Corticosteroids and the control of function in the hypothalamo-pituitary-adrenal (HPA) axis

Excretion of electrolytes in Brown Norway and Fischer 344 rats: effects of adrenalectomy and of mineralocorticoid and glucocorticoid receptor ligands

Our previous studies showed that adrenalectomy (ADX) has surprisingly no effect on body weight and fluid intake in the Brown Norway rat strain, suggesting that mineralocorticoid receptor (MR)-mediated effects are present even in absence of corticosteroids in this strain. Moreover, glucocorticoid receptor (GR)-mediated mechanisms are more effective in Brown Norway than in Fischer 344 rats. Such functional differences in corticosteroid receptor pathways between Brown Norway and Fischer 344 rats led us to compare the effect of ADX and MR/GR-mediated actions on sodium and potassium excretion between these two rat strains. To this end, we first measured the effect of an acute high dose of aldosterone on the urinary Na+/K+ concentration ratio in intact and ADX Brown Norway and Fischer 344 rats. Second, to discriminate mineralocorticoid from glucocorticoid actions, we treated chronically ADX rats with increasing doses of aldosterone or RU28362, a pure GR agonist, in the drinking fluid. As sodium homeostasis involves salt appetite regulation, behaviour under mineralocorticoid control, we also measured saline preference in Brown Norway and Fischer 344 rats. Our data illustrate: (1) the very limited effect of ADX on body weight, food and fluid intake, diuresis, natriuresis, kaliuresis and salt appetite in Brown Norway rats, supporting the presence of MR signalling pathways in the absence of adrenal steroids in these rats; (2) the insensitivity of MR to aldosterone in intact Brown Norway rats, and the reduced sensitivity of MR to aldosterone in ADX Brown Norway rats compared with ADX Fischer 344 rats; and (3) the greater sensitivity of GR-related mechanisms to RU28362 in Brown Norway than in Fischer 344 rats in terms of body weight gain and electrolyte excretion. Considering that both MRs and GRs regulate hypothalamic-pituitary-adrenal axis processes, such functional differences in corticosteroid receptors could be at the origin, at least partly, of the strain differences in corticotropic activity/reactivity to stress previously described.

Altered hypothalamic-pituitary-adrenocortical function in rhesus monkeys (Macaca mulatta) with self-injurious behavior

Individually housed rhesus monkeys sometimes spontaneously develop self-injurious behavior (SIB) in the form of self-directed biting that, on occasion, results in severe tissue damage and mutilation. We previously demonstrated lower levels of plasma cortisol in rhesus monkeys with a history of self-wounding (SW) when compared to non-wounders (NW). Furthermore, cortisol levels were negatively correlated with rates of self-directed biting. The present study was designed to further characterize the relationships between hypothalamic-pituitary-adrenocortical (HPA) activity, self-wounding, and self-directed biting. Basal 24-h urinary free cortisol excretion, the urinary free cortisol response to a low dose of dexamethasone, and the plasma cortisol response to ACTH were examined in 24 individually housed rhesus monkeys, based on wounding history, i.e. the presence/absence of a veterinary record of self-wounding, and current rates of self-directed biting, i.e. the median split of self-directed biting frequency (independent of wounding status). There were no reliable group differences on any of the physiological measures when analyzed by wounding history. However, the plasma cortisol response 30 min post-ACTH stimulation was significantly correlated with wounding recency, such that lower responsivity was associated with more recent wounding episodes. When the results were analyzed on the basis of biting frequency, high frequency biters (HFB) compared to low frequency biters (LFB) showed decreased HPA negative feedback sensitivity to dexamethasone and a trend towards an attenuated plasma cortisol response to ACTH stimulation. These findings suggest that SIB in socially reared monkeys is associated with complex changes in HPA axis function that are related to the expression of the pathology, i.e. self-directed biting, and to the recency of a wounding episode. It remains to be determined whether humans who exhibit SIB show similar alterations in HPA function.

Long-term adaptations in glucocorticoid receptor and mineralocorticoid receptor mRNA and negative feedback on the hypothalamo-pituitary-adrenal axis following neonatal maternal separation

BACKGROUND

Maternally separated rats exhibit exaggerated hypothalamic-pituitary-adrenal responses to an acute stressor but normal diurnal trough functioning. We hypothesized that maternally separated rats experience adequate proactive glucocorticoid negative feedback but deficient "reactive" negative feedback, contributing to prolonged hypothalamic-pituitary-adrenal stress responses.

METHODS

We measured plasma adrenocorticotropic hormone and corticosterone concentrations following an acute stressor or 6 to 8 hours after dexamethasone administration in adult rats previously exposed to daily handling-maternal separation for 15 minutes (HMS15) or 180 minutes (HMS180) during postnatal days 2 to 14. We also examined regional mineralocorticoid receptor and glucocorticoid receptor messenger RNA density in these two groups.

RESULTS

HMS180 rats appeared to escape dexamethasone suppression of plasma adrenocorticotropic hormone and corticosterone faster than their HMS15 counterparts (p <.01). In situ hybridization analysis revealed increased hippocampal mineralocorticoid receptor messenger RNA density (p <.05) with decreased cortical (p <.05) and hippocampal (p <.05) glucocorticoid receptor messenger RNA density in HMS180 versus HMS15 animals.

CONCLUSIONS

These results are consistent with the hypothesis that in rats exposed to moderate neonatal handling-maternal separation, enhanced proactive feedback maintains the hypothalamic-pituitary-adrenal axis during the diurnal trough, while decreased reactive feedback contributes to prolonged responsiveness of the hypothalamic-pituitary-adrenal axis following an acute stressor.

Reinterpretation of Basal Glucocorticoid Feedback: Implications to Behavioral and Metabolic Disease

A number of metabolic (e.g., abdominal obesity) and psychological (e.g., depression) pathologies commonly present together and have been associated with dysregulation in the hypothalamo-pituitary-adrenal (HPA) axis. Glucocorticoid hormones represent the final product of this classic neuroendocrine axis, and these steroids modulate neuroendocrine, metabolic, and behavioral function. A primary characteristic of the HPA axis is a negative feedback loop, and glucocorticoids act through the brain to inhibit drive to this neuroendocrine system. Slight and chronic perturbations in glucocorticoid levels, below or above normal, throughout the body lead to metabolic (e.g., abdominal obesity) and behavioral (e.g., depression) pathology. Appropriate feedback in the HPA axis is, therefore, critical, and determining how and where glucocorticoids act to impart their feedback effects have been the focus of many laboratories. However, the answer to these questions remain, in part, elusive. In this chapter, I review findings that have led me to reinterpret glucocorticoid feedback in the HPA axis. I propose that, under basal (nonstress) conditions, glucocorticoid feedback is a consequence of the metabolic actions of the adrenal steroid, not a direct effect on brain. This new perspective may provide insight into the etiology of diseases such as major depression and the metabolic syndrome X, and might explain the commonly observed coexistence of affective and metabolic disturbances.

Attenuation by reactive oxygen species of glucocorticoid suppression on proopiomelanocortin gene expression in pituitary corticotroph cells

Up-regulation of hypothalamo-pituitary-adrenal axis is maintained during acute inflammation and/or infection, in the face of sustained elevation of plasma glucocorticoid hormone. Inflammatory stress is usually associated with high plasma cytokine levels and increased generation of reactive oxygen species (ROS) as well. In this study, we examined the effect of ROS on the negative feedback regulation of glucocorticoid in hypothalamo-pituitary-adrenal axis using AtT20 corticotroph cells in vitro. When the cells were treated with H2O2, glucocorticoid suppression on the proopiomelanocortin gene promoter activity was attenuated in a dose-dependent manner. H2O2 also inhibited the ligand-stimulated nuclear translocation of glucocorticoid receptor. The released glucocorticoid suppression by H2O2 was not observed when the cells were cotreated with antioxidants. Together, these results suggest that increased ROS generation in the oxidative redox state attenuates the glucocorticoid negative feedback system, at least in part, by interfering with the nuclear translocation of glucocorticoid receptor and eliminating the repression on proopiomelanocortin gene expression.

Prostaglandins mediate lipopolysaccharide effects upon cholecystokinin and neurotensin phenotypes in neuroendocrine corticotropin-releasing hormone neurons: in situ hybridization evidence in the rat

Intraperitoneal injection of the endotoxin lipopolysaccharide produces an inflammation accompanied by immune system activation and secretion of cytokines that stimulate the hypothalamo-pituitary-adrenal (HPA) axis to release the anti-inflammatory corticosterone. Upstream in HPA axis are neuroendocrine corticotropin-releasing hormone neurons in the paraventricular nucleus whose multipeptidergic phenotype changes during inflammation: coexisting corticotropin-releasing hormone and cholecystokinin mRNAs are up-regulated whereas neurotensin mRNA expression is induced de novo. These changes may be mediated by prostaglandins released from perivascular and microglial cells in response to circulating cytokines. We examined by quantitative in situ hybridization histochemistry whether blockade of prostaglandin synthesis by indomethacin alters phenotypic expression in paraventricular nucleus neurons after lipopolysaccharide. Because indomethacin also elevated circulating corticosterone, animals were adrenalectomized and corticosterone replaced. Results showed that i.p. indomethacin administration suppressed lipopolysaccharide effects in a phenotype non-specific manner: one injection was sufficient to prevent both the increase in corticotropin-releasing hormone and cholecystokinin mRNAs expression and the induction of neurotensin mRNA expression. Therefore, neuroendocrine corticotropin-releasing hormone neurons with different peptidergic phenotypes appear to respond as a whole in the acute phase response to systemic infection.

Interaction between alpha-melanocyte-stimulating hormone and corticotropin-releasing hormone in the regulation of feeding and hypothalamo-pituitary-adrenal responses

Both central alpha-melanocyte-stimulating hormone and corticotropin-releasing hormone (CRH) have been implicated in feeding and neuroendocrine mechanisms. The anatomical overlap and functional similarities between these two neurotransmitter systems led to the hypothesis that CRH might act as one of the mediators of the central actions of the melanocortin system. By double-labeling in situ hybridization, a subpopulation of CRH neurons in the paraventricular nucleus of the hypothalamus (PVN) were shown to contain the melanocortin-4 receptor (MC4R), concentrated in the ventromedial part of the parvicellular PVN (up to 33%). Intracerebroventricular injection of melanocortin agonist MTII to conscious and freely moving rats induced a rapid induction of CRH gene transcription in the PVN. This effect was accompanied by a rise in plasma corticosterone levels in a dose- and time-dependent manner, with the maximum response observed 30 min after MTII injection. MTII (0.5 nmol)-induced increase in plasma corticosterone was attenuated by the selective MC4R antagonist HS014 (0.25-1.0 nmol) and nonselective CRH receptor antagonist alpha-helical-CRH9-41 (0.125-0.5 nmol) in a dose-dependent manner. Moreover, the anorectic effect of MTII was evaluated at 1, 2, and 24 hr after intracerebroventricular injection. Approximately half of the inhibitory effect of MTII (0.5 nmol) on food intake was reversed by pretreatment with alpha-helical-CRH9-41 at 0.25 and 0.5 nmol doses. Collectively, these results provide evidence that CRH acts as a downstream mediator of melanocortin signaling and contributes to the mechanisms by which the central melanocortin system controls feeding and neuroendocrine responses.

The role of corticosterone in food deprivation-induced reinstatement of cocaine seeking in the rat

RATIONAL AND OBJECTIVES

Acute 1-day food deprivation stress reinstates heroin seeking in rats, but the generality of this effect to other drugs, and its underlying mechanisms, are largely unknown. Here we studied whether food deprivation would reinstate cocaine seeking and whether the stress hormone, corticosterone, is involved in this effect.

METHODS

Rats were trained to press a lever for cocaine for 10-12 days (0.5-1.0 mg/kg per infusion, IV, 4 h/day) and were then divided into four groups that underwent different manipulations of plasma corticosterone levels: (1) bilateral adrenalectomy (ADX) surgery, (2) ADX surgery+50-mg corticosterone pellets (ADX+P), (3) ADX surgery+50-mg corticosterone pellets+4-h access (0800-1200 hours) to corticosterone (50 micro g/ml) dissolved in a drinking solution (ADX+P/W), or (4) sham surgery. Next, rats were given 7-12 days of extinction training (during which lever presses were not reinforced with cocaine), and after reaching an extinction criterion they were tested for reinstatement of cocaine seeking following exposure to 21 h of food deprivation.

RESULTS

Food deprivation was found to reinstate cocaine seeking in sham-operated rats, but not in rats in which circulating corticosterone was removed (ADX group). In addition, the effect of food deprivation on reinstatement of cocaine seeking was significantly attenuated in rats maintained on basal diurnal levels of corticosterone (ADX+P group). However, food deprivation reinstated cocaine seeking in rats with limited daily access to additional corticosterone in the drinking water (ADX+P/W group). In this group, corticosterone levels were twice as high as the ADX+P group but were significantly lower than those of sham rats.

CONCLUSIONS

The present data, together with previous work on footshock-induced reinstatement of drug seeking, suggest that corticosterone plays a permissive role in stress-induced reinstatement of cocaine seeking, yet its effects are not associated with the stressor-induced increases in plasma corticosterone levels.

Negative feedback functions in chronically stressed rats: role of the posterior paraventricular thalamus

A gradual decrement in hypothalamic-pituitary-adrenal (HPA) activity is observed following repeated exposure to the same stressor, such as repeated restraint. This decrement, termed habituation, may be partly due to alterations in corticosterone-mediated negative feedback inhibition of the HPA axis. We have previously found that the posterior division of the paraventricular thalamus (pPVTh) regulates habituated HPA activity without altering HPA responses to acute stress. Therefore, in the present study, we examined the role of the pPVTh in delayed feedback inhibition of plasma corticosterone responses to repeated restraint. Dexamethasone was administered subcutaneously 2 h prior to 30 min restraint to induce delayed negative feedback inhibition of the HPA axis. In the first experiment, we determined that a 0.05-mg/kg dose of dexamethasone produced submaximal suppression of corticosterone responses to acute restraint and used this dose in the remainder of the experiments. In Experiment 2, we examined dexamethasone-induced feedback inhibition to corticosterone responses to a single or eighth restraint exposure since negative feedback functions in chronically stressed rats are not well studied. We found that corticosterone levels following dexamethasone treatment were similar in repeatedly restrained compared to acutely restrained rats. In Experiment 3, we lesioned the pPVTh and examined dexamethasone-induced feedback inhibition of corticosterone responses to a single or eighth exposure to restraint. pPVTh lesions attenuated dexamethasone-induced inhibition of corticosterone at 30 min in chronically stressed rats but had no effect in acutely stressed rats. These data suggest that negative feedback functions are maintained in rats exposed to repeated restraint and implicate the pPVTh as a site that contributes to these negative feedback functions specifically under chronic stress conditions.

Loss of WAVE-1 causes sensorimotor retardation and reduced learning and memory in mice

The Scar/WAVE family of scaffolding proteins organize molecular networks that relay signals from the GTPase Rac to the actin cytoskeleton. The WAVE-1 isoform is a brain-specific protein expressed in variety of areas including the regions of the hippocampus and the Purkinje cells of the cerebellum. Targeted disruption of the WAVE-1 gene generated mice with reduced anxiety, sensorimotor retardation, and deficits in hippocampal-dependent learning and memory. These sensorimotor and cognitive deficits are analogous to the symptoms of patients with 3p-syndrome mental retardation who are haploinsufficient for WRP/MEGAP, a component of the WAVE-1 signaling network. Thus WAVE-1 is required for normal neural functioning.

Stereotaxic localization of corticosterone to the amygdala enhances hypothalamo-pituitary-adrenal responses to behavioral stress

The amygdala is involved in behavioral, autonomic, and neuroendocrine responses to stressful stimuli. The goal of the current study was to determine the effect of directly elevating glucocorticoids in the amygdala on hypothalamo-pituitary-adrenocortical (HPA) responses to the elevated plus maze, a behavioral stressor known to activate the amygdala. Micropellets (30 microg) of crystalline corticosterone or cholesterol (control) were implanted bilaterally at the dorsal margin of the CeA in male Wistar rats; vascular catheters were also placed at this time. Five days post-surgery, blood samples were drawn at 07:00 and 19:00 h to assess diurnal rhythm of plasma corticosterone. At 7 days post-implantation, rats were subjected to behavioral stress using an elevated plus maze and blood was collected 15 min prior to stress, and at 15, 45, and 90 min after the initiation of the stressor. Corticotropin releasing factor (CRF) and arginine vasopressin (AVP) mRNA levels were analyzed by in situ hybridization in the medial parvocellular division of the hypothalamic paraventricular nucleus (mpPVN) in corticosterone- and cholesterol-implanted rats either not exposed to the elevated plus maze (control) or 4 h post-behavioral stress. Localization of corticosterone to the amygdala had no effect on diurnal rhythm of corticosterone secretion. Behavioral stress significantly increased peak plasma corticosterone levels in both groups to a similar level. However, in the corticosterone implanted rats, plasma corticosterone concentrations at 45 and 90 min post-stress were significantly greater compared to control rats indicating a prolonged corticosterone response to behavioral stress. In non-stressed rats, corticosterone delivery to the amygdala elevated basal CRF mRNA in the mpPVN to levels similar to those observed post-stress in control animals; no further increase was observed in CRF mRNA following stress. Behavioral stress resulted in a significant elevation in CRF mRNA in cholesterol controls. Basal AVP mRNA levels were unaffected by corticosterone implants. AVP mRNA did not increase in cholesterol implanted rats in response to behavioral stress. However, AVP mRNA levels were higher in corticosterone implanted rats post stress compared to cholesterol treated controls. In conclusion, direct administration of corticosterone to the amygdala increases plasma corticosterone in response to a behavioral stressor without altering the diurnal rhythm in plasma corticosterone. Elevated basal levels of mpPVN CRF mRNA, and the induction of a mpPVN AVP mRNA response to the behavioral stressor implicate enhanced ACTH secretagogue expression in the increased HPA response to corticosterone modulation of amygdala function.

Effect of chronic stress on synaptic currents in rat hippocampal dentate gyrus neurons

We investigated the effect of chronic stress on synaptic responses of rat dentate granule cells to perforant path stimulation. Rats were subjected for 3 wk to unpredictable stressors twice daily or to control handling. One day after the last stressor, hippocampal slices were prepared and synaptic responses were determined with whole-cell recording. At that time, adrenal weight was found to be increased and thymus weight as well as gain in body weight were decreased in the stressed versus control animals, indicative of corticosterone hypersecretion during the stress period. In slices from rats with basal corticosteroid levels (at the circadian trough, under rest), no effect of prior stress exposure was observed on synaptic responses. However, synaptic responses of dentate granule cells from chronically stressed and control rats were differently affected by in vitro activation of glucocorticoid receptors, i.e., 1-4 h after administration of 100 nM corticosterone for 20 min. Thus the maximal response to synaptic activation of dentate cells at holding potential of -70 mV [when N-methyl-D-aspartate (NMDA) receptors are blocked by magnesium] was significantly enhanced after corticosterone administration in chronically stressed but not in control animals. In accordance, the amplitude of alpha-amino-3-hydroxy-5-methylisolazole-4-propionic acid (AMPA) but not of NMDA receptor-mediated currents was increased by corticosterone in stressed rats, over the entire voltage range. Corticosterone treatment also decreased the time to peak of AMPA currents, but this effect did not depend on prior stress exposure. The data indicate that following chronic stress exposure synaptic excitation of dentate granule cells may be enhanced when corticosterone levels rise. This enhanced synaptic flow could contribute to enhanced excitation of projection areas of the dentate gyrus, most notably the CA3 hippocampal region.

Hyperactivation of the hypothalamo-pituitary-adrenocortical axis in streptozotocin-diabetes is associated with reduced stress responsiveness and decreased pituitary and adrenal sensitivity

Although increased hypothalamo-pituitary-adrenocortical (HPA) activity has been reported in diabetic patients, the mechanisms underlying hyperactivation are still unclear. We investigated whether alterations in pituitary, adrenal and/or glucocorticoid negative feedback sensitivity in diabetes are responsible for 1) the impaired HPA response to stress and 2) basal hyperactivation of the HPA axis. Normal control, untreated streptozotocin-diabetic and insulin-treated diabetic rats were chronically catheterized. Eight days following surgery, pituitary-adrenal function was monitored throughout the day. Stress responsiveness was evaluated using 20 min of restraint on d 10. Thereafter, the rats were treated with CRH (0.5 microg/kg), ACTH(1-24) (75ng/kg) or dexamethasone (25 microg/kg) iv on d 12, 14, and 16 to evaluate pituitary, adrenal and glucocorticoid feedback sensitivity, respectively. Plasma ACTH and corticosterone (B) concentrations in untreated diabetic rats were significantly higher at 0800 h, but no different at 1300 h or 1800 h. Insulin treatment of diabetic rats normalized ACTH and B concentrations at 0800 h. The pituitary-adrenal response to restraint was greatly diminished in untreated diabetic rats, whereas insulin treatment partially restored this response in diabetic rats. Administration of CRH and ACTH revealed reduced pituitary and adrenal sensitivity in untreated diabetic animals compared with both control and insulin-treated diabetic animals. The dexamethasone suppression test indicated decreased glucocorticoid negative feedback sensitivity in diabetic rats, which was restored with insulin treatment. In conclusion, these studies demonstrate that: 1) impaired stress responsiveness of the diabetic HPA axis involves both decreased pituitary and adrenal sensitivity; and 2) basal hyperactivation of the diabetic HPA axis in the morning is due, in part, to decreased glucocorticoid negative feedback sensitivity.

Antenatal glucocorticoids and the developing brain: mechanisms of action

Glucocorticoids are critical for normal brain development. There is no doubt that prenatal treatment with synthetic glucocorticoid affords great benefit to the preterm infant. However, animal studies, now carried out in many species, indicate that there may be some long-term physiological costs of early exposure to excess glucocorticoid, and that these appear sex-dependent. Further, the effects may not become apparent until later life. Given the dynamics of corticosteroid receptor systems in late gestation, it is likely that there are critical windows of development when specific regions of the brain are more sensitive to the influence of synthetic glucocorticoid. Once such windows have been identified it will be possible to target prenatal treatments, so as to maximize benefit and reduce risk of long-term effects. Notwithstanding, the data reviewed below indicate that caution should be exercised in the use of multiple course glucocorticoid therapy during pregnancy.

State-of-the-art adrenal imaging

The adrenal gland is a common site of disease, and detection of adrenal masses has increased with the expanding use of cross-sectional imaging. Radiology is playing a critical role in not only the detection of adrenal abnormalities but in characterizing them as benign or malignant. The purpose of the article is to illustrate and describe the appropriate radiologic work-up for diseases affecting the adrenal gland. The work-up of a suspected hyperfunctioning adrenal mass (pheochromocytoma and aldosteronoma) should start with appropriate biochemical screening tests followed by thin-collimation computed tomography (CT). If results of CT are not diagnostic, magnetic resonance (MR) and nuclear medicine imaging examinations should be performed. CT has become the study of choice to differentiate a benign adenoma from a metastasis in the oncology patient. If the attenuation of the adrenal gland is over 10 HU at nonenhanced CT, contrast material-enhanced CT should be performed and washout calculated. Over 50% washout of contrast material on a 10-minute delayed CT scan is diagnostic of an adenoma. For adrenal lesions that are indeterminate at CT in the oncology patient, chemical shift MR imaging or adrenal biopsy should be performed. Certain features can be used by the radiologist to establish a definitive diagnosis for most adrenal masses (including carcinoma, infections, and hemorrhage) based on imaging findings alone.

Chronic stress regulates levels of mRNA transcripts encoding beta subunits of the GABA(A) receptor in the rat stress axis

Semi-quantitative hybridization histochemical analyses were undertaken to determine expression levels of mRNA transcripts encoding the beta1-3 subunits of the GABA(A)receptor within the rat hypothalamic paraventricular nucleus (PVN) and hippocampal formation following exposure to a chronic non-habituating stress protocol. After delivery of a battery of stressors on a randomized schedule over a 3-week period, expression levels of the beta1 subunit of the GABA(A) receptor were found to be decreased in the medial parvocellular PVN (mpPVN) by 48.3% relative to control animals. Levels of beta2 mRNA following chronic stress were also found to be decreased in the mpPVN (29.8%), but increased in hippocampal subfields CA(1) and CA(3) (33.9 and 23.2%, respectively) and increased (24%) in the dentate gyrus. The results suggest that GABA(A) receptor subunit composition may be altered at a key regulatory site, and may have important implications for studies aimed at understanding GABAergic inhibitory influences upon the hypothalamic-pituitary-adrenocortical (HPA) axis. Hypophysiotropic CRH neurons serve as the origin of the final common pathway for glucocorticoid secretion in response to stressful stimuli, and GABAergic afferents have been implicated in afferent control of these neurons. Regulation of GABA(A) receptors at these sites may alter the efficacy of a major inhibitory influence upon the stress axis, and thereby modulate stress-induced glucocorticoid secretion.

Corticosteroids regulate 5-HT(1A) but not 5-HT(1B) receptor mRNA in rat hippocampus

The role of mineralocorticoid and glucocorticoid receptors (MR and GR, respectively) in the regulation of serotonin receptors has not been clearly delineated. There is no consensus regarding the regulation of 5-HT(1A) receptors, and corticosteroid regulation of 5-HT(1B) mRNA has not been previously studied. We compared the effects of long-term (two week) adrenalectomy (no MR or GR activation) and several hormone replacement protocols designed to stimulate MR selectively (ALDO), MR and GR (HCT), and continuous MR with cyclical GR activation (SHAM adrenalectomy). 5-HT(1A) and 5-HT(1B) mRNAs were measured by in situ hybridization in hippocampus and raphe nuclei. None of the experimental manipulations altered 5-HT(1B) mRNA levels in the hippocampus or dorsal raphe, and also had no effect on 5-HT(1A) mRNA in dorsal or median raphe. However, 5-HT(1A) mRNA levels were regulated in a complex manner in the different subfields of hippocampus. We conclude that both MR and GR play an integrated role in regulating 5-HT(1A) mRNA levels in hippocampus while having no effect on 5-HT(1B) mRNA levels under these conditions.

Blunted pituitary-adrenocortical stress response in adult rats following neonatal dexamethasone treatment

Glucocorticoids have a prominent impact on the maturation of the stress-related neuroendocrine system and on the postnatal establishment of adaptive behaviour. The present study aimed at investigating the stress responsiveness of the hypothalamo-pituitary-adrenocortical (HPA) axis in young and adult rats after neonatal treatment with the synthetic glucocorticoid agonist, dexamethasone. Newborn male Wistar rats were injected s.c. with 1 microg/g dexamethasone on postnatal days 1, 3 and 5. Circulating adrenocorticotropic hormone (ACTH) and corticosterone concentrations were measured in the resting state and following a 30-min cold stress at the age of 10 days, as well as after a 30-min restraint stress at the age of 14 weeks. Also in adults, pituitary and adrenocortical hormone responsiveness was evaluated after i.v. administration of 2 microg/kg corticotropin releasing hormone (CRH). In addition, glucocorticoid (GR) and mineralocorticoid receptor (MR) binding capacities were assessed in the pituitaries of adult rats. The results showed that at day 10 basal ACTH concentration was elevated while the cold stress-evoked ACTH response was attenuated in the dexamethasone-treated rats. As adults, treated rats showed a suppressed elevation of both ACTH and corticosterone plasma concentrations in response to restraint, while basal hormonal concentrations were not altered. There was no difference in the magnitude of the CRH-induced elevation of ACTH and corticosterone concentrations initially; however, the dexamethasone-treated animals showed a prolonged secretion of both hormones. These animals also showed a selective decrease in pituitary GR binding capacity. Neonatal dexamethasone treatment strongly suppressed body weight gain, and adrenal and thymus weights in the early phase of postnatal development. By adulthood, the body and adrenal weights were normalized while thymus weight was greater than in controls. These findings indicate that neonatal dexamethasone treatment permanently alters HPA axis activity by reducing stress responses to cold and restraint probably through supra-pituitary actions, and by decreasing the effectiveness of feedback through a diminished GR binding in the pituitary.

Glucocorticosteroids up-regulate the expression of cholecystokinin mRNA in the rat paraventricular nucleus

Adrenalectomy abolishes corticosteroid feedback onto the hypothalamic-pituitary-adrenal axis. This results in an increased biosynthetic and secretory activity of corticotropin-releasing hormone (CRH) neurons of the hypothalamic paraventricular nucleus (PVN), sustained in the absence of hormone replacement. In the PVN, cholecystokinin (CCK) is present both in parvicellular CRH-containing and in magnocellular oxytocin (OXY)-containing neurons. We presently studied the glucocorticoid feedback regulation of the expression of cholecystokinin (CCK) mRNA in rats after: (i) adrenalectomy, (ii) sham surgery or (iii) adrenalectomy with corticosterone replacement. Using 35S-labeled CRH and p-CCK cRNA probes and in situ hybridization, CRH and CCK mRNAs were radiolabeled. The total amount of hybridization labeling (integrated density), was quantified in adjacent series of cryosections regularly spaced throughout the PVN. The OXY mRNA detection served to identify PVN magnocellular areas. Adrenalectomy was shown to induce: (i) a 75% increase in CRH mRNA labeling in the PVN, (ii) a concomitant 43% decrease in CCK mRNA labeling but only in the anterior part of the PVN and occurring both in CCK/CRH area (two thirds of it) and CCK/OXY area (one third of it) and (iii) that they were fully reversed by corticosterone replacement. Thus, glucocorticoids that are well known to negatively feedback on CRH expression in parvicellular PVN neurons are also capable of positively regulating CCK expression in anterior PVN neurons, both in parvicellular and magnocellular areas.

A subset of kappa opioid ligands bind to the membrane glucocorticoid receptor in an amphibian brain

Previous studies demonstrated that a membrane receptor for glucocorticoids (mGR) exists in neuronal membranes from the roughskin newt (Taricha granulosa) and that this receptor appears to be a G protein-coupled receptor (GPCR). The present study investigated the question of whether this mGR recognizes nonsteroid ligands that bind to cognate receptors in the GPCR superfamily. To address this question, ligand-binding competition studies evaluated the potencies of various ligands to displace [3H]corticosterone (CORT) binding to neuronal membranes. Initial screening studies tested 21 different competitors and found that [3H]CORT binding was displaced only by dynorphin 1-13 amide (an endogenous kappa-selective opioid peptide), U50,488 (a synthetic kappa-specific agonist) and naloxone (a nonselective opioid antagonist). Follow-up studies revealed that the kappa agonists bremazocine (BRE) and ethylketocyclazocine (EKC) also displaced [3H]CORT binding to neuronal membranes, but that U69,593 (a kappa specific agonist) and nor-BNI (a kappa specific antagonist) were ineffective. The Ki values measured for the opioid competitors were in the subnanomolar to low micromolar range and had the following rank-order: dynorphin > U50,488 > naloxone > BRE > EKC. Because these ligands displaced, at most, only 70% of [3H]CORT specific binding, it appears that some [3H]CORT binding sites are opioid insensitive. Kinetic analysis of [3H]CORT off-rates in the presence of U50,488 and/or CORT revealed no differences in dissociation rate constants, suggesting that there is a direct, rather than allosteric, interaction with the [3H]CORT binding site. In summary, these results are consistent with the hypothesis that the high-affinity membrane binding site for [3H] CORT is located on a kappa opioid-like receptor.

Is the mineralocorticoid receptor in Brown Norway rats constitutively active?

In a previous study using corticosterone treatment of adrenalectomized rats, we hypothesized that mineralocorticoid receptor (MR)-related mechanisms are constitutively active and that glucocorticoid receptor (GR)-mediated mechanisms are more efficient in Brown Norway rats compared to Fischer 344 (F344) rats. In order to discriminate the mineralocorticoid from the glucocorticoid actions exerted by corticosterone, F344 and Brown Norway adrenalectomized rats were treated with increasing doses (1, 5 and 25 microg/ml of drinking water) of deoxycorticosterone (DOC, MR-specific ligand) or RU 28362 (GR-specific ligand). These rats were compared with long-term adrenalectomized (ADX) untreated rats and sham-ADX rats. This study confirms our previous results, notably the lack of effect of ADX on body weight and fluid intake in Brown Norway rats. Moreover, DOC treatment had no effect in Brown Norway rats whereas the higher dose restored fluid intake of the F344 ADX group to sham values. These results support the hypothesis of a constitutive activation of the MR and therefore the insensitivity of this receptor to its ligand in Brown Norway rats. Alternatively, RU 28362 treatment induced greater weight loss, decrease in food intake, anxiolysis, thymus involution, and decrease in plasma transcortin concentration and pituitary corticosteroid receptor densities in Brown Norway rats than in F344 rats, which is consistent with greater efficiency of GR mechanisms in Brown Norway rats than in F344 rats. Therefore, these strains are of great utility to disentangle MR and GR effects on complex phenotypes.

Effect of acute adrenalectomy on sympathetic responses to peripheral lipopolysaccharide or central PGE(2)

The impact of plasma corticosterone levels on the sympathetic nervous system (SNS) response to intravenous lipopolysaccharide (LPS) or intracerebroventricular injections of PG was studied in anesthetized (urethan-chloralose) male Sprague-Dawley rats. For this, electrophysiological recordings of splenic and renal nerves were completed in control or adrenalectomized (ADX) rats. LPS (10 microgram iv) similarly increased splenic and renal nerve activity in control rats with a shorter onset latency for the splenic nerve. Acute ADX enhanced the response of both nerves to LPS (P < 0.005) and reduced the onset latency of the renal nerve (P < 0.05). PGE(2) (2 microgram icv) rapidly increased the activity of both nerves but preferentially (magnitude and onset latency) stimulated the renal nerve (P < 0.05). The magnitude of the splenic nerve response to PGE(2) was unaffected by ADX. Unexpectedly, PGE(2) was less effective at stimulating renal nerve activity in ADX animals relative to intact controls (P < 0.05). Pretreatment of ADX rats with a CRF antagonist ([D-Phe(12), Nle(21,38), Calpha-MeLeu(37)]CRF-(12-41)) reversed this effect such that the renal nerve responded to central PGE(2) to a greater extent than the splenic nerve (P < 0.05), as was the case in non-ADX rats. These data indicate that enhanced sensitivity of central sympathetic pathways does not account for the enhanced SNS responses to LPS in ADX rats. Also, a CRF-related process appears to diminish renal sympathetic outflow in ADX rats.

GABA(A) receptor subunit expression within hypophysiotropic CRH neurons: a dual hybridization histochemical study

Dual hybridization histochemical studies were conducted to investigate the extent of colocalization of mRNA transcripts encoding the alpha1-2 and beta1-3 subunits of the gamma aminobutyric acid (GABA)(A) receptor with those for corticotropin-releasing hormone (CRH) within the rat hypothalamic paraventricular nucleus (PVN). A vast majority of CRH neurons (>94.5%) were found to express transcripts specific for the the alpha2, beta1 and beta3 subunits; mRNAs for the alpha1 and beta2 subunits of the GABA(A) receptor were detected within 53.3% and 65.7% of PVN CRH neurons, respectively. The results may have important implications for studies aimed at understanding GABAergic influences upon the hypothalamic-pituitary-adrenocortical (HPA) axis. Hypophysiotropic CRH neurons serve as the origin of the final common pathway for glucocorticoid secretion in response to stressful stimuli, and GABAergic afferents have been implicated in afferent control of these neurons. The subunit composition of GABA(A) receptors at this key regulatory locus may affect the efficacy of a major inhibitory input, and thus the magnitude and/or duration of stress-induced glucocorticoid secretion. The present findings reveal basal expression patterns of transcripts encoding several subunits of the GABA(A) receptor within stress-integrative CRH neurons, data which may be used to guide regulatory studies of GABAergic influences on the HPA axis under a variety of conditions.

Hypothalamic-pituitary-adrenal dysfunction in Apoe(-/-) mice: possible role in behavioral and metabolic alterations

Several neurological diseases are frequently accompanied by dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis. The HPA axis regulates the secretion of glucocorticoids (GCs), which play important roles in diverse brain functions, including cognition, emotion, and feeding. Under physiological conditions, GCs are adaptive and beneficial; however, prolonged elevations in GC levels may contribute to neurodegeneration and brain dysfunction. In the current study, we demonstrate that apolipoprotein E (apoE) deficiency results in age-dependent dysregulation of the HPA axis through a mechanism affecting primarily the adrenal gland. Apoe(-/-) mice, which develop neurodegenerative alterations as they age, had an age-dependent increase in basal adrenal corticosterone content and abnormally increased plasma corticosterone levels after restraint stress, whereas their plasma and pituitary adrenocorticotropin levels were either unchanged or lower than those in controls. HPA axis dysregulation was associated with behavioral and metabolic alterations. When anxiety levels were assessed in the elevated plus maze, Apoe(-/-) mice showed more anxiety than wild-type controls. Apoe(-/-) mice also showed reduced activity in the open field. Finally, Apoe(-/-) mice showed age-dependent increases in food and water intake, stomach and body weights, and decreases in brown and white adipose tissues. These results support a key role for apoE in the tonic inhibition of steroidogenesis and HPA axis activity and have important implications for the behavioral analysis of Apoe(-/-) mice.

Antenatal glucocorticoids and programming of the developing CNS

Glucocorticoids (GCs) are essential for many aspects of normal brain development. However, there is growing evidence from a number of species that exposure of the fetal brain to excess GC, at critical stages of development, can have life-long effects on behavior and neuroendocrine function. The hypothalamo-pituitary-adrenal axis, which is central to the integration of the individual's endocrine and behavioral response to stress, appears highly sensitive to excess GC exposure during development. A number of animal studies have shown that exposure to synthetic GCs in utero results in adult offspring that exhibit hyperactivity of the hypothalamo-pituitary-adrenal axis. This will have a long-term impact on health, inasmuch as increased life-long exposure to endogenous GC has been linked to the premature onset of diseases associated with aging. The mechanisms involved in the permanent programming of hypothalamo-pituitary-adrenal function and behavior are not well understood. Synthetic GCs are used extensively to promote pulmonary maturation in fetuses at risk of being delivered before term. Therefore, it is important that we understand the potential long-term consequences of prenatal GC exposure on brain development as well as the underlying mechanisms involved. This review will explore the current state of knowledge in this rapidly expanding field.

Effects of chronic stress on hypothalamic lnterleukin-1beta, interleukin-2, and gonadotrophin-releasing hormone gene expression in ovariectomized rats

The influence of chronic stress on the expression of interleukin (IL)-1beta and IL-2 mRNAs in ovariectomized rat brains, and the physiological consequences of the expression of these cytokines on hypothalamic-pituitary-gonadal (HPG) activity were investigated. Using polymerase chain reaction (PCR)-assisted semiquantitative analysis, we demonstrated alterated expression of IL-1beta and IL-2 mRNA during repeated cold stress; the expression of both IL-beta and IL-2 mRNA increased in the medial preoptic area and ventromedial hypothalamus, and decreased in the lateral hypothalamic area. In the arcuate nucleus/median eminence, IL-2 mRNA expression was dramatically decreased, in contrast to the increase in IL-1beta mRNA expression. Concomitant analysis of GnRH mRNA expression indicated significant suppression of GnRH synthesis in the chronic phase, and a strong negative correlation with cytokine expression in the medial preoptic area. Similar results were obtained in intact females exposed to this stress. These results, together with previous pharmacological studies, suggest that chronic stress may induce reproductive dysfunction through the effects of stress-induced expression of endogenous cytokines.

Glucocorticoids-potent modulators of astrocytic calcium signaling

Glucocorticoids are the first line of choice in the treatment of cerebral edema associated with brain tumors. High-dose glucocorticoids reduce the extent of edema within hours, often relieving critical increases in intracranial pressure, but the mechanisms by which glucocorticoids modulate brain water content are not well-understood. A possible target of action may be glucocorticoid receptor-expressing astrocytes, which are the primary regulators of interstitial ion homeostasis in brain. In this study, we demonstrate that two glucocorticoids, methylprednisolone and dexamethasone, potentiate astrocytic signaling, via long-range calcium waves. Glucocorticoid treatment increased both resting cytosolic calcium (Ca2+i) level and the extent and amplitude of Ca2+ wave propagation two-fold, compared to matched controls. RU-486, a potent steroid receptor antagonist, inhibited the effects of methylprednisolone. The glucocorticoid-associated potentiation of Ca2+ signaling may result from upregulation of the cellular ability to mobilize Ca2+ and release ATP, because both agonist-induced Ca2+i increments (via ATP and bradykinin) and ATP release were proportionally enhanced by glucocorticoids. In contrast, neither gap junction expression (as manifested connexin 43 immunoreactivity) nor functional coupling was significantly affected by methylprednisolone. Confocal microscopy revealed both the expression of glucocorticoid receptors and nuclear translocation of these receptors when exposed to methylprednisolone. We postulate that the edemolytic effects of glucocorticoids may result from enhanced astrocytic calcium signaling.

Strain differences in corticosteroid receptor efficiencies and regulation in Brown Norway and Fischer 344 rats

During the dark phase of the diurnal cycle, and during recovery from restraint stress, Brown Norway (BN) rats secrete less corticosterone than Fischer 344 (F344) rats. These strains also display different levels of corticosteroid receptors in the hippocampus, and of plasma transcortin. Because corticosteroid receptors, plasma transcortin and corticosterone secretion are mutually regulated, we examined brain and pituitary mineralocorticoid receptor (MR) and glucocorticoid receptor (GR) expression and some of the parameters modulated by these receptors (i.e. body and thymus weight, fluid intake, plasma transcortin) in BN and F344 rat strains, by comparing the effects of either hormone deprivation by long-term (21 days) adrenalectomy (ADX), or chronic elevation of corticosterone given in drinking fluid to ADX rats. In BN rats, body weight gain and fluid intake were insensitive to corticosterone deprivation, suggesting that MR-related mechanisms are constitutively active in this strain. Body weight (b.w.) gain, plasma transcortin and thymus weight were reduced to a greater extent by chronic corticosterone in BN rats than in F344 rats, possibly as a consequence of higher free, active fraction of plasma corticosterone due to lower plasma transcortin concentrations and/or a greater efficiency of GR-related mechanisms in BN rats. F344 rats displayed twofold higher brain and pituitary MR levels than BN rats, whereas tissue-and strain-specific regulations were observed for GR levels. The differences in MR levels observed between BN and F344 strains cannot completely explain the differences in corticosterone actions, suggesting that strain differences in response to ADX or corticosterone treatment result from variable receptor efficiencies.

Glucocorticoid receptor antagonists in the hippocampus modify the negative feedback following neural stimuli

The effects of local glucocorticoid receptor antagonists implanted into the dorsal hippocampus on the hypothalamo-pituitary-adrenal (HPA) axis responses following neural stimuli in freely moving rats, as well as their effects on the negative feedback exerted by dexamethasone (DEX) was studied in male rats. In animals with hippocampal cholesterol implants, photic and acoustic stimuli caused depletion in median eminence (ME) CRH-41 and a consequent rise in plasma ACTH and corticosterone levels. These effects were inhibited by systemic DEX, and the latter phenomenon was partially reversed by hippocampal implants of glucocorticoid (GR) and to a lesser degree by mineralocorticoid (MR) receptor antagonists. These data indicate that GR and MR receptors in the hippocampus play a role in the glucocorticoid negative feedback on the HPA axis, although the hippocampus may have also a modulatory effect, which does not depend on glucocorticoids.

Modeling the involvement of the hypothalamic-pituitary-adrenal and hypothalamic-pituitary-gonadal axes in autoimmune and stress-related rheumatic syndromes in women

Autoimmune and stress-related rheumatic diseases are significantly more common in women than in men. Our group has focused on the role of two principal neuroendocrine axes, the hypothalamic-pituitary-adrenal (HPA) axis and the hypothalamic-pituitary-gonadal (HPG) axis, in this increased susceptibility to rheumatic disease. We review the physiology of the HPA and HPG axes and discuss their reciprocal interactions. Mechanisms by which hormones of the HPA and HPG axes influence the immune system and modulate the course of autoimmune inflammatory diseases in animal models of rheumatic disease are described. In addition, we review the data suggesting the importance of these neurohormonal systems in rheumatic diseases. These data provide insights into why women may be at increased risk and how we might better understand the mechanisms that provoke expression of rheumatic diseases in women. To advance research in this area, it is critical to develop methods to evaluate the function of the neuroendocrine axes. Secretion of both HPA and HPG axis hormones, particularly the hormones of the hypothalamus and anterior pituitary, is largely by intermittent pulses. In addition, the HPA axis exhibits a profound circadian, or near 24-hour, variation, and HPG axis hormones fluctuate over the monthly cycle. These factors make meaningful analysis of these axes quite complex. We discuss models used in the analyses of neuroendocrine axes and the use of challenge testing to assess the integrity of neuroendocrine axes.

Effects of adrenalectomy and subsequent corticosterone replacement on rat sleep state and EEG power spectra

Individual effects of corticotropin-releasing hormone (CRH) and glucocorticoids on sleep have been difficult to discern due to the feedback effects each hormone exerts on the other. In addition, it is not known whether hypothalamic-pituitary-adrenal axis hormones alter sleep homeostasis or circadian influences on sleep propensity. We therefore analyzed sleep architecture and electroencephalographic (EEG) power in freely moving rats before and after removal of corticosterone (thus elevating endogenous CRH) by surgical adrenalectomy. Adrenalectomy reduced the amplitude of the diurnal rhythms of maximal and average sleep bout lengths (P < 0.004). After adrenalectomy, power from 1 to 4 Hz decreased (P < 0.042), whereas power from 9 to 12 Hz increased in the power spectra of the EEG recording (P = 0.001). Administration of physiological corticosterone replacement reversed some of these effects. Supraphysiological corticosterone replacement in adrenalectomized rats reduced the amount of non-rapid-eye-movement sleep in the 24-h cycle (P = 0.001). During each endocrine condition, rats were sleep deprived for 6 h. Endocrine status did not alter the subsequent homeostatic response to sleep deprivation. Thus ADX and supraphysiological corticosteroid replacement each altered sleep architecture without a demonstrable effect on sleep homeostasis.

Neuroendocrine abnormalities in fibromyalgia and related disorders

Fibromyalgia (FM) and related syndromes are poorly understood disorders that share symptoms such as pain, fatigue, sleep disturbances, and psychological distress. These syndromes are more common in women, and they are associated with psychological or physical stressors. The neuroendocrine axes are essential physiologic systems that allow for communication between the brain and the body. Interconnections among the neuroendocrine axes lead to coordinate regulation of these systems in both a positive and negative fashion. Several neuroendocrine axes have been shown to be dysfunctional in patients with FM. Although we do not yet understand the relationship between the reported disturbances of neuroendocrine function and the development or maintenance of FM and related syndromes, the authors have proposed that these abnormalities are important in symptomatic manifestations. This article reviews data showing disturbances of the neuroendocrine axes in FM and proposes a hypothesis of the development and maintenance of FM related to neuroendocrine disturbances.

Principles of psychoneuroendocrinology

The goal of this article is to describe some of the central nervous system circuits involved in the regulation of the hypothalamopituitary-adrenocortical (HPA) axis, with an emphasis on animal models believed to mimic the human experience of emotional stress. First, the basic constitutive elements of the HPA axis that control glucocorticoid secretion are reviewed. A description of the neural systems assumed to regulate the activity of the HPA axis, both anatomically and functionally, follows. It is argued that hypothalamic, septal and bed nucleus of the stria terminalis neurons are involved in the regulation of the HPA axis by situations eliciting emotional responses.

Dynamic changes in glucocorticoid and mineralocorticoid receptor mRNA in the developing guinea pig brain

The guinea pig has a high degree of neurological maturity at birth. Since glucocorticoid receptors (GR) and mineralocorticoid receptors (MR) are central to several aspects of brain and neuroendocrine development, we examined the hypothesis that development of central GR and MR systems takes place during fetal life, in species which give birth to mature young. Fetal guinea pigs were retrieved on gestational days (gd) 40-45, 50-55, 60-65. A group of 7-day old neonates was also euthanized. Levels of GR and MR mRNA were determined by in situ hybridization followed by computerized image analysis. MR mRNA was confined to limbic structures, and was present at high levels in the hippocampus and dentate gyrus by gd40. Hippocampal MR mRNA levels decreased with the progression of gestation. GR mRNA was more widely distributed, with highest levels being expressed in the cingulate cortex, hippocampus, amygdala and hypothalamic paraventricular nucleus (PVN). In the hippocampus, GR mRNA levels increased with progression of gestation, attaining highest levels near term. In contrast to the hippocampus, GR mRNA levels were highest in the PVN at gd40-45, but decreased dramatically in the last 25 days of gestation. In conclusion, there are dynamic site-specific changes in the expression of corticosteroid receptors in the brain of the fetal guinea pig, at the time of most rapid brain growth. The decreases in GR mRNA levels in the PVN in late gestation likely facilitate the simultaneous increases in ACTH and cortisol that occur near term, and which are critical for the delivery of viable young.

Excess corticotropin releasing hormone-binding protein in the hypothalamic-pituitary-adrenal axis in transgenic mice

Corticotropin-releasing hormone (CRH) is the primary hypothalamic releasing factor that mediates the mammalian stress response. The CRH-binding protein (CRH-BP) is secreted from corticotropes, the pituitary CRH target cells, suggesting that the CRH-BP may modulate hypothalamic-pituitary-adrenal (HPA) axis activity by preventing CRH receptor stimulation. Transgenic mice were generated that constitutively express elevated levels of CRH-BP in the anterior pituitary gland. RNA and protein analyses confirmed the elevation of pituitary CRH-BP. Basal plasma concentrations of corticosterone and adrenocorticotropin hormone (ACTH) are unchanged, and a normal pattern of increased corticosterone and ACTH was observed after restraint stress. However, CRH and vasopressin (AVP) mRNA levels in the transgenic mice are increased by 82 and 35%, respectively, to compensate for the excess CRH-BP, consistent with the idea that CRH-BP levels are important for homeostasis. The transgenic mice exhibit increased activity in standard behavioral tests, and an altered circadian pattern of food intake which may be due to transgene expression in the brain. Alterations in CRH and AVP in response to elevated pituitary CRH-BP clearly demonstrate that regulation of CRH-BP is important in the function of the HPA axis.

Inherent glucocorticoid response potential of isolated hypothalamic neuroendocrine neurons

Within the broader framework of facilitating investigations into the inherent responses of restricted neuronal phenotypes devoid of their in vivo afferents, serum- and steroid-free cultures enriched in corticotropin-releasing hormone (CRH), arginine vasopressin (AVP), and beta-endorphin (beta-END) peptidergic neurons were prepared from the hypothalamic paraventricular (PVN: CRH and AVP) and/or arcuate (ARC: beta-END) nuclei of juvenile male rats. The functional viability of these ARC/PVN cultures was verified by their ability to synthesize and secrete CRH, AVP, and beta-END under basal and depolarizing (veratridine) conditions in vitro. Peptide secretion was shown to be Ca2+ and Na+ dependent in that it was blocked in the presence of verapamil and tetrodotoxin, respectively. Exposure of ARC/PVN cocultures to the glucocorticoid dexamethasone (DEX) resulted in a dose-dependent increase of CRH secretion and an inhibition of AVP and beta-END; the CRH responses deviated strikingly from predictions based on in vivo experiments. Steroid withdrawal or treatment with the glucocorticoid receptor antagonist RU38486 reversed these trends. Opposite effects of DEX on CRH secretion were observed in cultures consisting of PVN cells only. Supported by studies using an opioid receptor agonist (morphine) and antagonist (naloxone), these observations demonstrate that ARC-derived (beta-END) neurons modulate the responses of PVN neurons to DEX.

Photoperiod regulation of mineralocorticoid receptor mRNA expression in hamster hippocampus

Hippocampal mineralocorticoid receptor mRNA expression was increased in male hamsters exposed to 18 days of short photoperiod relative to animals maintained under long day illumination (p < 0.05). Short day hamsters were also characterized by increased weight gain, and heavier adrenal glands (p < 0.05). The larger adrenals showed selective increases in the widths of the zonae reticularis and glomerulosa (p < 0.001). Incidences of torpor and reduced body temperature were observed in the short day animals. No changes were found in reproductive organ weights, systolic blood pressure, open-field behavior, or stress levels of plasma corticosteroids. We conclude that the hamster brain-adrenal axis responds rapidly to changes in photoperiod, raising the possibility that this axis is a primary mediator of shortened photoperiod responses.

Nerve growth factor, central nervous system apoptosis, and adrenocortical activity in aged Fischer-344/brown Norway F1 hybrid rats

During aging there is a progressive loss of neuronal function in the basal forebrain that results in cognitive impairment and cholinergic deficits. While altered neurotrophin (NT)-mediated signal transduction may account for some age-associated deficits, there are differences in the extent of NT responsiveness among different laboratory rat strains. Here we measured nerve growth factor (NGF) protein levels and fragmented DNA in the CNS, and basal and NGF-stimulated activity levels of the hypothalamus-pituitary-adrenocortical axis (HPAA) in 3-, 18-, and 30-month-old Fischer-344/Brown Norway rats. Our results show that while there is no age-associated differences in NGF protein levels, in aged Fischer-344/Brown Norway rats, there are increases in levels of immunoreactive fragmented DNA in the CNS and in adrenocortical responses to the peripheral administration of NGF. These data contribute to the characterization of the Fischer-344/Brown Norway F1 hybrid rat and provide baseline values useful for future studies on aged CNS.

Distribution of glucocorticoid receptor immunoreactivity and mRNA in the rat brain: an immunohistochemical and in situ hybridization study

The localization of glucocorticoid receptor (GR) immunoreactivity and mRNA in the adult rat brain was examined by light microscopic and electron microscopic immunohistochemistries, and in situ hybridization. For the purpose of detailed investigation of the distribution and comparison of GR immunoreactivities and mRNAs, specific polyclonal antibodies against a part of the transcription modulation (TR) domain of rat GR were used in the immunohistochemistry, whereas fluorescein-labeled RNA probes, complementary to the TR domain in the GR cDNA were used in the in situ hybridization. In the rat brain, GR immunoreactivity was predominantly localized in the cell nucleus, and the expression of GR mRNA was detected in the cytoplasm. GR-immunoreactive and GR mRNA-containing cells were widely distributed from the olfactory bulb of the forebrain to the gracile-cuneate nuclei of the medulla oblongata. The highest densities of GR-immunoreactive and mRNA-containing cells were observed in the subfields of cerebral cortex, olfactory cortex, hippocampal formation, amygdala, septal region, dorsal thalamus, hypothalamus, trapezoid body, cerebellar cortex, locus coeruleus and dorsal nucleus raphe. The distributional pattern of GR immunoreactivity in many regions was well-correlated with that of GR mRNA, but in the CA3 and CA4 pyramidal layers of the hippocampus, different localization was noted. The present study provides the groundwork for elucidating the role of GRs in brain function.

Evidence that abnormalities of central neurohormonal systems are key to understanding fibromyalgia and chronic fatigue syndrome

Fibromyalgia (FM) and chronic fatigue syndrome (CFS) fall into the spectrum of what might be termed stress-associated syndromes by virtue of frequent onset after acute or chronic stressors and apparent exacerbation of symptoms during periods of physical or emotional stress. These illnesses also share perturbation of the hypothalamic-pituitary-adrenal axis and sympathetic stress response systems. In this article, the authors discuss the specific neurohormonal abnormalities found in FM and CFS and potential mechanisms by which dysfunction of neurohormonal stress-response systems could contribute to vulnerability to stress-associated syndromes and to the symptoms of FM and CFS.