Function and plasticity of brain corticosteroid receptor systems: action of neuropeptides

The effects of left dorsolateral prefrontal transcranial direct current stimulation on episodic future thinking following acute psychosocial stress

INTRODUCTION

Research on stress-related disorders and brain imaging suggests that (acute) stress might impact the capacity to mentally simulate specific episodic future events (EFT) through the effects of cortisol on brain regions supporting this cognitive function, such as the prefrontal cortices. This study aims to examine the mechanisms underlying this link, using transcranial Direct Current Stimulation (tDCS) over the left dorsolateral prefrontal cortex.

METHODS

60 healthy participants were subjected to the Montreal Imaging Stress Task (MIST), followed by either active or sham tDCS. After stimulation, the EFT task was administered. Salivary cortisol was measured throughout the protocol.

RESULTS

Higher cortisol AUCi values were linked to less specific episodic future thoughts. Moreover, active tDCS enhanced EFT specificity irrespective of cortisol, especially in high trait ruminators. We did not observe an effect from active tDCS on cortisol AUCi, and equally there was no interaction effect between cortisol AUCi and stimulation condition predictive for EFT specificity.

CONCLUSION

Although we did not find evidence for the effects of tDCS on the HPA-system, our data reveal a crucial link between two critical predictors of mental health for the first time, and provide a solution to help rehabilitate EFT deficits.Trial registration: Netherlands National Trial Register identifier: ntr004..

Short and prolonged maternal separation impacts on ethanol-related behaviors in rats: sex and age differences

Maternal separation (MS) is an animal model widely used to evaluate the influence of early-life stress exposure on ethanol consumption and dependence. The goal of this study was to evaluate the effects of brief and prolonged MS on the pattern of consumption and ethanol conditioned place preference (CPP) in male and female rats during adolescence and adulthood. Wistar rat pups were separated daily from their dams for 15 or 180 minutes during the 2 to 10 postnatal days (PND). In adolescence, half of the litter from each group was evaluated in the ethanol consumption test using the three-bottle test choice paradigm. In addition, using biased procedure, ethanol-conditioned place preference was also evaluated. In adulthood, the other half of the litter was evaluated on the same tests. Our results showed that there are differences in consumption pattern and in alcohol reinforcement between males and females, adolescents and adults. While prolonged MS had no effect on total ethanol consumption in adolescents of both sexes, it induced CPP in these animals. In turn, in adults, previous exposure to prolonged MS increased ethanol consumption without altering ethanol-CPP.Lay summaryGiving the importance of the mother-children (dam-pups when talking about rodents) relationship to proper brain development, the separation of pups from their dam is broadly used as an animal model to study the impact of early-life stress exposure. Here, we used a protocol of brief or prolonged maternal separation to study the impact of early-life stress exposure in the alcohol consumption and conditioned place preference in rats, and how age and sex influence it. We showed that, overall, the prolonged maternal separation increased alcohol consumption in both males and females, but only when animals were tested during the adulthood. In the other hand, prolonged maternal separation increased ethanol conditioned place preference in adolescent rats, both male and female.

Stress leads to aberrant hippocampal involvement when processing schema-related information

Prior knowledge, represented as a mental schema, has critical impact on how we organize, interpret, and process incoming information. Recent findings indicate that the use of an existing schema is coordinated by the medial prefrontal cortex (mPFC), communicating with parietal areas. The hippocampus, however, is crucial for encoding schema-unrelated information but not for schema-related information. A recent study indicated that stress mediators may affect schema-related memory, but the underlying neural mechanisms are currently unknown. Here, we thus tested the impact of acute stress on neural processing of schema-related information. We exposed healthy participants to a stress or control manipulation before they processed, in the MRI scanner, words related or unrelated to a preexisting schema activated by a specific cue. Participants’ memory for the presented material was tested 3–5 d after encoding. Overall, the processing of schema-related information activated the mPFC, the precuneus, and the angular gyrus. Stress resulted in aberrant hippocampal activity and connectivity while participants processed schema-related information. This aberrant engagement of the hippocampus was linked to altered subsequent memory. These findings suggest that stress may interfere with the efficient use of prior knowledge during encoding and may have important practical implications, in particular for educational settings.

Impact of Stress and Glucocorticoids on Schema-Based Learning

Pre-existing knowledge, a 'schema', facilitates the encoding, consolidation, and retrieval of schema-relevant information. Such schema-based memory is key to every form of education and provides intriguing insights into the integration of new information and prior knowledge. Stress is known to have a critical impact on memory processes, mainly through the action of glucocorticoids and catecholamines. However, whether stress and these major stress mediators affect schema-based learning is completely unknown. To address this question, we performed two experiments, in which participants acquired a schema on day 1 and learned schema-related as well as schema-unrelated information on day 2. In the first experiment, participants underwent a stress or control manipulation either immediately or about 25 min before schema-based memory testing. The second experiment tested whether glucocorticoid and/or noradrenergic activation is sufficient to modulate schema-based memory. To this end, participants received orally a placebo, hydrocortisone, the α2-adrenoceptor-antagonist yohimbine, leading to increased noradrenergic stimulation, or both drugs, before completing the schema-based memory test. Our data indicate that stress, irrespective of the exact timing of the stress exposure, impaired schema-based learning, while leaving learning of schema-unrelated information intact. A very similar effect was obtained after hydrocortisone, but not yohimbine, administration. These data show that stress disrupts participants' ability to benefit from prior knowledge during learning and that glucocorticoid activation is sufficient to produce this effect. Our findings provide novel insights into the impact of stress and stress hormones on the dynamics of human memory and have important practical implications, specifically for educational contexts.

Perceived Stress and Cognitive Decline in Different Cognitive Domains in a Cohort of Older African Americans

BACKGROUND

Research indicates that stress is linked to cognitive dysfunction. However, few community-based studies have explored the relationship between perceived stress and cognitive decline, and fewer still have utilized cognitive domains rather than a global measure of cognition.

OBJECTIVE

We examined the relation between perceived stress and the rate of decline in different cognitive domains.

METHODS

Participants were older African Americans without dementia from the Minority Aging Research Study (MARS; N = 467, mean age: 73 years, SD: 6.1 years). A battery of 19 cognitive tests was administered at baseline and at annual intervals for up to 9 years (mean follow-up: 4 years), from which composite measures of global cognitive function and five specific cognitive domains were derived. The four-item Cohen's Perceived Stress Scale (PSS) was also administered at baseline.

RESULTS

In linear mixed-effects models adjusted for age, sex, education, and vascular risk factors, higher perceived stress was related to faster declines in global cognition (β = -0.019; SE: 0.008; t₍₁₉₅₁₎ = -2.46), episodic memory (β = -0.022; SE: 0.011; t₍₁₉₅₄₎ = -1.99), and visuospatial ability (β = -0.021; SE: 0.009; t₍₁₉₃₉₎ = -2.38) all p < 0.05. Findings were similar in subsequent models adjusted for demographics, vascular diseases, and depressive symptoms.

CONCLUSIONS

Results indicate that older African Americans with higher levels of perceived stress have more rapid declines in global cognition than those with lower levels, most notably for episodic memory and visuospatial ability.

Hippocampal-prefrontal circuit and disrupted functional connectivity in psychiatric and neurodegenerative disorders

In rodents, the hippocampus has been studied extensively as part of a brain system responsible for learning and memory, and the prefrontal cortex (PFC) participates in numerous cognitive functions including working memory, flexibility, decision making, and rewarding learning. The neuronal projections from the hippocampus, either directly or indirectly, to the PFC, referred to as the hippocampal-prefrontal cortex (Hip-PFC) circuit, play a critical role in cognitive and emotional regulation and memory consolidation. Although in certain psychiatric and neurodegenerative diseases, structural connectivity viewed by imaging techniques has been consistently found to be associated with clinical phenotype and disease severity, the focus has moved towards the investigation of connectivity correlates of molecular pathology and coupling of oscillation. Moreover, functional and structural connectivity measures have been emerging as potential intermediate biomarkers for neuronal disorders. In this review, we summarize progress on the anatomic, molecular, and electrophysiological characters of the Hip-PFC circuit in cognition and emotion processes with an emphasis on oscillation and functional connectivity, revealing a disrupted Hip-PFC connectivity and electrical activity in psychiatric and neurodegenerative disorders as a promising candidate of neural marker for neuronal disorders.

Stress induced a shift from dorsal hippocampus to prefrontal cortex dependent memory retrieval: role of regional corticosterone

Most of the deleterious effects of stress on memory retrieval are due to a dysfunction of the hippocampo-prefrontal cortex interplay. The role of the stress-induced regional corticosterone increase in such dysfunction remains however unclear, since there is no published study as yet dedicated to measuring corticosterone concentrations simultaneously in both the prefrontal cortex (mPFC) and the hippocampus (dHPC) in relation with memory impairments. To that aim, we first showed in Experiment 1 that an acute stress (3 electric footschocks; 0.9 mA each) delivered before memory testing reversed the memory retrieval pattern (MRP) in a serial discrimination task in which mice learned two successive discriminations. More precisely, whereas non-stressed animals remembered accurately the first learned discrimination and not the second one, stressed mice remembered more accurately the second discrimination but not the first one. We demonstrated that local inactivation of dHPC or mPFC with the anesthetic lidocaine recruited the dHPC activity in non-stress conditions whereas the stress-induced MRP inversion recruited the mPFC activity. In a second experiment, we showed that acute stress induced a very similar time-course evolution of corticosterone rises within both the mPFC and dHPC. In a 3rd experiment, we found however that in situ injections of corticosterone either within the mPFC or the dHPC before memory testing favored the emergence of the mPFC-dependent MRP but blocked the emergence of the dHPC-dependent one. Overall, our study evidences that the simultaneous increase of corticosterone after stress in both areas induces a shift from dHPC (non-stress condition) to mPFC-dependent MRP and that corticosterone is critically involved in mediating the deleterious effects of stress on cognitive functions involving the mPFC-HPC interplay.

Perinatal stress: characteristics and effects on adult eating behavior

Many studies have pointed out the importance of mother-child interaction in the early months of life. A few decades ago, a method called kangaroo care was developed and its main goal was to keep underweight or premature newborns in direct contact with the mother. This method has reduced the morbidity and mortality of these newborns, increasing their growth rate, breastfeeding time and mother-child contact. In rodents, the dam's presence is crucial for avoiding aggression factors that may trigger phenotypic adaptations in the pups with irreversible morphological, functional and behavioral consequences. Eating behavior is an adaptive response stemming from the external environment demand and modulated by opportunities and limitations imposed by the external environment. This behavior is regulated by a complex interaction of peripheral and central mechanisms that control hunger and satiety. The hypothalamus is a brain structure that integrates central and peripheral signals to regulate energy homeostasis and body weight. The hypothalamic nucleus have orexigenic peptides, such as neuropeptide Y and the Agouti-related peptide, and anorexigenic peptides, such as cocaine and amphetamine regulated transcript and proopiomelanocortin. An innovative study of eating behavior in experimental models of neonatal stress separates the mother from the offspring during lactation. This review describes the effects of stress during the neonatal period on general physiological factors, particularly on the control of eating behavior.

Stress-induced memory retrieval impairments: different time-course involvement of corticosterone and glucocorticoid receptors in dorsal and ventral hippocampus

The present study was aimed at determining the relative contribution of the dorsal (DH) and ventral (VH) hippocampus in stress-induced memory retrieval impairments. Thus, we studied the temporal involvement of corticosterone and its receptors, i.e. mineralocorticoid (MR) and glucocorticoid (GR) in the DH and VH, in relation with the time-course evolution of stress-induced memory retrieval impairments. In a first experiment, double microdialysis allowed showing on the same animal that an acute stress (electric footshocks) induced an earlier corticosterone rise in the DH (15-60 min post-stress) and then in the VH (90-105 min post-stress). The return to baseline was faster in the DH (105 min) than in the VH (120 min). Memory deficits assessed by delayed alternation occurred at 15-, 60-, and 105-min delays after stress and were closely related to the kinetic of corticosterone rises within the DH and VH. In a second experiment, the GR antagonist RU-38486 and the MR antagonist RU-28318 were administered in the DH or VH 15 min before stress. RU-38486 restored memory at 60 but not at 105 min post-stress delays in the DH, whereas the opposite pattern was observed in the VH. By contrast, RU-28318 had no effect on memory impairments at both the 60- and 105-min post-stress delays, showing that MR receptors are not involved at these delays. However, RU-28318 administered in the DH restored memory when administered at a shorter post-stress delay (15 min). Overall, our data are first to evidence that stress induces a functional switch from the DH to VH via different corticosterone time-course evolutions in these areas and the sequential GR receptors involvement in the DH and then in the VH, as regards the persistence of stress-induced memory retrieval deficits over time.

Stress risk factors and stress-related pathology: neuroplasticity, epigenetics and endophenotypes

This paper highlights a symposium on stress risk factors and stress susceptibility, presented at the Neurobiology of Stress workshop in Boulder, CO, in June 2010. This symposium addressed factors linking stress plasticity and reactivity to stress pathology in animal models and in humans. Dr. J. Radley discussed studies demonstrating prefrontal cortical neuroplasticity and prefrontal control of hypothalamo-pituitary-adrenocortical axis function in rats, highlighting the emerging evidence of the critical role that this region plays in normal and pathological stress integration. Dr. M. Kabbaj summarized his studies of possible epigenetic mechanisms underlying behavioral differences in rat populations bred for differential stress reactivity. Dr. L. Jacobson described studies using a mouse model to explore the diverse actions of antidepressants in brain, suggesting mechanisms whereby antidepressants may be differentially effective in treating specific depression endophenotypes. Dr. R. Yehuda discussed the role of glucocorticoids in post-traumatic stress disorder (PTSD), indicating that low cortisol level may be a trait that predisposes the individual to development of the disorder. Furthermore, she presented evidence indicating that traumatic events can have transgenerational impact on cortisol reactivity and development of PTSD symptoms. Together, the symposium highlighted emerging themes regarding the role of brain reorganization, individual differences, and epigenetics in determining stress plasticity and pathology.

Dietary restriction and brain health

The benefits of dietary restriction (DR) on health and aging prevention have been well recognized. Recent studies suggest that DR may enhance brain functions including learning and memory, synaptic plasticity, and neurogenesis, all of which are associated with brain health. Under the stress stimulated by DR, a favorable environment is established for facilitating neuronal plasticity, enhancing cognitive function, stimulating neurogenesis and regulating inflammatory response. DR-induced expressions of factors such as heat shock proteins (HSPs), neurotrophic factors, and Sirtuin1 (SIRT1) are responsible for the effect of DR on the brain. Due to the difficulty in practising long-term DR in human, the potential mimics of DR are also discussed.

Rapid stress-induced corticosterone rise in the hippocampus reverses serial memory retrieval pattern

We previously showed that an acute stress (electric footshocks) induced both a rapid plasma corticosterone rise and a reversal of serial memory retrieval pattern in a contextual serial discrimination (CSD) task. This study is aimed at determining (i) if the rapid stress effects on CSD performance are mediated by the hippocampus; (ii) if hippocampal corticosterone membrane receptor activation is involved in the rapid stress effects on CSD performance. In experiment 1, microdialysis in the dorsal hippocampus (dHPC) was used to measure the stress-induced corticosterone rise; in parallel, the effect of acute stress on CSD performance was evaluated. In addition, the functional involvement of corticosterone in the behavioral effects of stress was assessed by administering metyrapone, a corticosterone synthesis inhibitor, before stress. In experiment 2, the involvement of hippocampal corticosterone membrane receptors in the stress-induced reversal of CSD performance was studied by injecting corticosterone-bovine serum albumin (BSA) (a membrane-impermeable complex) in the dHPC in non stressed mice. Results showed that (i) the acute stress induced a rapid (15 min) and transitory (90 min) corticosterone rise into the hippocampus dHPC, and a reversal of serial memory retrieval pattern; (ii) both the endocrinal and memory stress-induced effects were blocked by metyrapone; (iii) corticosterone-BSA injection into the dHPC in non stressed mice mimicked the effects of stress on serial retrieval pattern. Overall, our study is first to show that (i) a rapid stress-induced corticosterone rise into the dHPC transitorily reverses serial memory retrieval pattern and (ii) hippocampal corticosterone membrane receptors activation is involved in the rapid effects of acute stress on serial memory retrieval.

Status of glucocorticoid alterations in post-traumatic stress disorder

The current status of glucocorticoid alterations in post-traumatic stress disorder (PTSD) will be described in this chapter. Emphasis will be placed on data that suggest that at least some glucocorticoid-related observations in PTSD reflect pretraumatic glucocorticoid status. Recent observations have provided some evidence that pretraumatic glucocorticoid alterations may arise from genetic, epigenetic, and possibly other environmental influences that serve to increase the likelihood of developing PTSD following trauma exposure, as well as modulate attendant biological alterations associated with its pathophysiology. Current studies in the field of PTSD employ glucocorticoid challenge strategies to delineate effects of exogenously administered glucocorticoids on neuroendocrine, cognitive, and brain function. Results of these studies have provided an important rationale for using glucocorticoid strategies in the treatment of PTSD.

Cytosolic glucocorticoid receptor expression in the rat vestibular nucleus and hippocampus following unilateral vestibular deafferentation

It has been suggested that vestibular compensation, the process of behavioural recovery that occurs following peripheral vestibular damage, might be partially dependent on the release of glucocorticoids (GC) during the early stages of recovery from the lesion. One possibility is that glucocorticoid receptors (GRs) in the vestibular nucleus complex (VNC) might change following the lesion, altering their response to GCs. We sought to test this hypothesis by quantifying the expression of cytosolic GRs in the bilateral VNCs at 10 h, 58 h and 2 weeks following unilateral vestibular deafferentation (UVD) in rat, using western blotting. We also examined GR expression in the CA1, CA2/3 and dentate gyrus (DG) subregions of the hippocampus and measured serum corticosterone levels. Compared with sham surgery and anaesthetic controls, we found no significant changes in GR expression in the ipsilateral or contralateral VNCs at any time post-UVD. However, we did find a significant decrease in GR expression in the ipsilateral CA1 at 2 weeks post-UVD. Serum corticosterone levels were significantly lower in all groups at 58 h post-op. compared to 10 h and 2 weeks; however, there were no significant differences between the UVD and control groups at any time point. These results suggest that changes in GR expression in the VNC are unlikely to contribute to the development of vestibular compensation. However, long-term changes in GR expression in CA1 might be related to chronic deficits in hippocampal function and spatial cognition following vestibular damage.

Type II glucocorticoid receptors are involved in neuronal death and astrocyte activation induced by trimethyltin in the rat hippocampus

According to our previous study, trimethyltin (TMT), a neurotoxicant, induces the loss of pyramidal neurons in the rat hippocampus, which is preceded by a transient increase in plasma corticosterone concentration. To address whether this transient activation of the hypothalamopituitary-adrenocortical axis is related to neuronal loss in the hippocampus, we evaluated the effects of bilateral adrenalectomy (ADX) and the chronic supplemental treatment of glucocorticoid receptor agonists after ADX on TMT-induced hippocampal damage. Peroral administration of a single dose of TMT (9 mg/kg body wt) induced the extensive loss of CA3 pyramidal neurons and reactive astrocytosis in the hippocampus, as evidenced by results of vimentin and glial fibrillary acidic protein immunohistochemistry, and the effects were profoundly exacerbated by bilateral adrenalectomy. Prolonged administration of corticosterone not only attenuated the exacerbating effects of adrenalectomy but also partially reversed the TMT-induced neuronal loss and reactive astrocytosis. Dexamethasone, but not aldosterone, could be substituted for corticosterone, suggesting a novel neuroprotective action of type II glucocorticoid receptors in the hippocampus.

Glucocorticoids and cognitive function: from physiology to pathophysiology

This paper reviews the literature on the relationship between glucocorticoids and cognitive functioning, including memory and selective attention. The main body of evidence suggests that hypothalamic-pituitary-adrenal (HPA) axis dysfunction or a state of hypercortisolaemia can be correlated with cognitive deficits specific to the medial temporal lobe declarative memory system. These impairments are discussed in relation to patients with HPA abnormalities, as seen in a significant number of patients with major depression or Cushing's syndrome, and also in relation to healthy volunteers after administration of glucocorticoids. It remains to be seen whether there are differential effects on acquisition, consolidation or retrieval processes. However, it would seem that glucocorticoids have a preferential effect on recall of information as opposed to recognition, possibly because recognition is more automatic.Type 2 glucocorticoid receptors (GRs), which are occupied by cortisol in humans in times of stress, are thought to be responsible for the glucocorticoid-induced memory impairment. GRs alter the feedback of the HPA axis, which in turn disrupts hippocampal functioning. While this can be reversible, animal studies suggest that chronic elevation of glucocorticoid levels can lead to the loss of hippocampal neurons and irreversible decline in declarative memory. Copyright 2001 John Wiley & Sons, Ltd.

Testosterone is required for corticosteroid-binding globulin upregulation by morphine to be fully manifested

We previously reported that morphine increases the concentration of corticosteroid-binding globulin (CBG) in blood of male, but not female, rats. This pronounced sexual dimorphism suggested that CBG upregulation by morphine might be androgen-dependent. In the current studies, we found that castration, whether performed just before or just after puberty or in adulthood, increased the concentration of CBG in adult male rats. Naltrexone did not prevent this increase and, therefore, it does not appear to be attributable to the release of endogenous opioids. Exposure to morphine for 1 week in adulthood increased ( approximately 100%) the concentration of CBG in intact, i.e., sham-castrated, males. The CBG levels of castrated rats treated with morphine did not differ from those of intact rats treated with morphine. However, because castration increased the concentration of CBG, the difference between the placebo and morphine groups decreased with time after castration. At 4 weeks after castration, the difference between the morphine and placebo groups (19%) was no longer statistically significant. Testosterone replacement prevented the rise in CBG levels following castration and maintained the magnitude of the difference between placebo and morphine-treated rats within the normal range. Thus, testosterone appears necessary for morphine effects on CBG to be fully manifested.

Corticosterone peak is responsible for stress-induced elevation of glutamate in the hippocampus

Effect of ether stress on dialysate concentration of extracellular amino acids in the hippocampus was studied by microdialysis in freely moving rats that have been either sham operated (SHAM) or adrenalectomized and supplemented with subcutaneous steroid pellets (ADX+CORT) providing constant corticosterone (CORT) plasma levels. In SHAM rats, ether stress resulted in a peak of glutamate and taurine 30 min after stress, while extracellular aspartate concentration was increased 120 min after challenge. These changes in amino acid levels as well as in glutamate/glutamine ratio were paralleled by stress-induced rise of plasma CORT. No significant alterations were detected in the concentration of hippocampal arginine, alanine, glycine, glutamine, threonine or serine. In contrast to SHAM animals, ether stress failed to have an effect on dialysate concentration of amino acid transmitters in the hippocampus of adrenalectomized rats supplemented with 50 mg CORT-pellets. Our results demonstrate that ether stress alters aspartate, glutamate, glutamate/glutamine ratio and taurine concentration in the hippocampus and indicate that stress-induced CORT release in plasma may be responsible for these amino acid alterations. These changes may also contribute to negative feedback effect of CORT on hypothalamo-pituitary-adrenocortical (HPA) axis via the hippocampus during stress.

Effects of acute and chronic administration of high-dose corticosterone and dexamethasone on regional brain dopamine and serotonin metabolism in rats

1. The effects of acute and chronic treatment with high-dose corticosterone (50 mg/kg) and dexamethasone (0.7 mg/kg) on monoamines and their metabolites levels in four regions of the rat brain were investigated. 2. Acute corticosterone and dexamethasone treatment decreased serotonin (5-HT) levels, but did not alter dopamine (DA),3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) or 5-hydroxyindoleacetic acid (5-HIAA) levels in any of the brain regions. 3. Chronic corticosterone treatment significantly increased the HVA and 5-HIAA levels only in the medial prefrontal cortex, while chronic dexamethasone treatment did not alter. Chronic corticosterone and dexamethasone treatment did not change DA, DOPAC or 5-HT levels in any of the brain regions. 4. These findings suggest that chronic treatment with high-dose corticosterone activates the dopaminergic and serotonergic neurotransmission in the medial prefrontal cortex.

Fluorine-substituted corticosteroids: synthesis and evaluation as potential receptor-based imaging agents for positron emission tomography of the brain

We have prepared eight fluorine-substituted corticosteroids representing ligands selective for Type I and Type II corticosteroid receptor subtypes as potential imaging agents for corticosteroid receptor-containing regions of the brain. Receptor binding affinity assays show that fluorine substitution for hydroxyl or hydrogen in these steroids generally results in some reduction in affinity, with the result that the absolute affinity of these fluorine-substituted ligands for receptor is less than that typical for steroid hormones that show receptor-based, target selective uptake in vivo. Five of these compounds were prepared in fluorine-18 labeled form by a simple sulfonate ester displacement reaction, and their tissue distribution was studied in the adrenalectomized rat. There is no selective accumulation nor selective retention of the Type I selective corticosteroids (18F-RU 26752, 21-[18F]fluoroprogesterone, 21-[18F]fluoro-11 beta-hydroxyprogesterone) in either the brain, or other target tissues (pituitary, kidney, liver). The Type II selective corticosteroids (18F-RU 28362, 18F-triamcinolone acetonide) show uptake into the hippocampus which can be partially blocked by a competing ligand; in target tissues outside the brain, the blocking is more complete. All of the 18F-labeled compounds show considerable defluorination, evident as high bone activity levels. These results, coupled with earlier findings in the literature, suggest that radiolabeled corticosteroid receptor ligands with both greater metabolic stability and higher receptor binding affinity and selectivity are needed for imaging corticosteroid receptors in the hippocampus.

The effect of dexamethasone on neuropeptide Y concentrations in specific hypothalamic regions

Neuropeptide Y (NPY) is a major hypothalamic peptide which is implicated in the regulation of energy balance and in the activation of the hypothalamo-pituitary adrenal axis. This study aimed primarily to determine the effects on regional hypothalamic NPY levels, of catabolism and weight loss induced in rats by the synthetic glucocorticoid, dexamethasone, injected daily at a dose of 0.4 mg/kg for 7 days. NPY concentrations were significantly raised in the paraventricular nucleus (PVN) of male Wistar rats (45%, p = 0.009; n = 10) compared with saline-injected controls (n = 10). Body weight (p less than 0.001) and food intake (p less than 0.001) were significantly reduced, plasma insulin concentrations were increased (p less than 0.001), but there was no change in glucose concentrations. Chronic dexamethasone treatment did not cause the marked NPY increases in the arcuate nucleus (ARC) and other hypothalamic regions which have been observed in other catabolic states causing weight loss. One possible explanation is the high insulin levels induced by dexamethasone, which may have prevented compensatory hyperphagia by suppressing an increase in hypothalamic NPYergic activity. We also examined the acute effects of a single dexamethasone injection on regional hypothalamic levels, to determine whether the drug had a direct action separate from that due to sustained weight loss. In the acute study, groups of rats (n = 7) were examined at 4 h after a single injection of dexamethasone or saline. NPY concentrations were significantly increased in the lateral hypothalamic area (LHA), (60%, p = 0.008) when compared with saline-injected controls, but there was no change in body weight or glucose or insulin concentrations during the 4h interval. Altered transport or release of NPY in the lateral hypothalamic area may be a result of acute feedback regulation by glucocorticoids on the hypothalamus.

The effect of aging on stress responsiveness and central corticosteroid receptors in the brown Norway rat

The present study examined the stress responsiveness of the hypothalamic-pituitary-adrenal axis in relation to the properties of corticosteroid receptors in the brain and pituitary of old (30 months) and young (3 months) male Brown Norway rats. Adrenocorticotropin hormone (ACTH) and corticosterone (B) were measured following exposure to novelty and to a conditioned emotional stimulus in blood samples sequentially obtained from chronically cannulated animals. Mineralocorticoid (MR) and glucocorticoid (GR) receptors were quantified by radioligand binding assay and in situ hybridization. The receptor binding constants were determined in tissue of rats that were adrenalectomized 24 hours previously, whereas gene expression was measured in the brain of intact animals. Aged Brown Norway rats showed a small but significant elevation in basal circulating ACTH level. The conditioned emotional stimulus, rather than the exposure to novelty, triggered a more than two-times higher ACTH response in the aged compared to the young rat. The termination of the stress-induced ACTH response seemed to proceed more efficiently in the aged rat. Basal and stress-induced total plasma B level did not differ in the young and old rats. The latter showed a 65% lower binding capacity of corticosteroid-binding globulin (CBG). Interestingly, in the aged rat the stress-induced rise in free circulating plasma B level was not elevated, but only prolonged. The hippocampus of aged rats displayed a decrease of maximally 44% in the apparent Bmax of MR, but no change in GR number. The Bmax of GR showed a 40% reduction in the hypothalamus and a 50% reduction in the anterior pituitary. GR affinity was considerably increased in the anterior pituitary, but was unchanged in the hippocampus and hypothalamus. Old age affected MR and GR gene expression differentially. GR mRNA was significantly reduced in cell field CA3 (-42%), CA4 (-41%) and the dentate gyrus (-26%) of the dorsal hippocampus, but did not change either in hippocampal cell field CA1 or in the hypothalamic paraventricular nucleus (PVN) of the old rat. There was no significant difference in MR mRNA between young and aged rats in the different cell fields of the hippocampus. The aged rat, therefore, is characterized by site- and receptor-specific changes in binding constants as well as by changes in receptor transcription and translation. The data demonstrate that in the old Brown Norway rats, a conditioned emotional stimulus results in enhanced pituitary ACTH release.(ABSTRACT TRUNCATED AT 400 WORDS)

Corticosteroids and the brain

Mineralocorticoid (MR) and glucocorticoid receptors (GR) are expressed in the central nervous system. Radioligand binding studies, autoradiography, immunocytochemistry and in situ hybridization have shown that MR and GR are found in abundance in neurons of the limbic system (hippocampus), a structure involved in mood, affect and subtle control of the hypothalamic-pituitary-adrenal (HPA) axis. In the hippocampus MR binds corticosterone (CORT) as well as aldosterone (ALDO) with high affinity. MR seems mainly occupied by CORT in the face of its 2-3 order higher circulating concentration. GR binds CORT with a 6-10-fold lower affinity. MR and GR gene expression, as well as the native receptor proteins, seem to be controlled in a coordinative manner. When GR is down-regulated by excess homologous steroid, MR appears to be increased. Down regulation of MR reduces GR as well. MR and GR display a differential ontogenetic pattern. Ontogeny, particularly that of GR, can be permanently influenced when animals are exposed during the first post-natal week of maternal deprivation, handling, CORT or ACTH1-24 injections. These MR and GR changes persist into senescence and have been proposed to result in altered CORT responsiveness, stress regulation, behavioural adaptation and brain aging.

Dexamethasone treatment attenuates the development of ischaemic brain oedema in gerbils

Transient global forebrain ischaemia was produced in Mongolian gerbils by occluding both common carotid arteries for 10 min followed by 48 h recirculation. Dexamethasone, 5 mg/kg i.p., was given 5 h before the occlusion and every 12 h thereafter. After occlusion an increase in water, sodium and calcium content was found in the parietal cortex and hippocampus, while the concentration of potassium decreased. Exudation of plasma albumin was not found in the brain. The activity of Na+, K(+)-ATPase decreased in the hippocampus. Morphological signs of cerebral oedema were also observed, both in the CA1 region of the hippocampus and in the cortex. Dexamethasone treatment prevented the accumulation of water, sodium and calcium in the ischaemic brain. It also attenuated the oedematous morphological changes of the blood-brain barrier. Thus dexamethasone treatment may also have therapeutic relevance in the acute, high-risk phase of patients suffering from repetitive, transitoric cerebral ischaemia.

Glucocorticoids potentiate the dipsogenic action of angiotensin II

The effect of a short-term, acute treatment with a glucocorticoid, dexamethasone sodium phosphate, on the drinking induced by angiotensin II (AII) was investigated in a series of experiments. Initial studies indicated that a single injection of dexamethasone (700-750 micrograms/kg, i.p.) reduced food intake, body weight and water intake for up to 48 h, but had little effect on blood pressure when it was measured 6 h subsequent to the injection. The drinking elicited by peripherally administered AII (200 micrograms/kg, s.c.) was enhanced if the glucocorticoid (700 micrograms/kg, i.p.) was given 3 h or 6 h prior to the dipsogen. There was no effect of pretreatment with the steroid if the drinking test was delayed by 24 h. The subsequent experiment showed that the glucocorticoid effect on AII-stimulated drinking was dose dependent (100 micrograms-1600 micrograms/kg). The drinking stimulated by intracerebroventricular (i.c.v.) AII (2.5 ng) was enhanced in terms of volume and total duration by prior treatment with dexamethasone, but i.c.v. carbachol (200 ng)-induced drinking remained unaffected. The final study showed that binding of AII to its receptors in five different areas of the rat brain was not affected by prior treatment with dexamethasone.

Behavioral sensitization to amphetamine is dependent on corticosteroid receptor activation

Thirty rats received 3 amphetamine injections (1.5 mg/kg, s.c.) 6 days apart and the locomotor response was measured. One day before the second injection they were adrenalectomized or sham operated. Corticosteroid replacement treatments (500 micrograms/kg, s.c.) were given every evening. Sham adrenalectomized animals exhibited behavioral sensitization to successive injections of amphetamine, which was prevented by adrenalectomy. Treatment with corticosterone or deoxycorticosterone did not reverse the effect of adrenalectomy, whereas dexamethasone completely restored and even potentiated sensitization to amphetamine. These results demonstrate that corticosteroids are necessary for sensitization of the dopaminergic system to occur and that they most probably act through the type II (or glucocorticoid) receptor subtype.

Heterogeneity and properties of transformation of corticosteroid receptors in spinal cord and hippocampus

The central nervous system contains two classes of corticoid receptors, named types I and II following terminology accepted for the kidney. Phenotypically, type I sites are differentiated into a corticosterone (CORT)-preferring species (Ia) and a mineralocorticoid receptor (Ib). These populations were tentatively compared in the spinal cord and hippocampus. Using [3H]dexamethasone (DEX) and selective blockage of sites, we have observed that type II receptors were comparable in both tissues, while Ia was almost exclusive of the hippocampus. Saturation analysis using [3H]DEX demonstrated that type Ia was a low affinity receptor (Kd approximately equal to 2-5 nM) while type II was a higher affinity site (KdII less than KdI). Using [3H]CORT, or [3H]aldosterone (ALDO), as ligand, preferential labeling of type I sites was achieved, always showing higher concentrations in the hippocampus. Therefore, [3H]DEX seems a ligand of choice to visualize types Ia and II receptors. Another difference noted between the spinal cord and hippocampus, pertained to the sensitivity towards the enzyme RNAse A, which increases heat-induced transformation of the bound receptor, according to the results of DNA cellulose affinity chromatography. In these experiments, type I sites of both spinal cord and hippocampus, plus type II of hippocampus, showed sensitivity toward the enzyme, whereas type II of the spinal cord was refractory to RNAse A enhancement of transformation. These results indicate that the dynamics of transformation is different among receptors showing similar affinity and competition, suggesting further heterogeneity due to receptors themselves, or to tissue factors regulating their biochemical properties.

Regional alterations in blood-to-brain transfer of alpha-aminoisobutyric acid and sucrose, after chronic administration and withdrawal of dexamethasone

The effect of dexamethasone administration and withdrawal was studied with respect to blood-brain barrier function. The tracers alpha-[3H]aminoisobutyric acid (AIB) (MW 104) and [14C]sucrose (MW 342), which have a low permeability across the intact endothelium, were simultaneously injected intravenously in rats treated with dexamethasone and placebo-treated control animals or in rats in which dexamethasone treatment was discontinued 3 days before the experiment. Unidirectional transfer constants (Ki) were determined in discrete brain regions. Steroid administration reduced the rate of influx of AIB and sucrose, whereas discontinuation of drug resulted in an increased permeability. These findings suggest that when exposure to glucocorticoids is prolonged, the efficiency of medical treatment of CNS diseases may decrease due to reduction of drug delivery to CNS. Thus, these experimental findings may have particular importance in the clinical setting of drug administration when considering the combination of steroids with other drugs, and may aid in understanding better the pathogenesis of some types of brain edema seen in patients from whom corticosteroid therapy has been withdrawn.

Modulation of angiotensin II binding sites in neuronal cultures by mineralocorticoids

Previous studies have determined that mineralocorticoid hormones are able to increase the number of angiotensin II (ANG II)-specific binding sites in rat diencephalon and in neuronal cultures and also increase the drinking response elicited by centrally injected ANG II. In the present study, we have examined the specificity and mechanisms of this mineralocorticoid action. In neuronal cultures from the hypothalamus and brain stem (H/BS), both D-aldosterone and deoxycorticosterone acetate (DOCA) caused significant time- and dose-dependent increases in 125I-labeled ANG II-specific binding. This effect was not mimicked by the synthetic glucocorticoid dexamethasone, or by testosterone, beta-estradiol or progesterone. However, the steroid corticosterone induced a moderate increase in [125I] ANG II binding. This may have occurred as a result of its high affinity for the mineralocorticoid type I receptor. DOCA was ineffective in increasing [125I]ANG II specific binding both in neuronal cultures prepared from the cerebellum and in pure astrocytic glial cultures, indicating that this mineralocorticoid effect is specific both for neurons and for certain brain regions. The increase in [125I]ANG II-specific binding elicited by DOCA was abolished by cotreatment with the mineralocorticoid receptor blockers mespirenone or ZK97894 and by cotreatment with cycloheximide. Taken together, these observations suggest that the mineralocorticoid-induced increase in [125I]ANG II-specific binding in H/BS neuronal cultures is a specific event, which is mediated via mineralocorticoid type I receptors and which requires protein synthesis.

The biopotency of dexamethasone at causing hepatic glucocorticoid receptor down-regulation in the intact mouse

The effect of dexamethasone administered intraperitoneally on hepatic glucocorticoid receptor binding capacity was measured in adrenalectomized male Swiss Webster mice. The liver content of dexamethasone was also measured. Within 30 min of a 5 micrograms injection, the hepatic content of dexamethasone reached a maximum and fell quickly thereafter. By 6 h the hepatic content of dexamethasone had decreased to 25% of maximum and by 24 h the liver did not contain detectable dexamethasone. At this 24 h point, the glucocorticoid binding capacity was reduced to 50% of control. This decrease reflected down-regulation. Other studies revealed that only glucocorticoids caused this effect and doses of dexamethasone as low as 0.5-5 ng caused a clear down-regulation in binding capacity. Doses that cause receptor down-regulation are also effective at inducing tyrosine aminotransferase, suggesting that dexamethasone down-regulates its own receptors over a physiologically meaningful dosage range. It is concluded that dexamethasone causes a dose-dependent down-regulation of the glucocorticoid receptor in mouse liver.

Modulation of benzodiazepine receptor binding in mouse brain by adrenalectomy and steroid replacement

Adrenal steroids alter neuronal excitability in the central nervous system (CNS), and evidence from in vitro studies indicates that at least some of these effects are mediated by the GABAergic system. Benzodiazepine receptor binding, among other sites on the GABA complex, has been implicated in steroid-induced alterations in the CNS. To investigate the modulation of benzodiazepine receptor binding by adrenal steroids, we examined receptor binding determined by an in vivo technique in mice after adrenalectomy, hypophysectomy and after replacement with several naturally occurring and synthetic steroids. Benzodiazepine receptor binding was substantially augmented in cortex, hypothalamus, and hippocampus in mice 1 week after adrenalectomy, and these increases appeared to be due to increased receptor number rather than changes in apparent affinity. Similar results in cortex were found after hypophysectomy. Replacement with physiologic, but not lower doses, of corticosterone reversed the changes induced by adrenalectomy. Chronic treatment with deoxycorticosterone also returned binding to control values, but chronic administration with dexamethasone, aldosterone and dihydroprogesterone did not alter binding after adrenalectomy. Adrenalectomy did not alter non-specific binding or GABA concentrations in cortex, and delivery of radioligand did not appear to be affected. These results indicate that adrenal steroids modulate benzodiazepine receptor binding in vivo, perhaps via the CR subtype of corticosteroid receptors. The steroid-benzodiazepine interaction may be especially important in the stress response.

Investigation of the corticosteroid receptor system in rat hippocampus by ion exchange fast protein liquid chromatography

In order to study the receptor system for adrenocortical steroids, hippocampal cytosolic preparations--containing both type I and type II receptors--were subjected to anion exchange fast protein liquid chromatography (FPLC). With running buffer containing Tris, EDTA, and glycerol three peaks (1-3) were eluted from the column at 220, 400 and 560 mM NaCl respectively regardless of whether [3H]corticosterone or [3H]RU 28362 had been used as radiotracer. None of the peaks was caused by serum transcortin as revealed by control studies. However, the sequestering influence of transcortin on receptor binding of corticosterone could be demonstrated by the FPLC technique with mixtures containing serum and hippocampus cytosol. Competition experiments with cytosolic samples revealed that type I receptor was present only in peaks 2 and 3 while type II was found in all three peaks in variable amounts, depending on the presence of molybdate. When molybdate was added to the running buffer only two peaks (2 and 3) were eluted, both containing type I and type II receptors. Peak 1 was attributed to the activated type II receptor while peak 2 represented nonactivated receptors. The origin of peak 3 remains uncertain. The data indicate that molybdate must be present in the cytosolic preparation and in the running buffer to keep type II receptor in its nonactivated form. Type I receptor was probably not transformed into the activated form in the absence of molybdate but lost binding capacity and/or affinity for corticosterone.

Immunocytochemical study on the intracellular localization of the type 2 glucocorticoid receptor in the rat brain

The localization of the glucocorticoid receptor (GR) (type 2) in the rat brain was studied with immunocytochemistry using a monoclonal antibody against the rat liver GR. Strong GR immunoreactivity (GR-ir) was observed in neurons of limbic and brainstem structures known to be associated with the stress-activated circuitry, which suggest that these sites are responsive to glucocorticoid feedback. The intracellular localization of GR-ir was examined in CA1 and CA2 pyramidal neurons of the hippocampus. In intact rats GR-ir is predominantly present in the cell nucleus. Adrenalectomy (ADX) caused a slow depletion of the GR-ir signal from the cell nucleus until near detection limits at two weeks postsurgery. At that time, 1 h after administration to longterm ADX rats the synthetic glucocorticoid (type 2) agonist RU 28362 as well as a moderate and high dose of corticosterone (CORT) markedly enhanced the cell nuclear GR-ir. The type 2 antagonist RU 38486 also caused an increase of GR immunostaining in cell nuclei upon acute administration to ADX rats. The mineralocorticoid aldosterone (ALDO) and a low dose of CORT, which bind almost exclusively to type 1 corticosteroid receptors, were ineffective. In conclusion, our data suggest that in the hippocampal CA1-2 neurons type 1 and type 2 corticosteroid receptors may coexist. The steroid-induced changes in cell nuclear immunoreactive GR staining intensity suggest possible cytoplasmic-cell nuclear translocation of GR and/or exposure of immunogenic GR domains.

Neurotrophic peptide ACTH-(4-10) permits glucocorticoid-facilitated retention of acquired immobility response of hypophysectomized rats

The Porsolt swimming test, which was originally designed as an experimental model to screen potential antidepressants demands that rats be forced to swim for 15 min in a narrow cylinder. Twenty four hours later they are retested for 5 min during which they stay immobile for approximately 70% of the time. The present study showed that hypophysectomized animals, 14 days after operation, were unable to retain the acquired immobility. Subcutaneous glucocorticoid administration did not restore the retention of acquired immobility in contrast to our earlier finding with adrenalectomized animals. The deficit in responsiveness to glucocorticoids was eliminated when the hypophysectomized rats received ACTH-(4-10)s.c. (20 micrograms/rat) every other day. Chronic treatment with only the peptide did not improve the impaired retention of hypophysectomized rats and a single ACTH-(4-10) injection 1 day or 1 h prior to initial testing was also ineffective. We conclude that the neurotrophic peptide ACTH-(4-10) permits the expression of the glucocorticoid effect on retention of acquired immobility in the swimming test.