DNA and transactivate or transrepress specific genes. Additionally, it can interact with other transcription factors to affect gene expression indirectly. The two membrane GR can interact with mitogen-activated protein (MAP) kinases or activate cAMP and Ca(2+)-dependent pathways, respectively. Glucocorticoids have been widely used as co-treatment of patients with breast cancer (BC) due to reduction of chemotherapy-induced side effects such as nausea, lack of appetite, and inflammation. However, GC may exert a direct effect on tumor response to chemotherapy. In vitro, GC inhibits chemotherapy, radiation and cytokine-induced apoptosis by upregulating antiapoptotic genes and detoxifying proteins. They also upregulate the proto-oncogene c-fms, tumor suppressor gene Nm23, several members of the epidermal growth factor (EGF) signaling pathway and the estrogen sulfotransferase signaling pathway, thus indirectly inhibiting estrogen receptor activation. They inhibit the proangiogenic gene (vascular endothelial growth factor (VEGF); Therefore, they could play a role in reducing angiogenesis. Interestingly, the phosphorylation status of ser-211 in the GR is dependent on the expression of the BRCA1 gene, a tumor suppressor gene that is mutated in the majority of patients with triple negative BC. Some clinical randomized trials have also attempted to address the effect of GC on patients with BC. Thus, in this review we summarize GC mechanisms of action and their participation in several facets of BC.

Dissection of glucocorticoid receptor-mediated inhibition of the hypothalamic-pituitary-adrenal axis by gene targeting in mice

Negative feedback regulation of glucocorticoid (GC) synthesis and secretion occurs through the function of glucocorticoid receptor (GR) at sites in the hypothalamic-pituitary-adrenal (HPA) axis, as well as in brain regions such as the hippocampus, prefrontal cortex, and sympathetic nervous system. This function of GRs in negative feedback coordinates basal glucocorticoid secretion and stress-induced increases in secretion that integrate GC production with the magnitude and duration of the stressor. This review describes the effects of GR loss along major sites of negative feedback including the entire brain, the paraventricular nucleus of the hypothalamus (PVN), and the pituitary. In genetic mouse models, we evaluate circadian regulation of the HPA axis, stress-stimulated neuroendocrine response and behavioral activity, as well as the integrated response of organism metabolism. Our analysis provides information on contributions of region-specific GR-mediated negative feedback to provide insight in understanding HPA axis dysregulation and the pathogenesis of psychiatric and metabolic disorders.

Mood, food, and obesity

Food is a potent natural reward and food intake is a complex process. Reward and gratification associated with food consumption leads to dopamine (DA) production, which in turn activates reward and pleasure centers in the brain. An individual will repeatedly eat a particular food to experience this positive feeling of gratification. This type of repetitive behavior of food intake leads to the activation of brain reward pathways that eventually overrides other signals of satiety and hunger. Thus, a gratification habit through a favorable food leads to overeating and morbid obesity. Overeating and obesity stems from many biological factors engaging both central and peripheral systems in a bi-directional manner involving mood and emotions. Emotional eating and altered mood can also lead to altered food choice and intake leading to overeating and obesity. Research findings from human and animal studies support a two-way link between three concepts, mood, food, and obesity. The focus of this article is to provide an overview of complex nature of food intake where various biological factors link mood, food intake, and brain signaling that engages both peripheral and central nervous system signaling pathways in a bi-directional manner in obesity.

Forebrain glucocorticoid receptor gene deletion attenuates behavioral changes and antidepressant responsiveness during chronic stress

Stress is an important risk factor for mood disorders. Stress also stimulates the secretion of glucocorticoids, which have been found to influence mood. To determine the role of forebrain glucocorticoid receptors (GR) in behavioral responses to chronic stress, the present experiments compared behavioral effects of repeated social defeat in mice with forebrain GR deletion and in floxed GR littermate controls. Repeated defeat produced alterations in forced swim and tail suspension immobility in floxed GR mice that did not occur in mice with forebrain GR deletion. Defeat-induced changes in immobility in floxed GR mice were prevented by chronic antidepressant treatment, indicating that these behaviors were dysphoria-related. In contrast, although mice with forebrain GR deletion exhibited antidepressant-induced decreases in tail suspension immobility in the absence of stress, this response did not occur in mice with forebrain GR deletion after defeat. There were no marked differences in plasma corticosterone between genotypes, suggesting that behavioral differences depended on forebrain GR rather than on abnormal glucocorticoid secretion. Defeat-induced gene expression of the neuronal activity marker c-fos in the ventral hippocampus, paraventricular thalamus and lateral septum correlated with genotype-related differences in behavioral effects of defeat, whereas c-fos induction in the nucleus accumbens and central and basolateral amygdala correlated with genotype-related differences in behavioral responses to antidepressant treatment. The dependence of both negative (dysphoria-related) and positive (antidepressant-induced) behaviors on forebrain GR is consistent with the contradictory effects of glucocorticoids on mood, and implicates these or other forebrain regions in these effects.

Antidepressant effects of the water extract from Taraxacum officinale leaves and roots in mice

CONTEXT

The leaves and roots of the Taraxacum officinale F. (Asteraceae) is widely used as traditional medicinal herb in Eastern Asian countries.

OBJECTIVE

In the present study, the antidepressant-like effects of the water extract of T. officinale (WETO) leaves and roots were investigated in mice using forced swimming test (FST), tail suspension test (TST) and open field test (OFT).

MATERIALS AND METHODS

Effects of acute (1-day) and chronic treatments (14-days) with WETO (50, 100 and 200 mg/kg) on the behavioral changes in FST, TST and OFT, and the serum corticotrophin releasing factor (CRF), adrenocorticotropic hormone (ACTH) and corticosterone concentration were assessed in mice.

RESULTS

Chronic treatment (14-days) with WETO at the doses of 50, 100 and 200 mg/kg significantly decreased the immobility time in both FST (92.6, 85.1 and 77.4 s) and TST (84.8, 72.1 and 56.9 s). Acute treatment (1-day) with WETO at a dose of 200 mg/kg also markedly decreased the immobility time in both FST (81.7 s) and TST (73.2 s). However, all treatments did not affect the locomotor activity in the OFT. Moreover, FST induced a significant increase in serum CRF (5.8 ng/ml), ACTH (104.7 pg/ml) and corticosterone levels (37.3 ng/ml). Chronic treatment (14-days) with WETO decreased the serum CRF (200 mg/kg: 3.9 ng/ml) and corticosterone (50 mg/kg: 29.9 ng/ml; 100 mg/kg: 22.5 ng/ml; 200 mg/kg: 19.8 ng/ml) levels.

DISCUSSION AND CONCLUSION

These results clearly demonstrated the antidepressant effects of WETO in animal models of behavioral despair and suggested the mechanism involved in the neuroendocrine system.

From receptor balance to rational glucocorticoid therapy

Corticosteroids secreted as end product of the hypothalamic-pituitary-adrenal axis act like a double-edged sword in the brain. The hormones coordinate appraisal processes and decision making during the initial phase of a stressful experience and promote subsequently cognitive performance underlying the management of stress adaptation. This action exerted by the steroids on the initiation and termination of the stress response is mediated by 2 related receptor systems: mineralocorticoid receptors (MRs) and glucocorticoid receptors (GRs). The receptor types are unevenly distributed but colocalized in abundance in neurons of the limbic brain to enable these complementary hormone actions. This contribution starts from a historical perspective with the observation that phasic occupancy of GR during ultradian rhythmicity is needed to maintain responsiveness to corticosteroids. Then, during stress, initially MR activation enhances excitability of limbic networks that are engaged in appraisal and emotion regulation. Next, the rising hormone concentration occupies GR, resulting in reallocation of energy to limbic-cortical circuits with a role in behavioral adaptation and memory storage. Upon MR:GR imbalance, dysregulation of the hypothalamic-pituitary-adrenal axis occurs, which can enhance an individual's vulnerability. Imbalance is characteristic for chronic stress experience and depression but also occurs during exposure to synthetic glucocorticoids. Hence, glucocorticoid psychopathology may develop in susceptible individuals because of suppression of ultradian/circadian rhythmicity and depletion of endogenous corticosterone from brain MR. This knowledge generated from testing the balance hypothesis can be translated to a rational glucocorticoid therapy.

The selective glucocorticoid receptor antagonist CORT 108297 decreases neuroendocrine stress responses and immobility in the forced swim test

Pre-clinical and clinical studies have employed treatment with glucocorticoid receptor (GR) antagonists in an attempt to limit the deleterious behavioral and physiological effects of excess glucocorticoids. Here, we examined the effects of GR antagonists on neuroendocrine and behavioral stress responses, using two compounds: mifepristone, a GR antagonist that is also a progesterone receptor antagonist, and CORT 108297, a specific GR antagonist lacking anti-progestin activity. Given its well-documented impact on neuroendocrine and behavioral stress responses, imipramine (tricyclic antidepressant) served as a positive control. Male rats were treated for five days with mifepristone (10mg/kg), CORT 108297 (30mg/kg and 60mg/kg), imipramine (10mg/kg) or vehicle and exposed to forced swim test (FST) or restraint stress. Relative to vehicle, imipramine potently suppressed adrenocorticotropin hormone (ACTH) responses to FST and restraint exposure. Imipramine also decreased immobility in the FST, consistent with antidepressant actions. Both doses of CORT 108297 potently suppressed peak corticosterone responses to FST and restraint stress. However, only the higher dose of CORT 108297 (60mg/kg) significantly decreased immobility in the FST. In contrast, mifepristone induced protracted secretion of corticosterone in response to both stressors, and modestly decreased immobility in the FST. Taken together, the data indicate distinct effects of each compound on neuroendocrine stress responses and also highlight dissociation between corticosterone responses and immobility in the FST. Within the context of the present study, our data suggest that CORT 108297 may be an attractive alternative for mitigating neuroendocrine and behavioral states associated with excess glucocorticoid secretion.

Glucocorticoid receptor deletion from the dorsal raphé nucleus of mice reduces dysphoria-like behavior and impairs hypothalamic-pituitary-adrenocortical axis feedback inhibition

Glucocorticoids can cause depression and anxiety. Mechanisms for glucocorticoid effects on mood are largely undefined. The dorsal raphé nucleus (DRN) produces the majority of serotonin in the brain, and expresses glucocorticoid receptors (GR). Because we previously showed that antidepressants used to treat depression and anxiety decrease DRN GR expression, we hypothesized that deleting DRN GR would have anxiolytic- and antidepressant-like effects. We also hypothesized that DRN GR deletion would disinhibit activity of the hypothalamic-pituitary-adrenal (HPA) axis. Adeno-associated virus pseudotype AAV2/9 expressing either Cre recombinase (DRNGRKO mice) or GFP (DRN-GFP mice) was injected into the DRN of floxed GR mice to test these hypotheses. Three weeks after injection, mice underwent 21 days of social defeat or control handling and were tested for anxiety-like behavior (open-field test, elevated-plus maze), depression-like behavior [sucrose preference, forced-swim test (FST), tail-suspension test (TST)], social interaction, and circadian and stress-induced HPA activity. DRN GR deletion decreased anxiety-like behavior in control but not in defeated mice. DRN GR deletion decreased FST and tended to decrease TST despair-like behavior in both control and defeated mice, but did not affect sucrose preference. Exploration of social (a novel mouse) as well as neutral (an empty box) targets was increased in DRNGRKO mice, suggesting that DRN GR deletion also promotes active coping. DRN GR deletion increased stress-induced HPA activity without strongly altering circadian HPA activity. We have shown a novel role for DRN GR to mediate anxiety- and despair-like behavior and to regulate HPA negative feedback during acute stress.

Adult hippocampal neurogenesis in depression: behavioral implications and regulation by the stress system

Adult hippocampal neurogenesis, the birth of new neurons in the dentate gyrus of the adult brain, can be regulated by stress and antidepressant treatment, and has consistently been implicated in the behavioral neurobiology of stress-related disorders, especially depression and anxiety. A reciprocal relationship between hippocampal neurogenesis and the hypothalamus-pituitary-adrenal (HPA) axis has recently been suggested, which may play a crucial role in the development and in the resolution of depressive symptoms. This chapter will review some of the existing evidence for stress- and antidepressant-induced changes in adult hippocampal neurogenesis, and critically evaluate the behavioral effects of these changes for depression and anxiety. The potential role of neurogenesis as a neurobiological mechanism for sustained remission from depressive symptoms will be discussed, integrating existing data from clinical studies, animal work, and cellular models. The effect of glucocorticoid hormones and the glucocorticoid receptor (GR) will thereby be evaluated as a central mechanism by which stress and antidepressant may exert their opposing effects on neurogenesis, and ultimately, on mood and behavior.

Metabolic disturbances connecting obesity and depression

Obesity markedly increases the odds of developing depression. Depressed mood not only impairs motivation, quality of life and overall functioning but also increases the risks of obesity complications. Abdominal obesity is a better predictor of depression and anxiety risk than overall adipose mass. A growing amount of research suggests that metabolic abnormalities stemming from central obesity that lead to metabolic disease may also be responsible for the increased incidence of depression in obesity. As reviewed here, a higher mass of dysfunctional adipose tissue is associated with several metabolic disturbances that are either directly or indirectly implicated in the control of emotions and mood. To better comprehend the development of depression in obesity, this review pulls together select findings addressing the link between adiposity, diet and negative emotional states and discusses the evidence that alterations in glucocorticoids, adipose-derived hormones, insulin and inflammatory signaling that are characteristic of central obesity may be involved.

Disrupting hypothalamic glucocorticoid receptors causes HPA axis hyperactivity and excess adiposity

The glucocorticoid receptor (GR) regulates hypothalamic-pituitary-adrenal (HPA) axis activity during the stress response. The paraventricular nucleus (PVN) is a major site of negative feedback to coordinate the degree of the HPA axis activity with the magnitude of the exposed stressor. To define the function of endogenous PVN GR, we used Cre-loxP technology to disrupt different GR exons in Sim1-expressing neurons of the hypothalamus. GR exon 2-deleted mice (Sim1Cre-GRe2Δ) demonstrated 43% loss of PVN GR compared with an 87% GR loss in exon 3-deleted mice (Sim1Cre-GRe3Δ). Sim1Cre-GRe3Δ mice display stunted growth at birth but develop obesity in adulthood and display impaired stress-induced glucose release. We observed elevated basal and stress-induced corticosterone levels in Sim1Cre-GRe3Δ mice, compared with control and Sim1Cre-GRe2Δ mice, and impaired dexamethasone suppression, indicating an inability to negatively regulate corticosterone secretion. Sim1Cre-GRe3Δ mice also showed increased CRH mRNA in the PVN, increased basal plasma ACTH levels, and reduced locomotor behavior. We observed no differences in Sim1Cre-GRe2Δ mice compared with control mice in any measure. Our behavioral data suggest that GR deletion in Sim1-expressing neurons has no effect on anxiety or despair-like behavior under basal conditions. We conclude that loss of PVN GR results in severe HPA axis hyperactivity and Cushing's syndrome-like phenotype but does not affect anxiety and despair-like behaviors.

Are BDNF and glucocorticoid activities calibrated?

One hypothesis to account for the onset and severity of neurological disorders is the loss of trophic support. Indeed, changes in the levels and activities of brain-derived neurotrophic factor (BDNF) occur in numerous neurodegenerative and neuropsychiatric diseases. A deficit promotes vulnerability whereas a gain of function facilitates recovery by enhancing survival, synapse formation and synaptic plasticity. Implementation of 'BDNF therapies', however, faces numerous methodological and pharmacokinetic issues. Identifying BDNF mimetics that activate the BDNF receptor or downstream targets of BDNF signaling represent an alternative approach. One mechanism that shows great promise is to study the interplay of BDNF and glucocorticoid hormones, a major class of natural steroid secreted during stress reactions and in synchrony with circadian rhythms. While small amounts of glucocorticoids support normal brain function, excess stimulation by these steroid hormones precipitates stress-related affective disorders. To date, however, because of the paucity of knowledge of underlying cellular mechanisms, deleterious effects of glucocorticoids are not prevented following extreme stress. In the present review, we will discuss the complementary roles shared by BDNF and glucocorticoids in synaptic plasticity, and delineate possible signaling mechanisms mediating these effects.

Sensitivity of depression-like behavior to glucocorticoids and antidepressants is independent of forebrain glucocorticoid receptors

The location of glucocorticoid receptors (GR) implicated in depression symptoms and antidepressant action remains unclear. Forebrain glucocorticoid receptor deletion on a C57B/6×129×CBA background (FBGRKO-T50) reportedly produces increased depression-like behavior and elevated glucocorticoids. We further hypothesized that forebrain GR deletion would reduce behavioral sensitivity to glucocorticoids and to antidepressants. We have tested this hypothesis in mice with calcium calmodulin kinase IIα-Cre-mediated forebrain GR deletion derived from a new founder on a pure C57BL/6 background (FBGRKO-T29-1). We measured immobility in forced swim or tail suspension tests after manipulating glucocorticoids or after dose response experiments with tricyclic or monoamine oxidase inhibitor antidepressants. Despite forebrain GR deletion that was at least as rapid and more extensive than reported in the mixed-strain FBGRKO-T50 mice (Boyle et al. 2005), and possibly because of their different founder, our FBGRKO-T29-1 mice did not exhibit increases in depression-like behavior or adrenocortical axis hormones. Nevertheless, FBGRKO-T29-1 mice were at least as sensitive as floxed GR controls to the depressive effects of glucocorticoids and the effects of two different classes of antidepressants. FBGRKO-T29-1 mice also unexpectedly exhibited increased mineralocorticoid receptor (MR) gene expression. Our results reinforce prior evidence that antidepressant action does not require forebrain GR, and suggest a correlation between the absence of depression-like phenotype and combined MR up-regulation and central amygdala GR deficiency. Our findings demonstrate that GR outside the areas targeted in FBGRKO-T29-1 mice are involved in the depressive effects of glucocorticoids, and leave open the possibility that these GR populations also contribute to antidepressant action.

Site-specific modulation of brain glucocorticoid receptor and corticotropin-releasing hormone expression using lentiviral vectors

The glucocorticoid receptor (GR) and corticotropin-releasing hormone (CRH) are important molecular regulators of an individual's ability to respond to stressful stimuli in an adaptive manner. Impaired signaling of both GR and CRH often leads to dysfunction of the hypothalamic-pituitary-adrenal axis, which underlies the etiology of many affective disorders such as anxiety and depression. Studies focusing on how GR and CRH influence the stress response are limited as they generalize to broad brain regions, thus hindering identification of how specific CNS nuclei contribute to maladaptive stress responses. Our objective is to distinguish the site-specific involvement of GR and CRH in limbic regions involved in the stress response. With that intent, we use lentiviral (LV) vectors in combination with transgenic mouse lines, enabling us to modify expression of GR or CRH in a very localized manner. This paper describes the generation of several distinct LV vectors and transgenic mice models that will help further elucidate the site-specific actions of GR and CRH.

The disruption of Celf6, a gene identified by translational profiling of serotonergic neurons, results in autism-related behaviors

The immense molecular diversity of neurons challenges our ability to understand the genetic and cellular etiology of neuropsychiatric disorders. Leveraging knowledge from neurobiology may help parse the genetic complexity: identifying genes important for a circuit that mediates a particular symptom of a disease may help identify polymorphisms that contribute to risk for the disease as a whole. The serotonergic system has long been suspected in disorders that have symptoms of repetitive behaviors and resistance to change, including autism. We generated a bacTRAP mouse line to permit translational profiling of serotonergic neurons. From this, we identified several thousand serotonergic-cell expressed transcripts, of which 174 were highly enriched, including all known markers of these cells. Analysis of common variants near the corresponding genes in the AGRE collection implicated the RNA binding protein CELF6 in autism risk. Screening for rare variants in CELF6 identified an inherited premature stop codon in one of the probands. Subsequent disruption of Celf6 in mice resulted in animals exhibiting resistance to change and decreased ultrasonic vocalization as well as abnormal levels of serotonin in the brain. This work provides a reproducible and accurate method to profile serotonergic neurons under a variety of conditions and suggests a novel paradigm for gaining information on the etiology of psychiatric disorders.

Stress modulation of reconsolidation

Memories are consolidated and are inscribed as stable traces in the brain; however, once they are retrieved, they are rendered labile and can be modified in a process termed reconsolidation. Studies illustrate the power of behavioral stress and stress hormones to modulate memory processes while focusing on consolidation. However, sparse evidence indicates a critical role of stress in modulating reconsolidation. In this review, we discuss the effects of stress and stress-related neurotransmitter systems on reconsolidation of emotional and non-emotional types of memories. We show that although some general features underlie consolidation and reconsolidation, there is a possible dissimilarity between the two processes that may be dependent on factors such as the cognitive task employed, specific type of stressor, and the arousal state of the animal. The ability to disrupt or facilitate the reconsolidation of emotional and drug-related memories by stress exposure has important implications for the treatment of anxiety disorders linked to traumatic memories, such as post-traumatic stress disorder and of drug-of-abuse memories.

Glucocorticoid-related molecular signaling pathways regulating hippocampal neurogenesis

Stress and glucocorticoid hormones regulate hippocampal neurogenesis, but the molecular mechanisms underlying their effects are unknown. We, therefore, investigated the molecular signaling pathways mediating the effects of cortisol on proliferation, neuronal differentiation, and astrogliogenesis, in an immortalized human hippocampal progenitor cell line. In addition, we examined the molecular signaling pathways activated in the hippocampus of prenatally stressed rats, characterized by persistently elevated glucocorticoid levels in adulthood. In human hippocampal progenitor cells, we found that low concentrations of cortisol (100 nM) increased proliferation (+16%), decreased neurogenesis into microtubule-associated protein 2 (MAP2)-positive neurons (-24%) and doublecortin (Dcx)-positive neuroblasts (-21%), and increased differentiation into S100β-positive astrocytes (+23%). These effects were dependent on the mineralocorticoid receptor (MR) as they were abolished by the MR antagonist, spironolactone, and mimicked by the MR-agonist, aldosterone. In contrast, high concentrations of cortisol (100 μM) decreased proliferation (-17%) and neuronal differentiation into MAP2-positive neurons (-22%) and into Dcx-positive neuroblasts (-27%), without regulating astrogliogenesis. These effects were dependent on the glucocorticoid receptor (GR), blocked by the GR antagonist RU486, and mimicked by the GR-agonist, dexamethasone. Gene expression microarray and pathway analysis showed that the low concentration of cortisol enhances Notch/Hes-signaling, the high concentration inhibits TGFβ-SMAD2/3-signaling, and both concentrations inhibit Hedgehog signaling. Mechanistically, we show that reduced Hedgehog signaling indeed critically contributes to the cortisol-induced reduction in neuronal differentiation. Accordingly, TGFβ-SMAD2/3 and Hedgehog signaling were also inhibited in the hippocampus of adult prenatally stressed rats with high glucocorticoid levels. In conclusion, our data demonstrate novel molecular signaling pathways that are regulated by glucocorticoids in vitro, in human hippocampal progenitor cells, and by stress in vivo, in the rat hippocampus.

Antidepressant-like effects of young green barley leaf (Hordeum vulgare L.) in the mouse forced swimming test

BACKGROUND

Young green barley leaf is one of the richest sources of antioxidants and has been widely consumed for health management in Japan. In this study, we examined whether oral administration of young green barley leaf has an antidepressant effect on the forced swimming test in mice.

MATERIALS AND METHODS

Mice were individually forced to swim in an open cylindrical container, one hour after oral administration of young green barley leaf (400 or 1000 mg / kg) or imipramine (100 mg / kg). Expression of mRNA for nerve growth factor (NGF), brain-derived neurotrophic factor, and glucocorticoid receptor in the brain was analyzed using real-time quantitative polymerase chain reaction (PCR).

RESULTS

There was a significant antidepressant-like effect in the forced swimming test; both 400 and 1000 mg / kg young green barley leaves, as well as the positive control imipramine (100 mg / kg), reduced the immobility duration compared to the vehicle group. The expression of mRNA for NGF detected in the hippocampus immediately after the last swimming test was higher than that in the non-swimming group (Nil). Oral administration of imipramine suppressed this increase to the level of the Nil group. Young green barley leaf (400 and 1000 mg / kg) also showed a moderate decrease in the expression of mRNA for NGF, in a dose-dependent manner.

CONCLUSION

Oral administration of young green barley leaf is able to produce an antidepressant-like effect in the forced swimming test. Consequently it is possible that the antidepressant-like effects of the young green barley leaf are, at least in part, mediated by an inhibition of the increase in the hippocampus levels of NGF.

Sex, stress, and mood disorders: at the intersection of adrenal and gonadal hormones

The risk for neuropsychiatric illnesses has a strong sex bias, and for major depressive disorder (MDD), females show a more than 2-fold greater risk compared to males. Such mood disorders are commonly associated with a dysregulation of the hypothalamo-pituitary-adrenal (HPA) axis. Thus, sex differences in the incidence of MDD may be related with the levels of gonadal steroid hormone in adulthood or during early development as well as with the sex differences in HPA axis function. In rodents, organizational and activational effects of gonadal steroid hormones have been described for the regulation of HPA axis function and, if consistent with humans, this may underlie the increased risk of mood disorders in women. Other developmental factors, such as prenatal stress and prenatal overexposure to glucocorticoids can also impact behaviors and neuroendocrine responses to stress in adulthood and these effects are also reported to occur with sex differences. Similarly, in humans, the clinical benefits of antidepressants are associated with the normalization of the dysregulated HPA axis, and genetic polymorphisms have been found in some genes involved in controlling the stress response. This review examines some potential factors contributing to the sex difference in the risk of affective disorders with a focus on adrenal and gonadal hormones as potential modulators. Genetic and environmental factors that contribute to individual risk for affective disorders are also described. Ultimately, future treatment strategies for depression should consider all of these biological elements in their design.

Differential glucocorticoid receptor exon 1(B), 1(C), and 1(H) expression and methylation in suicide completers with a history of childhood abuse

BACKGROUND

Childhood abuse alters hypothalamic-pituitary-adrenal (HPA) function and increases the risk of suicide. Hippocampal glucocorticoid receptor (GR) activation regulates HPA activity, and human GR expression (hGR) is reduced in the hippocampus of suicide completers with a history of childhood abuse compared with controls. The abuse-related decrease in hGR expression associates with increased DNA methylation of the promoter of the hGR(1F) variant in the hippocampus.

METHODS

In this study, we investigated the expression and methylation levels of other hGR splice variants in the hippocampus and anterior cingulate gyrus in suicide completers with and without a history of childhood abuse and in controls. Expression levels were quantified using quantitative reverse-transcriptase polymerase chain reaction and promoter methylation was assessed by pyrosequencing.

RESULTS

In the hippocampus, the expression of total hGR and variants 1(B), 1(C), and 1(H) was decreased in suicide completers with histories of abuse compared with suicides with no histories of abuse and with control subjects. In the anterior cingulate gyrus, however, no group differences in hGR total or variant expression were found. Site-specific methylation in hGR1(B) and 1(C) promoter sequences were negatively correlated with total hGR messenger RNA, as well as with hGR1(B) and 1(C) expression. Luciferase assay showed that methylation in hGR promoter decreases transcriptional activity. In contrast, total and site-specific methylation in the hGR1(H) promoter was positively correlated with total hGR messenger RNA and hGR1(H) expression.

CONCLUSION

These findings suggest that early-life events alter the expression of several hGR variants in the hippocampus of suicide completers through effects on promoter DNA methylation.

Effects of environmental manipulations in genetically targeted animal models of affective disorders

Mental illness is the leading cause of disability worldwide. We are only just beginning to reveal and comprehend the complex interaction that exists between the genetic makeup of an organism and the potential modifying effect of the environment in which it lives, and how this translates into mediating susceptibility to neurological and psychiatric conditions. The capacity to address this issue experimentally has been facilitated by the availability of rodent models which allow the precise manipulation of genetic and environmental factors. In this review, we discuss the valuable nature of animal models in furthering our understanding of the relationship between genetic and environmental factors in affective illnesses, such as anxiety and depressive disorders. We first highlight the behavioral impairments exhibited by genetically targeted animal models of affective disorders, and then provide a discussion of the underlying neurobiology, focusing on animal models that involve exposure to stress. This is followed by a review of recent studies that report of beneficial effects of environmental manipulations such as environmental enrichment and enhanced physical activity and discuss the likely mechanisms that mediate those benefits.

Deletion of forebrain glucocorticoid receptors impairs neuroendocrine stress responses and induces depression-like behavior in males but not females

Dysfunction in central glucocorticoid signaling is implicated in hypothalamic-pituitary-adrenocortical (HPA) axis dysregulation and major depression. In comparison with men, women are twice as likely to suffer from depression and have heightened HPA axis responses to stress. We hypothesized that this striking increase in stress vulnerability in females may be because of sex differences in central glucocorticoid signaling. The current study tests the role of the forebrain type II glucocorticoid receptor (GR) on HPA axis function in female mice and depression-like behavior in both female and male mice. This was accomplished by using mice with selective deletion of GR in forebrain cortico-limbic sites including the prefrontal cortex, hippocampus, and basolateral amygdala (forebrain glucocorticoid receptor knockout mouse (FBGRKO)). In order to examine HPA axis function in female FBGRKO, we measured nadir, peak circadian and restraint-induced corticosterone concentrations in female FBGRKO. The data indicate that unlike male FBGRKO, basal and stress-induced corticosterone concentrations are not increased in female FBGRKO. Given the pronounced effect of central glucocorticoid signaling on mood, we also examined the necessity of corticolimbic GR on depression-like behavior with the sucrose preference and forced swim tests (FST) in male and female FBGRKO mice. Consistent with previous studies, male FBGRKO displayed increased depression-like behavior as indicated by greater immobility in the FST and decreased sucrose preference compared with littermate controls, effects that were not observed in females. Overall the findings indicate a marked sex difference in the function of forebrain GR on HPA axis regulation and depression-like behaviors, and may have implications for therapeutic approaches using GR-modulating drugs.

Inhibitory effects of corticosterone in the hypothalamic paraventricular nucleus (PVN) on stress-induced adrenocorticotrophic hormone secretion and gene expression in the PVN and anterior pituitary

Endogenous glucocorticoid negative-feedback influence on the hypothalamic-pituitary-adrenal (HPA) axis depends on glucocorticoid actions exerted on multiple glucocorticoid-sensitive tissues and differential glucocorticoid effects that are expressed within several distinct temporal domains. The relative contribution and underlying molecular mechanisms of action for the effects of location and timing of glucocorticoid exposure on HPA axis activity remain to be determined. In the present study, we examined the effects of acute exposure to corticosterone (CORT) at the level of the paraventricular nucleus (PVN) on the HPA axis response to a subsequent stressor in a short-term (1 h) timeframe. Intra-PVN CORT microinjection 1 h before restraint suppressed the adrenocorticotrophic hormone (ACTH) response and blunted restraint-induced corticotrophin-releasing hormone (CRH) heterogeneous nuclear (hn)RNA expression in the PVN and pro-opiomelanocortin hnRNA expression in the anterior pituitary (AP); however, it had no effect on restraint-induced plasma prolactin levels and c-fos mRNA expression (PVN and AP). This pattern of results suggests that CORT acts locally at the level of the PVN within a short-term timeframe to suppress stress-induced excitation-exocytosis coupling within CRH neurones and CRH gene induction without altering the stress-associated trans-synaptic input and intracellular signal transduction that converges on PVN c-fos gene induction. The present study is the first to demonstrate that an acute infusion of CORT into the PVN is sufficient to suppress the ACTH response to stress initiated 1 h after CORT infusion.

Lack of elevations in glucocorticoids correlates with dysphoria-like behavior after repeated social defeat

Activity of the hypothalamic-pituitary-adrenocortical (HPA) axis is often abnormal in depression and could hold clues for better treatment of this debilitating disease. However, it has been difficult to use HPA activity as a depression biomarker because both HPA hyperactivity and HPA hypoactivity have been reported in depression. Melancholic depression has typically been associated with HPA hyperactivity, while atypical depression has been linked with HPA hypoactivity. Many animal models of chronic stress recapitulate behavioral aberrations and elevated HPA activity that could represent a model for melancholic depression. However, there are no animal models that could be used to elucidate the etiology or treatment of atypical depression. We have used repeated social defeat in mice to test the hypothesis that this chronic stress would induce dysphoria-like behavior associated with HPA hypoactivity in a subset of subjects. Intruder mice were placed in the home cage of an aggressive resident mouse for 5 min/d for 30 days. The majority of intruder mice had elevated basal plasma corticosterone (High Morning Corticosterone, or HMC) and adrenal 11β hydroxylase mRNA levels relative to control mice that were handled daily. However, a subset of intruder mice (Low Morning Corticosterone; LMC) exhibited basal plasma corticosterone and 11β hydroxylase mRNA levels that were indistinguishable from control levels. Significant changes in emotional behavior only occurred in LMC mice, which exhibited anxiety-like increases in activity and defecation during tail suspension and anhedonia-like decreases in sucrose preference. Relative to HMC mice, LMC mice also showed increases in gene expression of mineralocorticoid receptor in CA2 hippocampus, consistent with the possibility that HPA activity in this group is constrained by increased sensitivity to glucocorticoid negative feedback. LMC mice also exhibited increased c-fos gene expression compared to HMC mice in the paraventricular hypothalamus and lateral septum suggesting that central pathways fail to habituate to chronic stress even though adrenocortical activity is not stimulated. We conclude that LMC mice showed adrenocortical hyporesponsiveness, which in combination with the behavioral abnormalities in this group may represent a model for the HPA hypoactivity associated with atypical depression.

Serum brain-derived neurotrophic factor and glucocorticoid receptor levels in lymphocytes as markers of antidepressant response in major depressive patients: a pilot study

Depressive patients often have altered cortisol secretion, an effect that likely derives from impaired activity of the glucocorticoid receptor (GR), the main regulator of the hypothalamus-pituitary-adrenal (HPA) axis. Glucocorticoids reduce the levels of brain-derived neurotrophic factor (BDNF), a downstream target of antidepressants. Antidepressants promote the transcriptional activity of cyclic adenosine monophosphate (cAMP) response element binding protein (CREB), a regulator of BDNF expression. To identify potential biomarkers for the onset of antidepressant action in depressive patients, GR and phospho-CREB (pCREB) levels in lymphocytes and serum BDNF levels were repeatedly measured during the course of antidepressant treatment. Thirty-four depressed outpatients (10 male and 24 female) were treated with venlafaxine (75mg/day), and individuals exhibiting a 50% reduction in their baseline 17-Item Hamilton Depression Rating Scale score by the 6th week of treatment were considered responders. Responders showed an early improvement in parallel with a rise in BDNF levels during the first two weeks of treatment. Non-responders showed increased GR levels by the third week and reduced serum BDNF by the sixth week of treatment. In contrast, venlafaxine did not affect levels of pCREB. We conclude that levels of BDNF in serum and GR levels in lymphocytes may represent biomarkers that could be used to predict responses to venlafaxine treatment.

Disruption of the neuregulin 1 gene in the rat alters HPA axis activity and behavioral responses to environmental stimuli

Exposure to stress can result in an increased risk for psychiatric disorders, especially among genetically predisposed individuals. Neuregulin 1 (NRG1) is a susceptibility gene for schizophrenia and is also associated with psychotic bipolar disorder. In the rat, the neurons of the hypothalamic paraventricular nucleus show strong expression of Nrg1 mRNA. In patients with schizophrenia, a single nucleotide polymorphism in the 5' region of NRG1 interacts with psychosocial stress to affect reactivity to expressed emotion. However, there is virtually no information on the role of NRG1 in hypothalamic-pituitary-adrenal axis function, and whether the protein is expressed in the paraventricular nucleus is unknown. The present studies utilize a unique line of Nrg1 hypomorphic rats (Nrg1(Tn)) generated by gene trapping with the Sleeping Beauty transposon. We first established that the Nrg1(Tn) rats displayed reduced expression of both the mRNA and protein corresponding to the Type II NRG1 isoform. After confirming, using wild type animals, that Type II NRG1 is expressed in the neurocircuitry involved in regulating hypothalamic-pituitary-adrenal axis responses to environmental stimuli, the Nrg1(Tn) rats were then used to test the hypothesis that altered expression of Type II NRG1 disrupts stress regulation and reactivity. In support of this hypothesis, Nrg1(Tn) rats have disrupted basal and acute stress recovery corticosterone secretion, differential changes in expression of glucocorticoid receptors in the pituitary, paraventricular nucleus and hippocampus, and a failure to habituate to an open field. Together, these findings point to NRG1 as a potential novel regulator of neuroendocrine responses to stress as well as behavioral reactivity.

11β-hydroxysteroid dehydrogenases and the brain: from zero to hero, a decade of progress

Glucocorticoids have profound effects on brain development and adult CNS function. Excess or insufficient glucocorticoids cause myriad abnormalities from development to ageing. The actions of glucocorticoids within cells are determined not only by blood steroid levels and target cell receptor density, but also by intracellular metabolism by 11β-hydroxysteroid dehydrogenases (11β-HSD). 11β-HSD1 regenerates active glucocorticoids from their inactive 11-keto derivatives and is widely expressed throughout the adult CNS. Elevated hippocampal and neocortical 11β-HSD1 is observed with ageing and causes cognitive decline; its deficiency prevents the emergence of cognitive defects with age. Conversely, 11β-HSD2 is a dehydrogenase, inactivating glucocorticoids. The major central effects of 11β-HSD2 occur in development, as expression of 11β-HSD2 is high in fetal brain and placenta. Deficient feto-placental 11β-HSD2 results in a life-long phenotype of anxiety and cardiometabolic disorders, consistent with early life glucocorticoid programming.

Susceptibility to the long-term anxiogenic effects of an acute stressor is mediated by the activation of the glucocorticoid receptors

The specificity of the response of an organism is an important variable influencing stress-related parameters and psychopathological states. We have shown that trait anxiety in C57BL/6 mice, determined by their emergence latencies in the free choice open field test, positively correlates with the long-term behavioral and neuroendocrinological changes induced by a stressor. Here, we show that this interindividual variability is caused by a different reactivity of the hypothalamus-pituitary-adrenal (HPA) axis upon exposure to a stressor. Mice with high trait anxiety (long emergence latency, LEL) display a more pronounced stress-induced activation of the HPA axis than mice with low trait anxiety (short emergence latency, SEL). Moreover, stress-induced activation of tyrosine hydroxylase and corticotropin-releasing hormone occurred in LEL but not SEL mice. In search of the molecular mechanisms underlying these differences, we found that under non-stressed conditions mRNA and protein levels of the glucocorticoid receptor in the hippocampus were higher in LEL mice compared to SEL mice. Also, systemic injection of the glucocorticoid receptor antagonist RU486 decreased the stress-induced activation of the HPA axis and the long-term anxiogenic effects of stress observed in LEL mice. Finally, the rewarding properties of cocaine were enhanced in LEL mice compared to SEL mice, suggesting a causal link between trait anxiety, stress activity and the behavioral responses to drugs of addiction.

Sex-specific neuroendocrine and behavioral phenotypes in hypomorphic Type II Neuregulin 1 rats

Neuregulin 1 (NRG1) is an important growth factor involved in the development and plasticity of the central nervous system. Since its identification as a susceptibility gene for schizophrenia, several transgenic mouse models have been employed to elucidate the role NRG1 may play in the pathogenesis of psychiatric disease. Unfortunately very few studies have included females, despite the fact that some work suggests that the consequences of disrupted NRG1 expression may be sex-specific. Here, we used Nrg1 hypomorphic (Nrg1(Tn)) Fischer rats to demonstrate sex-specific changes in neuroendocrine and behavioral phenotypes as a consequence of reduced Type II NRG1 expression. We have previously shown that male Nrg1(Tn) rats have increased basal corticosterone levels, and fail to habituate to an open field despite normal overall levels of locomotor activity. The current studies show that, in contrast, female Nrg1(Tn) rats exhibit enhanced suppression of corticosterone levels following an acute stress, reduced locomotor activity, and enhanced habituation to novel environments. Furthermore, we also show that female, but not male, Nrg1(Tn) rats have impaired prepulse inhibition. Finally, we provide evidence that sex-specific changes are not likely attributable to major disruptions in the hypothalamic-pituitary-gonadal axis, as measures of pubertal onset, estrous cyclicity, and reproductive capacity were unaltered in female Nrg1(Tn) rats. Our results provide further support for both the involvement of NRG1 in the control of hypothalamic-pituitary-adrenal axis function and the sex-specific nature of this relationship.

Behavioral insights from mouse models of forebrain--and amygdala-specific glucocorticoid receptor genetic disruption

Genetic modulation of glucocorticoid receptor (GR) function in the brain using transgenic and gene knockout mice has yielded important insights into many aspects of GR effects on behavior and neuroendocrine responses, but significant limitations regarding interpretation of region-specific and temporal requirements remain. Here, we summarize the behavioral phenotype associated with two knockout mouse models to define the role of GRs specifically within the forebrain and amygdala. We report that forebrain-specific GR knockout mice exhibit impaired negative feedback regulation of the hypothalamic-pituitary-adrenal (HPA) axis and increased despair- and anxiety-like behaviors. In addition, mice with a disruption of GR specifically within the central nucleus of the amygdala (CeA) are deficient in conditioned fear behavior. Overall, these models serve as beneficial tools to better understand the biology of GR signaling in the normal stress response and in mood disorders.

Aging of the hypothalamic-pituitary-adrenal axis in nonhuman primates with depression-like and aggressive behavior

We have investigated aging of the hypothalamic-pituitary-adrenal (HPA) axis in female rhesus monkeys that differ in adaptive behavior. Plasma cortisol (F) and dehydroepiandrosterone sulfate (DHEA-S) concentrations under basal conditions and under acute psycho-emotional stress were evaluated in blood plasma of young (6-8 years) and old (20-27 years) female rhesus monkeys with various types of adaptive behavior (aggressive, depression-like, and average). We have found that the age-related changes in the HPA axis of monkeys with depression-like behavior were accompanied by the maximal absolute and relative hypercortisolemia under both basal conditions and stress. Moreover, young aggressive monkeys, in comparison with young monkeys of other behavior groups, demonstrated the highest plasma levels of DHEA-S and the lowest molar ratios between F and DHEA-S. Thus, age-related dysfunctions of the HPA axis are associated with adaptive behavior of animals.

The prefrontal-limbic network in depression: Modulation by hypothalamus, basal ganglia and midbrain

The anterior cingulate cortex, amygdala and hippocampus form part of an interconnected prefrontal neocortical and limbic archicortical network that is dysregulated in major depressive disorders (MDD). Modulation of this prefrontal-limbic network (PLN) is principally through the hypothalamus, basal ganglia and midbrain. Here the likely mechanisms by which these modulations are affected are described and the implications of their failure for depression associated with suicidal diathesis, late-life and psychoses discussed.

Regulation of glucocorticoid receptor transcription and nuclear translocation during single and repeated immobilization stress

We have previously reported reduced glucocorticoid receptor (GR) mRNA levels in the hippocampus and hypothalamic paraventricular nucleus (PVN) during repeated immobilization, which is potentially associated with persistent activation of the hypothalamic-pituitary-adrenocortical axis. We used in situ hybridization and Western blot to examine the transcriptional regulation of the GR gene, GR nuclear translocation, and expression of cytosolic heat shock protein 90 (hsp90), a chaperone protein essential for GR nuclear translocation, in the hippocampus, PVN, and anterior pituitary (AP) during single immobilization (sIMO) and the final immobilization on d 7 after daily IMO for 6 days (rIMO). As with GR mRNA, GR heteronuclear RNA levels decreased in the hippocampus and PVN and increased in the AP during sIMO and rIMO, indicating that the GR mRNA levels in these regions were regulated at the transcriptional level. In both sIMO and rIMO, nuclear GR levels were significantly increased in the hippocampus, medial basal hypothalamus (MBH), and AP. However, GR nuclear translocation was reduced in the hippocampus, unchanged in the MBH, and enhanced in the AP during rIMO, as compared with sIMO. Cytosolic hsp90 expression was unchanged in the hippocampus and MBH, whereas it significantly increased in the AP at 30 min during rIMO but not during sIMO. These results suggest that the site-specific changes in GR nuclear translocation during sIMO vs. rIMO are partially linked to hsp90 responses to immobilization. The reduced nuclear translocation of GR in the hippocampus during rIMO may reflect decreased glucocorticoid-mediated negative feedback on the hypothalamic-pituitary-adrenocortical axis.

Forebrain glucocorticoid receptor overexpression increases environmental reactivity and produces a stress-induced spatial discrimination deficit

Reactivity to environmental stressors influences vulnerability to neurological and psychiatric illnesses, but little is known about molecular mechanisms that control this reactivity. Since mice with forebrain-specific glucocorticoid receptor overexpression (GRov mice) display anxiety-like behaviors in novel environments and have difficulty adjusting to change in memory tasks, we hypothesized that these may be facets of a broader phenotype of altered reactivity to environmental demands. Male GRov and wild-type mice were tested in a multiple-trial object interaction test comprising environmental and object habituation and spatial and object novelty trials. Half the mice received restraint stress before testing. GRov mice exhibited more locomotor activity and, without stress, more object interaction than wild-type mice. Following acute stress, GRov mice no longer showed increased object exploration. While stress dampened responses to object novelty in both groups, GRov mice were particularly impaired in discrimination of spatial novelty post-stress. These data demonstrate that GRov leads to increased environmental reactivity, responsiveness to salience, and vulnerability to stress-induced cognitive deficits. They implicate forebrain glucocorticoid receptor (GR) in fine-tuning interactions with the environment and the interplay of emotional salience, coping abilities, and cognitive function.

Cyclin-dependent kinase 5 modulates the transcriptional activity of the mineralocorticoid receptor and regulates expression of brain-derived neurotrophic factor

Glucocorticoids, major end effectors of the stress response, play an essential role in the homeostasis of the central nervous system (CNS) and contribute to memory consolidation and emotional control through their intracellular receptors, the glucocorticoid and mineralocorticoid receptors. Cyclin-dependent kinase 5 (CDK5), on the other hand, plays important roles in the morphogenesis and functions of the central nervous system, and its aberrant activation has been associated with development of neurodegenerative disorders. We previously reported that CDK5 phosphorylated the glucocorticoid receptor and modulated its transcriptional activity. Here we found that CDK5 also regulated mineralocorticoid receptor-induced transcriptional activity by phosphorylating multiple serine and threonine residues located in its N-terminal domain through physical interaction. Aldosterone and dexamethasone, respectively, increased and suppressed mRNA/protein expression of brain-derived neurotrophic factor (BDNF) in rat cortical neuronal cells, whereas the endogenous glucocorticoid corticosterone showed a biphasic effect. CDK5 enhanced the effect of aldosterone and dexamethasone on BDNF expression. Because this neurotrophic factor plays critical roles in neuronal viability, synaptic plasticity, consolidation of memory, and emotional changes, we suggest that aberrant activation of CDK5 might influence these functions through corticosteroid receptors/BDNF.

Transient early-life forebrain corticotropin-releasing hormone elevation causes long-lasting anxiogenic and despair-like changes in mice

During development, early-life stress, such as abuse or trauma, induces long-lasting changes that are linked to adult anxiety and depressive behavior. It has been postulated that altered expression of corticotropin-releasing hormone (CRH) can at least partially account for the various effects of stress on behavior. In accord with this hypothesis, evidence from pharmacological and genetic studies has indicated the capacity of differing levels of CRH activity in different brain areas to produce behavioral changes. Furthermore, stress during early life or adulthood causes an increase in CRH release in a variety of neural sites. To evaluate the temporal and spatial specificity of the effect of early-life CRH exposure on adult behavior, the tetracycline-off system was used to produce mice with forebrain-restricted inducible expression of CRH. After transient elevation of CRH during development only, behavioral testing in adult mice revealed a persistent anxiogenic and despair-like phenotype. These behavioral changes were not associated with alterations in adult circadian or stress-induced corticosterone release but were associated with changes in CRH receptor type 1 expression. Furthermore, the despair-like changes were normalized with antidepressant treatment. Overall, these studies suggest that forebrain-restricted CRH signaling during development can permanently alter stress adaptation leading to increases in maladaptive behavior in adulthood.

Shaping adult phenotypes through early life environments

A major question in the biology of stress and environmental adaptation concerns the neurobiological basis of how neuroendocrine systems governing physiological regulatory mechanisms essential for life (metabolism, immune response, organ function) become harmful. The current view is that a switch from protection to damage occurs when vulnerable phenotypes are exposed to adverse environmental conditions. In accordance with this theory, sequelae of early life social and environmental stressors, such as childhood abuse, neglect, poverty, and poor nutrition, have been associated with the emergence of mental and physical illness (i.e., anxiety, mood disorders, poor impulse control, psychosis, and drug abuse) and an increased risk of common metabolic and cardiovascular diseases later in life. Evidence from animal and human studies investigating the associations between early life experiences (including parent-infant bonding), hypothalamus-pituitary-adrenal axis activity, brain development, and health outcome provide important clues into the neurobiological mechanisms that mediate the contribution of stressful experiences to personality development and the manifestation of illness. This review summarizes our current molecular understanding of how early environment influences brain development in a manner that persists through life and highlights recent evidence from rodent studies suggesting that maternal care in the first week of postnatal life establishes diverse and stable phenotypes in the offspring through epigenetic modification of genes expressed in the brain that shape neuroendocrine and behavioral stress responsivity throughout life.

Plasma transcortin influences endocrine and behavioral stress responses in mice

Glucocorticoids are released after hypothalamus-pituitary-adrenal axis stimulation by stress and act both in the periphery and in the brain to bring about adaptive responses that are essential for life. Dysregulation of the stress response can precipitate psychiatric diseases, in particular depression. Recent genetic studies have suggested that the glucocorticoid carrier transcortin, also called corticosteroid-binding globulin (CBG), may have an important role in stress response. We have investigated the effect of partial or total transcortin deficiency using transcortin knockout mice on hypothalamus-pituitary-adrenal axis functioning and regulation as well as on behaviors linked to anxiety and depression traits in animals. We show that CBG deficiency in mice results in markedly reduced total circulating corticosterone at rest and in response to stress. Interestingly, free corticosterone concentrations are normal at rest but present a reduced surge after stress in transcortin-deficient mice. No differences were detected between transcortin-deficient mice for anxiety-related traits. However, transcortin-deficient mice display increased immobility in the forced-swimming test and markedly enhanced learned helplessness after prolonged uncontrollable stress. The latter is associated with an approximately 30% decrease in circulating levels of free corticosterone as well as reduced Egr-1 mRNA expression in hippocampus in CBG-deficient mice. Additionally, transcortin-deficient mice show no sensitization to cocaine-induced locomotor responses, a well described corticosterone-dependent test. Thus, transcortin deficiency leads to insufficient glucocorticoid signaling and altered behavioral responses after stress. These findings uncover the critical role of plasma transcortin in providing an adequate endocrine and behavioral response to stress.

Mechanisms generating diversity in glucocorticoid receptor signaling

Glucocorticoids regulate diverse biological processes throughout the body via the glucocorticoid receptor (GR). Ligand-bound GR translocates into the nucleus and can elicit changes in gene expression by direct contact with the DNA or by protein-protein interactions with other transcription factors. The GR can also mediate rapid nongenomic signaling events initiated in the cytoplasm. In this chapter, we review the biological and physiological implications of glucocorticoids, the GR, and many of the signal transduction mechanisms that mediate their action.