Brain corticosteroid receptor balance in health and disease

An inflammatory review of glucocorticoid actions in the CNS

In recent years, the classic view that glucocorticoids, the adrenal steroids secreted during stress, are universally anti-inflammatory has been challenged at a variety of levels. It was first observed that under some circumstances, acute GC exposure could have pro-inflammatory effects on the peripheral immune response. More recently, chronic exposure to GCs has been found to have pro-inflammatory effects on the specialized immune response to injury in the central nervous system. Here we review the evidence that in some cases, glucocorticoids can increase pro-inflammatory cell migration, cytokine production, and even transcription factor activity in the brain. We consider how these unexpected effects of glucocorticoids can co-exist with their well-established anti-inflammatory properties, as well as the considerable clinical implications of these findings.

Recent Studies on the Trimethyltin Actions in Central Nervous Systems

Trimethyltin (TMT) is a toxic organotin compound that produces injury to the central nervous systems of mammals. Recently, high-dose TMT (2.8 mg/kg) has been shown to produce neurodegeneration and subsequent neurogenesis specifically in the hippocampal dentate gyrus of mice, indicating that mice injected with TMT serve as a useful in vivo model to study neurogenesis as well as neurodegeneration in this brain region. In addition, gene-engineered mice have allowed research to focuse on the mechanisms of TMT toxicity. These studies have revealed the involvement of stannin, nuclear factor kappa B (NF-kappaB), presenilin-1, apolipoprotein E, and pituitary adenylyl cyclase-activating polypeptide (PACAP) in TMT toxicity and suggested the relationship between genetic mutations and neuronal susceptibility to degeneration. In this review, we briefly summarize the previous studies and discuss the current status of research on TMT.

The role of the hypothalamic-pituitary-adrenal axis in neuroendocrine responses to stress

Animals respond to stress by activating a wide array of behavioral and physiological responses that are collectively referred to as the stress response. Corticotropin-releasing factor (CRF) plays a central role in the stress response by regulating the hypothalamic-pituitary-adrenal (HPA) axis. In response to stress, CRF initiates a cascade of events that culminate in the release of glucocorticoids from the adrenal cortex. As a result of the great number of physiological and behavioral effects exerted by glucocorticoids, several mechanisms have evolved to control HPA axis activation and integrate the stress response. Glucocorticoid feedback inhibition plays a prominent role in regulating the magnitude and duration of glucocorticoid release. In addition to glucocorticoid feedback, the HPA axis is regulated at the level of the hypothalamus by a diverse group of afferent projections from limbic, mid-brain, and brain stem nuclei. The stress response is also mediated in part by brain stem noradrenergic neurons, sympathetic andrenornedullary circuits, and parasympathetic systems. In summary, the aim of this review is to discuss the role of the HPA axis in the integration of adaptive responses to stress. We also identify and briefly describe the major neuronal and endocrine systems that contribute to the regulation of the HPA axis and the maintenance of homeostasis in the face of aversive stimuli.

Restraint-induced corticosterone secretion and hypothalamic CRH mRNA expression are augmented during acute withdrawal from chronic cocaine administration

Stress responses during cocaine withdrawal likely contribute to drug relapse and may be intensified as a consequence of prior cocaine use. The present study examined changes in stressor-induced activation of the hypothalamic-pituitary-adrenal (HPA) axis during acute withdrawal from chronic cocaine administration. Adult male Sprague-Dawley rats received daily administration of cocaine (30 mg/kg, i.p.) or saline for 14 days. Twenty-four hours after the last injection, rats in each group were sacrificed under stress-free conditions or following 30 min of immobilization. Plasma corticosterone (CORT) was measured in trunk-blood using radioimmunoassay, corticotropin-releasing hormone (CRH) mRNA levels in the paraventricular nucleus (PVN) of the hypothalamus were measured using in situ hybridization and glucocorticoid receptor (GR) protein expression in the pituitary gland and dissected brain regions was measured using Western blot analysis. Basal CRH mRNA in the PVN was unaltered as a result of prior cocaine administration. However, a significant increase in CRH mRNA was observed 90 min following the termination of restraint in cocaine withdrawn, but not saline-treated, rats. Basal CORT was also unaffected by prior cocaine administration, but the CORT response measured immediately after restraint was significantly augmented in cocaine-withdrawn rats. Differences in GR protein expression in number of regions implicated in negative feedback regulation of HPA function, including the hypothalamus, were not observed. These findings indicate that the HPA response to stressors is intensified during early withdrawal from cocaine administration and may be independent of changes in GR-mediated negative feedback.

The role of the medial prefrontal cortex-amygdala circuit in stress effects on the extinction of fear

Stress exposure, depending on its intensity and duration, affects cognition and learning in an adaptive or maladaptive manner. Studies addressing the effects of stress on cognitive processes have mainly focused on conditioned fear, since it is suggested that fear-motivated learning lies at the root of affective and anxiety disorders. Inhibition of fear-motivated response can be accomplished by experimental extinction of the fearful response to the fear-inducing stimulus. Converging evidence indicates that extinction of fear memory requires plasticity in both the medial prefrontal cortex and the amygdala. These brain areas are also deeply involved in mediating the effects of exposure to stress on memory. Moreover, extensive evidence indicates that gamma-aminobutyric acid (GABA) transmission plays a primary role in the modulation of behavioral sequelae resulting from a stressful experience, and may also partially mediate inhibitory learning during extinction. In this review, we present evidence that exposure to a stressful experience may impair fear extinction and the possible involvement of the GABA system. Impairment of fear extinction learning is particularly important as it may predispose some individuals to the development of posttraumatic stress disorder. We further discuss a possible dysfunction in the medial prefrontal cortex-amygdala circuit following a stressful experience that may explain the impaired extinction caused by exposure to a stressor.

Cytokine-effects on glucocorticoid receptor function: relevance to glucocorticoid resistance and the pathophysiology and treatment of major depression

Glucocorticoids play an essential role in the response to environmental stressors, serving initially to mobilize bodily responses to challenge and ultimately serving to restrain neuroendocrine and immune reactions. A number of diseases including autoimmune, infectious and inflammatory disorders as well as certain neuropsychiatric disorders such as major depression have been associated with decreased responsiveness to glucocorticoids (glucocorticoid resistance), which is believed to be related in part to impaired functioning of the glucocorticoid receptor (GR). Glucocorticoid resistance, in turn, may contribute to excessive inflammation as well as hyperactivity of corticotropin releasing hormone and sympathetic nervous system pathways, which are known to contribute to a variety of diseases as well as behavioral alterations. Recent data indicate that glucocorticoid resistance may be a result of impaired GR function secondary to chronic exposure to inflammatory cytokines as may occur during chronic medical illness or chronic stress. Indeed, inflammatory cytokines and their signaling pathways including mitogen-activated protein kinases, nuclear factor-kappaB, signal transducers and activators of transcription, and cyclooxygenase have been found to inhibit GR function. Mechanisms include disruption of GR translocation and/or GR-DNA binding through protein-protein interactions of inflammatory mediators with the GR itself or relevant steroid receptor cofactors as well as alterations in GR phosphorylation status. Interestingly, cAMP signal transduction pathways can enhance GR function and inhibit cytokine signaling. Certain antidepressants have similar effects. Thus, further understanding the effects of cytokines on GR signaling and the mechanisms involved may reveal novel therapeutic targets for reversal of glucocorticoid resistance and restoration of glucocorticoid-mediated inhibition of relevant bodily/immune responses during stress and immune challenge.

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.

Glucocorticoids: exemplars of multi-tasking

Well over 80 years ago Philip Smith described the beneficial clinical effects of adrenocortical extracts in animal models of adrenal insufficiency. In the ensuing years, scientists across the globe have sought to understand the mechanisms by which adrenal hormones and their synthetic analogues produce their complex and varied actions. Particular attention has focused on the glucocorticoids, partly because they have a vital place in the treatment of inflammatory and autoimmune disorders but also because dysregulation of the secretion and/or activity of endogenous glucocorticoids is increasingly implicated in a number of common disorders that pose a growing clinical burden, such as obesity, type II diabetes, the metabolic syndrome, hypertension and depression. This review considers some of the key advances that have been made in our understanding of the physiology, pathology and pharmacology of the glucocorticoids. Emphasis is placed on the molecular mechanisms of glucocorticoid signalling and the complex mechanisms that regulate the access of steroids in the systemic circulation to their receptors in their various target cells and tissues. In addition, consideration is given to the irreversible 'organisational' actions of glucocorticoids in perinatal life and to the potential role of the steroids in the aetiology of disease.

Cortisol responses of healthy volunteers undergoing magnetic resonance imaging

Self-reported anxiety is associated with various medical procedures, including structural and functional magnetic resonance imaging (MRI). The present study tested the hypothesis that MRI scanning would be associated with elevated cortisol levels in participants with no prior scanning experience. Baseline and post-scan cortisol levels, as well as measures of state and trait anxiety, were obtained from scanner-naive (n = 6) and scanner-experienced (n = 8) research participants. The anxiety scores and cortisol responses of the scanner-naive and scanner-experienced participants were compared. Subjects novel to MRI were no more anxious before the scan than were subjects familiar with the MRI examination, but the scanner-naive subjects manifested heightened post-scan cortisol secretion when compared to their pre-scan level and when compared to the scanner-experienced participants. The results are consistent with the hypothesis that the scanning environment can induce cortisol elevations and are congruent with the well-established effects of acute stressors on activity of the hypothalamic-pituitary-adrenal (HPA) axis. The implications for neuroimaging studies are discussed.

Different responses to dexamethasone and prednisolone in the same depressed patients

RATIONALE

Patients with major depression show hypothalamic-pituitary-adrenal (HPA) axis hyperactivity, but the mechanisms underlying this abnormality are still unclear.

OBJECTIVES

We have compared two synthetic glucorticoids, dexamethasone and prednisolone, in their ability to suppress the hypothalamic-pituitary-adrenal (HPA) axis in depressed patients. Dexamethasone probes glucocorticoid receptor (GR) function, while prednisolone probes both GR and mineralocorticoid receptor (MR) function.

MATERIALS AND METHODS

We used a single-blind, repeated-measure design. We administered placebo, prednisolone (5 mg) or dexamethasone (0.5 mg), at 22:00, to 18 severe, treatment-resistant depressed inpatients (15 of them with a history of childhood trauma) and 14 healthy volunteers. On the following days, we collected salivary cortisol from 9:00 to 22:00.

RESULTS

Depressed patients had higher salivary cortisol levels compared with controls, at baseline and after both prednisolone and dexamethasone (p<0.001). Consistent with previous studies, depressed inpatients showed impaired suppression by dexamethasone: based on the analysis of the areas under the curve (AUCs), suppression by dexamethasone (0.5 mg) was -85% in controls vs -46% in depressed patients (p=0.018). However, the same depressed patients showed normal suppression by prednisolone (5 mg): suppression was -41% in controls and -36% in depressed patients (p=0.6).

CONCLUSIONS

We suggest that the additional effects of prednisolone on the MR explain the different responses to these glucocorticoids in the same depressed patients.

Chronic activation of dorsal hindbrain corticosteroid receptors augments the arterial pressure response to acute stress

Augmented cardiovascular responses to acute stress can predict cardiovascular disease in humans. Chronic systemic increases in glucocorticoids produce enhanced cardiovascular responses to psychological stress; however, the site of action is unknown. Recent evidence indicates that glucocorticoids can act within the dorsal hindbrain to modulate cardiovascular function. Therefore, we tested the hypothesis that the endogenous glucocorticoid corticosterone can act in the dorsal hindbrain to enhance cardiovascular responses to restraint stress in conscious rats. Adrenal-intact animals with indwelling arterial catheters were treated for 4 or 6 days with 3- to 4-mg pellets of corticosterone or silastic (sham pellets) implanted on the dorsal hindbrain surface. Corticosterone pellets were also implanted either on the surface of the dura or subcutaneously to control for the systemic effects of corticosterone (systemic corticosterone). The integrated increase in arterial pressure during 1 hour of restraint stress was significantly (P<0.05) greater in dorsal hindbrain corticosterone (912+/-98 mm Hg per 60 minutes) relative to dorsal hindbrain sham (589+/-57 mm Hg per 60 minutes) or systemic corticosterone (592+/-122 mm Hg per 60 minutes) rats. The plasma glucose response after 10 minutes of stress was also significantly higher in dorsal hindbrain corticosterone-treated rats relative to both other groups. There were no significant between-group differences in the heart rate or corticosterone responses to stress. There were no differences in baseline values for any measured parameters. We conclude that corticosterone can act selectively in the dorsal hindbrain in rats with normal plasma corticosterone levels to augment the arterial pressure response to restraint stress.

Contrasting roles of corticosteroid receptors in hippocampal plasticity

Elevated levels of corticosteroid hormones, presumably occupying both mineralocorticoid receptors (MRs) and glucocorticoid receptors (GRs), have been reported to impair synaptic plasticity in the hippocampus as well as the acquisition of hippocampus-dependent memories. In contrast, recent evidence suggests that activation of MRs enhance cognitive functions. To clarify the roles of different steroid receptors in hippocampal plasticity, young adult rats were injected with the GR antagonist RU38486 (mifepristone) or the MR antagonist Spironolactone before the exposure to an acute swim stress. Hippocampal responses to perforant path stimulation were then recorded in anesthetized rats. Stress combined with RU38486 produced a striking facilitation of LTP. Spironolactone enabled only short-term potentiation that reversed to long-term depression (LTD) in the stressed animals. Finally, the blockade of both MRs and GRs led to impairment of long-term potentiation. These findings indicate that MRs and GRs assume opposite roles in regulation of synaptic plasticity after acute exposure to stressors.

Ontogeny of the adrenal response to (+)-methamphetamine in neonatal rats: the effect of prior drug exposure

We examined the ontogeny of the corticosterone response to (+)-methamphetamine in neonatal rats. In experiment-1, animals were injected with 10 mg/kg of (+)-methamphetamine or saline and plasma corticosterone levels were examined in separate groups 30 or 105 min later on postnatal day (P) 1, 3, 5, 7, 9, 11, 13, 15, 17, or 19. The adrenal response to methamphetamine was best described by a U-shaped function with the nadir of corticosterone release occurring between P7 and P13. Experiment-2 was similar except that the effect of four consecutive days of exposure to (+)-methamphetamine (four times daily at 2 h intervals with 10 mg/kg) was assessed with a single final dose early on the fifth day (i.e. P1-5, 3-7, 5-9, 7-11, 9-13, 11-15, 13-17, 15-19). The 30 min corticosterone response after multiple methamphetamine doses was augmented compared to single exposures, with the exception of the two earliest dosing intervals ending on P5 and P7, where the responses were lower. In addition, at 105 min, the levels of corticosterone were attenuated relative to a single drug administration. With the exception of animals receiving methamphetamine from P15 to P19, thymus weights were unaffected. The data demonstrate that (+)-methamphetamine is a robust activator of corticosterone release in developing animals and this release is extensively modified by age and previous drug exposure.

From bedside to bench and back again: research issues in animal models of human disease

To improve outcomes for patients with many serious clinical problems, multifactorial research approaches by nurse scientists, including the use of animal models, are necessary. Animal models serve as analogies for clinical problems seen in humans and must meet certain criteria, including validity and reliability, to be useful in moving research efforts forward. This article describes research considerations in the development of rodent models. As the standard of diabetes care evolves to emphasize intensive insulin therapy, rates of severe hypoglycemia are increasing among patients with type 1 and type 2 diabetes mellitus. A consequence of this change in clinical practice is an increase in rates of two hypoglycemia-related diabetes complications: hypoglycemia-associated autonomic failure (HAAF) and resulting hypoglycemia unawareness. Work on an animal model of HAAF is in an early developmental stage, with several labs reporting different approaches to model this complication of type 1 diabetes mellitus. This emerging model serves as an example illustrating how evaluation of validity and reliability is critically important at each stage of developing and testing animal models to support inquiry into human disease.

Permissive influence of stress in the expression of a U-shaped relationship between serum corticosterone levels and spatial memory errors in rats

The relationship between glucocorticoids (GCs) and memory is complex, in that memory impairments can occur in response to manipulations that either increase or decrease GC levels. We investigated this issue by assessing the relationship between serum corticosterone (the primary rodent GC) and memory in rats trained in the radial arm water maze, a hippocampus-dependent spatial memory task. Each day, rats learned a new location of the hidden escape platform and then 30 min later their memory of the location of the platform was tested. Under control conditions, well-trained rats had excellent spatial memory and moderately elevated corticosterone levels (approximately 26 microg/dl versus a baseline of approximately 2 microg/dl). Their memory was impaired when corticosterone levels were either reduced by metyrapone (a corticosterone synthesis inhibitor) or increased by acute stress (predator exposure), forming an overall U-shaped relationship between corticosterone levels and memory. We then addressed whether there was a causal relationship between elevated corticosterone levels and impaired memory. If elevated corticosterone levels were a sufficient condition to impair memory, then exogenously administered corticosterone, alone, should have impaired performance. However, we found that spatial memory was not impaired in corticosterone-injected rats that were not exposed to the cat. This work demonstrates that an intermediate level of corticosterone correlated with optimal memory, and either a decrease or an increase in corticosterone levels, in conjunction with strong emotionality, impaired spatial memory. These findings indicate that fear-provoking conditions, which are known to engage the amygdala, interact with stress levels of corticosterone to influence hippocampal functioning.

Concentration dependent actions of glucocorticoids on neuronal viability and survival

A growing body of evidence based on experimental data demonstrates that glucocorticoids (GCs) can play a potent role in the survival and death of neurons. However, these observations reflect paradoxical features of GCs, since these adrenal stress hormones are heavily involved in both neurodegenerative and neuroprotective processes. The actual level of GCs appears to have an essential impact in this bimodal action. In the present short review we aim to show the importance of concentration dependent action of GCs on neuronal cell viability and cell survival in the brain. Additionally, we will summarize the possible GC-induced cellular mechanisms at different GC concentrations providing a background for their effect on the fate of nerve cells in conditions that are a challenge to their survival.

Glucocorticoid hormones decrease proliferation of embryonic neural stem cells through ubiquitin-mediated degradation of cyclin D1

Corticosteroids can influence brain function, and glucocorticoid hormone receptors (GRs) are present in brain tissue. We observed that GR and also mineralocorticoid receptor (MR) are expressed by embryonic rat neural stem cells (NSCs). NSCs in developing ventricular epithelium were positive for GR. Stimulation of cultured NSCs with the specific receptor ligands dexamethasone and corticosterone reduced cell proliferation, shown by 5'-bromo-2-deoxy-uridine labeling. The effect of the hormones was dose dependent and inhibited by the GR blocker mifepristone but not by spironolactone, blocking MR. Dexamethasone inhibited the cell cycle by decreasing the levels of cyclin D1 in NSCs. The hormone-induced decline was inhibited by MG132 (benzyloxycarbonyl-leucyl-leucyl-leucinal), showing an involvement of the ubiquitin proteasome system, In keeping with this, dexamethasone increased the ubiquitination of cyclin D1. In embryonic brain, dexamethasone inhibited cell proliferation of NSCs. This demonstrates that embryonic NSCs are critically influenced by glucocorticoids, which can have long-term effects in the brain.

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

Stress potently modulates anxiety- and depression-related behaviors. In response to stressors, the hypothalamic-pituitary-adrenal (HPA) axis is activated, resulting in the release of glucocorticoids from the adrenal cortex. These hormones act peripherally to restore homeostasis but also feed back to the CNS to control the intensity and duration of the stress response. Glucocorticoids act in limbic areas of the CNS to mediate the psychological and behavioral effects of stress. In this study, we investigate the effect of forebrain-specific disruption of the glucocorticoid receptor (GR) on stress- and anxiety-related behaviors. We demonstrate that mice with disruption of forebrain GR show alterations in stress-induced locomotor activation in a number of anxiety-related behavioral paradigms. These changes are associated with alterations in stress-induced HPA axis activation and, importantly, are not attenuated by chronic treatment with the tricyclic antidepressant imipramine. These data demonstrate the importance of forebrain GR in regulation of physiological and behavioral stress reactivity and suggest that distinct pathways regulate despair- and anxiety-related behaviors.

Identification of genes regulated by chronic social stress in the rat dorsal raphe nucleus

1. Changes in the serotonergic (5-HT) system are suspected to play a role in stress-induced neuropathologies and neurochemical measures indicate that serotonergic neurons in the dorsal raphe nucleus (DRN) are activated during stress. In the present study we analyzed gene expression in the DRN after chronic social stress using subtractive cDNA hybridization. 2. In the resident intruder paradigm, male Wistar rats were chronically stressed by daily social defeat during 5 weeks, RNA was isolated from their DRN, cDNA was generated, and subtractive hybridization was performed to clone sequences that are differentially expressed in the stressed animals. 3. From the cDNA libraries that were obtained, we selected the following genes for quantitative Real-time PCR: Two genes related to neurotransmission (synaptosomal associated protein 25 and synaptic vesicle glycoprotein 2b), a glial gene presumptively supporting neuroplasticity (N-myc downstream-regulated gene 2), and a gene possibly related to stress-induced regulation of transcription (CREB binding protein). These four genes were upregulated after the chronic social stress. Quantitative Western blotting revealed increased expression of synaptosomal associated protein 25 and synaptic vesicle glycoprotein 2b. 4. Genes directly related to 5-HT neurotransmission were not contained in the cDNA libraries and quantitative Real-time PCR for the serotonin transporter, tryptophan hydroxylase 2 and the 5-HT(1A) autoreceptor confirmed that these genes are not differentially expressed after 5-weeks of daily social stress. 5. These data show that 5 weeks of daily social defeat lead to significant changes in expression of genes related to neurotransmission and neuroplasticity in the DRN, whereas expression of genes directly related to 5-HT neurotransmission is apparently normal after this period of chronic stress.

Neuroplasticity of the hypothalamic-pituitary-adrenal axis early in life requires recurrent recruitment of stress-regulating brain regions

An eloquent example of experience-induced neuroplasticity involves the enduring effects of daily "handling" of rat pups on the expression of genes regulating hormonal and behavioral responses to stress. Handling-evoked augmentation of maternal care of pups induces long-lasting reduction of hypothalamic corticotropin releasing hormone (CRH) expression and upregulates hippocampal glucocorticoid receptor levels. These changes promote a lifelong attenuation of hormonal stress responses. We have found previously that handling-evoked downregulation of CRH expression occurs already by postnatal day 9, implicating it as an early step in this experience-induced neuroplasticity. Here, we investigated the neuronal pathways and cellular mechanisms involved. CRH mRNA expression in hypothalamic paraventricular nucleus (PVN) diminished after daily handling but not after handling once only, indicating that "recurrent" handling was required for this effect. Return of handled pups to their cage provoked a burst of nurturing behavior in dams that, in turn, induced transient, coordinate Fos expression in selected regions of the pups' brains. These included central nucleus of the amygdala (ACe) and bed nucleus of the stria terminals (BnST), regions that are afferent to PVN and influence CRH expression there. Whereas handling once sufficed to evoke Fos expression within ACe and BnST, expression in thalamic paraventricular nucleus, a region involved in storing and processing stress-related experience, required recurrent handling. Fos induction in all three regions elicited reduced transcription factor phosphorylation, followed by attenuated activation of CRH gene transcription within the PVN. These studies provide a neurobiological foundation for the profound neuroplasticity of stress-related genes evoked by early-life experience.

Maternal stress produces learning deficits associated with impairment of NMDA receptor-mediated synaptic plasticity

Stress in adulthood can have a profound effect on physiology and behavior, but the extent to which prolonged maternal stress affects the brain function of offspring when they are adult remains primarily unknown. In the present work, chronic immobilization stress to pregnant mice affected fetal growth and development. When pups born from stressed mice were reared to adulthood in an environment identical to that of nonstressed controls, several physiological parameters were essentially unaltered. However, spatial learning and memory was significantly impaired in the maternally stressed offspring in adulthood. Furthermore, electrophysiological examination revealed a significant reduction in NMDA receptor-mediated long-term potentiation in the CA1 area of hippocampal slices. Subsequent biochemical analysis demonstrated a substantial decrease in NR1 and NR2B subunits of the NMDA receptor in synapses of the hippocampus, and the interaction between these two subunits appeared to be reduced. These results suggest that prolonged maternal stress leads to long-lasting malfunction of the hippocampus, which extends to and is manifested in adulthood.

Impaired memory retrieval after psychosocial stress in healthy young men

Glucocorticoids (GCs) are known to modulate memory in animals and humans. One popular model suggests that stress or GC treatment enhances memory consolidation while impairing delayed memory retrieval. Studies in humans have documented that treatment with GCs impairs delayed memory retrieval. Similar alterations after exposure to stress have not been observed thus far. In the present study, 19 young healthy male subjects were exposed to either a standardized psychosocial laboratory stressor (Trier Social Stress Test) or a control condition in a crossover manner. After both treatments, retrieval of a word list (learned 24 h earlier) containing 10 neutral, 10 negative, and 10 positive words was tested. The stressor induced a significant increase in salivary free cortisol and a decrease in mood. Memory retrieval (free recall) was significantly impaired after the stress condition. Follow-up analysis revealed that negative and positive words (i.e., emotionally arousing words) were affected, whereas no effect was observed for neutral words. No changes were detected for cued recall, working memory, or attention. The present study thus demonstrates that psychosocial stress impairs memory retrieval in humans and suggests that emotionally arousing material is especially sensitive to this effect.

Reversal of maternal programming of stress responses in adult offspring through methyl supplementation: altering epigenetic marking later in life

Stress responses in the adult rat are programmed early in life by maternal care and associated with epigenomic marking of the hippocampal exon 1(7) glucocorticoid receptor (GR) promoter. To examine whether such epigenetic programming is reversible in adult life, we centrally infused the adult offspring with the essential amino acid L-methionine, a precursor to S-adenosyl-methionine that serves as the donor of methyl groups for DNA methylation. Here we report that methionine infusion reverses the effect of maternal behavior on DNA methylation, nerve growth factor-inducible protein-A binding to the exon 1(7) promoter, GR expression, and hypothalamic-pituitary-adrenal and behavioral responses to stress, suggesting a causal relationship among epigenomic state, GR expression, and stress responses in the adult offspring. These results demonstrate that, despite the inherent stability of the epigenomic marks established early in life through behavioral programming, they are potentially reversible in the adult brain.

Morphological correlates of corticosteroid-induced changes in prefrontal cortex-dependent behaviors

Imbalances in the corticosteroid milieu have been implicated in several neuropsychiatric disorders, including depression and schizophrenia. Prefrontal cortex (PFC) dysfunction is also a hallmark of these conditions, causing impairments in executive functions such as behavioral flexibility and working memory. Recent studies have suggested that the PFC might be influenced by corticosteroids released during stress. To test this possibility, we assessed spatial working memory and behavioral flexibility in rats submitted to chronic adrenalectomy or treatment with corticosterone (25 mg/kg) or the synthetic glucocorticoid dexamethasone (300 microg/kg); the behavioral analysis was complemented by stereological evaluation of the PFC (prelimbic, infralimbic, and anterior cingulate regions), the adjacent retrosplenial and motor cortices, and the hippocampal formation. Dexamethasone treatment resulted in a pronounced impairment in working memory and behavioral flexibility, effects that correlated with neuronal loss and atrophy of layer II of the infralimbic, prelimbic, and cingulate cortices. Exposure to corticosterone produced milder impairments in behavioral flexibility, but not in working memory, and reduced the volume of layer II of all prefrontal areas. Interestingly, adrenalectomy-induced deleterious effects only became apparent on the reverse learning task and were not associated with structural alterations in the PFC. None of the experimental procedures influenced the morphology of retrosplenial or motor cortices, but stereological measurements confirmed previously observed effects of corticosteroids on hippocampal structure. Our results describe, for the first time, that imbalances in the corticosteroid environment can induce degeneration of specific layers of the PFC; these changes appear to be the morphological correlate of corticosteroid-induced impairment of PFC-dependent behavior(s).

Akinetic mutism followed by a manic reaction on introduction of steroid replacement for Addison's disease

Neuropsychiatric changes during exogenous corticosteroid administration are well-recognized. However, reports of neuropsychiatric reactions to corticosteroid replacement for Addison's disease are distinctively rare. We report on a patient with primary adrenocortical insufficiency, initially presenting with depressive symptoms, who developed akinetic mutism followed by acute manic illness shortly after the initiation of steroid replacement. Both disorders occurred with physiological doses of hydrocortisone and resolved spontaneously. The pathogenesis of the above neuropsychiatric reactions is discussed in the context of glucocorticoid receptor-related brain effects of glucocorticoids. In addition, this report points to the need for accurate psychiatric assessment of patients with Addison's disease upon introduction of replacement therapy.

Maternal care effects on the hippocampal transcriptome and anxiety-mediated behaviors in the offspring that are reversible in adulthood

Early-life experience has long-term consequences on behavior and stress responsivity of the adult. We previously proposed that early-life experience results in stable epigenetic programming of glucocorticoid receptor gene expression in the hippocampus. The aim of this study was to examine the global effect of early-life experience on the hippocampal transcriptome and the development of stress-mediated behaviors in the offspring and whether such effects were reversible in adulthood. Adult offspring were centrally infused with saline vehicle, the histone deacetylase inhibitor trichostatin A (TSA), or the essential amino acid l-methionine. The animals were assessed in an unfamiliar open-field arena, and the hippocampal transcriptome of each animal was evaluated by microarray analysis. Here we report that TSA and methionine treatment reversed the effect of maternal care on open-field behavior. We identified >900 genes stably regulated by maternal care. A fraction of these differences in gene expression is reversible by either the histone deacetylase inhibitor TSA or the methyl donor l-methionine. These results suggest that early-life experience has a stable and broad effect on the hippocampal transcriptome and anxiety-mediated behavior, which is potentially reversible in adulthood.

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

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

Loss of the limbic mineralocorticoid receptor impairs behavioral plasticity

Corticosteroid action in the brain is mediated by the mineralocorticoid (MR) and the glucocorticoid (GR) receptor. Disturbances in MR- and GR-mediated effects are thought to impair cognition, behavior, and endocrine control. To assess the function of the limbic MR in these processes, we inactivated the MR gene in the forebrain of the mouse using the Cre/loxP-recombination system. We screened the mice with a limbic MR deficiency in various learning and exploration tests. The mutant mice show impaired learning of the water-maze task and deficits in measures of working memory on the radial maze due to behavioral perseverance and stereotypy. They exhibit a hyperreactivity toward a novel object but normal anxiety-like behavior. The behavioral changes are associated with abnormalities of the mossy fiber projection and an up-regulation of GR expression in the hippocampus. Adult mutant mice show normal corticosterone levels at circadian trough and peak. This genetic model provides important information about the consequences of a permanently altered balance between limbic MR and GR, with implications for stress-related neuroendocrine and neuropsychiatric diseases.

Environmental programming of stress responses through DNA methylation: life at the interface between a dynamic environment and a fixed genome

Early experience permanently alters behavior and physiology. These effects are, in part, mediated by sustained alterations in gene expression in selected brain regions. The critical question concerns the mechanism of these environmental “programming” effects. We examine this issue with an animal model that studies the consequences of variations in mother-infant interactions on the development of individual differences in behavioral and endocrine responses to stress in adulthood. Increased levels of pup licking/grooming by rat mothers in the first week of life alter DNA structure at a glucocorticoid receptor gene promoter in the hippocampus of the offspring. Differences in the DNA methylation pattern between the offspring of high- and low-lickinglgrooming mothers emerge over the first week of life; they are reversed with cross-fostering; they persist into adulthood; and they are associated with altered histone acetylation and transcription factor (nerve growth factor-induced clone A [NGFIA]) binding to the glucocorticoid receptor promoter. DNA methylation alters glucocorticoid receptor expression through modifications of chromatin structure. Pharmacological reversal of the effects on chromatin structure completely eliminates the effects of maternal care on glucocorticoid receptor expression and hypothalamic-pituitary-adrenal (HPA) responses to stress, thus suggesting a causal relation between the maternally induced, epigenetic modification of the glucocorticoid receptor gene and the effects on stress responses in the offspring. These findings demonstrate that the structural modifications of the DNA can be established through environmental programming and that, in spite of the inherent stability of this epigenomic marker, it is dynamic and potentially reversible.

Corticosteroid receptor genetic polymorphisms and stress responsivity

A fundamental question in the neuroendocrinology of stress-related psychopathology is why some individuals flourish and others perish under similar adverse conditions. In this contribution we focus on the variants of mineralocorticorticoid (MR) and glucocorticoid receptors (GR) that operate in balance and coordinate behavioral, autonomic, and neuroendocrine response patterns involved in homeostasis and health. In the GR-gene, three single nucleotide polymorphism (SNPs) have been associated with changes in metabolic profile and cardiovascular parameters: the ER22/23EK with a favorable and the N363S and the Bcl1 with a more adverse profile. Importantly, the N363S and the Bcl1 are found to increase cortisol responses to a psychosocial stressor. As a result, the whole body will suffer from overexposure with possible adverse effects on metabolism, cardiovascular control, immune function, and behavior. Also in the MR gene, variants are being identified that are associated with dysregulated autonomic, behavioral, and neuroendocrine responses. The data suggest that these MR and GR variants contribute to individual differences in resilience and vulnerability to stressors, and that these receptors therefore are potential drug targets for recovery of homeostasis and health.

Enduring, handling-evoked enhancement of hippocampal memory function and glucocorticoid receptor expression involves activation of the corticotropin-releasing factor type 1 receptor

Early-life experience, including maternal care, influences hippocampus-dependent learning and memory throughout life. Handling of pups during postnatal d 2-9 (P2-9) stimulates maternal care and leads to improved memory function and stress-coping. The underlying molecular mechanisms may involve early (by P9) and enduring reduction of hypothalamic corticotropin-releasing factor (CRF) expression and subsequent (by P45) increase in hippocampal glucocorticoid receptor (GR) expression. However, whether hypothalamic CRF levels influence changes in hippocampal GR expression (and memory function), via reduced CRF receptor activation and consequent lower plasma glucocorticoid levels, is unclear. In this study we administered selective antagonist for the type 1 CRF receptor, NBI 30775, to nonhandled rats post hoc from P10-17 and examined hippocampus-dependent learning and memory later (on P50-70), using two independent paradigms, compared with naive and vehicle-treated nonhandled, and naive and antagonist-treated handled rats. Hippocampal GR and hypothalamic CRF mRNA levels and stress-induced plasma corticosterone levels were also examined. Transient, partial selective blockade of CRF1 in nonhandled rats improved memory functions on both the Morris watermaze and object recognition tests to levels significantly better than in naive and vehicle-treated controls and were indistinguishable from those in handled (naive, vehicle-treated, and antagonist-treated) rats. GR mRNA expression was increased in hippocampal CA1 and the dentate gyrus of CRF1-antagonist treated nonhandled rats to levels commensurate with those in handled cohorts. Thus, the extent of CRF1 activation, probably involving changes in hypothalamic CRF levels and release, contributes to the changes in hippocampal GR expression and learning and memory functions.

3,4-Methylenedioxymethamphetamine administration on postnatal day 11 in rats increases pituitary-adrenal output and reduces striatal and hippocampal serotonin without altering SERT activity

We have previously shown that +/-3,4-methylenedioxymethamphetamine (MDMA) treatment from P11 to P20 in rats produces deficits in cognitive ability when these animals are tested in adulthood. The purpose of this experiment was to explore the neuroendocrine and neurochemical changes produced by MDMA treatment on P11. We examined monoamines in the hippocampus and striatum and the serotonin transporter in the hippocampus as well as pituitary and adrenal output following administration of MDMA (10 mg/kg, 4 times) on postnatal day 11. Significant depletions in serotonin were evident in the hippocampus 1 h and in the striatum 24 h after the first dose and remained reduced 78 h later. No changes in serotonin transporter were observed following MDMA treatment, although females had lower levels than males. No changes in dopamine were detected. The metabolites of serotonin and dopamine had different profiles than the parent compounds after MDMA administration. Plasmatic ACTH was elevated immediately following MDMA and remained elevated for at least 1 h after the last dose and returned to baseline by 24 h. Corticosterone was increased after the first dose and remained increased for at least 24 h, and returned to baseline by 30 h. The decreases in serotonin in regions important for learning and memory in conjunction with elevated levels of corticosterone during a period of stress hyporesponsiveness suggest that these initial responses to MDMA may contribute to the long-term learning and memory deficits following neonatal MDMA exposure.

Effects of psychologic stress on fetal development and pregnancy outcome

Data from animal studies show that maternal stress is associated with disturbances in pregnancy outcomes and offspring development and behavior, possibly as a result of permanent structural and functional changes termed "early-life programming." There is growing interest in whether similar relationships are present in humans. Here we review recent significant findings from the literature on the impact of prenatal psychologic stressors on pregnancy outcome and offspring development, with a particular focus on the developing brain. Relevant papers were searched using PubMed, and reference lists from obtained articles were checked. In humans, prenatal stress is associated with pregnancy complications, developmental, cognitive, and behavioral disorders, and possible onset of psychopathology in later life. In contrast to the available research done in animals, virtually nothing is known about the effects of prenatal stress on morphologic fetal brain development, and the mechanisms underlying subsequent associated behavioral changes.

Prenatal corticosteroid impact on hippocampus: implications for postnatal outcomes

Prenatal administration of corticosteroids is common in obstetrics to improve the outcome of premature deliveries. Many pregnant women receive multiple corticosteroid courses. Long-term follow-up studies in humans are limited, but those available suggest detrimental effects on the behavior of those children. Animal data also show adverse effects of prenatal corticosteroids mainly in the hippocampus, a structure sensitive to corticosteroid action. Several molecules involved in neuronal survival, seizure susceptibility, and behavior have been identified as possible targets of prenatal corticosteroid effects. These molecules include hippocampal glucocorticoid receptors, brain-derived neurotrophic factor, corticotropin-releasing hormone, and neuropeptide Y. Prenatal corticosteroid treatment permanently reprograms expression of these molecules. The future goals of research in this area include development of specific antagonists of corticosteroid activation pathways that would help differentiate between positive main effects and undesired adverse effects of prenatally administered corticosteroids.

Structural and functional brain development after hydrocortisone treatment for neonatal chronic lung disease

OBJECTIVE

There is much concern about potential neurodevelopmental impairment after neonatal corticosteroid treatment for chronic lung disease. Dexamethasone is the corticosteroid most often used in this clinical setting, and it has been shown to impair cortical growth among preterm infants. This study evaluated long-term effects of prematurity itself and of neonatal hydrocortisone treatment on structural and functional brain development using three-dimensional MRI with advanced image-processing and neurocognitive assessments.

METHODS

Sixty children born preterm, including 25 children treated with hydrocortisone and 35 children not treated with hydrocortisone, and 21 children born at term were evaluated, at a mean age of 8 years, with quantitative MRI and neurocognitive assessments (Wechsler Intelligence Scales for Children-Revised [WISC-R]). Automatic image segmentation was used to determine the tissue volumes of cerebral gray matter, white matter, and cerebrospinal fluid. In addition, the volume of the hippocampus was determined manually. WISC-R scores were recorded as mean intelligence scores at evaluation. Neonatal hydrocortisone treatment for chronic lung disease consisted of a starting dose of 5 mg/kg per day tapered over a minimum of 3 weeks.

RESULTS

Cerebral gray matter volume was reduced among preterm children (regardless of hydrocortisone treatment), compared with children born at term (preterm: 649 +/- 4.4 mL; term: 666 +/- 7.3 mL). Birth weight was shown to correlate with gray matter volume at 8 years of age in the preterm group (r = 0.421). Cerebrospinal fluid volume was increased among children born preterm, compared with children born at term (preterm: 228 +/- 4.9 mL; term: 206 +/- 8.2 mL). Total hippocampal volume tended to be lower among children born preterm, with a more pronounced reduction of hippocampal volume among boys (preterm: 6.1 +/- 0.13 mL; term: 6.56 +/- 0.2 mL). The WISC-R score was lower for children born preterm, compared with children born at term (preterm: 99.4 +/- 12.4; term: 109.6 +/- 8.8). Children treated with neonatal hydrocortisone had very similar volumes of gray matter (preterm with hydrocortisone: 650 +/- 7.0 mL; preterm without hydrocortisone: 640 +/- 5.6 mL), white matter (preterm with hydrocortisone: 503 +/- 6.1 mL; preterm without hydrocortisone: 510 +/- 4.9 mL), and cerebrospinal fluid (preterm with hydrocortisone: 227 +/- 7.4 mL; preterm without hydrocortisone: 224 +/- 6.0 mL), compared with untreated infants. The hippocampal volumes were similar in the 2 groups (preterm with hydrocortisone: 5.92 +/- 0.15 mL; preterm without hydrocortisone: 5.81 +/- 0.12 mL). The WISC-R score assessments were within the normal range for both groups, with no difference between the groups (preterm with hydrocortisone: 100.8 +/- 13; preterm without hydrocortisone: 98.6 +/- 12.3).

CONCLUSIONS

Prematurity is associated with mild brain structural differences that persist at 8 years of age, with associated lower scores in neurocognitive assessments. The data suggest that perinatal hydrocortisone given at the described dosage has no long-term effects on either neurostructural brain development or neurocognitive outcomes.

Cellular mechanisms underlying the effects of an early experience on cognitive abilities and affective states

In the present study we investigated the effects of neonatal handling, an animal model of early experience, on spatial learning and memory, on hippocampal glucocorticoid (GR), mineralocorticoid (MR) and type 1A serotonin (5-HT1A) receptors, as well as brain derived neurotrophic factor (BDNF), and on circulating leptin levels, of male rats.

METHOD

Spatial learning and memory following an acute restraint stress (30 min) were assessed in the Morris water maze. Hippocampal GR, MR and BDNF levels were determined immunocytochemically. 5-HT1A receptors were quantified by in vitro binding autoradiography. Circulating leptin levels, following a chronic forced swimming stress, were measured by radioimmunoassay (RIA). Data were statistically analyzed by analysis of variance (ANOVA).

RESULTS

Neonatal handling increased the ability of male rats for spatial learning and memory. It also resulted in increased GR/MR ratio, BDNF and 5-HT1A receptor levels in the hippocampus. Furthermore, leptin levels, body weight and food consumption during chronic forced swimming stress were reduced as a result of handling.

CONCLUSION

Neonatal handling is shown to have a beneficial effect in the males, improving their cognitive abilities. This effect on behavior could be mediated by the handling-induced increase in hippocampal GR/MR ratio and BDNF levels. The handling-induced changes in BDNF and 5-HT1A receptors could underlie the previously documented effect of handling in preventing "depression". Furthermore, handling is shown to prevent other maladaptive states such as stress-induced hyperphagia, obesity and resistance to leptin.

Declarative memory consolidation: mechanisms acting during human sleep

Of late, an increasing number of studies have shown a strong relationship between sleep and memory. Here we summarize a series of our own studies in humans supporting a beneficial influence of slow-wave sleep (SWS) on declarative memory formation, and try to identify some mechanisms that might underlie this influence. Specifically, these experiments show that declarative memory benefits mainly from sleep periods dominated by SWS, whereas there is no consistent benefit of this memory from periods rich in rapid eye movement (REM) sleep. A main mechanism of declarative memory formation is believed to be the reactivation of newly acquired memory representations in hippocampal networks that stimulates a transfer and integration of these representations into neocortical neuronal networks. Consistent with this model, spindle activity and slow oscillation-related EEG coherence increase during early sleep after intense declarative learning in humans, signs that together point toward a neocortical reprocessing of the learned material. In addition, sleep seems to provide an optimal milieu for declarative memory reprocessing and consolidation by reducing cholinergic activation and the cortisol feedback to the hippocampus during SWS.

A role for corticotropin-releasing factor in repeated cold stress-induced anxiety-like behavior during forced swimming and elevated plus-maze tests in mice

SART (specific alternation of rhythm in temperature) stress is known to cause anxiety-like behavior in mice/rats in several anxiety-related behavioral tests. In the present study, we investigated possible roles for corticotropin-releasing factor (CRF) and glucocorticoids in SART stress-induced anxiety-like behavior in two different anxiety-related behavioral tests. In the forced swimming test, CRF, administered intracerebroventricular (i.c.v.) at 0.5-2 pmol/mouse, dose-dependently reduced immobility time in unstressed and SART-stressed mice. alpha-Helical CRF, a specific CRF receptor antagonist, administered i.c.v. at 0.1-1 nmol/mouse, dose-dependently increased immobility time in SART-stressed mice, but not in unstressed mice. In the elevated plus-maze test, CRF at 10-20 pmol/mouse significantly decreased the time spent in open arms in unstressed mice. CRF at a high dose tended to decrease this time in SART-stressed mice, but this decrease was not statistically significant. alpha-Helical CRF failed to modify the time in unstressed mice. In contrast, alpha-helical CRF at 0.38 and 0.75 nmol/mouse increased the time in SART-stressed mice. Both immobility time in the forced swimming test and time spent in open arms in the elevated plus-maze test in unstressed and SART-stressed mice were unaffected by adrenalectomy. These results suggest that CRF plays an important role in anxiety-like behavior caused by SART stress.

Acquired deficit of forebrain glucocorticoid receptor produces depression-like changes in adrenal axis regulation and behavior

Dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis is a hallmark of major depressive disorder. A number of studies have shown that this dysregulation is correlated with impaired forebrain glucocorticoid receptor (GR) function. To determine whether a primary, acquired deficit in forebrain GR signaling is an etiologic factor in the pathogenesis of depression, we generated a line of mice with time-dependent, forebrain-specific disruption of GR (FBGRKO). These mice develop a number of both physiological and behavioral abnormalities that mimic major depressive disorder in humans, including hyperactivity of the HPA axis, impaired negative feedback regulation of the HPA axis and, increased depression-like behavior. Importantly, a number of these abnormalities are normalized by chronic treatment with the tricyclic antidepressant, imipramine. Our findings suggest that imipramine's proposed activities on forebrain GR function are not essential for its antidepressant effects, and that alteration in GR expression may play a causative role in disease onset of major depressive disorder.

Glucocorticoid receptor overexpression in forebrain: a mouse model of increased emotional lability

The molecular mechanisms that control the range and stability of emotions are unknown, yet this knowledge is critical for understanding mood disorders, especially bipolar illness. Here, we show that the glucocorticoid receptor (GR) modulates these features of emotional responsiveness. We generated transgenic mice overexpressing GR specifically in forebrain. These mice display a significant increase in anxiety-like and depressant-like behaviors relative to wild type. Yet, they are also supersensitive to antidepressants and show enhanced sensitization to cocaine. Thus, mice overexpressing GR in forebrain have a consistently wider than normal range of reactivity in both positive and negative emotionality tests. This phenotype is associated, in specific brain regions, with increased expression of genes relevant to emotionality: corticotropin-releasing hormone, serotonin, norepinephrine and dopamine transporters, and 5-hydroxytryptamine(1A) receptor. Thus, GR overexpression in forebrain causes higher "emotional lability" secondary to a unique pattern of molecular regulation. This finding suggests that natural variations in GR gene expression can contribute to the fine-tuning of emotional stability or lability and may play a role in bipolar disorder.

Effect of adrenalectomy and corticosterone replacement on prepulse inhibition and locomotor activity in mice

1 Stress is a risk factor in psychiatric illnesses such as schizophrenia. The aim of the present study was to investigate the effect of different circulating levels of the adrenal steroid corticosterone (CORT) on locomotor hyperactivity and prepulse inhibition of acoustic startle, two behavioural animal models of aspects of schizophrenia. 2 Male C57BL/6J mice (n=10 per group) were anaesthetised with isoflurane and sham-operated or adrenalectomised (ADX). ADX mice were implanted with 50 mg pellets consisting of 100% cholesterol, or 2, 10 or 50 mg of CORT mixed with cholesterol. CORT pellet implantation dose dependently increased plasma CORT levels 3 weeks after surgery. Starting 1 week after surgery, mice were tested for prepulse inhibition after injection of saline or 5 mg kg(-1) of haloperidol. 3 In intact mice and in mice implanted with 10 mg of CORT, haloperidol treatment significantly increased prepulse inhibition (average values from 38 - 42 to 52%). Similar results were observed when testing the mice for amphetamine-induced locomotor hyperactivity (5 mg kg(-1)). In contrast, there was no significant effect of haloperidol in mice implanted either with cholesterol or 2 or 50 mg of CORT. 4 These results in behavioural animal models of schizophrenia suggest an important role of the stress hormone CORT in modulating dopaminergic activity in this illness.

Visualization of glucocorticoid receptor and mineralocorticoid receptor interactions in living cells with GFP-based fluorescence resonance energy transfer

Adrenal corticosteroids readily enter the brain and exert markedly diverse effects, including stress responses in the target neural cells via two receptor systems, the mineralocorticoid receptor (MR) and the glucocorticoid receptor (GR). It has been shown that the GR and MR are highly colocalized in the hippocampus. Given the differential action of the MR and GR in the hippocampal region, it is important to elucidate how these receptors interact with each other in response to corticosteroids. We investigated the heterodimerization of the MR and GR with green fluorescent protein-based fluorescence resonance energy transfer (FRET) microscopy in living cells with spatiotemporal manner. FRET was evaluated in three ways: (1) ratio imaging; (2) emission spectra; and (3) acceptor photobleaching. FRET analysis demonstrated that cyan fluorescent protein-GR and yellow fluorescent protein-MR form heterodimers after corticosterone (CORT) treatment both in the nucleus of cultured hippocampal neurons and COS-1 cells, whereas they do not form heterodimers in the cytoplasm. The content of the GR-MR heterodimer was higher at 10(-6) m CORT than at 10(-9) m CORT and reached a maximum level after 60 min of CORT treatment in both cultured hippocampal neurons and COS-1 cells. The distribution pattern of heterodimers in the nucleus of cultured hippocampal neurons was more restricted than that in COS-1 cells. The present study using mutant fusion proteins in nuclear localization signal showed that these corticosteroid receptors are not translocated into the nucleus in the form of heterodimers even after treatment with ligand and thus allow no heterodimerization to take place in the cytoplasm. These results obtained with FRET analyses give new insights into the sites, time course, and effects of ligand concentration on heterodimersization of the GR and MR.

Prenatal glucocorticoid exposure alters hypothalamic-pituitary-adrenal function and blood pressure in mature male guinea pigs

Pregnant guinea pigs were treated with dexamethasone (1 mg kg(-1)) or vehicle on days 40-41, 50-51 and 60-61 of gestation, after which animals delivered normally. Adult male offspring were catheterized at 145 days of age and subjected to tests of hypothalamic-pituitary-adrenal (HPA) axis function in basal and activated states. Animals exposed to dexamethasone in utero (mat-dex) exhibited increased hippocampus-to-brain weight ratio, increased adrenal-to-body weight ratio and increased mean arterial pressure. There were no effects on gestation length, birth weight and postnatal growth. There were no overall differences in diurnal plasma adrenocorticotropic hormone (ACTH) and cortisol profiles, though there were subtle differences during the subjective afternoon between control and mat-dex offspring. A significant decrease in initial ACTH suppression was observed following dexamethasone injection in mat-dex offspring compared to control offspring. Molecular analysis revealed significantly increased MR mRNA expression in the limbic system and particularly in the dentate gyrus in mat-dex offspring. In the anterior pituitary, both pro-opiomelanocortin (POMC) and glucocorticoid receptor (GR) mRNA levels were significantly elevated in mat-dex offspring. In conclusion, (1) repeated prenatal treatment with synthetic glucocorticoid (sGC) permanently programmes organ growth, blood pressure and HPA regulation in mature male offspring and these changes involve modification of corticosteroid receptor expression in the brain and pituitary; (2) the effects of prenatal sGC exposure on HPA function appear to change as a function of age, indicating the importance of investigating HPA and cardiovascular outcome at multiple time points throughout life.

The renin-angiotensin-aldosterone system in patients with depression compared to controls--a sleep endocrine study

BACKGROUND

Hypercortisolism as a sign of hypothamamus-pituitary-adrenocortical (HPA) axis overactivity and sleep EEG changes are frequently observed in depression. Closely related to the HPA axis is the renin-angiotensin-aldosterone system (RAAS) as 1. adrenocorticotropic hormone (ACTH) is a common stimulus for cortisol and aldosterone, 2. cortisol release is suppressed by mineralocorticoid receptor (MR) agonists 3. angiotensin II (ATII) releases CRH and vasopressin from the hypothalamus. Furthermore renin and aldosterone secretion are synchronized to the rapid eyed movement (REM)-nonREM cycle.

METHODS

Here we focus on the difference of sleep related activity of the RAAS between depressed patients and healthy controls. We studied the nocturnal plasma concentration of ACTH, cortisol, renin and aldosterone, and sleep EEG in 7 medication free patients with depression (1 male, 6 females, age: (mean +/-SD) 53.3 +/- 14.4 yr.) and 7 age matched controls (2 males, 5 females, age: 54.7 +/- 19.5 yr.). After one night of accommodation a polysomnography was performed between 23.00 h and 7.00 h. During examination nights blood samples were taken every 20 min between 23.00 h and 7.00 h. Area under the curve (AUC) for the hormones separated for the halves of the night (23.00 h to 3.00 h and 3.00 h to 7.00 h) were used for statistical analysis, with analysis of co variance being performed with age as a covariate.

RESULTS

No differences in ACTH and renin concentrations were found. For cortisol, a trend to an increase was found in the first half of the night in patients compared to controls (p < 0.06). Aldosterone was largely increased in the first (p < 0.05) and second (p < 0.01) half of the night. Cross correlations between hormone concentrations revealed that in contrast to earlier findings, which included only male subjects, in our primarily female sample, renin and aldosterone secretion were not coupled and no difference between patients and controls could be found, suggesting a gender difference in RAAS regulation. No difference in conventional sleep EEG parameters were found in our sample.

CONCLUSION

Hyperaldosteronism could be a sensitive marker for depression. Further our findings point to an altered renal mineralocorticoid sensitivity in patients with depression.

Methylprednisolone increases neuronal apoptosis during autoimmune CNS inflammation by inhibition of an endogenous neuroprotective pathway

Optic neuritis is one of the most common clinical manifestations of multiple sclerosis (MS), a chronic inflammatory disease of the CNS. High-dosage methylprednisolone treatment has been established as the standard therapy of acute inflammation of the optic nerve (ON). The rationale for corticosteroid treatment lies in the antiinflammatory and immunosuppressive properties of these drugs, as shown in experimental autoimmune encephalomyelitis (EAE), the animal model of MS. To investigate the influence of methylprednisolone therapy on the survival of retinal ganglion cells (RGCs), the neurons that form the axons of the ON, we used a rat model of myelin oligodendrocyte glycoprotein (MOG)-induced EAE. Optic neuritis was diagnosed by recording visual evoked potentials, and RGC function was monitored by measuring electroretinograms. Methylprednisolone treatment significantly increased RGC apoptosis during MOG-EAE. By Western blot analysis, we identified the underlying molecular mechanism: a suppression of mitogen-activated protein kinase (MAPK) phosphorylation, which is a key event in an endogenous neuroprotective pathway. The methylprednisolone-induced inhibition of MAPK phosphorylation was calcium dependent. Hence, we provide evidence for negative effects of steroid treatment on neuronal survival during chronic inflammatory autoimmune disease of the CNS, which should result in a reevaluation of the current therapy regimen.

Antidepressant fluoxetine enhances glucocorticoid receptor function in vitro by modulating membrane steroid transporters

1. Incubation of LMCAT fibroblast cells with antidepressants potentiates glucocorticoid receptor (GR)-mediated gene transcription in the presence of dexamethasone and cortisol, but not of corticosterone. We have shown that antidepressants do so by inhibiting the LMCAT cell membrane steroid transporter (which is virtually identical to the multidrug resistance P-glycoprotein) and thus by increasing dexamethasone or cortisol intracellular concentrations. However, previous experiments with the antidepressant fluoxetine in the presence of dexamethasone have produced negative results (Pariante et al. (2001). Br. J. Pharmacol., 134, 1335-1343). 2. We have since re-examined the effects of fluoxetine on GR-mediated gene transcription in the presence of dexamethasone. Moreover, we have examined the effects of fluoxetine on GR-mediated gene transcription in the presence of cortisol and corticosterone, and on the intracellular accumulation of radioactive cortisol and corticosterone. Finally, we have examined the effects of fluoxetine on inhibition of P-glycoprotein activity in Caco-2 cells. 3. We now find that fluoxetine (1-10 micro M) enhances GR-mediated gene transcription in the presence of dexamethasone and cortisol (+140-170%), but not of corticosterone, and increases the intracellular accumulation of (3)H-cortisol (+5-15%), but not of (3)H-corticosterone. Moreover, fluoxetine (10 micro M) induces approximately 30% inhibition of PGP activity in Caco-2 cells. 4. Our results show that fluoxetine, like other antidepressants, inhibits membrane steroid transporters.

The glucocorticoid receptor as a potential target to reduce cocaine abuse

Several findings suggest that glucocorticoid hormones are involved in determining the propensity of an individual to develop cocaine abuse. These hormones activate two related transcription factors, the glucocorticoid receptor (GR) and the mineralocorticoid receptor. In this study, we show that the selective inactivation of the GR gene in the brains of mice profoundly flattened the dose-response function for cocaine intravenous self-administration and suppressed sensitization, two experimental procedures considered relevant models of addiction. Furthermore, administration of a GR antagonist dose-dependently reduced the motivation to self-administer cocaine. Importantly, the absence of GR did not modify the basal behavioral and molecular effects of cocaine but selectively modified the excessive response to the drug spontaneously present in certain vulnerable individuals or induced by repeated drug exposure in others. In conclusion, we provide the first genetic evidence that the GR gene can modulate cocaine abuse. This suggests that targeting GR function in the brain could provide new therapeutic strategies to treat cocaine addiction for which there is no available treatment.

Cortisol, DHEAS and aging: resistance to cortisol suppression in frail institutionalized elderly

Convincing evidences has linked the hypothalamus-pituitary-adrenal (HPA) axis to aging patterns. F excess is implicated in the development of frailty characteristics whereas DHEAS is positively correlated to successful aging. We compared serum F and DHEAS levels of independent community-living (successful group, 19 M and 28 F, 69 to 87 yr) with those of institutionalized elderly (frail group, 20 M and 30 F, 65 to 95 yr). Serum F was determined at 1) baseline (08:00 h, 16:00 h and 23:00 h), 2) after 2 overnight dexamethasone (DEX) suppression tests (DST, using 0.25 and 1.0 mg doses), and 3) 60 min after ACTH stimulation (250 microg i.v. bolus); serum DHEAS was determined at 08:00 h. Basal serum F at 08:00 h, 16:00 h and 23:00 h and serum DHEAS levels were similar in both groups; however F: DHEAS ratio at 08:00 h was higher in the frail, compared to the successful group (mean +/- SD: 0.55 +/- 0.53 and 0.35 +/- 0.41, respectively; p = 0.04). In response to DST, F suppression was less effective in frail elderly after either 0.25 or 1.0 mg doses (9.0 +/- 6.0 and 2.0 +/- 0.9 microg/dl), as compared to the successful group (5.8 +/- 4.4 and 1.5 +/- 0.5 microg/dl) (p = 0.01). In addition, a significant correlation was observed between post-DEX F levels (both doses) and parameters of cognitive and physical frailty. Normal and similar F levels were observed after ACTH stimulation in both groups. Our data suggest a deficient feedback regulation of the HPA axis in frail institutionalized elderly, as demonstrated by a higher set point for F suppression. This augmented HPA tonus enforces the hypothesis that even milder F excess may be related to characteristics of frailty in the elderly.

Mechanisms of amygdala modulation of hippocampal plasticity

Basolateral amygdala (BLA) activation by emotional arousal modulates memory-related processes in the hippocampus. We have shown (Akirav and Richter-Levin, 1999b) that activating the BLA before perforant path (PP) tetanization has a biphasic effect on hippocampal plasticity; priming the BLA immediately before PP tetanization results in the enhancement of dentate gyrus (DG) long-term potentiation (LTP) (an "emotional tag"), whereas stimulation in a spaced interval results in the suppression of DG-LTP. Here, we aimed to elucidate the mechanisms underlying BLA modulation of DG-LTP and specifically to examine whether the stress hormones norepinephrine (NE) and corticosterone (CORT) are main mediators of the BLA biphasic effects. We found that the BLA affects hippocampal plasticity in a complex manner; BLA priming enhanced DG-LTP, and both NE and CORT mediated this effect. Furthermore, we found that ipsilateral BLA spaced activation (2 hr before PP tetanization) suppressed DG-LTP and that this suppressive effect was also mediated by NE and CORT. Priming the contralateral BLA enhanced DG-LTP similarly to the ipsilateral enhancement, but neither NE nor CORT mediated this effect. The spaced activation of the contralateral BLA did not suppress DG-LTP. Taken together, these results suggest that differential mechanisms underlie the ipsilateral and contralateral BLA effects on hippocampal plasticity. Hence, the BLA modulates hippocampal memory processes, presumably via the mediation of the stress hormones NE and CORT, to establish a diverse memory of the experience. Possibly, at the onset of an emotional event the stress hormones permissively mediate plasticity. However, their prolonged presence in the system may suppress the cognitive response to stress.