Anxiogenic-like effect of chronic corticosterone in the light-dark emergence task in mice

Chronobiology by moonlight

Most studies in chronobiology focus on solar cycles (daily and annual). Moonlight and the lunar cycle received considerably less attention by chronobiologists. An exception are rhythms in intertidal species. Terrestrial ecologists long ago acknowledged the effects of moonlight on predation success, and consequently on predation risk, foraging behaviour and habitat use, while marine biologists have focused more on the behaviour and mainly on reproduction synchronization with relation to the Moon phase. Lately, several studies in different animal taxa addressed the role of moonlight in determining activity and studied the underlying mechanisms. In this paper, we review the ecological and behavioural evidence showing the effect of moonlight on activity, discuss the adaptive value of these changes, and describe possible mechanisms underlying this effect. We will also refer to other sources of night-time light ('light pollution') and highlight open questions that demand further studies.

Depression as an evolutionary strategy for defense against infection

Recent discoveries relating depression to inflammation and immune function may help to solve an important evolutionary puzzle: If depression carries with it so many negative consequences, including notable costs to survival and reproduction, then why is it common and heritable? What countervailing force or compensatory advantage has allowed susceptibility genes for depression to persist in the population at such high rates? A priori, compensatory advantages in combating infection are a promising candidate, given that infection has been the major cause of mortality throughout human history. Emerging evidence on deeply rooted bidirectional pathways of communication between the nervous and immune systems further supports this notion. Here we present an updated review of the "infection-defense hypothesis" of depression, which proposes that moods-with their ability to orchestrate a wide array of physical and behavioral responses-have played an adaptive role throughout human history by helping individuals fight existing infections, as well as helping both individuals and their kin avoid new ones. We discuss new evidence that supports several key predictions derived from the hypothesis, and compare it with other major evolutionary theories of depression. Specifically, we discuss how the infection-defense hypothesis helps to explain emerging data on psychoimmunological features of depression, as well as depression's associations with a diverse array of conditions and illnesses-including nutritional deficiencies, seasonal changes, hormonal fluctuations, and chronic diseases-that previous evolutionary theories of depression have not accounted for. Finally, we note the potential implications of the hypothesis for the treatment and prevention of depression.

The endocrine stress response is linked to one specific locus on chromosome 3 in a mouse model based on extremes in trait anxiety

Background

The hypothalamic-pituitary-adrenal (HPA) axis is essential to control physiological stress responses in mammals. Its dysfunction is related to several mental disorders, including anxiety and depression. The aim of this study was to identify genetic loci underlying the endocrine regulation of the HPA axis.

Method

High (HAB) and low (LAB) anxiety-related behaviour mice were established by selective inbreeding of outbred CD-1 mice to model extremes in trait anxiety. Additionally, HAB vs. LAB mice exhibit comorbid characteristics including a differential corticosterone response upon stress exposure. We crossbred HAB and LAB lines to create F1 and F2 offspring. To identify the contribution of the endocrine phenotypes to the total phenotypic variance, we examined multiple behavioural paradigms together with corticosterone secretion-based phenotypes in F2 mice by principal component analysis. Further, to pinpoint the genomic loci of the quantitative trait of the HPA axis stress response, we conducted genome-wide multipoint oligogenic linkage analyses based on Bayesian Markov chain Monte Carlo approach as well as parametric linkage in three-generation pedigrees, followed by a two-dimensional scan for epistasis and association analysis in freely segregating F2 mice using 267 single-nucleotide polymorphisms (SNPs), which were identified to consistently differ between HAB and LAB mice as genetic markers.

Results

HPA axis reactivity measurements and behavioural phenotypes were represented by independent principal components and demonstrated no correlation. Based on this finding, we identified one single quantitative trait locus (QTL) on chromosome 3 showing a very strong evidence for linkage (2ln (L-score) > 10, LOD > 23) and significant association (lowest Bonferroni adjusted p < 10^-28) to the neuroendocrine stress response. The location of the linkage peak was estimated at 42.3 cM (95% confidence interval: 41.3 - 43.3 cM) and was shown to be in epistasis (p-adjusted < 0.004) with the locus at 35.3 cM on the same chromosome. The QTL harbours genes involved in steroid synthesis and cardiovascular effects.

Conclusion

The very prominent effect on stress-induced corticosterone secretion of the genomic locus on chromosome 3 and its involvement in epistasis highlights the critical role of this specific locus in the regulation of the HPA axis.

Chronic non-invasive corticosterone administration abolishes the diurnal pattern of tph2 expression

Both hypothalamic-pituitary-adrenal (HPA) axis activity and serotonergic systems are commonly dysregulated in stress-related psychiatric disorders. We describe here a non-invasive rat model for hypercortisolism, as observed in major depression, and its effects on physiology, behavior, and the expression of tph2, the gene encoding tryptophan hydroxylase 2, the rate-limiting enzyme for brain serotonin (5-hydroxytryptamine; 5-HT) synthesis. We delivered corticosterone (40 μg/ml, 100 μg/ml or 400 μg/ml) or vehicle to adrenal-intact adult, male rats via the drinking water for 3 weeks. On days 15, 16, 17 and 18, respectively, the rats' emotionality was assessed in the open-field (OF), social interaction (SI), elevated plus-maze (EPM), and forced swim tests (FST). On day 21, half of the rats in each group were killed 2h into the dark phase of a 12/12 h reversed light/dark cycle; the other half were killed 2h into the light phase. We then measured indices of HPA axis activity, plasma glucose and interleukin-6 (IL-6) availability, and neuronal tph2 expression at each time point. Chronic corticosterone intake was sufficient to cause increased anxiety- and depressive-like behavior in a dose-dependent manner. It also disrupted the diurnal pattern of plasma adrenocorticotropin (ACTH), corticosterone, and glucose concentrations, caused adrenal atrophy, and prevented regular weight gain. No diurnal or treatment-dependent changes were found for plasma concentrations of IL-6. Remarkably, all doses of corticosterone treatment abolished the diurnal variation of tph2 mRNA expression in the brainstem dorsal raphe nucleus (DR) by elevating the gene's expression during the animals' inactive (light) phase. Our data demonstrate that chronic elevation of corticosterone creates a vulnerability to a depression-like syndrome that is associated with increased tph2 expression, similar to that observed in depressed patients.

Major depressive disorders in chronic hemodialysis patients in Nazareth: identification and assessment

OBJECTIVE

Depression illnesses are commonly observed in hemodialysis (HD) patients, which can influence the quality of life of end-stage renal disease patients. We evaluate the prevalence and predictive risk factors of depression in the Arab population undergoing HD in Nazareth, Israel.

METHODS

We conducted a prospective study that included 71 patients in the HD unit with a mean age of 61.9 ± 14.13 years who had undergone HD and 26 healthy control subjects with a mean age of 59.3 ± 7.3. Beck's Depression Inventory and Hamilton Depression Scale assessments were administered. Blood analysis for hematological and biochemical parameters was obtained. Diagnosis was made using the Diagnostic and Statistical Manual of Mental Disorders scale to correlate psychological variables with clinical, hematological, and biochemical parameters. Statistical analysis was carried out using analysis of variance followed by Tukey post-hoc multiple comparison tests.

RESULTS

The prevalence of depression was 43.7% in HD patients. Between HD patients and controls, cortisol values were 16.96 ± 0.5476 and 11.96 ± 1.116, respectively (P < 0.0001; 95% confidence intervals [CI]: 2.416-6.825). Between depressed HD patients versus control subjects, cortisol values were 16.48 ± 0.72 and 11.96 ± 1.116, respectively (P = 0.0013; 95% CI: 1.878-7.184). Hematological and biochemical parameters were compared between depressed HD and nondepressed patients, but differences between the two groups were found to be insignificant (P > 0.05).

CONCLUSION

Our HD patients were severely depressed. Studies of glucocorticoid turnover activity such as cortisol, a potent chemical stress hormone, may be used as a model and marker for early diagnosis of depression among HD patients. The strong familial support system in Arabic traditions has failed to decrease depression among these patients.

Cysteamine attenuates the decreases in TrkB protein levels and the anxiety/depression-like behaviors in mice induced by corticosterone treatment

OBJECTIVE

Stress and glucocorticoid hormones, which are released into the circulation following stressful experiences, have been shown to contribute significantly to the manifestation of anxiety-like behaviors observed in many neuropsychiatric disorders. Brain-derived neurotrophic factor (BDNF) signaling through its receptor TrkB plays an important role in stress-mediated changes in structural as well as functional neuroplasticity. Studies designed to elucidate the mechanisms whereby TrkB signaling is regulated in chronic stress might provide valuable information for the development of new therapeutic strategies for several stress-related psychiatric disorders.

MATERIALS AND METHODS

We examined the potential of cysteamine, a neuroprotective compound to attenuate anxiety and depression like behaviors in a mouse model of anxiety/depression induced by chronic corticosterone exposure.

RESULTS

Cysteamine administration (150 mg/kg/day, through drinking water) for 21 days significantly ameliorated chronic corticosterone-induced decreases in TrkB protein levels in frontal cortex and hippocampus. Furthermore, cysteamine treatment reversed the anxiety and depression like behavioral abnormalities induced by chronic corticosterone treatment. Finally, mice deficient in TrkB, showed a reduced response to cysteamine in behavioral tests, suggesting that TrkB signaling plays an important role in the antidepressant effects of cysteamine.

CONCLUSIONS

The animal studies described here highlight the potential use of cysteamine as a novel therapeutic strategy for glucocorticoid-related symptoms of psychiatric disorders.

The effect of the lunar cycle on fecal cortisol metabolite levels and foraging ecology of nocturnally and diurnally active spiny mice

We studied stress hormones and foraging of nocturnal Acomys cahirinus and diurnal A. russatus in field populations as well as in two field enclosures populated by both species and two field enclosures with individuals of A. russatus alone. When alone, A. russatus individuals become also nocturnally active. We asked whether nocturnally active A. russatus will respond to moon phase and whether this response will be obtained also in diurnally active individuals. We studied giving-up densities (GUDs) in artificial foraging patches and fecal cortisol metabolite levels. Both species exhibited elevated fecal cortisol metabolite levels and foraged to higher GUDs in full moon nights; thus A. russatus retains physiological response and behavioral patterns that correlate with full moon conditions, as can be expected in nocturnal rodents, in spite of its diurnal activity. The endocrinological and behavioral response of this diurnal species to moon phase reflects its evolutionary heritage.

The clinical implications of mouse models of enhanced anxiety

Mice are increasingly overtaking the rat model organism in important aspects of anxiety research, including drug development. However, translating the results obtained in mouse studies into information that can be applied in clinics remains challenging. One reason may be that most of the studies so far have used animals displaying 'normal' anxiety rather than 'psychopathological' animal models with abnormal (elevated) anxiety, which more closely reflect core features and sensitivities to therapeutic interventions of human anxiety disorders, and which would, thus, narrow the translational gap. Here, we discuss manipulations aimed at persistently enhancing anxiety-related behavior in the laboratory mouse using phenotypic selection, genetic techniques and/or environmental manipulations. It is hoped that such models with enhanced construct validity will provide improved ways of studying the neurobiology and treatment of pathological anxiety. Examples of findings from mouse models of enhanced anxiety-related behavior will be discussed, as well as their relation to findings in anxiety disorder patients regarding neuroanatomy, neurobiology, genetic involvement and epigenetic modifications. Finally, we highlight novel targets for potential anxiolytic pharmacotherapeutics that have been established with the help of research involving mice. Since the use of psychopathological mouse models is only just beginning to increase, it is still unclear as to the extent to which such approaches will enhance the success rate of drug development in translating identified therapeutic targets into clinical trials and, thus, helping to introduce the next anxiolytic class of drugs.

Neurogenesis and affective disorders

The neurogenesis hypothesis of depression was originally formed upon the demonstration that stress impacts levels of adult neurogenesis in the hippocampus. Since then much work has established that newborn neurons in the dentate gyrus are required for mediating some of the beneficial effects of antidepressant treatment. Recent studies combining behavioral, molecular and electrophysiological approaches have attempted to make sense of the role young neurons play in modulating mood by demonstrating a potential role in regulating the circuitry in the brain that underlies depression. Here we discuss the work that led to the neurogenesis hypothesis of depression, and the subsequent studies that have sought to test this hypothesis. We also discuss different animal models of depression that have been used to test the role of neurogenesis in mediating the antidepressant response.

Long-term continuous corticosterone treatment decreases VEGF receptor-2 expression in frontal cortex

OBJECTIVE

Stress and increased glucocorticoid levels are associated with many neuropsychiatric disorders including schizophrenia and depression. Recently, the role of vascular endothelial factor receptor-2 (VEGFR2/Flk1) signaling has been implicated in stress-mediated neuroplasticity. However, the mechanism of regulation of VEGF/Flk1 signaling under long-term continuous glucocorticoid exposure has not been elucidated.

MATERIAL AND METHODS

We examined the possible effects of long-term continuous glucocorticoid exposure on VEGF/Flk1 signaling in cultured cortical neurons in vitro, mouse frontal cortex in vivo, and in post mortem human prefrontal cortex of both control and schizophrenia subjects.

RESULTS

We found that long-term continuous exposure to corticosterone (CORT, a natural glucocorticoid) reduced Flk1 protein levels both in vitro and in vivo. CORT treatment resulted in alterations in signaling molecules downstream to Flk1 such as PTEN, Akt and mTOR. We demonstrated that CORT-induced changes in Flk1 levels are mediated through glucocorticoid receptor (GR) and calcium. A significant reduction in Flk1-GR interaction was observed following CORT exposure. Interestingly, VEGF levels were increased in cortex, but decreased in serum following CORT treatment. Moreover, significant reductions in Flk1 and GR protein levels were found in postmortem prefrontal cortex samples from schizophrenia subjects.

CONCLUSIONS

The alterations in VEGF/Flk1 signaling following long-term continuous CORT exposure represents a molecular mechanism of the neurobiological effects of chronic stress.

Stress- and allostasis-induced brain plasticity

The brain is the key organ of stress processes. It determines what individuals will experience as stressful, it orchestrates how individuals will cope with stressful experiences, and it changes both functionally and structurally as a result of stressful experiences. Within the brain, a distributed, dynamic, and plastic neural circuitry coordinates, monitors, and calibrates behavioral and physiological stress response systems to meet the demands imposed by particular stressors. These allodynamic processes can be adaptive in the short term (allostasis) and maladaptive in the long term (allostatic load). Critically, these processes involve bidirectional signaling between the brain and body. Consequently, allostasis and allostatic load can jointly affect vulnerability to brain-dependent and stress-related mental and physical health conditions. This review focuses on the role of brain plasticity in adaptation to, and pathophysiology resulting from, stressful experiences. It also considers interventions to prevent and treat chronic and prevalent health conditions via allodynamic brain mechanisms.

The glucocorticoid receptor: pivot of depression and of antidepressant treatment?

Hyperactivity of the hypothalamus-pituitary-adrenal (HPA) axis and increased levels of glucocorticoid hormones in patients with depression have mostly been ascribed to impaired feedback regulation of the HPA axis, possibly caused by altered function of the receptor for glucocorticoid hormones, the glucocorticoid receptor (GR). Antidepressants, in turn, ameliorate many of the neurobiological disturbances in depression, including HPA axis hyperactivity, and thereby alleviate depressive symptoms. There is strong evidence for the notion that antidepressants exert these effects by modulating the GR. Such modulations, however, can be manifold and range from regulation of receptor expression to post-translational modifications, which may result in differences in GR nuclear translocation and GR-dependent gene transcription. The idea that the therapeutic action of antidepressants is mediated, at least in part, by restoring GR function, is consistent with studies showing that decreased GR function contributes to HPA axis hyperactivity and to the development of depressive symptoms. Conversely, excessive glucocorticoid signalling, which requires an active GR, is associated with functional impairments in the depressed brain, especially in the hippocampus, where it results in reduced neurogenesis and impaired neuroplasticity. In this review, we will focus on the GR as a key player in the precipitation, development and resolution of depression. We will discuss potential explanations for the apparent controversy between glucocorticoid resistance and the detrimental effects of excessive glucocorticoid signalling. We will review some of the evidence for modulation of the GR by antidepressants and we will provide further insight into how antidepressants may regulate the GR to overcome depressive symptoms.

Modeling treatment-resistant depression

Depression is a polygenic and highly complex psychiatric disorder that is currently a major burden on society. Depression is highly heterogeneous in presentation and frequently exhibits high comorbidity with other psychiatric and somatic disorders. Commonly used treatments, such as selective serotonin reuptake inhibitors (SSRIs), are not ideal since only a subset of patients achieve remission. In addition, the reason why some individuals respond to SSRIs while others don't are unknown. Here we begin to ask what the basis of treatment resistance is, and propose new strategies to model this phenomenon in animals. We focus specifically on animal models that offer the appropriate framework to study treatment resistance with face, construct and predictive validity.

Integrated behavioral z-scoring increases the sensitivity and reliability of behavioral phenotyping in mice: relevance to emotionality and sex

Defining anxiety- and depressive-like states in mice (emotionality) is best characterized by the use of complementary tests, leading sometimes to puzzling discrepancies and lack of correlation between similar paradigms. To address this issue, we hypothesized that integrating measures along the same behavioral dimensions in different tests would reduce the intrinsic variability of single tests and provide a robust characterization of the underlying "emotionality" of individual mouse, similarly as mood and related syndromes are defined in humans through various related symptoms over time. We describe the use of simple mathematical and integrative tools to help phenotype animals across related behavioral tests (syndrome diagnosis) and experiments (meta-analysis). We applied z-normalization across complementary measures of emotionality in different behavioral tests after unpredictable chronic mild stress (UCMS) or prolonged corticosterone exposure - two approaches to induce anxious-/depressive-like states in mice. Combining z-normalized test values, lowered the variance of emotionality measurement, enhanced the reliability of behavioral phenotyping, and increased analytical opportunities. Comparing integrated emotionality scores across studies revealed a robust sexual dimorphism in the vulnerability to develop high emotionality, manifested as higher UCMS-induced emotionality z-scores, but lower corticosterone-induced scores in females compared to males. Interestingly, the distribution of individual z-scores revealed a pattern of increased baseline emotionality in female mice, reminiscent of what is observed in humans. Together, we show that the z-scoring method yields robust measures of emotionality across complementary tests for individual mice and experimental groups, hence facilitating the comparison across studies and refining the translational applicability of these models.

Implications of the functional integration of adult-born hippocampal neurons in anxiety-depression disorders

Adult neurogenesis in the dentate gyrus of the hippocampus has gained considerable attention as a cellular substrate for both the pathophysiology and treatment of depression. Overall, the studies of adult hippocampal neurogenesis are still in their infancy because most of them explore only one stage of this process. Importantly, given the built-in homeostatic mechanisms that act at each stage during the progression from stem cells to mature neurons (proliferation, differentiation, maturation, survival), it is very difficult to extrapolate the efficiency of a drug on adult neurogenesis from analysis of one stage alone. Here, we review the most significant data on hippocampal neurogenesis, focusing on the importance of studying each stage of adult hippocampal neurogenesis and also on the importance of choosing the appropriate mouse strain to perform the experiment. Specifically, strains with a high number of basal proliferating cells in the dentate gyrus of the hippocampus should be used only under stressed conditions to detect the effects of antidepressants on adult neurogenesis. We also discuss how adult hippocampal neurogenesis could be involved in affective state disorders such as depression and anxiety. Finally, we reveal that the behavioral effects of fluoxetine are mediated through both neurogenesis-dependent and -independent actions.

Blockade of mineralocorticoid and glucocorticoid receptors reverses stress-induced motor impairments

AIM

Stress and glucocorticoids can influence movement performance and pathologies of the motor system. The classic notion assumes that the glucocorticoid receptor (GR) mediates the majority of stress-induced behavioral changes. Nevertheless, recent findings have attributed a more prominent role to the mineralocorticoid receptor (MR) in modulating behavior. The purpose of this study was to dissociate the impact of MR versus GR activation in movement and stress-associated motor disruption.

METHODS

Groups of male and female rats were tested in skilled reaching and open field behavior and treated peri-orally with either agonists or antagonists for MR and GR, respectively.

RESULTS

Selective acute activation of MR (aldosterone) and GR (dexamethasone) decreased movement success with a magnitude similar to stress-induced impairment in male and female animals. By contrast, antagonist treatment to block MR (RU-28318) or GR (Mifepristone, RU-486) prevented motor impairments caused by acute restraint stress or corticosterone treatment. Moreover, both antagonists reversed chronic stress- and glucocorticoid-induced motor impairments to values comparable to baseline levels. Higher success rates in treated animals were accompanied by improved performance of skilled limb movements. In addition, combined treatment with MR and GR antagonists had additive benefit on aim and advance towards the reaching target.

CONCLUSION

These observations suggest that MR or GR equally influence motor system function with partially synergistic effects. Males and females show comparable responses to MR and GR activation or blockade. The need for balanced activation of MRs and GRs in motor control requires consideration in intervention strategies to improve performance in health and disease.

Stress, sex, and neural adaptation to a changing environment: mechanisms of neuronal remodeling

The adult brain is much more resilient and adaptable than previously believed, and adaptive structural plasticity involves growth and shrinkage of dendritic trees, turnover of synapses, and limited amounts of neurogenesis in the forebrain, especially the dentate gyrus of the hippocampal formation. Stress and sex hormones help to mediate adaptive structural plasticity, which has been extensively investigated in the hippocampus and to a lesser extent in the prefrontal cortex and amygdala, all brain regions that are involved in cognitive and emotional functions. Stress and sex hormones exert their effects on brain structural remodeling through both classical genomic as well as non-genomic mechanisms, and they do so in collaboration with neurotransmitters and other intra- and extracellular mediators. This review will illustrate the actions of estrogen on synapse formation in the hippocampus and the process of stress-induced remodeling of dendrites and synapses in the hippocampus, amygdala, and prefrontal cortex. The influence of early developmental epigenetic events, such as early life stress and brain sexual differentiation, is noted along with the interactions between sex hormones and the effects of stress on the brain. Because hormones influence brain structure and function and because hormone secretion is governed by the brain, applied molecular neuroscience techniques can begin to reveal the role of hormones in brain-related disorders and the treatment of these diseases. A better understanding of hormone-brain interactions should promote more flexible approaches to the treatment of psychiatric disorders, as well as their prevention through both behavioral and pharmaceutical interventions.

Melatonin treatment mimics the antidepressant action in chronic corticosterone-treated mice

Melatonin, involved in circadian cycle, provides protective effects on neuronal cells and acts as antidepressant by restoration of corticosterone levels. A mouse model of anxiety/depressive-like behavior, induced by chronic corticosterone treatment, has been used to evaluate behavior and adult hippocampal neurogenesis in mice and their possible modulation under melatonin. With this aim, CD1 mice were subjected to 7 wk of corticosterone administration, and then behavioral tests as novelty-suppressed feeding, open field and a forced swim test were performed. Cell proliferation in hippocampal dentate gyrus (DG) was investigated by 5-bromo-2'-deoxyuridine and doublecortin immunohistochemistry techniques, and stereological procedure was used to quantify labeled cells. Golgi-impregnated method was used to evaluate the changes of dendritic spines in DG neurons. A new therapeutic approach with antidepressant-like substances (3 wk) such as melatonin (8 mg/kg) was employed to possibly modulate neural development in the adult hippocampus and the behavioral changes. The depressive-like state caused by chronic corticosterone treatment was reversed by exogenous administration of melatonin; the proliferation of progenitor cells in mice hippocampus was significantly reduced under chronic corticosterone treatment (cort- 83.7 +/- 20.3 versus cort+ 60.5 +/- 18.2; P < 0.05), whereas long-term treatment with melatonin prevented the corticosterone-induced reduction in hippocampal cell proliferation (cort- 60.5 +/- 18.2 versus mel 133.4 +/- 26.9; P < 0.05). Corticosterone-treated mice exhibited a reduced spine density, which was ameliorated by melatonin administration. These findings suggest a strong correspondence between behavior and neurogenesis, strengthening the hypothesis that neurogenesis contributes to the effects of melatonin as an antidepressant.

Central role of the brain in stress and adaptation: links to socioeconomic status, health, and disease

The brain is the key organ of stress reactivity, coping, and recovery processes. Within the brain, a distributed neural circuitry determines what is threatening and thus stressful to the individual. Instrumental brain systems of this circuitry include the hippocampus, amygdala, and areas of the prefrontal cortex. Together, these systems regulate physiological and behavioral stress processes, which can be adaptive in the short-term and maladaptive in the long-term. Importantly, such stress processes arise from bidirectional patterns of communication between the brain and the autonomic, cardiovascular, and immune systems via neural and endocrine mechanisms underpinning cognition, experience, and behavior. In one respect, these bidirectional stress mechanisms are protective in that they promote short-term adaptation (allostasis). In another respect, however, these stress mechanisms can lead to a long-term dysregulation of allostasis in that they promote maladaptive wear-and-tear on the body and brain under chronically stressful conditions (allostatic load), compromising stress resiliency and health. This review focuses specifically on the links between stress-related processes embedded within the social environment and embodied within the brain, which is viewed as the central mediator and target of allostasis and allostatic load.

Eplerenone, a selective mineralocorticoid receptor blocker, exerts anxiolytic effects accompanied by changes in stress hormone release

The aim of this study was to investigate the impact of chronic treatment with eplerenone, a mineralocorticoid receptor antagonist and clinically used antihypertensive drug, on animal correlates of mood disorders, namely anxiety-like behaviour, stress hormones release and brain plasticity. Male rats (n = 40) were injected subcutaneously twice daily with eplerenone (50 mg/kg body weight) or vehicle for 11 days. Open-field and elevated plus-maze tests were used as both anxiety-related paradigms and stress stimuli to evaluate hormone responses. Eplerenone-treated rats showed reduced anxiety-like behaviour manifested by both conventional and ethological parameters related to exploration and risk assessment behaviour in the elevated plus-maze test and partially in the open-field test. Eplerenone treatment resulted in an elevation of plasma aldosterone and oxytocin levels. Chronic treatment with eplerenone prevented the stress-induced rise in plasma corticosterone levels and vasopressin concentrations in the posterior pituitary. Eplerenone treatment failed to induce substantial changes in hippocampal brain derived neurotrophic factor protein concentrations. In conclusions, chronic treatment with eplerenone (1) exerts anxiolytic effects and (2) influences corticosterone, oxytocin and vasopressin concentrations in a manner consistent with the anxiolytic outcome.

Recapitulation and reversal of a persistent depression-like syndrome in rodents

Alterations in multiple biological functions, such as transcription factor activity, are implicated in the neurobiology of depression, based primarily on the characterization of antidepressant efficacy in naïve rodents rather than on models that capture the protracted feelings of anhedonia and helplessness that typify depression. This unit presents rat and mouse models of depression that involve chronic oral exposure to the stress-associated adrenal hormone, corticosterone (CORT), resulting in anhedonic- and helplessness-like behaviors that are persistent yet reversible by chronic antidepressant treatment. Prior CORT exposure also chronically influences molecular targets hypothesized to contribute to negative mood. One example is phosphorylation of cAMP response element binding protein in the hippocampus and nucleus accumbens. Prior chronic CORT exposure provides an alternative method to chronic mild stress models of depression that is easily replicable and persists well beyond the CORT exposure period, thereby modeling the persistent depressive-like state in humans.

Molecular and genetic substrates linking stress and addiction

Drug addiction is one of the top three health concerns in the United States in terms of economic and health care costs. Despite this, there are very few effective treatment options available. Therefore, understanding the causes and molecular mechanisms underlying the transition from casual drug use to compulsive drug addiction could aid in the development of treatment options. Studies in humans and animal models indicate that stress can lead to both vulnerability to develop addiction, and increased drug taking and relapse in addicted individuals. Exposure to stress or drugs of abuse results in long-term adaptations in the brain that are likely to involve persistent alterations in gene expression or activation of transcription factors, such as the cAMP Response Element Binding (CREB) protein. The signaling pathways controlled by CREB have been strongly implicated in drug addiction and stress. Many potential CREB target genes have been identified based on the presence of a CRE element in promoter DNA sequences. These include, but are not limited to CRF, BDNF, and dynorphin. These genes have been associated with initiation or reinstatement of drug reward and are altered in one direction or the other following stress. While many reviews have examined the interactions between stress and addiction, the goal of this review was to focus on specific molecules that play key roles in both stress and addiction and are therefore posed to mediate the interaction between the two. Focus on these molecules could provide us with new targets for pharmacological treatments for addiction.

Neurogenesis-dependent and -independent effects of fluoxetine in an animal model of anxiety/depression

Understanding the physiopathology of affective disorders and their treatment relies on the availability of experimental models that accurately mimic aspects of the disease. Here we describe a mouse model of an anxiety/depressive-like state induced by chronic corticosterone treatment. Furthermore, chronic antidepressant treatment reversed the behavioral dysfunctions and the inhibition of hippocampal neurogenesis induced by corticosterone treatment. In corticosterone-treated mice where hippocampal neurogenesis is abolished by X-irradiation, the efficacy of fluoxetine is blocked in some, but not all, behavioral paradigms, suggesting both neurogenesis-dependent and -independent mechanisms of antidepressant action. Finally, we identified a number of candidate genes, the expression of which is decreased by chronic corticosterone and normalized by chronic fluoxetine treatment selectively in the hypothalamus. Importantly, mice deficient in one of these genes, beta-arrestin 2, displayed a reduced response to fluoxetine in multiple tasks, suggesting that beta-arrestin signaling is necessary for the antidepressant effects of fluoxetine.

Endogenous cortisol suppression with metyrapone enhances acoustic startle in healthy subjects

Previous human studies have shown that excess cortisol sufficient to fully occupy central nervous system (CNS) corticosteroid receptors may reduce startle eye blink. The present study tested whether cortisol depletion and the resulting reduction in activity of CNS corticosteroid receptors has the opposite effect. In a single-blind, placebo-controlled, randomized study, eye blink EMG responses to 105 dB acoustic startle stimuli were assessed in 25 healthy subjects who received oral metyrapone (1500 mg) to suppress endogenous cortisol production, while 24 controls received oral placebo. As expected, metyrapone significantly reduced salivary cortisol, indicating effective endogenous cortisol suppression. Startle eye blink responses were significantly increased in the metyrapone group. Short-term habituation of the startle reflex was not different between groups. Our results suggest that startle is enhanced during depletion of cortisol. This effect may be mediated by CNS mechanisms controlling cortisol feedback.

Recurrence of major depressive disorder is predicted by inhibited startle magnitude while recovered

BACKGROUND

Major depressive disorder, for some, follows a chronic relapsing course. However, no reliable marker has been established that allows the identification of this sub-group of patients. Preliminary findings suggest that baseline startle magnitude may be such a marker. This study evaluated whether differences in baseline startle magnitude during remission could prospectively predict depressive symptomatology and recurrence.

METHODS

A group of previously depressed individuals (n=25), who were in full remission at the time of testing, had their startle reflex measured via surface EMG electrodes on the left orbicularis oculi muscle. These people were then followed-up 2 years later and their depressive symptomatology during the intervening period was assessed using the psychiatric ratings scale of the Longitudinal Interval Follow-up Evaluation (LIFE; [Keller, M.B., Lavori, P.W., Friedman, B., Nielsen, E., Endicott, J., McDonald-Scott, P., et al. (1987). The Longitudinal Interval Follow-up Evaluation. A comprehensive method for assessing outcome in prospective longitudinal studies. Arch. Gen. Psychiatry, 44(6), 540-548]) and incidents of recurrence assessed using the Structured Clinical Interview for DSM-IV (SCID-I/P; [First, M.B., Spitzer, R.L., Gibbon, M., & Williams, J.B.W. (2001). Structured clinical interview for axis 1 DSM-IV disorders. New York: New York State Psychiatric Institute]).

RESULTS

It was found that a relatively attenuated startle response at initial assessment was strongly predictive of both depressive symptomatology and those who would experience relapse.

LIMITATIONS

This study has a relatively small sample size that limits the degree to which a thorough co-variant analysis can be conducted and also makes the analysis of gender-based difference impracticable. Additionally, as no healthy control group is included, we report a relative rather than absolute attenuation of startle to be indicative of symptom severity and recurrence proclivity.

CONCLUSIONS

These preliminary findings suggest that an attenuated startle response may have utility as an endophenotypic marker of risk for recurrence of Major Depression and residual sub-syndromal symptomatology. Such a marker may facilitate the early identification and treatment of those most at risk of recurrent Major Depression.

van der Mark M, de Kloet ER, S. Oitzl M. Differential MR/GR activation in mice results in emotional states beneficial or impairing for cognition

Corticosteroids regulate stress response and influence emotion, learning, and memory via two receptors in the brain, the high-affinity mineralocorticoid (MR) and low-affinity glucocorticoid receptor (GR). We test the hypothesis that MR- and GR-mediated effects interact in emotion and cognition when a novel situation is encountered that is relevant for a learning process. By adrenalectomy and additional constant corticosterone supplement we obtained four groups of male C57BL/6J mice with differential chronic MR and GR activations. Using a hole board task, we found that mice with continuous predominant MR and moderate GR activations were fast learners that displayed low anxiety and arousal together with high directed explorative behavior. Progressive corticosterone concentrations with predominant action via GR induced strong emotional arousal at the expense of cognitive performance. These findings underline the importance of a balanced MR/GR system for emotional and cognitive functioning that is critical for mental health.

Physiology and neurobiology of stress and adaptation: central role of the brain

The brain is the key organ of the response to stress because it determines what is threatening and, therefore, potentially stressful, as well as the physiological and behavioral responses which can be either adaptive or damaging. Stress involves two-way communication between the brain and the cardiovascular, immune, and other systems via neural and endocrine mechanisms. Beyond the "flight-or-fight" response to acute stress, there are events in daily life that produce a type of chronic stress and lead over time to wear and tear on the body ("allostatic load"). Yet, hormones associated with stress protect the body in the short-run and promote adaptation ("allostasis"). The brain is a target of stress, and the hippocampus was the first brain region, besides the hypothalamus, to be recognized as a target of glucocorticoids. Stress and stress hormones produce both adaptive and maladaptive effects on this brain region throughout the life course. Early life events influence life-long patterns of emotionality and stress responsiveness and alter the rate of brain and body aging. The hippocampus, amygdala, and prefrontal cortex undergo stress-induced structural remodeling, which alters behavioral and physiological responses. As an adjunct to pharmaceutical therapy, social and behavioral interventions such as regular physical activity and social support reduce the chronic stress burden and benefit brain and body health and resilience.

Neuroendocrine mechanisms of stress and social interaction: implications for mental disorders

PURPOSE OF REVIEW

The purpose of the present review is to consider further evidence for the role of neuroendocrine mechanisms in mental disorders by focusing on recent trends and advances in the field of psychoneuroendocrinology.

RECENT FINDINGS

Recent studies confirm the importance of the hypothalamic-pituitary-adrenal axis for the development and course of mental disorders. Notably, the neuropeptide oxytocin has been shown to reduce the responsiveness of the hypothalamic-pituitary-adrenal axis to social stress and to improve social approach behavior. A better understanding of the neuroendocrine mechanisms of action underlying normal behavior has recently been translated to studies investigating novel therapeutic approaches using hormone administration.

SUMMARY

Neuroendocrine systems relevant to behavior clearly demonstrate their impact for the field of psychiatry. Further neuroendocrine research provides insight into the origins of mental disorders both from an etiological perspective and an interventional perspective.

Multidrug-resistance gene 1-type p-glycoprotein (MDR1 p-gp) inhibition by tariquidar impacts on neuroendocrine and behavioral processing of stress

The multidrug-resistance gene 1-type p-glycoprotein (MDR1 p-gp) is a major gate-keeper at the blood-brain barrier (BBB), protecting the central nervous system from accumulation of toxic xenobiotics and drugs. In addition, MDR1 p-gp has been found to control the intracerebral access of glucocorticoid hormones and thus to modulate the activity of the hypothalamic-pituitary-adrenocortical (HPA) system. In view of the implication of glucocorticoids in the control of behavior, we examined how acute pharmacological inhibition of MDR1 p-gp at the BBB by tariquidar (XR9576; 12 mg/kg, PO) impacts the neuroendocrine and behavioral processing of stress in C57BL/6JIcoHim inbred mice. Inhibition of MDR1 p-gp at the BBB did not alter emotional behavior at baseline. However, mice that were sensitized by water-avoidance stress, a mild psychological stressor, displayed significantly reduced anxiety-related behavior in the elevated plus-maze test when treated with tariquidar. Tariquidar, however, had no effect on stress-coping performance assessed in the forced swim test. Investigating the impact of acute MDR1 p-gp inhibition on the glucocorticoid system, we observed a significant attenuation of the mild stress-induced increase of plasma corticosterone after tariquidar administration. In order to examine whether the anti-anxiety effect of tariquidar in sensitized animals is mediated by glucocorticoids, the animals were treated with corticosterone (1mg/kg, SC) immediately after exposure to water-avoidance stress. Corticosterone caused a significant anxiolytic-like effect in this stress-related anxiety protocol, whereas tariquidar could not further enhance corticosterone's anti-anxiety effects. The current data show for the first time that pharmacological inhibition of MDR1 p-gp at the murine BBB by tariquidar alters emotional behavior and HPA axis activity. By facilitating the entry of corticosterone into the brain, tariquidar enhances feedback inhibition of the HPA system and in this way improves anxiety-related stress processing. These findings highlight a novel approach to the treatment of stress-related affective disorders in humans.

Day-to-day dynamics of experience--cortisol associations in a population-based sample of older adults

In 156 older adults, day-to-day variations in cortisol diurnal rhythms were predicted from both prior-day and same-day experiences, to examine the temporal ordering of experience-cortisol associations in naturalistic environments. Diary reports of daily psychosocial, emotional, and physical states were completed at bedtime on each of three consecutive days. Salivary cortisol levels were measured at wakeup, 30 min after awakening, and at bedtime each day. Multilevel growth curve modeling was used to estimate diurnal cortisol profiles for each person each day. The parameters defining those profiles (wakeup level, diurnal slope, and cortisol awakening response) were predicted simultaneously from day-before and same-day experiences. Prior-day feelings of loneliness, sadness, threat, and lack of control were associated with a higher cortisol awakening response the next day, but morning awakening responses did not predict experiences of these states later the same day. Same-day, but not prior-day, feelings of tension and anger were associated with flatter diurnal cortisol rhythms, primarily because of their association with higher same-day evening cortisol levels. Although wakeup cortisol levels were not predicted by prior-day levels of fatigue and physical symptoms, low wakeup cortisol predicted higher levels of fatigue and physical symptoms later that day. Results are consistent with a dynamic and transactional function of cortisol as both a transducer of psychosocial and emotional experience into physiological activation and an influence on feelings of energy and physical well-being.