Impaired type II glucocorticoid-receptor function in mice bearing antisense RNA transgene

Context is key: glucocorticoid receptor and corticosteroid therapeutics in outcomes after traumatic brain injury

Traumatic brain injury (TBI) is a global health burden, and survivors suffer functional and psychiatric consequences that can persist long after injury. TBI induces a physiological stress response by activating the hypothalamic-pituitary-adrenal (HPA) axis, but the effects of injury on the stress response become more complex in the long term. Clinical and experimental evidence suggests long lasting dysfunction of the stress response after TBI. Additionally, pre- and post-injury stress both have negative impacts on outcome following TBI. This bidirectional relationship between stress and injury impedes recovery and exacerbates TBI-induced psychiatric and cognitive dysfunction. Previous clinical and experimental studies have explored the use of synthetic glucocorticoids as a therapeutic for stress-related TBI outcomes, but these have yielded mixed results. Furthermore, long-term steroid treatment is associated with multiple negative side effects. There is a pressing need for alternative approaches that improve stress functionality after TBI. Glucocorticoid receptor (GR) has been identified as a fundamental link between stress and immune responses, and preclinical evidence suggests GR plays an important role in microglia-mediated outcomes after TBI and other neuroinflammatory conditions. In this review, we will summarize GR-mediated stress dysfunction after TBI, highlighting the role of microglia. We will discuss recent studies which target microglial GR in the context of stress and injury, and we suggest that cell-specific GR interventions may be a promising strategy for long-term TBI pathophysiology.

Role of glucocorticoid receptor mutations in hypertension and adrenal gland hyperplasia

Hypertension is one of the leading causes of premature death in humans and exhibits a complex aetiology including environmental and genetic factors. Mutations within the glucocorticoid receptor (GR) can cause glucocorticoid resistance, which is characterized by several clinical features like hypercortisolism, hypokalaemia, adrenal hyperplasia and hypertension. Altered glucocorticoid receptor signalling further affects sodium and potassium homeostasis as well as blood pressure regulation and cell proliferation and differentiation that influence organ development and function. In salt-sensitive hypertension, excessive renal salt transport and sympathetic nervous system stimulation may occur simultaneously, and, thus, both the mineralocorticoid receptor (MR) and the GR-signalling may be implicated or even act interdependently. This review focuses on identified GR mutations in human primary generalized glucocorticoid resistance (PGGR) patients and their related clinical phenotype with specific emphasis on adrenal gland hyperplasia and hypertension. We compare these findings to mouse and rat mutants harbouring genetically engineered mutations to further dissect the cause and/or the consequence of clinical features which are common or different.

Excess sucrose intake during pregnancy programs fetal brain glucocorticoid receptor expression in female but not male C57Bl/6J mice

BACKGROUND

Sex-specific mechanisms explaining the association between mothers with obesity and the development of obesity in children are poorly characterized. Permanent changes in fetal brain glucocorticoid receptor (GR) expression caused by exposure to overnutrition in utero may program aberrant energy homeostasis, thereby predisposing the offspring to obesity. This study explores sex differences in brain GR expression using an established mouse model of overnutrition during pregnancy.

METHODS

Female C57Bl/6J mice were fed control (CON) or high-fat-high-sucrose (HFHS) diets. Dam cholesterol, insulin, and triglycerides were measured by colorimetric assays. Fetal corticosterone exposure was measured by placental Abca1, Hsd11β1, Hsd11β2, and brain Nr3c1 (GR); Pomc expression measured by RT-qPCR.

RESULTS

Female, but not male, HFHS fetuses had 46% decreased brain GR and twofold increased Pomc expression. There was decreased Abca1 and Hsd11β1 but not Hsd11β2 expression in HFHS placentas. Caloric and sucrose intake, but not fat intake, in dams inversely correlated with fetal GR expression in both sexes. Excess sucrose consumption by dams inversely correlated with female fetal GR and directly correlated with female fetal Pomc expression.

CONCLUSIONS

Excess sucrose consumption in pregnant dams caused lower GR and higher Pomc expression in the female fetal brain. Clinical investigation of excess sucrose intake during pregnancy and its subsequent effect on hypothalamic-pituitary-adrenal axis activity and appetite in offspring may lead to novel, sex-specific obesity prevention strategies in the development of obesity in children.

Effect of Biochar on TDR-Based Volumetric Soil Moisture Measurements in a Loamy Sand Podzolic Soil

Considering the increased interests in biochar (BC) as a soil amendment and a growing media substrate in agriculture, we evaluated the effect of BC incorporation on TDR (time-domain reflectometer)-based volumetric soil moisture content (VSMC) estimations in a loamy sand podzolic soil. Two commercial BC types (powdered—BCP, and granular—BCG) were mixed in different rates (w/w) with a podzolic soil. The dielectric constants measured using a TDR cable tester (MOHR CT 100) were converted to VSMC. Three commonly used models: (i) Topp’s equation, M-1; (ii) mixing model, M-2; and (iii) the forest soil model, M-3, were used. The accuracy of the estimated VSMC using these three models was statistically compared with measured VSMC. BCP at lower rates produced very similar results to the actual VSMC with M-1 and M-2 but deviated with increasing rates. The M-3 showed a non-linear relationship with measured VSMC. In BCG treatments, all models overestimated the VSMC. BCG rates higher than 15% (w/w) resulted in highly attenuated TDR waveforms and the signal was completely dissipated when rates higher than 50% (w/w) were used (typical application for field soils is less than 5% w/w). These results showed that predictions of the soil moisture content based on the soil dielectric constant might not be feasible for tested podzolic soils amended at high BC rates.

Fetal glucocorticoid receptor (Nr3c1) deficiency alters the landscape of DNA methylation of murine placenta in a sex-dependent manner and is associated to anxiety-like behavior in adulthood

Prenatal stress defines long-term phenotypes through epigenetic programming of the offspring. These effects are potentially mediated by glucocorticoid release and by sex. We hypothesized that the glucocorticoid receptor (Gr, Nr3c1) fashions the DNA methylation profile of offspring. Consistent with this hypothesis, fetal Nr3c1 heterozygosity leads to altered DNA methylation landscape in fetal placenta in a sex-specific manner. There was a significant overlap of differentially methylated genes in fetal placenta and adult frontal cortex in Nr3c1 heterozygotes. Phenotypically, Nr3c1 heterozygotes show significantly more anxiety-like behavior than wildtype. DNA methylation status of fetal placental tissue is significantly correlated with anxiety-like behavior of the same animals in adulthood. Thus, placental DNA methylation might predict behavioral phenotypes in adulthood. Our data supports the hypothesis that Nr3c1 influences DNA methylation at birth and that DNA methylation in placenta correlates with adult frontal cortex DNA methylation and anxiety-like phenotypes.

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

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

Glucocorticoid-induced changes in glucocorticoid receptor mRNA and protein expression in the human placenta as a potential factor for altering fetal growth and development

Glucocorticoids (GCs) control essential metabolic processes in virtually every cell in the body and play a vital role in the development of fetal tissues and organ systems. The biological actions of GCs are mediated via glucocorticoid receptors (GRs), the cytoplasmic transcription factors that regulate the transcription of genes involved in placental and fetal growth and development. Several experimental studies have demonstrated that fetal exposure to high maternal GC levels early in gestation is associated with adverse fetal outcomes, including low birthweight, intrauterine growth restriction and anatomical and structural abnormalities that may increase the risk of cardiovascular, metabolic and neuroendocrine disorders in adulthood. The response of the fetus to GCs is dependent on gender, with female fetuses becoming hypersensitive to changes in GC levels whereas male fetuses develop GC resistance in the environment of high maternal GCs. In this paper we review GR function and the physiological and pathological effects of GCs on fetal development. We propose that GC-induced changes in the placental structure and function, including alterations in the expression of GR mRNA and protein levels, may play role in inhibiting in utero fetal growth.

Animal models of major depression and their clinical implications

Major depressive disorder is a common, complex, and potentially life-threatening mental disorder that imposes a severe social and economic burden worldwide. Over the years, numerous animal models have been established to elucidate pathophysiology that underlies depression and to test novel antidepressant treatment strategies. Despite these substantial efforts, the animal models available currently are of limited utility for these purposes, probably because none of the models mimics this complex disorder fully. It is presumable that psychiatric illnesses, such as affective disorders, are related to the complexity of the human brain. Here, we summarize the animal models that are used most commonly for depression, and discuss their advantages and limitations. We discuss genetic models, including the recently developed optogenetic tools and the stress models, such as the social stress, chronic mild stress, learned helplessness, and early-life stress paradigms. Moreover, we summarize briefly the olfactory bulbectomy model, as well as models that are based on pharmacological manipulations and disruption of the circadian rhythm. Finally, we highlight common misinterpretations and often-neglected important issues in this field.

Behavioral and neurochemical characterization of TrkB-dependent mechanisms of agomelatine in glucocorticoid receptor-impaired mice

Growing evidence indicates that impairment of the stress response, in particular the negative feedback regulation mechanism exerted by the hypothalamo-pituitary-adrenal (HPA) axis, might be responsible for the hippocampal atrophy observed in depressed patients. Antidepressants, possibly through the activation of BDNF signaling, may enhance neuroplasticity and restore normal hippocampal functions. In this context, glucocorticoid receptor-impaired (GR-i) mice-a transgenic mouse model of reduced GR-induced negative feedback regulation of the HPA axis-were used to investigate the role of BDNF/TrkB signaling in the behavioral and neurochemical effects of the new generation antidepressant drug, agomelatine. GR-i mice exhibited marked alterations in depressive-like and anxiety-like behaviors, together with a decreased cell proliferation and altered levels of neuroplastic and epigenetic markers in the hippocampus. GR-i mice and their wild-type littermates were treated for 21 days with vehicle, agomelatine (50mg/kg/day; i.p) or the TrkB inhibitor Ana-12 (0.5mg/kg/day, i.p) alone, or in combination with agomelatine. Chronic treatment with agomelatine resulted in antidepressant-like effects in GR-i mice and reversed the deficit in hippocampal cell proliferation and some of the alterations of mRNA plasticity markers in GR-i mice. Ana-12 blocked the effect of agomelatine on motor activity as well as its ability to restore a normal hippocampal cell proliferation and expression of neurotrophic factors. Altogether, our findings indicate that agomelatine requires TrkB signaling to reverse some of the molecular and behavioral alterations caused by HPA axis impairment.

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.

Behavioral and molecular alterations in mice resulting from chronic treatment with dexamethasone: relevance to depression

Chronic stress, the administration of glucocorticoids and the prolonged activation of glucocorticoid receptors (GRs) are reported to induce affective changes in humans and rodents that resemble a depressive state. However, data concerning the behavioral and molecular effects of the selective activation of specific GRs are limited, and the conclusions derived remain debatable. In this study, our goal was to investigate the behavioral and molecular changes following the prolonged activation of GRs in mice via exposure to the specific agonist dexamethasone (DEX). C57BL/6J mice were injected daily with DEX (4 mg/kg, i.p.) or saline, and the behavior of the animals was assessed in the following paradigms: the forced swimming test (FST), the light-dark box test, the saccharin preference test and activity boxes. The mRNA expression levels of the corticosteroid receptors mineralocorticoid (MR, Nr3c2) and glucocorticoid (GR, Nr3c1), selected stress dependent genes and glial markers were analyzed in the prefrontal cortex, hippocampus and striatum. DEX-treated mice exhibited a variety of depression-like behaviors: increased time of immobility in the FST, a reduced preference for saccharin consumption and increased anxiety-like behavior. Behavioral alterations were accompanied by a decrease in the mRNA expression of GR and the increased expression of Fkbp5 and Sgk1 in the prefrontal cortex, hippocampus and striatum of DEX-treated mice. Furthermore, our results indicate a decrease in the mRNA expression of glutamate aspartate transporter (GLAST, Slc1a3), an astroglial cell marker, in the hippocampus and prefrontal cortex. These results demonstrate that the prolonged activation of GR receptors induced a depression-like state in mice, activated stress-related genes and induced a decrease in the mRNA expression of GLAST, an astroglial marker, in the prefrontal cortex and hippocampus. Together, the results reported here challenge several hypotheses concerning the role of GRs in the development of behavioral and molecular alterations relevant to stress-related disorders, such as depression, under the same experimental conditions.

Agomelatine: mechanism of action and pharmacological profile in relation to antidepressant properties

Agomelatine behaves both as a potent agonist at melatonin MT1 and MT2 receptors and as a neutral antagonist at 5-HT2C receptors. Accumulating evidence in a broad range of experimental procedures supports the notion that the psychotropic effects of agomelatine are due to the synergy between its melatonergic and 5-hydroxytryptaminergic effects. The recent demonstration of the existence of heteromeric complexes of MT1 and MT2 with 5-HT2C receptors at the cellular level may explain how these two properties of agomelatine translate into a synergistic action that, for example, leads to increases in hippocampal proliferation, maturation and survival through modulation of multiple cellular pathways (increase in trophic factors, synaptic remodelling, glutamate signalling) and key targets (early genes, kinases). The present review focuses on the pharmacological properties of this novel antidepressant. Its mechanism of action, strikingly different from that of conventional classes of antidepressants, opens perspectives towards a better understanding of the physiopathological bases underlying depression.

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

The meso-cortico-limbic system, via dopamine release, encodes the rewarding and reinforcing properties of natural rewards. It is also activated in response to abused substances and is believed to support drug-related behaviors. Dysfunctions of this system lead to several psychiatric conditions including feeding disorders and drug addiction. These disorders are also largely influenced by environmental factors and in particular stress exposure. Stressors activate the corticotrope axis ultimately leading to glucocorticoid hormone (GCs) release. GCs bind the glucocorticoid receptor (GR) a transcription factor ubiquitously expressed including within the meso-cortico-limbic tract. While GR within dopamine-innervated areas drives cocaine's behavioral responses, its implication in responses to other psychostimulants such as amphetamine has never been clearly established. Moreover, while extensive work has been made to uncover the role of this receptor in addicted behaviors, its contribution to the rewarding and reinforcing properties of food has yet to be investigated. Using mouse models carrying GR gene inactivation in either dopamine neurons or in dopamine-innervated areas, we found that GR in dopamine responsive neurons is essential to properly build amphetamine-induced conditioned place preference and locomotor sensitization. c-Fos quantification in the nucleus accumbens further confirmed defective neuronal activation following amphetamine injection. These diminished neuronal and behavioral responses to amphetamine may involve alterations in glutamate transmission as suggested by the decreased MK801-elicited hyperlocomotion and by the hyporeactivity to glutamate of a subpopulation of medium spiny neurons. In contrast, GR inactivation did not affect rewarding and reinforcing properties of food suggesting that responding for natural reward under basal conditions is preserved in these mice.

Glucocorticoids in multiple sclerosis and experimental autoimmune encephalomyelitis

Glucocorticoids exert a variety of immunomodulatory activities. Since changes in glucocorticoid homeostasis impact on susceptibility to autoimmune diseases, and synthetic glucocorticoids are widely used in the treatment of multiple sclerosis, a detailed understanding of their mechanism of action is desirable. Experimental autoimmune encephalomyelitis is a common animal model that mirrors many hallmarks of multiple sclerosis, a chronic inflammatory disease of the CNS with presumed autoimmune origin. Experimental autoimmune encephalomyelitis has been instrumental for many years in studying multiple sclerosis, revealing the blood-brain barrier, the microglia and T-cell apoptosis as major targets of glucocorticoids in this disease. Despite the great advances in the field, the answers to many questions concerning the mechanism of glucocorticoids; for example, the contribution of nongenomic effects or the cell-type specificity of their action, remain elusive. This review will critically discuss what we have learned so far from the analysis of animal models of the molecular mode of therapeutic and endogenous glucocorticoid action in multiple sclerosis. With this knowledge in mind, we should be able to further improve the management of multiple sclerosis using this class of drugs.

Deficiency of FK506-binding protein (FKBP) 51 alters sleep architecture and recovery sleep responses to stress in mice

FK506-binding protein 51 (FKBP51) is a co-chaperone of the glucocorticoid receptor, functionally linked to its activity via an ultra-short negative feedback loop. Thus, FKBP51 plays an important regulatory role in the hypothalamic-pituitary-adrenocortical (HPA) axis necessary for stress adaptation and recovery. Previous investigations illustrated that HPA functionality is influenced by polymorphisms in the gene encoding FKBP51, which are associated with both increased protein levels and depressive episodes. Because FKBP51 is a key molecule in stress responses, we hypothesized that its deletion impacts sleep. To study FKBP51-involved changes in sleep, polysomnograms of FKBP51 knockout (KO) mice and wild-type (WT) littermates were compared at baseline and in the recovery phase after 6-h sleep deprivation (SD) and 1-h restraint stress (RS). Using another set of animals, the 24-h profiles of hippocampal free corticosterone levels were also determined. The most dominant effect of FKBP51 deletion appeared as increased nocturnal wake, where the bout length was significantly extended while non-rapid eye movement sleep (NREMS) and rapid eye movement sleep were rather suppressed. After both SD and RS, FKBP51KO mice exhibited less recovery or rebound sleep than WTs, although slow-wave activity during NREMS was higher in KOs, particularly after SD. Sleep compositions of KOs were nearly opposite to sleep profiles observed in human depression. This might result from lower levels of free corticosterone in FKBP51KO mice, confirming reduced HPA reactivity. The results indicate that an FKBP51 deletion yields a pro-resilience sleep phenotype. FKBP51 could therefore be a therapeutic target for stress-induced mood and sleep disorders.

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.

Role of the hypothalamic-pituitary-adrenal axis in developmental programming of health and disease

Adverse environments during the fetal and neonatal development period may permanently program physiology and metabolism, and lead to increased risk of diseases in later life. Programming of the hypothalamic-pituitary-adrenal (HPA) axis is one of the key mechanisms that contribute to altered metabolism and response to stress. Programming of the HPA axis often involves epigenetic modification of the glucocorticoid receptor (GR) gene promoter, which influences tissue-specific GR expression patterns and response to stimuli. This review summarizes the current state of research on the HPA axis and programming of health and disease in the adult, focusing on the epigenetic regulation of GR gene expression patterns in response to fetal and neonatal stress. Aberrant GR gene expression patterns in the developing brain may have a significant negative impact on protection of the immature brain against hypoxic-ischemic encephalopathy in the critical period of development during and immediately after birth.

Beyond the monoaminergic hypothesis: neuroplasticity and epigenetic changes in a transgenic mouse model of depression

The monoamine hypothesis of depression has dominated our understanding of both the pathophysiology of depression and the action of pharmacological treatments for the last decades, and it has led to the production of several generations of antidepressant agents. However, there are serious limitations to the current monoamine theory, and additional mechanisms, including hypothalamic-pituitary-adrenal (HPA) axis dysfunctions, as well as neurodegenerative and inflammatory alterations, are potentially associated with the pathogenesis of mood disorders. Moreover, new data have recently indicated that epigenetic mechanisms such as histone modifications and DNA methylation could affect diverse pathways leading to depression-like behaviours in animal models. In a transgenic mouse model of depression, in which a downregulation of glucocorticoid receptors (GR) causes a deficit in the HPA axis feedback control, besides alterations in monoamine neurotransmission and neuroplasticity, we found modifications in the expression of many proteins involved in epigenetic regulation, as well as clock genes, in the hippocampus and the frontal cortex, that might be central in the genesis of depressive-like behaviours.

Association between reduced expression of hippocampal glucocorticoid receptors and cognitive dysfunction in a rat model of traumatic brain injury due to lateral head acceleration

Expression of hippocampal glucocorticoid receptors (GRs) and spatial learning and memory were observed in rat model of diffuse traumatic brain injury (TBI) due to lateral head acceleration with an aim at investigating the relation between GRs expression and cognitive deficits. Immunohistochemical staining, Western blotting, and RT-PCR indicated that down-regulation of GRs expression occurred in the hippocampus among TBI-rats which demonstrated reduced performance of learning and memory in Morris water maze. As the GRs expression bounced up, the cognitive function approached to normal. It is concluded that reduced expression of hippocampal GRs was closely associated with learning and memory deficits in TBI-rats. Hippocampal GRs was involved in the biochemical mechanisms of cognitive deficits after TBI.

Hypothalamic Fkbp51 is induced by fasting, and elevated hypothalamic expression promotes obese phenotypes

To discover hypothalamic genes that might play a role in regulating energy balance, we carried out a microarray screen for genes induced by a 48-h fast in male C57Bl/6J mouse hypothalamus. One such gene was Fkbp51 (FK506 binding protein 5; Locus NP_034350). The product of this gene is of interest because it blocks glucocorticoid action, suggesting that fasting-induced elevation of this gene in the hypothalamus may reduce glucocorticoid negative feedback, leading to elevated glucocorticoid levels, thus promoting obese phenotypes. Subsequent analysis demonstrated that a 48-h fast induces Fkbp51 in ventromedial, paraventricular, and arcuate hypothalamic nuclei of mice and rats. To assess if hypothalamic Fkbp51 promotes obesity, the gene was transferred to the hypothalamus via an adeno-associated virus vector. Within 2 wk following Fkbp51 overexpression, mice on a high-fat diet exhibited elevated body weight, without hyperphagia, relative to mice receiving the control mCherry vector. Body weight remained elevated for more than 8 wk and was associated with elevated corticosterone and impaired glucose tolerance. These studies suggest that elevated hypothalamic Fkbp51 promotes obese phenotypes.

Early-life forebrain glucocorticoid receptor overexpression increases anxiety behavior and cocaine sensitization

BACKGROUND

Genetic factors and early-life adversity are critical in the etiology of mood disorders and substance abuse. Because of their role in the transduction of stress responses, glucocorticoid hormones and their receptors could serve as both genetic factors and mediators of environmental influences. We have shown that constitutive overexpression of the glucocorticoid receptor (GR) in forebrain results in increased emotional reactivity and lability in mice. Here, we asked whether there was a critical period for the emergence of this phenotype.

METHODS

We generated a mouse line with inducible GR overexpression specifically in forebrain. Anxiety-like behaviors and cocaine-induced sensitization were assessed in adult mice following GR overexpression during different periods in development. The molecular basis of the behavioral phenotype was examined using microarray analyses of dentate gyrus and nucleus accumbens.

RESULTS

Transient overexpression of GR during early life led to increased anxiety and cocaine sensitization, paralleling the phenotype of lifelong GR overexpression. This increased emotional reactivity was not observed when GR overexpression was induced after weaning. Glucocorticoid receptor overexpression in early life is sufficient to alter gene expression patterns for the rest of the animal's life, with dentate gyrus being more responsive than nucleus accumbens. The altered transcripts are implicated in GR and axonal guidance signaling in dentate gyrus and dopamine receptor signaling in nucleus accumbens.

CONCLUSIONS

Transient overexpression of GR early in life is both necessary and sufficient for inducing transcriptome-wide changes in the brain and producing a lifelong increase in vulnerability to anxiety and drugs of abuse.

FK506 binding protein 5 shapes stress responsiveness: modulation of neuroendocrine reactivity and coping behavior

BACKGROUND

The Hsp90 cochaperone FK506 binding protein 5 (FKBP5) is an established regulator of the glucocorticoid receptor (GR), and numerous genetic studies have linked it to stress-related diseases such as major depression or posttraumatic stress disorder. However, translational studies including genetic animal models are lacking.

METHODS

Mice deficient of FKBP5 were generated and analyzed in comparison with wildtype littermates. They were subjected to several test paradigms characterizing their emotionality, stress reactivity, and coping behavior as well as hypothalamus-pituitary-adrenal axis function and regulation. Moreover, protein expression of GR and FKBP5 was determined in different brain structures 8 days after stress exposure. The combined dexamethasone/corticotropin-releasing hormone test was performed both in mice and healthy human subjects of different FKBP5 genotypes. The GR function was evaluated by reporter gene assays.

RESULTS

Under basal conditions, deletion of FKBP5 did not change exploratory drive, locomotor activity, anxiety-related behavior, stress-coping, or depression-like behavior. After exposure to different acute stressors of sufficient intensity, however, it led to a more active coping behavior. Moreover, loss of FKBP5 decreased hypothalamus-pituitary-adrenal axis reactivity and GR expression changes in response to stressors. In mice and humans, the FKBP5 genotype also determined the outcome of the dexamethasone/corticotropin-releasing hormone test.

CONCLUSIONS

This study in mice and humans presents FKBP5 as a decisive factor for the physiological stress response, shaping neuroendocrine reactivity as well as coping behavior. This lends strong support to the concept emerging from human studies of FKBP5 as important factor governing gene-environment interactions relevant for the etiology of affective disorders.

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.

Annual Research Review: Transgenic mouse models of childhood-onset psychiatric disorders

Childhood-onset psychiatric disorders, such as attention deficit hyperactivity disorder (ADHD), autism spectrum disorder (ASD), mood disorders, obsessive compulsive spectrum disorders (OCSD), and schizophrenia (SZ), affect many school-age children, leading to a lower quality of life, including difficulties in school and personal relationships that persist into adulthood. Currently, the causes of these psychiatric disorders are poorly understood, resulting in difficulty diagnosing affected children, and insufficient treatment options. Family and twin studies implicate a genetic contribution for ADHD, ASD, mood disorders, OCSD, and SZ. Identification of candidate genes and chromosomal regions associated with a particular disorder provide targets for directed research, and understanding how these genes influence the disease state will provide valuable insights for improving the diagnosis and treatment of children with psychiatric disorders. Transgenic mouse models are one important approach in the study of human diseases, allowing for the use of a variety of experimental approaches to dissect the contribution of a specific chromosomal or genetic abnormality in human disorders. While it is impossible to model an entire psychiatric disorder in a single mouse model, these models can be extremely valuable in dissecting out the specific role of a gene, pathway, neuron subtype, or brain region in a particular abnormal behavior. In this review we discuss existing transgenic mouse models for childhood-onset psychiatric disorders. We compare the strength and weakness of various transgenic mouse models proposed for each of the common childhood-onset psychiatric disorders, and discuss future directions for the study of these disorders using cutting-edge genetic tools.

The anti-inflammatory and immunosuppressive effects of glucocorticoids, recent developments and mechanistic insights

Since the discovery of glucocorticoids in the 1940s and the recognition of their anti-inflammatory effects, they have been amongst the most widely used and effective treatments to control inflammatory and autoimmune diseases. However, their clinical efficacy is compromised by the metabolic effects of long-term treatment, which include osteoporosis, hypertension, dyslipidaemia and insulin resistance/type 2 diabetes mellitus. In recent years, a great deal of effort has been invested in identifying compounds that separate the beneficial anti-inflammatory effects from the adverse metabolic effects of glucocorticoids, with limited effect. It is clear that for these efforts to be effective, a greater understanding is required of the mechanisms by which glucocorticoids exert their anti-inflammatory and immunosuppressive actions. Recent research is shedding new light on some of these mechanisms and has produced some surprising new findings. Some of these recent developments are reviewed here.

Nuclear orphan receptor Nor-1 contributes to depressive behavior in the Wistar-Kyoto rat model of depression

The current study explored the effects of prolonged antidepressant treatment on mRNA levels of two nuclear receptors in specific brain regions of an animal model of depression, the Wistar-Kyoto (WKY) rat. Both nuclear receptors have been implicated in the development or treatment of depression. The expression of nuclear orphan receptor-1 (Nor-1), a member of the NR4A nuclear orphan receptor family, is induced by electroconvulsive shock, an effective treatment for depression. Deficit in the levels or function of the glucocorticoid receptor (GR) found in depressed patients has been causally implicated in depression, as this deficit is normalized by antidepressant treatments. Baseline levels of amygdalar Nor-1 and GR mRNA were higher in the WKYs compared to the comparison control Sprague-Dawley rats (SD). Prolonged treatment with the antidepressant desipramine (DMI) decreased the expression of both transcripts in the WKY strain concomitantly with decreased immobility in the forced swim test (FST) of depressive behavior. Using short hairpin RNA (shRNA) targeted against Nor-1, we investigated the direct contribution of elevated Nor-1 expression in the amygdala of WKY to their exaggerated depressive behavior in the FST. After validating the shRNA targeting of Nor-1 in vitro, Nor-1 shRNA containing vector was infused intracerebroventricularly, using a linear polyethylenimine (PEI)-containing in vivo gene delivery system. Repeated administration of Nor-1 shRNA ameliorated the depressive behavior of WKYs in the FST and decreased amygdalar Nor-1 mRNA levels without affecting GR mRNA levels. These data demonstrate that brain region-specific changes in GR expression in response to DMI are strain dependent and that elevated amygdalar Nor-1 expression can contribute to depressive behavior in the WKY model of depression.

Behavioural and neuroplastic effects of the new-generation antidepressant agomelatine compared to fluoxetine in glucocorticoid receptor-impaired mice

Major depression is associated with reduced hippocampal volume linked to stress and high glucocorticoid secretion. Glucocorticoid receptor-impaired (GR-i) mice, a transgenic model for affective disorders with hypothalamic-pituitary-adrenal (HPA) axis feedback control deficit, were used to assess the antidepressant-like effects of the mixed melatonin receptor agonist/5-HT(2C) receptor antagonist, agomelatine, compared to the selective 5-HT reuptake inhibitor (SSRI), fluoxetine, on hippocampal neurogenesis, GR and BDNF expression and antidepressant-responsive behaviour (tail suspension test, TST). GR-i and paired wild-type (WT) mice were given acute or chronic (21 d) treatment with these drugs. Both hippocampal cell proliferation and BDNF mRNA expression were down-regulated in GR-i mice, and these alterations were reversed by chronic agomelatine and fluoxetine treatments, whereas GR mRNA down-regulation was reversed only by agomelatine. Furthermore, chronic agomelatine, but not fluoxetine, increased survival of newly formed cells in the ventral part of the hippocampus without changing their phenotypic differentiation into neurons. In the TST, the enhanced immobility of GR-i mice was reduced to WT level by acute (but not chronic) fluoxetine and chronic (but not acute) agomelatine. These results indicate that agomelatine reversed the neuroplastic changes and helpless behaviour associated with HPA axis alterations in GR-i mice, suggesting neurobiological and behavioural effects mostly similar to those typically seen with classical antidepressants such as fluoxetine, but through clearly distinct mechanisms.

Gender-specific association of galanin polymorphisms with HPA-axis dysregulation, symptom severity, and antidepressant treatment response

Galanin (GAL) is an estrogen-inducible neuropeptide, highly expressed in brain regions reported to be involved in regulation of mood and anxiety. GAL possibly has a direct modulatory effect on hypothalamic-pituitary-adrenal (HPA)-axis regulation. Recent data from pharmacological and genetic studies indicate a significant function of GAL in stress-related disorders. By using a tag SNP approach covering the locus encoding preprogalanin (PPGAL), earlier findings of female-specific associations of polymorphisms in this locus with panic disorder were expanded to a larger sample of 268 outpatients with anxiety disorders (ADs). Within a larger sample of 541 inpatients with major depressive disorder (MDD), we then tested associations of one PPGAL tag SNP with specific depression symptom clusters and HPA-axis activity assessed by the combined dexamethasone-suppression/CRH-stimulation test both at inpatient admission and discharge (n=298). Gender specificity as well as dependence of the association on levels of circulating estrogens was analyzed. Genotyping revealed high linkage disequilibrium in the promoter area of the PPGAL gene, which includes several estrogen-response elements. Confirming earlier results, rs948854, tagging this promoter region, was associated with more severe anxiety pathology in female AD patients, but not in males. In premenopausal female MDD patients, the same allele of rs948854 was associated with more severe vegetative but not cognitive depressive symptoms at discharge and worse treatment response on antidepressant medication. Furthermore, this allele was associated with higher HPA-axis activity at admission. No significant case-control associations could be observed. However, because of power limitations of both patient samples, small effects cannot be excluded. The reported associations in independent samples of AD and MDD support an estrogen-dependent function of GAL in pathophysiology of anxiety and depression, affecting response to antidepressant treatment.

Aberrant REST-mediated transcriptional regulation in major depressive disorder

There is growing evidence that aberrant transcriptional regulation is one of the key components of the pathophysiology of mood disorders. The repressor element-1 silencing transcription factor (REST) is a negative regulator of genes that contain the repressor element-1 (RE-1) binding site. REST has many target genes, including corticotropin releasing hormone (CRH), brain-derived neurotrophic factor, serotonin 1A receptor, which are suggested to be involved in the pathophysiology of depression and the action of antidepressants. However, a potential role for REST-mediated transcriptional regulation in mood disorders remains unclear. In this study, we examined the mRNA levels of REST and its known and putative target genes, using quantitative real-time PCR in peripheral blood cells of patients with major depressive and bipolar disorders in both a current depressive and a remissive state. We found reduced mRNA expression of REST and increased mRNA expression of CRH, adenylate cyclase 5, and the tumor necrosis factor superfamily, member 12-13 in patients with major depressive disorder in a current depressive state, but not in a remissive state. Altered expression of these mRNAs was not found in patients with bipolar disorder. Our results suggest that the aberrant REST-mediated transcriptional regulation of, at least, CRH, adenylate cyclase 5, and tumor necrosis factor superfamily, member 12-13, might be state-dependent and associated with the pathophysiology of major depression.

Transcriptional and physiological responses to chronic ACTH treatment by the mouse kidney

We investigated the effects on urinary steroid and electrolyte excretion and renal gene expression of chronic infusions of ACTH in the mouse. ACTH caused a sustained increase in corticosteroid excretion; aldosterone excretion was only transiently elevated. There was an increase in the excretion of deoxycorticosterone, a weak mineralocorticoid, to levels of physiological significance. Nevertheless, we observed neither antinatriuresis nor kaliuresis in ACTH-treated mice, and plasma renin activity was not suppressed. We identified no changes in expression of mineralocorticoid target genes. Water turnover was increased in chronic ACTH-treated mice, as were hematocrit and hypertonicity: volume contraction is consistent with high levels of glucocorticoid. ACTH-treated mice exhibited other signs of glucocorticoid excess, such as enhanced weight gain and involution of the thymus. We identified novel ACTH-induced changes in 1) genes involved in vitamin D (Cyp27b1, Cyp24a1, Gc) and calcium (Sgk, Calb1, Trpv5) metabolism associated with calciuria and phosphaturia; 2) genes that would be predicted to desensitize the kidney to glucocorticoid action (Nr3c1, Hsd11b1, Fkbp5); and 3) genes encoding transporters of enzyme systems associated with xenobiotic metabolism and oxidative stress. Although there is evidence that ACTH-induced hypertension is a function of physiological cross talk between glucocorticoids and mineralocorticoids, the present study suggests that the major changes in electrolyte and fluid homeostasis and renal function are attributable to glucocorticoids. The calcium and organic anion metabolism pathways that are affected by ACTH may explain some of the known adverse effects associated with glucocorticoid excess.

Prenatal stress, glucocorticoids and the programming of adult disease

Numerous clinical studies associate an adverse prenatal environment with the development of cardio-metabolic disorders and neuroendocrine dysfunction, as well as an increased risk of psychiatric diseases in later life. Experimentally, prenatal exposure to stress or excess glucocorticoids in a variety of animal models can malprogram offspring physiology, resulting in a reduction in birth weight and subsequently increasing the likelihood of disorders of cardiovascular function, glucose homeostasis, hypothalamic–pituitary–adrenal (HPA) axis activity and anxiety-related behaviours in adulthood. During fetal development, placental 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2) provides a barrier to maternal glucocorticoids. Reduced placental 11β-HSD2 in human pregnancy correlates with lower birth weight and higher blood pressure in later life. Similarly, in animal models, inhibition or knockout of placental 11β-HSD2 lowers offspring birth weight, in part by reducing glucose delivery to the developing fetus in late gestation. Molecular mechanisms thought to underlie the programming effects of early life stress and glucocorticoids include epigenetic changes in target chromatin, notably affecting tissue-specific expression of the intracellular glucocorticoid receptor (GR). As such, excess glucocorticoids in early life can permanently alter tissue glucocorticoid signalling, effects which may have short-term adaptive benefits but increase the risk of later disease.

Hypothalamic-pituitary-adrenal axis dysregulation and behavioral analysis of mouse mutants with altered glucocorticoid or mineralocorticoid receptor function

Corticosteroid receptors are critical for the maintenance of homeostasis after both psychological and physiological stress. To understand the different roles and interactions of the glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) during stress, it is necessary to dissect the role of corticosteroid signaling at both the system and sub-system level. A variety of GR transgenic mouse lines have recently been used to characterize the role of GR in the CNS as a whole and particularly in the forebrain. We will describe both the behavioral and cellular/molecular implications of disrupting GR function in these animal models and describe the implications of this data for our understanding of normal endocrine function and stress adaptation. MRs in tight epithelia have a long established role in sodium homeostasis. Recently however, evidence has suggested that MRs in the limbic brain also play an important role in psychological stress. Just as with GR, targeted mutations in MR induce a variety of behavioral changes associated with stress adaptation. In this review, we will discuss the implications of this work on MR. Finally, we will discuss the possible interaction between MR and GR and how future work using double mutants (through conventional means or virus based gene alteration) will be needed to more fully understand how signaling through these two steroid receptors provides the adaptive mechanisms to deal with a variety of stressors.

Glucocorticoid receptor haploinsufficiency causes hypertension and attenuates hypothalamic-pituitary-adrenal axis and blood pressure adaptions to high-fat diet

Glucocorticoid hormones are critical to respond and adapt to stress. Genetic variations in the glucocorticoid receptor (GR) gene alter hypothalamic-pituitary-adrenal (HPA) axis activity and associate with hypertension and susceptibility to metabolic disease. Here we test the hypothesis that reduced GR density alters blood pressure and glucose and lipid homeostasis and limits adaption to obesogenic diet. Heterozygous GR^βgeo/+ mice were generated from embryonic stem (ES) cells with a gene trap integration of a β-galactosidase-neomycin phosphotransferase (βgeo) cassette into the GR gene creating a transcriptionally inactive GR fusion protein. Although GR^βgeo/+ mice have 50% less functional GR, they have normal lipid and glucose homeostasis due to compensatory HPA axis activation but are hypertensive due to activation of the renin-angiotensin-aldosterone system (RAAS). When challenged with a high-fat diet, weight gain, adiposity, and glucose intolerance were similarly increased in control and GR^βgeo/+ mice, suggesting preserved control of intermediary metabolism and energy balance. However, whereas a high-fat diet caused HPA activation and increased blood pressure in control mice, these adaptions were attenuated or abolished in GR^βgeo/+ mice. Thus, reduced GR density balanced by HPA activation leaves glucocorticoid functions unaffected but mineralocorticoid functions increased, causing hypertension. Importantly, reduced GR limits HPA and blood pressure adaptions to obesogenic diet.—Michailidou, Z., Carter, R. N., Marshall, E., Sutherland, H. G., Brownstein, D. G., Owen, E., Cockett, K., Kelly, V., Ramage, L., Al-Dujaili, E. A. S., Ross, M., Maraki, I., Newton, K., Holmes, M. C., Seckl, J. R., Morton, N. M., Kenyon, C. J., Chapman, K. E. Glucocorticoid receptor haploinsufficiency causes hypertension and attenuates hypothalamic-pituitary-adrenal axis and blood pressure adaptions to high-fat diet.

Central CRH system in depression and anxiety--evidence from clinical studies with CRH1 receptor antagonists

Basic and clinical studies provide convincing evidence that altered stress hormone regulation frequently observed in depression and anxiety are caused by elevated secretion of the hypothalamic neuropeptides corticotrophin releasing hormone (CRH) and vasopressin. CRH predominantly acts through CRH(1) receptors to produce a number of anxiety- and depression-like symptoms, which resulted in extensive validation of CRH(1) receptors as potential drug target. A number of orally available nonpeptidergic small molecules capable to pass the blood-brain barrier have been discovered; only some of these compounds entered clinical development. Here, we summarize results from clinical studies of two CRH(1) receptor antagonists. In the first study originally designed as a safety and tolerability trial in major depression, it was observed that the CRH(1) receptor antagonist NBI-30775/R121919 has a clinical profile comparable to the antidepressant paroxetine. In a second study the effect of another CRH(1) receptor antagonist, NBI-34041, upon stress hormone secretion in response to a psychosocial stressor was investigated. Administration of this compound reduced the stress-elicited secretion of cortisol. Both compounds, however, did not impair the CRH-induced release of ACTH and cortisol rejecting the possibility that the peripheral stress hormone system is impaired by CRH(1) receptor antagonists. From these studies we conclude that both CRH(1) receptor antagonists have psychotropic effects unrelated to their neuroendocrine action, which is in line with behavioral data obtained from transgenic mice. The results of the clinical studies underscore that CRH(1) receptor antagonists represent promising novel therapeutics in the psychopharmacology of depression and anxiety.

High-affinity CRF1 receptor antagonist NBI-34041: preclinical and clinical data suggest safety and efficacy in attenuating elevated stress response

There is an extensive evidence that corticotropin releasing factor (CRF) is hypersecreted in depression and anxiety, and blockade of CRF could have therapeutic benefit. We report preclinical data and the results of a clinical Phase I study with the novel nonpeptide CRF(1) antagonist NBI-34041/SB723620. Preclinical data conducted with different cell lines expressing human CRF receptors and in Wistar and Sprague-Dawley rats indicate that NBI-34041 is effective in reducing endocrine responses to pharmacological and behavioral challenge mediated by CRF(1) receptors. These specific properties and its well-documented safety profile enabled a clinical Phase I study with 24 healthy male subjects receiving NBI-34041 (10, 50, or 100 mg) or placebo for 14 days. Regulation of the hypothalamic-pituitary-adrenocortical (HPA) axis was evaluated by intravenous stimulation with 100 microg of human CRF. Psychosocial stress response was investigated with the Trier Social Stress Test (TSST). Treatment with NBI-34041 did not impair diurnal adrenocorticotropic hormone (ACTH) and cortisol secretion or CRF evoked ACTH and cortisol responses but attenuated the neuroendocrine response to psychosocial stress. These results suggest that NBI-34041 is safe and does not impair basal regulation of the HPA system but improves resistance against psychosocial stress. NBI-34041 demonstrates that inhibition of the CRF system is a promising target for drug development against depression and anxiety disorders.

Overexpressing the glucocorticoid receptor in forebrain causes an aging-like neuroendocrine phenotype and mild cognitive dysfunction

Repeated stress enhances vulnerability to neural dysfunction that is cumulative over the course of the lifespan. This dysfunction contributes to cognitive deficits observed during aging. In addition, aging is associated with dysregulation of the limbic-hypothalamic-pituitary-adrenal (LHPA) axis, leading to a delayed termination of the stress response. This delay, in turn, increases exposure to glucocorticoids and exacerbates the likelihood of neural damage. Here we asked whether similar effects could emerge at an early age as a result of genetic variations in the level or function of the brain glucocorticoid receptor (GR). We investigated the effect of forebrain-specific overexpression of GR on LHPA axis activity. Transgenic mice with GR overexpression in forebrain (GRov) display normal basal circulating adrenocorticotropic hormone and corticosterone levels. However, young GRov mice exhibit a number of LHPA alterations, including a blunted initial response to acute restraint stress followed by a delayed turn-off of the stress response. This deficit in negative feedback is paradoxical in the face of elevated GR levels, resembles the stress response in aged animals, and continues to worsen as GRov mice age. The neuroendocrine dysregulation in young GRov mice is coupled with a mild cognitive deficit, also consistent with the accelerated aging hypothesis. The molecular basis of this phenotype was examined using microarray analysis of the hippocampus, which revealed a broad downregulation of glutamate receptor signaling in GRov mice. Thus, even in the absence of chronic stress, elevation of GR gene expression can lead to an increased allostatic load and result in an "aging-like" phenotype in young animals.

Glucocorticoid receptor transgenic mice as models for depression

In the era of mutant mice generated as molecular in vivo models for complex pathogenetic and therapeutic aspects of particular human diseases, glucocorticoid receptor transgenic mice represent an interesting and promising tool. Animals carrying mutations of this receptor show alterations in the hypothalamic-pituitary-adrenal (HPA)-system, which are comparable to those observed in depressed patients. Furthermore, similarities that may model the human disease have been described on the behavioral and pharmacological level, which increase the impact of such mutants. In this review we summarize different approaches used to alter or eliminate glucocorticoid receptor expression and function, and discuss their relevance as models for depression.

The pituitary function of androgen receptor constitutes a glucocorticoid production circuit

Androgen receptor (AR) mediates diverse androgen actions, particularly reproductive processes in males and females. AR-mediated androgen signaling is considered to also control metabolic processes; however, the molecular basis remains elusive. In the present study, we explored the molecular mechanism of late-onset obesity in male AR null mutant (ARKO) mice. We determined that the obesity was caused by a hypercorticoid state. The negative feedback system regulating glucocorticoid production was impaired in ARKO mice. Male and female ARKO mice exhibited hypertrophic adrenal glands and glucocorticoid overproduction, presumably due to high levels of adrenal corticotropic hormone. The pituitary glands of the ARKO males had increased expression of proopiomelanocortin and decreased expression of the glucocorticoid receptor (GR). There were no overt structural abnormalities and no alteration in the distribution of cell types in the pituitaries of male ARKO mice. Additionally, there was normal production of the other hormones within the glucocorticoid feedback system in both the pituitary and hypothalamus. In a cell line derived from pituitary glands, GR expression was under the positive control of the activated AR. Thus, this study suggests that the activated AR supports the negative feedback regulation of glucocorticoid production via up-regulation of GR expression in the pituitary gland.

Life-Long Hippocampal Neurogenesis: Environmental, Pharmacological and Neurochemical Modulations

It is now well documented that active neurogenesis does exist throughout the life span in the brain of various species including human. Two discrete brain regions contain progenitor cells that are capable of differentiating into neurons or glia, the subventricular zone and the dentate gyrus of the hippocampal formation. Recent studies have shown that neurogenesis can be modulated by a variety of factors, including stress and neurohormones, growth factors, neurotransmitters, drugs of abuse, and also strokes and traumatic brain injuries. In particular, the hippocampal neurogenesis may play a role in neuroadaptation associated with pathologies, such as cognitive disorders and depression. The increased neurogenesis at sites of injury may represent an attempt by the central nervous system to regenerate after damage. We herein review the most significant data on hippocampal neurogenesis in brain under various pathological conditions, with a special attention to mood disorders including depression and addiction.

Tissue specific glucocorticoid receptor expression, a role for alternative first exon usage?

The CpG island upstream of the GR is highly structured and conserved at least in all the animal species that have been investigated. Sequence alignment of these CpG islands shows inter-species homology ranging from 64 to 99%. This 3.1kb CpG rich region upstream of the GR exon 2 encodes 5' untranslated mRNA regions. These CpG rich regions are organised into multiple first exons and, as we and others have postulated, each with its own promoter region. Alternative mRNA transcript variants are obtained by the splicing of these alternative first exons to a common acceptor site in the second exon of the GR. Exon 2 contains an in-frame stop codon immediately upstream of the ATG start codon to ensure that this 5' heterogeneity remains untranslated, and that the sequence and structure of the GR is unaffected. Tissue specific differential usage of exon 1s has been observed in a range of human tissues, and to a lesser extent in the rat and mouse. The GR expression level is tightly controlled within each tissue or cell type at baseline and upon stimulation. We suggest that no single promoter region may be capable of containing all the necessary promoter elements and yet preserve the necessary proximity to the transcription initiation site to produce such a plethora of responses. Thus we further suggest that alternative first exons each under the control of specific transcription factors control both the tissue specific GR expression and are involved in the tissue specific GR transcriptional response to stimulation. Spreading the necessary promoter elements over multiple promoter regions, each with an associated alternative transcription initiation site would appear to vastly increase the capacity for transcriptional control of GR.

Glucocorticoid "Programming" and PTSD Risk

Epidemiological data have linked an adverse fetal environment with increased risks of cardiovascular, metabolic, neuroendocrine, and psychiatric disorders in adulthood. Prenatal stress and/or glucocorticoid excess might underlie this link. In animal models, prenatal stress, glucocorticoid exposure or inhibition/knockout of 11 beta-hydroxysteroid dehydrogenase type 2 (11 beta-HSD-2), the feto-placental barrier to maternal glucocorticoids, reduces birth weight and causes permanent hypertension, hyperglycemia, increased hypothalamic-pituitary-adrenal (HPA) axis activity and behavior resembling of anxiety. In humans, 11 beta-HSD-2 gene mutations cause low birth weight and placental 11 beta-HSD-2 activity correlates directly with birth weight and inversely with infant blood pressure. Low birth weight babies have higher plasma cortisol levels throughout adult life, indicating HPA programming. In human pregnancy, severe maternal stress affects the offspring HPA axis and associates with neuropsychiatric disorders. Posttraumatic stress disorder (PTSD) appears to be a variable in the effects. Intriguingly, some of these effects appear to be 'inherited' into a further generation, itself unexposed to exogenous glucocorticoids at any point in the lifespan from fertilization, implying epigenetic marks persist into subsequent generation(s). Overall, the data suggest that prenatal exposure to excess glucocorticoids programs peripheral and CNS functions in adult life, predisposing to some pathologies, perhaps protecting from others, and these may be transmitted perhaps to one or two subsequent generations.

Mice with mutations in the HPA-system as models for symptoms of depression

Genetically engineered mice hold promise to help us understand the effects of enhanced or reduced gene activity upon behavior and metabolism. Because many basic and clinical studies suggest that alterations of the hypothalamic pituitary adrenocortical (HPA) system are involved in the development and course of depression, mouse mutants with genetic modifications of genes regulating the HPA system were generated. This review summarizes these effects and concludes that advanced technologies allowing for regional overexpression or inactivation of genes or introduction of polymorphisms into the mouse genome are well suited to explain individual symptoms or symptom patterns prevalent among depressives. However, as depression is a complex disorder in which minor changes of many genes as well as environmental factors (including epigenetic programming) play a causal role and determine the phenotype, the use of mice with single gene mutations needs to be critically discussed when attempting to create a genetic animal model of depression.

[Neurobiology of depression: new data]

Monoaminergic systems, and in particular serotoninergic neurons of the raphe system, have been involved in the physiopathology and treatment of major depression in a great number of studies. One of the most reproducible effects of antidepressant treatment is the increase of central 5-HT (serotonin) tone. However, the identification of novel potential therapeutic targets (neurohormones, neuropeptides) for treating depression has led to elaborating novel cellular and molecular concepts accounting for stress-related mood disorders. In particular, recent studies have demonstrated that chronic administration of all classes of antidepressants up-regulates neurogenesis in adult rodent hippocampus. The possibility that structural remodelling may contribute to the physiopathology of mood disorders provides new avenues of research toward understanding the cellular basis of mood disorders.

Mice with genetically altered glucocorticoid receptor expression show altered sensitivity for stress-induced depressive reactions

Altered glucocorticoid receptor (GR) signaling is a postulated mechanism for the pathogenesis of major depression. To mimic the human situation of altered GR function claimed for depression, we generated mouse strains that underexpress or overexpress GR, but maintain the regulatory genetic context controlling the GR gene. To achieve this goal, we used the following: (1) GR-heterozygous mutant mice (GR+/-) with a 50% GR gene dose reduction, and (2) mice overexpressing GR by a yeast artificial chromosome resulting in a twofold gene dose elevation. GR+/- mice exhibit normal baseline behaviors but demonstrate increased helplessness after stress exposure, a behavioral correlate of depression in mice. Similar to depressed patients, GR+/- mice have a disinhibited hypothalamic-pituitary-adrenal (HPA) system and a pathological dexamethasone/corticotropin-releasing hormone test. Thus, they represent a murine depression model with good face and construct validity. Overexpression of GR in mice evokes reduced helplessness after stress exposure, and an enhanced HPA system feedback regulation. Therefore, they may represent a model for a stress-resistant strain. These mouse models can now be used to study biological changes underlying the pathogenesis of depressive disorders. As a first potential molecular correlate for such changes, we identified a downregulation of BDNF protein content in the hippocampus of GR+/- mice, which is in agreement with the so-called neurotrophin hypothesis of depression.