Long-term antidepressant treatment reduces behavioural deficits in transgenic mice with impaired glucocorticoid receptor function

Precision Psychiatry Approach to Treat Depression and Anxiety Targeting the Stress Hormone System - V1b-antagonists as a Case in Point

The future of depression pharmacotherapy lies in a precision medicine approach that recognizes that depression is a disease where different causalities drive symptoms. That approach calls for a departure from current diagnostic categories, which are broad enough to allow adherence to the "one-size-fits-all" paradigm, which is complementary to the routine use of "broad-spectrum" mono-amine antidepressants. Similar to oncology, narrowing the overinclusive diagnostic window by implementing laboratory tests, which guide specifically targeted treatments, will be a major step forward in overcoming the present drug discovery crisis.A substantial subgroup of patients presents with signs and symptoms of hypothalamic-pituitary-adrenocortical (HPA) overactivity. Therefore, this stress hormone system was considered to offer worthwhile targets. Some promising results emerged, but in sum, the results achieved by targeting corticosteroid receptors were mixed.More specific are non-peptidergic drugs that block stress-responsive neuropeptides, corticotropin-releasing hormone (CRH), and arginine vasopressin (AVP) in the brain by antagonizing their cognate CRHR1-and V1b-receptors. If a patient's depressive symptomatology is driven by overactive V1b-signaling then a V1b-receptor antagonist should be first-line treatment. To identify the patient having this V1b-receptor overactivity, a neuroendocrine test, the so-called dex/CRH-test, was developed, which indicates central AVP release but is too complicated to be routinely used. Therefore, this test was transformed into a gene-based "near-patient" test that allows immediate identification if a depressed patient's symptomatology is driven by overactive V1b-receptor signaling. We believe that this precision medicine approach will be the next major innovation in the pharmacotherapy of depression.

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.

Tricyclic antidepressants target FKBP51 SUMOylation to restore glucocorticoid receptor activity

FKBP51 is an important inhibitor of the glucocorticoid receptor (GR) signaling. High FKBP51 levels are associated to stress-related disorders, which are linked to GR resistance. SUMO conjugation to FKBP51 is necessary for FKBP51's inhibitory action on GR. The GR/FKBP51 pathway is target of antidepressant action. Thus we investigated if these drugs could inhibit FKBP51 SUMOylation and therefore restore GR activity. Screening cells using Ni²⁺ affinity and in vitro SUMOylation assays revealed that tricyclic antidepressants- particularly clomipramine- inhibited FKBP51 SUMOylation. Our data show that clomipramine binds to FKBP51 inhibiting its interaction with PIAS4 and therefore hindering its SUMOylation. The inhibition of FKBP51 SUMOylation decreased its binding to Hsp90 and GR facilitating FKBP52 recruitment, and enhancing GR activity. Reduction of PIAS4 expression in rat primary astrocytes impaired FKBP51 interaction with GR, while clomipramine could no longer exert its inhibitory action. This mechanism was verified in vivo in mice treated with clomipramine. These results describe the action of antidepressants as repressors of FKBP51 SUMOylation as a molecular switch for restoring GR sensitivity, thereby providing new potential routes of antidepressant intervention.

Multi-View Mouse Social Behaviour Recognition With Deep Graphic Model

Home-cage social behaviour analysis of mice is an invaluable tool to assess therapeutic efficacy of neurodegenerative diseases. Despite tremendous efforts made within the research community, single-camera video recordings are mainly used for such analysis. Because of the potential to create rich descriptions for mouse social behaviors, the use of multi-view video recordings for rodent observations is increasingly receiving much attention. However, identifying social behaviours from various views is still challenging due to the lack of correspondence across data sources. To address this problem, we here propose a novel multi-view latent-attention and dynamic discriminative model that jointly learns view-specific and view-shared sub-structures, where the former captures unique dynamics of each view whilst the latter encodes the interaction between the views. Furthermore, a novel multi-view latent-attention variational autoencoder model is introduced in learning the acquired features, enabling us to learn discriminative features in each view. Experimental results on the standard CRMI13 and our multi-view Parkinson's Disease Mouse Behaviour (PDMB) datasets demonstrate that our proposed model outperforms the other state of the arts technologies, has lower computational cost than the other graphical models and effectively deals with the imbalanced data problem.

Expression profiling of precuneus layer III cathepsin D-immunopositive pyramidal neurons in mild cognitive impairment and Alzheimer's disease: Evidence for neuronal signaling vulnerability

The precuneus (PreC; Brodmann area 7), a key hub within the default mode network (DMN) displays amyloid and tau-containing neurofibrillary tangle (NFT) pathology during the onset of Alzheimer's disease (AD). PreC layer III projection neurons contain lysosomal hydrolase cathepsin D (CatD), a marker of neurons vulnerable to NFT pathology. Here we applied single population laser capture microdissection coupled with custom-designed microarray profiling to determine the genetic signature of PreC CatD-positive-layer III neurons accrued from postmortem tissue obtained from the Rush Religious Orders Study (RROS) cases with a premortem clinical diagnosis of no cognitive impairment (NCI), mild cognitive impairment (MCI) and AD. Expression profiling revealed significant differential expression of key transcripts in MCI and AD compared to NCI that underlie signaling defects, including dysregulation of genes within the endosomal-lysosomal and autophagy pathways, cytoskeletal elements, AD-related genes, ionotropic and metabotropic glutamate receptors, cholinergic enzymes and receptors, markers of monoamine neurotransmission as well as steroid-related transcripts. Pervasive defects in both MCI and AD were found in select transcripts within these key gene ontology categories, underscoring the vulnerability of these corticocortical projection neurons during the onset and progression of dementia. Select PreC dysregulated genes detected via custom-designed microarray analysis were validated using qPCR. In summary, expression profiling of PreC CatD -positive layer III neurons revealed significant dysregulation of a mosaic of genes in MCI and AD that were not previously appreciated in terms of their indication of systems-wide signaling defects in a key hub of the DMN.

Profound effects of glucocorticoid resistance on anxiety-related behavior in zebrafish adults but not in larvae

Previously, adult zebrafish with a mutation in the gene encoding the glucocorticoid receptor (Gr) were demonstrated to display anxiety- and depression-like behavior that could be reversed by treatment with antidepressant drugs, suggesting that this model system could be applied to study novel therapeutic strategies against depression. Subsequent studies with zebrafish larvae from this gr^s357 line and a different gr mutant have not confirmed these effects. To investigate this discrepancy, we have analyzed the anxiety-like behavior in 5 dpf gr^s357 larvae using a dark/tapping stimulus test and a light/dark preference test. In addition, gr^s357 adult fish were subjected to an open field test. The results showed that in larvae the mutation mainly affected general locomotor activity (decreased velocity in the dark/tapping stimulus test, increased velocity in the light/dark preference test). However, parameters considered specific readouts for anxiety-like behavior (response to dark/tapping stimulus, time spent in dark zone) were not altered by the mutation. In adults, the mutants displayed a profound increase in anxiety-like behavior (time spent in outer zone in open field test), besides changes in locomotor activity (decreased velocity, increased angular velocity and freezing time). We conclude that the neuronal circuitry involved in anxiety- and depression-like behavior is largely affected by deficient Gr signaling in adult fish but not in larvae, indicating that this circuitry only fully develops after the larval stages in zebrafish. This makes the zebrafish an interesting model to study the ontology of anxiety- and depression-related pathology which results from deficient glucocorticoid signaling.

'Central' Actions of Corticosteroid Signaling Suggested by Constitutive Knockout of Corticosteroid Receptors in Small Fish

This review highlights recent studies of the functional implications of corticosteroids in some important behaviors of model fish, which are also relevant to human nutrition homeostasis. The primary actions of corticosteroids are mediated by glucocorticoid receptor (GR) and mineralocorticoid receptor (MR), which are transcription factors. Zebrafish and medaka models of GR- and MR-knockout are the first constitutive corticosteroid receptor-knockout animals that are viable in adulthood. Similar receptor knockouts in mice are lethal. In this review, we describe the physiological and behavioral changes following disruption of the corticosteroid receptors in these models. The GR null model has peripheral changes in nutrition metabolism that do not occur in a mutant harboring a point mutation in the GR DNA-binding domain. This suggests that these are not “intrinsic” activities of GR. On the other hand, we propose that integration of visual responses and brain behavior by corticosteroid receptors is a possible “intrinsic”/principal function potentially conserved in vertebrates.

Genetic Variant of Glucocorticoid Receptor Gene at rs41423247 and Its Association with Major Depressive Disorder: A Case-Control Study

Background

Extensive distribution of glucocorticoid receptors (GCRs) in different brain areas along with disruption of hypothalamic-pituitary-adrenal (HPA) axis in major depressive disorder (MDD) and the cross talk between GCRs and HPA proposes genetic variants of GC receptor genes as potential contributors in MDD. Among the GCR polymorphisms, rs41423247, rs6195 and rs6189/rs6190 are suggested to be involved in MDD.

Materials and Methods

We investigated the association between rs41423247, rs6195 and rs6189/rs6190 and MDD in a case-control study. One hundred MDD patients along with 100 healthy individuals were enrolled in this study. genetic variants of rs41423247, rs6195 and rs6189/rs6190 were determined in extracted DNAs using PCR-RFLP.

Result

The prevalence of heterozygote and mutant carriers of rs41423247 were significantly and by 1.9 fold greater in cases versus controls (P=0.033; OR; 95%CI=1.9; 1.1-3.3). Moreover, carriers of the mutant (G) allele were by 1.8 fold more prevalent in MDD group (P=0.013; OR;95%CI=1.8; 1.1-2.8).

Conclusion

Specific carriers of rs41423247 might be more susceptible to developing MDD. This supports the hypothesis of the involvement of GCRs in pathophysiology of MDD.

A possible principal function of corticosteroid signaling that is conserved in vertebrate evolution: Lessons from receptor-knockout small fish

Corticosteroid receptors are critical for homeostasis maintenance, but understanding of the principal roles of the glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) throughout vertebrates is limited. Lines of constitutive GR-knockout zebrafish and MR-knockout medaka have recently been generated as the first adult-viable corticosteroid receptor-knockout animals, in contrast to the lethality of these receptor knockouts in mice. Here, we describe behavioral and physiological modifications following disruption of corticosteroid receptor function in these animal models. We suggest these data point toward a potentially conserved function of corticosteroid receptors in integrating brain-behavior and visual responses in vertebrates. Finally, we discuss how future work in cartilaginous fishes (Chondrichthyes) will further advance understanding of the unity and diversity of corticosteroid receptor function, since distinct orthologs of GR and MR derived from an ancestral corticoid receptor appear in these basal jawed vertebrates.

Mineralocorticoid and glucocorticoid receptor-mediated control of genomic responses to stress in the brain

Successful coping with stressful events involves adaptive and cognitive processes in the brain that make the individual more resilient to similar stressors in the future. Stressful events result in the secretion of glucocorticoids (GCs) from the adrenal glands into the blood stream. Early work proved instrumental for developing the concept that these hormones act in the brain to coordinate physiological and behavioral responses to stress through binding to two different GC-binding receptors. Once activated these receptors translocate to the nucleus where they act on target genes to facilitate (or sometimes inhibit) transcription. There are two types of receptors in the brain, the mineralocorticoid receptor (MR), and glucocorticoid receptor (GR). This review summarizes recent work which provides new insights regarding the genomic action of these receptors, both under baseline conditions and following exposure to acute stress. This work is discussed alongside the extensive studies undertaken in this field previously and new, and exciting "big data" studies which have generated a wealth of relevant data. The consequence of these new insights will challenge existing assumptions about the role of MRs and GRs and pave the way for the implementation of novel and improved methodologies to identify the role these corticosteroid receptors have in stress-related behavioral adaptation.

Biological Mechanisms of Cancer-Induced Depression

Patients with cancer are more likely to develop depression than the general population, which negatively impacts their quality of life and prognosis. In order to identify effective antidepressants catered toward cancer patients, the biology of depression in the context of cancer must be well-understood. Many theories have emerged postulating the mechanisms underlying the development of depressive disorder. Here, we review the role inflammation, a hyperactive hypothalamic-pituitary-adrenal (HPA) axis, and glutamate excitotoxicity may play in cancer-induced depression. Hopefully, novel therapeutics targeting these dysregulated pathways may be potent in ameliorating depressive symptoms in the cancer population.

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.

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.

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.

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.

An affective disorder in zebrafish with mutation of the glucocorticoid receptor

Upon binding of cortisol, the glucocorticoid receptor (GR) regulates the transcription of specific target genes, including those that encode the stress hormones corticotropin-releasing hormone (CRH) and adrenocorticotropic hormone. Dysregulation of the stress axis is a hallmark of major depression in human patients. However, it is still unclear how glucocorticoid signaling is linked to affective disorders. We identified an adult-viable zebrafish mutant in which the negative feedback on the stress response is disrupted, due to abolition of all transcriptional activity of GR. As a consequence, cortisol is elevated, but unable to signal through GR. When placed into an unfamiliar aquarium ('novel tank'), mutant fish become immobile ('freeze'), show reduced exploratory behavior and do not habituate to this stressor upon repeated exposure. Addition of the antidepressant fluoxetine to the holding water and social interactions restore normal behavior, followed by a delayed correction of cortisol levels. Fluoxetine does not affect the overall transcription of CRH, the mineralocorticoid receptor (MR), the serotonin transporter (Serta) or GR itself. Fluoxetine, however, suppresses the stress-induced upregulation of MR and Serta in both wild-type fish and mutants. Our studies show a conserved, protective function of glucocorticoid signaling in the regulation of emotional behavior and reveal novel molecular aspects of how chronic stress impacts vertebrate brain physiology and behavior. Importantly, the zebrafish model opens up the possibility of high-throughput drug screens in search of new classes of antidepressants.

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.

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.

Local amplification of glucocorticoids in the aging brain and impaired spatial memory

The hippocampus is a prime target for glucocorticoids (GCs) and a brain structure particularly vulnerable to aging. Prolonged exposure to excess GCs compromises hippocampal electrophysiology, structure, and function. Blood GC levels tend to increase with aging and correlate with impaired spatial memory in aging rodents and humans. The magnitude of GC action within tissues depends not only on levels of steroid hormone that enter the cells from the periphery and the density of intracellular receptors but also on the local metabolism of GCs by 11β-hydroxysteroid dehydrogenases (11β-HSD). The predominant isozyme in the adult brain, 11β-HSD1, locally regenerates active GCs from inert 11-keto forms thus amplifying GC levels within specific target cells including in the hippocampus and cortex. Aging associates with elevated hippocampal and neocortical 11β-HSD1 and impaired spatial learning while deficiency of 11β-HSD1 in knockout (KO) mice prevents the emergence of cognitive decline with age. Furthermore, short-term pharmacological inhibition of 11β-HSD1 in already aged mice reverses spatial memory impairments. Here, we review research findings that support a key role for GCs with special emphasis on their intracellular regulation by 11β-HSD1 in the emergence of spatial memory deficits with aging, and discuss the use of 11β-HSD1 inhibitors as a promising novel treatment in ameliorating/improving age-related memory impairments.

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.

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.

Gene expression profiling in the stress control brain region hypothalamic paraventricular nucleus reveals a novel gene network including amyloid beta precursor protein

Background

The pivotal role of stress in the precipitation of psychiatric diseases such as depression is generally accepted. This study aims at the identification of genes that are directly or indirectly responding to stress. Inbred mouse strains that had been evidenced to differ in their stress response as well as in their response to antidepressant treatment were chosen for RNA profiling after stress exposure. Gene expression and regulation was determined by microarray analyses and further evaluated by bioinformatics tools including pathway and cluster analyses.

Results

Forced swimming as acute stressor was applied to C57BL/6J and DBA/2J mice and resulted in sets of regulated genes in the paraventricular nucleus of the hypothalamus (PVN), 4 h or 8 h after stress. Although the expression changes between the mouse strains were quite different, they unfolded in phases over time in both strains. Our search for connections between the regulated genes resulted in potential novel signalling pathways in stress. In particular, Guanine nucleotide binding protein, alpha inhibiting 2 (GNAi2) and Amyloid β (A4) precursor protein (APP) were detected as stress-regulated genes, and together with other genes, seem to be integrated into stress-responsive pathways and gene networks in the PVN.

Conclusions

This search for stress-regulated genes in the PVN revealed its impact on interesting genes (GNAi2 and APP) and a novel gene network. In particular the expression of APP in the PVN that is governing stress hormone balance, is of great interest. The reported neuroprotective role of this molecule in the CNS supports the idea that a short acute stress can elicit positive adaptational effects in the brain.

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.

Long-term anxiolytic and antidepressant-like behavioural effects of tiagabine, a selective GABA transporter-1 (GAT-1) inhibitor, coincide with a decrease in HPA system activity in C57BL/6 mice

Gamma-aminobutyric acid (GABA) system plays a pivotal role in the pathophysiology of anxiety and mood disorders. This study was aimed to assess the anxiolytic and antidepressant-like properties of tiagabine, an inhibitor of the GABA transporter-1 (GAT-1), after acute and chronic administration in C57BL/6JOlaHsD mice with paroxetine as a positive control. In first experiments, the acute administration of tiagabine (7.5 mg/kg, orally [PO]) and paroxetine (10 mg/kg PO) induced anxiolytic effects in the elevated plus maze test and the modified hole board test and an antidepressant-like effect in the forced swim test. Chronic application of tiagabine (7.5 mg/kg PO) and paroxetine (10 mg/kg PO) for 22 days revealed an anxiolytic and antidepressant-like efficacy of tiagabine only. In a further experiment, we analysed the impact of chronic tiagabine versus paroxetine treatment on the hypothalamic-pituitary-adrenocortical (HPA) system regulation. GAT-1 blockade induced a setpoint-shift of the stress hormone system toward lower levels as indicated by decreased plasma corticosterone concentrations and attenuated gene expression levels of corticotropin-releasing factor in the paraventricular nucleus of the hypothalamus and of hippocampal steroid receptors. This data indicate that both acute and long-term anxiolytic and antidepressant-like properties of brain GAT-1 inhibition coincide with a reduction in HPA system activity in mice.

The role of FKBP5, a co-chaperone of the glucocorticoid receptor in the pathogenesis and therapy of affective and anxiety disorders

FK506 binding protein 51 or FKBP5 is a co-chaperone of hsp90 which regulates glucocorticoid receptor (GR) sensitivity. When it is bound to the receptor complex, cortisol binds with lower affinity and nuclear translocation of the receptor is less efficient. FKBP5 mRNA and protein expression are induced by GR activation via intronic hormone response elements and this provides an ultra-short feedback loop for GR-sensitivity. Polymorphisms in the gene encoding this co-chaperone have been shown to associate with differential upregulation of FKBP5 following GR activation and differences in GR sensitivity and stress hormone system regulation. Alleles associated with enhanced expression of FKBP5 following GR activation, lead to an increased GR resistance and decreased efficiency of the negative feedback of the stress hormone axis in healthy controls. This results in a prolongation of stress hormone system activation following exposure to stress. This dysregulated stress response might be a risk factor for stress-related psychiatric disorders. In fact, the same alleles are over-represented in individuals with major depression, bipolar disorder and post-traumatic stress disorder. In addition, they are also associated with faster response to antidepressant treatment. FKBP5 might thus be an interesting therapeutic target for the prevention and treatment of stress-related psychiatric disorders.

Effects of escitalopram on the regulation of brain-derived neurotrophic factor and nerve growth factor protein levels in a rat model of chronic stress

Escitalopram (ES-CIT) is a widely used, highly specific antidepressant. Until now there has been very little evidence on how this drug under pathological conditions affects an important feature within the pathophysiology of stress-related disorders such as depression: the endogenous neurotrophins. By using a well-characterized rat model in which chronic stress induces depressive-like behavior, the levels of neurotrophins brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) were determined in representative brain regions and serum using a highly sensitive improved fluorometric two-site ELISA system. There was a significant increase of BDNF in the left and right cortices after stress treatment (twofold increase) that was reversed by application of ES-CIT. An ES-CIT-dependent NGF reduction in stressed rats was detectable in the right cortex only (P = 0.027). The left hippocampus revealed significantly higher amounts of BDNF (2.5-fold increase) protein than the right hippocampus. These interhemispheric differences were unrelated to stress or ES-CIT treatment in all animals. BDNF and NGF of the frontal cortex, cerebellum, and serum did not change between the study groups. There was a negative correlation between body weight and serum BDNF, independent of stress or ES-CIT treatment. In conclusion, BDNF and NGF show substantial changes in this rodent model of chronic social stress, which is susceptible to antidepressant treatment with ES-CIT and therefore may constitute a neurobiological correlate for the disease.

Combined effects of exonic polymorphisms in CRHR1 and AVPR1B genes in a case/control study for panic disorder

Accumulating evidence from animal studies suggests that the corticotropin releasing hormone (CRH) and arginine vasopressin (AVP) neuropeptide systems, contribute to anxiety behavior. To investigate whether polymorphisms in the genes regulating these two systems may alter susceptibility to anxiety disorders in humans, we genotyped 71 single nucleotide polymorphisms (SNPs) in CRH, CRHR1, CRHR2, AVP, AVPR1A, AVPR1B in a German sample from Munich with patients suffering from panic disorder and matched healthy controls (n = 186/n = 299). Significant associations were then replicated in a second German sample with 173 patients with panic disorder and 495 controls. In both samples separately and the combined sample, SNPs within CHRH1 and AVPR1B were nominally associated with panic disorder. We then tested two locus multiplicative and interaction effects of polymorphisms of these two genes on panic disorder. Fifteen SNP pairs showed significant multiplicative effects in both samples. The SNP pair with the most significant association in the combined sample (P = 0.00057), which withstood correction for multiple testing, was rs878886 in CRHR1 and rs28632197 in AVPR1B. Both SNPs are of potential functional relevance as rs878886 is located in the 3' untranslated region of the CRHR1 and rs28632197 leads to an arginine to histidine amino acid exchange at position 364 of AVPR1B which is located in the intracellular C-terminal domain of the receptor. These data suggest that polymorphisms in the AVPR1B and the CRHR1 genes alter the susceptibility to panic disorder.

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.

Effects of serotonin depletion on the hippocampal GR/MR and BDNF expression during the stress adaptation

Increased serotonin (5-hydroxytryptamine, 5-HT) release in the hippocampus induced by repeated stress is thought to be critical for the neuroadaptation that alleviates the adverse effects of stressors on emotion and behavior. A failure in this process may be one of the primary neuropathological mechanisms underlying the development of stress-related disorders. The para-chloroamphetamine (p-PCA) was used to deplete 5-HT in the rat prior to repeated restraint stress (6h/day for 10 days), and determined the consequences of 5-HT depletion on stress-induced alterations of animal behaviors, hippocampal corticosteroid receptor immunoreactivity and the brain-derived neurotrophic factor (BDNF) mRNA expression. Behavioral tests indicate that the stressed rats with 5-HT depletion showed pronounced anxiety, reduced reward sensitivity and enhanced learned-helplessness. In addition, they also developed learning impairments in Morris water maze tests. These results suggest that hippocampal 5-HT depletion compromised adaptation to chronic stress. Furthermore, repeated stress caused a lesser degree of glucocorticoid receptor increase and down-regulation of BDNF mRNA. The study suggest that 5-HT deficiency in the adult hippocampus may impair stress adaptation by suppressing hippocampal GR and BDNF expression.

HPA axis dysfunction in unmedicated major depressive disorder and its normalization by pharmacotherapy correlates with alteration of neural activity in prefrontal cortex and limbic/paralimbic regions

Dysregulation of the hypothalamic-pituitary-adrenocortical (HPA) axis is one of the most prominent neurobiological findings in major depressive disorder (MDD). The relationship of regional brain metabolism to HPA axis dysfunction in depressed patients, however, is still unclear. In this study, to examine the clinical pharmacotherapeutic effects on HPA axis function and brain metabolism in MDD patients, we performed the combined dexamethasone (DEX)/corticotropin-releasing hormone (CRH) test on 24 antidepressant-free patients with MDD a few days after positron emission tomography (PET) with a radiotracer, [(18)F]-fluorodeoxyglucose (FDG). Moreover, 10 patients who responded to pharmacotherapy were re-tested. 75% of unmedicated MDD patients exhibited a heightened cortisol response to the DEX/CRH test, and thus were defined as non-suppressors. Non-suppressors showed a marked hypometabolism in the medial prefrontal cortex as compared with suppressors. After successful pharmacotherapy, enhanced cortisol responsiveness normalized. Prior to treatment of the unmedicated MDD, a significant hypometabolism in various frontal regions and a significant hypermetabolism in the right hippocampus and parahippocampal gyrus were observed compared with controls. Metabolic activity in treatment responders showed a normalizing pattern in almost all the areas that had been characterized by metabolic abnormality at baseline except for the medial prefrontal cortex. These results indicate that depressed patients remitted with antidepressant treatment were accompanied by resolution of HPA dysregulation and alteration of regional glucose metabolism in the prefrontal cortical, limbic and paralimbic regions.

Combined dexamethasone/corticotropin releasing hormone test predicts treatment response in major depression - a potential biomarker?

BACKGROUND

Exaggerated corticotropin (ACTH) and cortisol response to the combined dexamethasone (DEX)/corticotropin releasing hormone (CRH) test, indicating impaired regulation of the hypothalamus-pituitary-adrenocortical (HPA) system, is frequently observed in depression. In the present study, we examined whether change in HPA system function during the first weeks of hospitalization predicts response to antidepressant treatment in major depression and thus constitutes a potential biomarker.

METHODS

We conducted the DEX/CRH test in 50 inpatients suffering from severe major depression, once after study inclusion and a second time 2 to 3 weeks later while under continuous antidepressant treatment.

RESULTS

We found increased ACTH and cortisol responses to the first DEX/CRH test compared with healthy control subjects. In the second DEX/CRH test 2 to 3 weeks later, 36 of the 50 patients showed an attenuated cortisol response, while 14 patients did not display improvement or exhibited even aggravation of the altered HPA system function. Improved HPA system regulation in the second DEX/CRH test was associated with beneficial treatment response after 5 weeks and a higher remission rate at the end of hospitalization.

CONCLUSIONS

The results suggest that change in HPA system regulation assessed with repeated DEX/CRH tests is a potential biomarker that may predict clinical outcome at follow-up. There is consensus that the drug development process could be improved, once reliable biomarkers become available that help to allow a judgement regarding the efficacy of a novel drug candidate. The combined DEX/CRH test seems to be a promising candidate for such a biomarker.

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.

Effect of chronic citalopram on serotonin-related and stress-regulated genes in the dorsal raphe nucleus of the rat

Using a model of depression in which chronic social stress induces depressive-like symptoms, we investigated effects of the selective serotonin-reuptake inhibitor (SSRI) citalopram on gene expression in the dorsal raphe nucleus of male rats. Expression of tryptophan hydroxylase (TPH) protein was found to be upregulated by the stress and normalized by citalopram, while mRNAs for genes TPH 1 and 2 were differentially affected. Citalopram had no effect on serotonin transporter mRNA but reduced serotonin-1A autoreceptor mRNA in stressed animals. The SSRI prevented the stress-induced upregulation of mRNA for CREB binding protein, synaptic vesicle glycoprotein 2b and the glial N-myc downstream-regulated gene 2, but increased mRNA for neuron-specific enolase (NSE) in both stressed and unstressed animals having no effect on stress-induced upregulation of NSE protein. These findings demonstrate that in the dorsal raphe nucleus of chronically stressed rats, citalopram normalizes TPH expression and blocks stress effects on distinct genes related to neurotransmitter release and neuroplasticity.

Mineralocorticoid receptor overexpression in forebrain decreases anxiety-like behavior and alters the stress response in mice

Although numerous stress-related molecules have been implicated in vulnerability to psychiatric illness, especially major depression and anxiety disorders, the role of the brain mineralocorticoid receptor (MR) in stress, depression, and affective function is not well defined. MR is a steroid hormone receptor that detects circulating glucocorticoids with high affinity and has been primarily implicated in controlling their basal level and circadian rhythm. To specifically address the role of MR in hypothalamic-pituitary-adrenal axis activity and anxiety-related behaviors, we generated transgenic mice with increased levels of MR in the forebrain (MRov mice) by using the forebrain-specific calcium/calmodulin-dependent protein kinase II alpha promoter to direct expression of MR cDNA. A mild but chronic elevation in forebrain MR results in decreased anxiety-like behavior in both male and female transgenic mice. Female MRov mice also exhibit a moderate suppression of the corticosterone response to restraint stress. Increased forebrain MR expression alters the expression of two genes associated with stress and anxiety, leading to a decrease in the hippocampal glucocorticoid receptor (GR) and an increase in serotonin receptor 5HT-1a, consistent with the decreased anxiety phenotype. These data suggest that the functions of forebrain MR may overlap with GR in hypothalamic-pituitary-adrenal axis regulation, but they dissociate significantly from GR in the modulation of affective responses, with GR overexpression increasing anxiety-like behavior and MR overexpression dampening it. These findings point to the importance of the MR:GR ratio in the control of emotional reactivity.

Antidepressant-like activity of a Kampo (Japanese herbal) medicine, Koso-san (Xiang-Su-San), and its mode of action via the hypothalamic-pituitary-adrenal axis

Koso-san (Xiang-Su-San in Chinese), a Kampo (Japanese herbal) medicine, is used clinically in East Asia for the treatment of depression-like symptoms associated with the initial stage of the common cold, allergic urticaria due to food ingestion, irritable bowel syndrome, chronic fatigue syndrome, insomnia, and autonomic imbalance. However, the antidepressant-like activity of Koso-san has never been evaluated scientifically. In this study, ddY mice subjected to a combination of forced swimming and chronic mild stresses were termed depression-like model mice. The degree of the depression-like state was measured by the animal's duration of immobility using the forced swimming test (FST). Oral administration of Koso-san (1.0 g/kg/body wt./day, 9 days) significantly shortened the duration of immobility of the depression-like model mice in the FST; however, locomotor activity was not affected. Hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis plays an important role in the pathophysiology of depression. Levels of corticotropin-releasing hormone mRNA expression in the hypothalamus and proopiomelanocortin mRNA expression in the pituitary were significantly increased, and glucocorticoid receptor protein expression in the hypothalamus paraventricular nucleus was downregulated in the depression-like model mice. However, Koso-san ameliorated these alterations to the normal conditions. The results of this study suggest that Koso-san shows the antidepressant-like effect through suppressing the hyperactivity of the HPA axis in depression-like model mice.

A polymorphic glucocorticoid receptor in a mouse population may explain inherited altered stress response and increased anxiety‐type behaviors

A polymorphic glucocorticoid receptor (GR(Qn)) with an expanded CAG track and two silent mutations, when compared with the sequence of other isoform (GR(wt)), is found in two outbred mouse lines that were produced by selection for high (SH) or low (SL) stress response from high or low heat loss lines of mice, respectively. The GR(Qn) allele, which is also found in 5 of 16 commonly used inbred mouse lines, had a much higher frequency in SL mice; the GR(wt/wt) was found only in the SH line. Both GR(Qn/Qn) and GR(wt/Qn) mice had a much weaker corticosterone response to stress than the GR(wt/wt) mice. Assessment of open field activity revealed that GR(Qn/Qn) and GR(wt/Qn) mice exhibited significantly lower velocity and locomotor activity, less time in the center, and much longer duration in corner zones than the GR(wt/wt) mice. The increased anxiety-type behaviors of the GR(Qn/Qn) and GR(wt/Qn) mice were confirmed by the "elevated plus maze" test in which GR(Qn/Qn) and GR(wt/Qn) mice spent significantly less time in the "open arm" and longer duration in the "closed arm," than GR(wt/wt) mice. These results suggest this GR polymorphism plays a role in complex mechanisms leading to lower corticosterone response to stress, and may also be associated with decreased locomotive and increased anxiety-type behaviors in mice.

Altered glucocorticoid receptor signaling cascade in lymphocytes of bipolar disorder patients

Bipolar disorder (BD) is characterized by hypothalamic pituitary adrenal (HPA) axis hyperactivity, glucocorticoid insensitivity and alterations in serotonin and inflammatory mediators. The glucocorticoid receptor (GR), activator protein-1 (AP-1), nuclear factor-kappa B (NF-kappaB) and c-jun N-terminal kinase (JNK) regulate the above mentioned processes; we therefore assessed their role in BD. Fifteen bipolar depressed patients under multiple anti-depressant therapy, 15 bipolar euthymics under lithium monotherapy and 25 matched controls were studied. Whole cell and nuclear extracts from lymphocytes were immunoblotted for GR, c-fos, JNK and NF-kappaB and nuclear aliquots were submitted to electrophoretic mobility shift assay for GR, AP-1 and NF-kappaB. Associations with the anti-depressant therapy and the state of the disease were also sought. Results, expressed as percentage of pooled protein standard sample intergraded optical density (IOD) (mean +/- SD), revealed: (a) depressed patients had significantly higher GR levels than controls in whole cell (82.63 +/- 6.18 versus 76.27 +/- 4.21%, P < 0.01) and nuclear extracts (86.66 +/- 3.81 versus 81.72 +/- 2.71%, P < 0.001) but lower GR-DNA binding (68.75 +/- 7.91 versus 81.84 +/- 4.25%, P < 0.05). Euthymics had normalized whole cell GR content (73.64 +/- 5.95%) and GR-DNA binding activity (76.82 +/- 7.29%) but higher nuclear GR content (86.89+/-3.96%, P<0.01) than controls; (b) nuclear c-fos content and AP-1-DNA-binding were significantly lower in depressed patients than controls (80.49 +/- 2.03 versus 84.82 +/- 3.48%, P < 0.05 and 78.46 +/- 4.17 versus 84.80 +/- 5.79%, P < 0.05, respectively). Euthymics however, showed similar nuclear c-fos and AP-1-DNA-binding to controls (85.48 +/- 2.71 and 87.78 +/- 3.54%, respectively) but lower whole cell c-fos than in controls (81.18 +/- 3.87 versus 87.01 +/- 4.22%, P < 0.001); (c) depressed patients had significantly lower whole cell and nuclear JNK than controls (67.01 +/- 4.29 versus 72.00 +/- 3.68%, P < 0.05 and 80.10 +/- 2.53 versus 86.96 +/- 2.49%, P < 0.001) whereas euthymics showed lower nuclear JNK (83.27 +/- 1.93%, P < 0.01); (d) whole cell NF-kB was higher in the depressed patients than in controls (67.30 +/- 5.00 versus 63.63 +/- 3.3%, P < 0.05). Concluding, intracellular signaling of GR, AP-1 and JNK are altered in BD and may underly disease aetiopathogenesis and/or reflect the effect of the anti-depressants.

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.

Genes and neurons: molecular insights to fear and anxiety

Experimental animal models provide an important tool for the identification of inheritable components of fear and anxiety. 'Pavlovian' fear conditioning has been tremendously successful to characterize the neuronal circuitry and cellular mechanisms of the formation, consolidation and extinction of fear memories. Here we summarize recent progress that has led to the identification of gene products contributing to such experience-dependent changes in fear and anxiety and may guide the search for genetic factors involved in the development and treatment of human anxiety disorders.

Polymorphisms of the glucocorticoid receptor gene and major depression

BACKGROUND

The most consistent biological finding in patients with depression is a hyperactivity of the hypothalamic-pituitary-adrenal (HPA)-axis, which might be caused by impaired glucocorticoid signaling. Glucocorticoids act through the glucocorticoid receptor (GR) for which several polymorphisms have been described. The N363S and BclI polymorphisms have been associated with hypersensitivity to glucocorticoids, whereas the ER22/23EK polymorphism is related to glucocorticoid resistance.

METHODS

We studied whether the susceptibility to develop a depression is related to these polymorphisms by comparing depressive inpatients (n = 490) and healthy control subjects (n = 496). Among depressed patients, we also investigated the relation between GR variants and dysregulation of the HPA-axis, as measured by the combined dexamethasone suppression/corticotropin-releasing hormone (CRH)-stimulation test, clinical response to antidepressive treatment, and cognitive functioning.

RESULTS

Homozygous carriers of the BclI polymorphism and ER22/23EK-carriers had an increased risk of developing a major depressive episode. We found no genetic associations with functional HPA-axis measures in depressed patients. The ER22/23EK-carriers, however, showed a significantly faster clinical response to antidepressant therapy as well as a trend toward better cognitive functioning during depression.

CONCLUSIONS

The BclI and ER22/23EK polymorphisms were associated with susceptibility to develop major depression. In addition, the ER22/23EK polymorphism is associated with a faster clinical response to antidepressant treatment. These findings support the notion that variants of the GR gene might play a role in the pathophysiology of a major depression and can contribute to the variability of antidepressant response.

Antidepressants reverse corticosterone-mediated decrease in brain-derived neurotrophic factor expression: differential regulation of specific exons by antidepressants and corticosterone

Earlier studies have implicated brain-derived neurotrophic factor in stress and in the mechanism of action of antidepressants. It has been shown that antidepressants upregulate, whereas corticosterone downregulates, brain-derived neurotrophic factor expression in rat brain. Whether various classes of antidepressants reverse corticosterone-mediated downregulation of brain-derived neurotrophic factor is unclear. Also not known is how antidepressants or corticosterone regulates brain-derived neurotrophic factor expression. To clarify this, we examined the effects of various classes of antidepressants and corticosterone, alone and in combination, on the mRNA expression of total brain-derived neurotrophic factor and of individual brain-derived neurotrophic factor exons, in rat brain. Normal or corticosterone pellet-implanted (100 mg, 21 days) rats were injected with different classes of antidepressants, fluoxetine, desipramine, or phenelzine, intraperitoneally for 21 days and killed 2 h after the last injection. mRNA expression of total brain-derived neurotrophic factor and of exons I-IV was measured in frontal cortex and hippocampus. Given to normal rats, fluoxetine increased total brain-derived neurotrophic factor mRNA only in hippocampus, whereas desipramine or phenelzine increased brain-derived neurotrophic factor mRNA in both frontal cortex and hippocampus. When specific exons were examined, desipramine increased expression of exons I and III in both brain areas, whereas phenelzine increased exon I in both frontal cortex and hippocampus but exon IV only in hippocampus. On the other hand, fluoxetine increased only exon II in hippocampus. Corticosterone treatment of normal rats decreased expression of total brain-derived neurotrophic factor mRNA in both brain areas, specifically decreasing exons II and IV. Treatment with desipramine or phenelzine of corticosterone pellet-implanted rats reversed the corticosterone-induced decrease in total brain-derived neurotrophic factor expression in both brain areas; however, fluoxetine reversed the decrease only partially in hippocampus. Interestingly, antidepressant treatment of corticosterone pellet-implanted rats increased only those specific exons that are increased during treatment of normal rats with each particular antidepressant. We found that although corticosterone and antidepressants both modulate brain-derived neurotrophic factor expression, and antidepressants reverse the corticosterone-induced brain-derived neurotrophic factor decrease, antidepressants and corticosterone differ in how they regulate the expression of brain-derived neurotrophic factor exon(s).