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In this 30th anniversary issue review, we focus on the glucocorticoid modulation of limbic-prefrontocortical circuitry during stress-coping. This action of the stress hormone is mediated by mineralocorticoid receptors (MRs) and glucocorticoid receptors (GRs) that are co-expressed abundantly in these higher brain regions. Via both receptor types, the glucocorticoids demonstrate, in various contexts, rapid nongenomic and slower genomic actions that coordinate consecutive stages of information processing. MR-mediated action optimises stress-coping, whereas, in a complementary fashion, the memory storage of the selected coping strategy is promoted via GR. We highlight the involvement of adipose tissue in the allocation of energy resources to central regulation of stress reactions, point to still poorly understood neuronal ensembles in the prefrontal cortex that underlie cognitive flexibility critical for effective coping, and evaluate the role of cortisol as a pleiotropic regulator in vulnerability to, and treatment of, trauma-related psychiatric disorders., (© 2018 The Authors. Journal of Neuroendocrinology published by John Wiley & Sons Ltd on behalf of British Society for Neuroendocrinology.)

Damage observed in the hippocampus of the adult spontaneously hypertensive rat (SHR) resembles the neuropathology of mineralocorticoid-induced hypertension, supporting a similar endocrine dysfunction in both entities. In the present study, we tested the hypothesis that increased expression of the hippocampal mineralocorticoid receptor (MR) in SHR animals is associated with a prevalent expression of pro-inflammatory over anti-inflammatory factors. Accordingly, in the hippocampus, we measured mRNA expression and immunoreactivity of the MR and glucocorticoid receptor (GR) using a quantitative polymerase chain reaction and histochemistry. We also measured serum-glucocorticoid-activated kinase 1 (Sgk1 mRNA), the number and phenotype of Iba1+ microglia, as well as mRNA expression levels of the pro-inflammatory factors cyclo-oxygenase 2 (Cox2), Nlrp3 inflammasome and tumour necrosis factor α (Tnfα). Expression of anti-inflammatory transforming growth factor (Tgf)β mRNA and the NADPH-diaphorase activity of nitric oxide synthase (NOS) were also determined. The results showed that, in the hippocampus of SHR rats, expression of MR and the number of immunoreactive MR/GR co-expressing cells were increased compared to Wistar-Kyoto control animals. Expression of Sgk1, Cox2, Nlrp3 and the number of ramified glia cells positive for Iba1+ were also increased, whereas Tgfβ mRNA expression and the NADPH-diaphorase activity of NOS were decreased. We propose that, in the SHR hippocampus, increased MR expression causes a bias towards a pro-inflammatory phenotype characteristic for hypertensive encephalopathy., (© 2017 British Society for Neuroendocrinology.)

Cortisol and corticosterone act on the appraisal process, which comprises the selection of an appropriate coping style and the encoding of the experience for storage in the memory. This action exerted by the stress hormones is mediated by mineralocorticoid receptors (MRs), which are expressed abundantly in the limbic circuitry, particularly in the hippocampus. Limbic MR is down-regulated by chronic stress and during depression but induced by antidepressants. Increased MR activity inhibits hypothalamic-pituitary-adrenal axis activity, promotes slow wave sleep, reduces anxiety and switches circuit connectivity to support coping. Cortisol and emotion-cognition are affected by MR gene haplotypes based on rs5522 and rs2070951. Haplotype 1 (GA) moderates the effects of (early) life stressors, reproductive cycle and oral contraceptives. MR haplotype 2 (CA) is a gain of function variant that protects females against depression by association with an optimistic, resilient phenotype. Activation of MR therefore may offer a target for alleviating depression and cognitive dysfunction. Accordingly, the MR agonist fludrocortisone was found to enhance the efficacy of antidepressants and to improve memory and executive functions in young depressed patients. In conclusion, CORT coordinates via MR the networks underlying how an individual copes with stress, and this action is complemented by the widely distributed lower affinity glucocorticoid receptor (GR) involved in the subsequent management of stress adaptation. In this MR:GR regulation, the MR is an important target for promoting resilience., (© 2016 British Society for Neuroendocrinology.)

We have analysed the long-term psychoneuroendocrine effects of maternal deprivation (MD) [24 h at postnatal day (PND) 9] and/or exposure to chronic unpredictable stress (CUS) during the periadolescent period (PND 28 to PND 43) in male and female Wistar rats. Animals were tested in the elevated plus maze (EPM, anxiety) at PND 44 and in two memory tests, spontaneous alternation and novel object recognition (NOT) in adulthood. The expression of hippocampal glucocorticoid (GR) and mineralocorticoid (MR) receptors, as well as of synaptophysin, neural cell adhesion molecule and brain-derived neurotrophic factor, was analysed by in situ hybridisation in selected hippocampal regions. Endocrine determinations of leptin, testosterone and oestradiol plasma levels were carried out by radioimmunoassay. Young CUS animals showed decreased anxiety behaviour in the EPM (increased percentage of time and entries in the open arms) irrespective of neonatal treatment. Memory impairments were induced by the two stressful treatments as was revealed by the NOT, with males being most clearly affected. Although each stressful procedure, when considered separately, induced different (always decrements) effects on the three synaptic molecules analysed and affected males and females differently, the combination of MD and CUS induced an unique disruptive effect on the three synaptic plasticity players. MD induced a long-term significant decrease in hippocampal GR only in males, whereas CUS tended to increase MR in males and decrease MR in females. Both neonatal MD and periadolescent CUS induced marked reductions in testosterone and oestradiol in males, whereas MD male animals also showed significantly decreased leptin levels. By contrast, in females, none of the hormones analysed was altered by any of the stressful procedures. Taking our data together in support of the 'two-hit' hypothesis, MD during neonatal life and/or exposure to CUS during the periadolescent period induced a permanent deficit in memory, which was accompanied by a decrement in markers for hippocampal plasticity. The long-term effects on body weight and hormone levels, particularly among males, might reflect sex-dependent lasting metabolic alterations as well as an impaired reproductive function., (© 2011 The Authors. Journal of Neuroendocrinology © 2011 Blackwell Publishing Ltd.)

In vivo glucocorticoid (GC) secretion exhibits a distinctive ultradian rhythmicity. The lipophilic hormone can rapidly diffuse into cells, although only the pulse peak is of sufficient amplitude to activate the low affinity glucocorticoid receptor (GR). Discrete pulses readily access brain regions such as the hippocampus where GR expression is enriched and known to regulate neuronal function, including memory and learning processes. In the present study, we have tested the hypothesis that GR brain targets are responsive to ultradian GC rhythmicity. We have used adrenalectomised rats replaced with pulses of corticosterone to determine the transcriptional effects of ultradian pulses in the hippocampus. Confocal microscopy confirmed that each GC pulse results in transient GR nuclear localisation in hippocampal CA1 neurones. Concomitant GR activation and DNA binding was demonstrated by synthetic glucocorticoid response element oligonucleotide binding, and verified for the Clock gene Period 1 promoter region by chromatin immunoprecipitation assays. Strikingly each GC pulse induced a 'burst' of transcription of Period 1 measured by heterogeneous nuclear RNA quantitative polymerase chain reaction. The net effect of pulsatile GC exposure on accumulation of the mature transcript was also assessed, revealing a plateau of mRNA levels throughout the time course of pulsatile exposure, indicating the pulse timing works optimally for steady state Per1 expression. The plateau dropped to baseline within 120 min of the final pulse, indicating a relatively short half-life for hippocampal Per1. The significance of this strict temporal control is that any perturbation to the pulse frequency or duration would have rapid quantitative effects on the levels of Per1. This in turn could affect hippocampal function, especially circadian related memory and learning processes., (© 2010 The Authors. Journal of Neuroendocrinology © 2010 Blackwell Publishing Ltd.)

Ultradian release of glucocorticoids is thought to be essential for homeostasis and health. Furthermore, deviation from this pulsatile release pattern is considered to compromise resilience to stress-related disease, even after hormone levels have normalised. In the present study, we investigate how constant exposure to different concentrations of corticosterone affects diurnal and ultradian pulsatility. The rate of recovery in pulsatile hypothalamic-pituitary-adrenal (HPA) activity after withdrawal of exogenous corticosterone is also examined. Finally, the behavioural and neuroendocrine responsiveness to an audiogenic stressor is studied. Adrenally intact male rats were subcutaneously implanted with vehicle, 40% or 100% corticosterone pellets for 7 days. The continuous release of corticosterone from these implants abolished diurnal and ultradian corticosterone variation, as measured with high-frequency automated blood sampling. Pellet removal on post-surgery day 8 allowed rapid recovery of endogenous rhythms in animals previously exposed to daily average concentrations (40%) but not after exposure to high concentrations (100%) of corticosterone. Behavioural and neuroendocrine responsiveness to stress was distinctly different between the treatment groups. Audiogenic stimulation 1 day after pellet removal resulted in a similar corticosterone response in animals previously exposed to 40% corticosterone or vehicle. The 40% pellet group, however, showed less and shorter behavioural activity (i.e. locomotion, risk assessment) to noise stress compared to 100% corticosterone and vehicle-treated animals. In conclusion, unlike the animals impanted with 100% corticosterone, we find that basal HPA axis activity in the 40% group, which had mean daily levels of circulating corticosterone in the physiological range, rapidly reverts to the characteristic pulsatile pattern of corticosterone secretion. Upon reinstatement of the ultradian rhythm, and despite the fact that these animals did not differ from controls in their response to noise stress, they did show substantial changes in their behavioural response to stress.

Neuroendocrinology links experience and behaviour to the action of hormones. This review focusses on the corticosteroids, released in hourly pulses and after stress, to illustrate the integration of body, brain and mind achieved by these hormones. Corticosteroids coordinate cell and organ function in concert with other mediators of the stress response over time spans from seconds to hours, days, weeks, or even permanently. The actions exerted by these stress hormones are mediated by two receptor types that control initial stress reactions and manage the later adaptive phases. How the balance between the stress and adaptive responses contributes to resilience and health is a conundrum to be resolved during the next two decades of the existence of the Journal of Neuroendocrinology.

Male wild house mice selected for a long (LAL) or a short (SAL) latency to attack a male intruder generally show opposing behavioural coping responses to environmental challenges. LAL mice, unlike SAL mice, adapt to novel challenges with a highly reactive hypothalamic-pituitary-adrenal axis and show an enhanced expression of markers for hippocampal plasticity. The present study aimed to test the hypothesis that these features of the more reactive LAL mice are reflected in parameters of hippocampal cell proliferation. The data show that basal cell proliferation in the subgranular zone (SGZ) of the dentate gyrus, assessed by the endogenous proliferation marker Ki-67, is lower in LAL than in SAL mice. Furthermore, application of bromodeoxyuridine (BrdU) over 3 days showed an almost two-fold lower cell proliferation rate in the SGZ in LAL versus SAL mice. Exposure to forced swimming resulted, 24 h later, in a significant reduction in BrdU + cell numbers in LAL mice, whereas cell proliferation was unaffected by this stressor in SAL mice. Plasma corticosterone and dentate gyrus glucocorticoid receptor levels were higher in LAL than in SAL mice. However, no differences between the SAL and LAL lines were found for hippocampal NMDA receptor binding. In conclusion, the data suggest a relationship between coping responses and hippocampal cell proliferation, in which corticosterone may be one of the determinants of line differences in cell proliferation responses to environmental challenges.

The paraventricular nucleus (PVN) in the hypothalamus receives inputs from the hippocampus The present study explored the influence of the hippocampus on genes mediating glucocorticoid feedback in the PVN. Accordingly, the expression of mRNAs for corticotrophin-releasing hormone (CRH), the mineralocorticoid receptor (MR) and the glucocorticoid receptor (GR) in the PVN was examined by in situ hybridisation in rats subjected to transection of the fornix. Significant increases in CRH, MR and GR mRNAs were observed in the parvocellular PVN after fornix transection (FT). FT-animals subjected to adrenalectomy also showed an increase in the number of cells positive for CRH and GR mRNAs. CRH, MR and GR mRNA expression was also increased by bilateral adrenalectomy, and GR mRNA expression was further enhanced in the parvocellular PVN of the FT transected animals. However, no such changes were evident in the magnocellular PVN. These results suggest that the input from the hippocampus to the PVN, particularly to its parvocellular region, has distinct and differential inhibitory effects on the expression of MR,GR and CRH mRNAs that may operate independently from the feedback actions of corticosterone.

The postnatal development of the mouse is characterised by a period of hypo-responsiveness of the hypothalamic-pituitary-adrenal (HPA) axis to moderate stressors. Maternal separation disinhibits this blockade of the HPA axis, but the mechanism responsible is not clear. The present study examined the influence of metabolic signals on the central and peripheral components of the HPA axis in neonatal mice aged 8 days in absence or presence of the mother. Reductions in plasma glucose and leptin as well as rapid increases in plasma ghrelin were apparent in the neonate 4 h following maternal deprivation and maximal at 8 h. In addition, maternal separation induced an increase of neuropeptide Y (NPY) mRNA expression in the arcuate nucleus, a decrease of corticotrophin-releasing hormone (CRH) mRNA expression in the paraventricular nucleus and a rise in serum corticosterone. Pharmacological manipulation of the metabolic signals attenuated the HPA response to maternal separation. Thus, the rise in plasma corticosterone induced by maternal separation was ameliorated by prevention of reduction in blood glucose or blockade of the ghrelin signalling pathway, as were the hypothalamic changes in NPY and CRH mRNAs. By contrast, leptin treatment did not affect the HPA axis response to maternal separation. Together these results suggest that metabolic signals play an important role in triggering the HPA response of the neonate to maternal separation.

The glucocorticoid receptor antagonist mifepristone has been shown to rapidly and effectively ameliorate symptoms of psychotic major depression. To better understand its mechanism, we investigated mifepristone's cellular effects, and found that it rapidly reversed a chronic corticosterone-induced reduction of adult neurogenesis in rats. Unlike other antidepressants, mifepristone is particularly potent in a high corticosterone environment. These data indicate that similarly to its clinical efficacy, mifepristone's effects on adult neurogenesis are rapid and positive, and may therefore be important for its mechanism of action.

Corticosteroids are an essential component of the body's homeostatic system. In common with other such systems, this implies that corticosteroid levels in blood and, more importantly, in the tissues remain within an optimal range. It also implies that this range may vary according to circumstance. Lack of corticosteroids, such as untreated Addison's disease, can be fatal in humans. In this review, we are principally concerned with excess or disturbed patterns of circulating corticosteroids in the longer or shorter term, and the effects they have on the brain.

Several aspects of hippocampal cell function are influenced by adrenal-secreted glucocorticoids in a delayed, genomic fashion. Previously, we used Serial Analysis of Gene Expression to identify glucocorticoid receptor (GR)-induced transcriptional changes in the hippocampus at a fixed time point. However, because changes in mRNA levels are transient and most likely precede the effects on hippocampal cell function, the aim of the current study was to assess the transcriptional changes in a broader time window by generating a time curve of GR-mediated gene expression changes. Therefore, we used rat hippocampal slices obtained from adrenalectomised rats, substituted in vivo with low corticosterone pellets, predominantly occupying the hippocampal mineralocorticoid receptors. To activate GR, slices were treated in vitro with a high (100 nM) dose of corticosterone and gene expression was profiled 1, 3 and 5 h after GR-activation. Using Affymetrix GeneChips, a striking pattern with different waves of gene expression was observed, shifting from exclusively down-regulated genes 1 h after GR-activation to both up and down regulated genes 3 h after GR-activation. After 5 h, the response was almost back to baseline. Additionally, real-time quantitative polymerase chain reaction was used for validation of a selection of responsive genes including genes involved in neurotransmission and synaptic plasticity such as the corticotropin releasing hormone receptor 1, monoamine oxidase A, LIMK1 and calmodulin 2. This permitted confirmation of GR-responsiveness of 15 out of 18 selected genes. In conclusion, direct activation of GR in hippocampal slices results in transient changes in gene expression. The pattern in which gene expression was modulated suggests that the fast genomic effects of glucocorticoids may be realised via transrepression, preceding a later wave of transactivation. Furthermore, we identified a number of interesting candidate genes which may underlie the glucocorticoid-mediated effects on hippocampal cell function.

A close contact between the dam and the litter is essential for the normal development of the hypothalamic-pituitary-adrenal (HPA) axis in rats and mice. Maternal signals, as licking and feeding, have been shown to sustain the HPA axis of the pups in a hypo-responsive state. Disruption of this mother-pup interaction by 24 h of maternal deprivation activates the otherwise quiescent stress system of the neonates, resulting in an enhanced adrenal sensitivity to adrenocorticotropic hormone (ACTH) and a decreased expression of central HPA markers, such as corticotropin-releasing hormone (CRH). However, the dynamics of these central and peripheral changes over the 24h period are largely unknown. In this study, we examined the time course of some of the central and peripheral indices of HPA activity during 24 h of maternal deprivation. We measured corticosterone and ACTH in the blood as well as CRH, mineralocorticoid and glucocorticoid receptor expression in the brain. Our results demonstrate that each of the components of the HPA axis responds to maternal deprivation at different time points following removal of the mother and with a very specific time course. The main activation of the HPA axis occurred between 4 h and 8 h of maternal absence. By contrast, during the second half of the deprivation period, negativefeedback mechanisms restrained the further increase in ACTH and corticosterone release. We conclude that maternal deprivation triggers a cascade of sequential changes at the various levels of the stress system, and that measuring only one aspect of the system at one time point does not accurately reflect the dynamic alterations of the HPA axis.

Genetically selected aggressive (SAL) and nonaggressive (LAL) male wild house-mice which show distinctly different coping styles, also display a differential regulation of the hypothalamic-pituitary-adrenal axis after exposure to an acute stressor. To test the hypothesis that coping style predicts stressor susceptibility, the present study examined line differences in response to a chronic stressor. Chronic psychosocial stress was evoked using two paradigms. In the first paradigm, a SAL or LAL male was living in sensory contact (except tactile contact) with a dominant SAL male for 25 days (sensory contact stress). In the second paradigm, a SAL or LAL male was, in addition to the first paradigm, defeated by a SAL male for 21 consecutive days (defeat stress). The sensory contact stressor induced in LAL mice chronic body weight loss and increased plasma adrenocorticotropic hormone levels compared to SAL mice and increased corticosterone levels, thymus involution and lower hippocampal mineralocorticoid receptor (MR) : glucocorticoid receptor (GR) ratio compared to LAL controls. The defeat stressor increased corticosterone secretion and caused adrenal hypertrophy and thymus involution in both mouse lines. Defeated LAL mice showed long-lasting body weight loss and higher corticosterone concentrations than SAL mice and lower hippocampal MR : GR ratio and decreased immobility behaviour in the forced swimming test than LAL controls. Hypothalamic corticotropin-releasing hormone mRNA expression was higher in defeated SAL than in controls. The present data show that both stress paradigms induced line-dependent physiological and neuroendocrine changes, but that the sensory contact stressor produced chronic stress symptoms in LAL mice only. This latter stress paradigm therefore seems promising to analyse the role of genetic factors in the individual differences in stress-related psychopathology.

To investigate the role of brain glucocorticoid (GR) and mineralocorticoid receptors (MR) in centrally evoked blood pressure responses, the effects of intracerebroventricular (i.c.v.) administration of angiotensin II and vasopressin were studied in adrenalectomized rats with and without corticosterone or aldosterone replacement. Five groups were examined: (i) Adrenalectomy (ADX); (ii) ADX + a subcutaneously implanted 20-mg corticosterone pellet (low corticosterone); (iii) ADX + 100 mg corticosterone pellet (high corticosterone); (iv) ADX + 6 microg/24 h aldosterone via Alzet minipump (Aldo); and (v) Sham adrenalectomy (Sham). Pressor responses to 150 ng angiotensin II and 50 ng vasopressin i.c.v. were determined in freely moving rats using biotelemetry. The results show that, compared to sham rats, ADX rats showed significantly reduced pressor responses. This reduction of the pressor response to angiotensin II could be reversed and even further enhanced by replacement of the ADX rats with high corticosterone concentrations. In contrast, with aldosterone, a depressor type response was observed. Corticosterone replacement could not restore the pressor response to vasopressin. We conclude that the pressor response to centrally administered vasoactive substances is substantially attenuated by removal of the adrenals and that, in the case of angiotensin II, this is due to the lack of high concentrations of circulating corticosterone occupying both MR and GR. However, predominant MR occupancy appears to play an opposite role and attenuates the angiotensin II-induced pressor response.

In this study, the hypothesis was tested that infants deprived from maternal care show persistent changes in hypothalamic-pituitary-adrenal activity. For this purpose, we studied the effect of maternal deprivation in one cohort of the healthy ageing Brown Norway rat strain showing still more than 80% survival rate at 32 months of age. Three-day-old male Brown Norway rats were either maternally deprived for 24 h or remained with the dam. In 3, 12 and 30-32 months (young, adult, senescent) deprived rats and their nondeprived littermates (controls), we determined basal resting and stress-induced plasma adrenocorticotropic hormone (ACTH) and corticosterone as well as corticotropin releasing hormone (CRH) mRNA expression in the paraventricular nucleus (PVN) of the hypothalamus. Mineralocorticoid (MR) and glucocorticoid receptors (GR) in hippocampus and PVN were also assessed using in vitro cytosol binding and in situ hybridization. The effect of ageing per se showed that in the control nondeprived Brown Norway rats, basal corticosterone and ACTH concentrations did not change during life. However, with age, the corticosterone response to novelty stress became progressively attenuated, but prolonged, while there was an age-related increase in the ACTH response. CRH mRNA expression in PVN decreased with age. Hippocampal MR binding and MR mRNA expression in the dentate gyrus were reduced at senescence, as were the GR binding capacities in hippocampus and hypothalamus. Maternal deprivation did not affect survival rate, body weight, nor adrenal weight of the ageing Brown Norway rats. Basal corticosterone and ACTH levels were not affected by deprivation, except for a rise in basal corticosterone concentrations at 3 months. At this age, the corticosterone output in response to novelty was attenuated in the deprived rats. In contrast, a striking surge in novelty stress-induced corticosterone output occurred at midlife while, at senescence, the corticosterone and ACTH responses were attenuated again in the deprived animals, particularly after the more severe restraint stressor. CRH mRNA expression was reduced only during adulthood in the deprived animals. After maternal deprivation, the MR mRNA in dentate gyrus showed a transient midlife rise. GR binding in hypothalamus and hippocampus GR binding was reduced in young rats while, in the senescent deprived animals, a reduced GRmRNA expression was observed in PVN and hippocampal CA1. In conclusion, in the Brown Norway rat, ageing causes a progressive decline in corticosterone output after stress, which is paralleled at senescence by decreased MR and GR mRNA expression in hippocampus and hypothalamus. The long-term effects of maternal deprivation become manifest differently at different ages and depend on test conditions. The deprivation effect culminates in a midlife corticosterone surge and results at senescence in a strongly reduced corticosterone output.

Maternal deprivation of neonatal rats for 24 h has immediate and persistent effects on hypothalamic-pituitary-adrenal (HPA) regulation. Immediately after deprivation corticosterone (CORT) is elevated. The primary purpose of our experiments was to determine if, by preventing this CORT elevation, the persistent effects could be reversed. In experiment 1, pups were injected with dexamethasone at the onset of the 24-h deprivation period on postnatal day 11 to suppress the rise in CORT. In experiment 2 some aspects of maternal behaviour known to suppress CORT levels were mimicked during deprivation from postnatal days 11-12. The pups were either: (1) left undisturbed; (2) stroked periodically; or (3) stroked and episodically fed. At postnatal day 20 basal and stress-induced adrenocorticotrophic hormone (ACTH) and CORT levels were measured as well as brain mineralocorticoid (MR) and glucocorticoid receptors (GR). Neonatal rats receiving dexamethasone prior to the onset of the deprivation on day 11 did not differ on day 20 from deprived pups that were exposed to elevated CORT levels. There were no detectable changes in the non-deprived pups that were treated with dexamethasone. In contrast, feeding and stroking during the period of deprivation obliterated the persistent effects both with regard to the reduced ACTH response and the decreased GR mRNA in hippocampus and hypothalamus. Stroking alone appears to have no influence. In conclusion, the persistent reduction of the ACTH response to mild stress and the decrease of GR mRNA is not mediated by deprivation-induced elevations in CORT, but appears to be reversible by reinstating specific aspects of the dam's nurturing behaviour.

Adrenocorticotropin (ACTH) secretion depends primarily on hypophysiotrophic factors released from neurons of the paraventricular nucleus of the hypothalamus. However, the neurochemical factors controlling these neurons, in particular neuropeptides, have had little investigation. In this study, we have investigated the role of neurotensin in the regulation of the different components of the hypothalamo-pituitary-adrenal (HPA) axis under basal and stress conditions in rats. For this purpose, animals were implanted with bilateral cannulae filled with crystals of the neurotensin antagonist, SR 48692, and which were located above the paraventricular nucleus. Five days after surgery, the effects of SR 48692 implants were studied on basal and stress-induced secretion of ACTH and corticosterone. Such treatment did not modify plasma levels of ACTH and corticosterone in basal conditions but reduced ACTH but not corticosterone levels after tail cut procedure. After an exposure to a novel environment for 30 min, both ACTH and corticosterone plasma levels were reduced in the SR 48692-treated group. In situ hybridization studies revealed that chronic administration of SR 48692 induced a significant reduction of CRF mRNA levels in the parvocellular division of the paraventricular nucleus of the hypothalamus. In addition, a 2-fold increase in basal levels of plasma vasopressin associated with an increase in vasopressin mRNA levels in the magnocellular neurons of the paraventricular nucleus was also detected. Finally, the basal plasma levels of oxytocin were not affected by the same treatment. Taken together, these findings strongly suggest that endogenous neurotensin in the paraventricular nucleus plays a tonic stimulatory role on HPA axis activity and an inhibitory effect on vasopressin secretion.

The influence of plasma corticosterone concentration on serotonin (5-HT) turnover in the dorsal hippocampus was investigated. The experiments were performed in freely moving male Wistar rats in their home cage. Blood samples were taken via a permanent jugular vein catheter to determine plasma corticosterone levels. Extracellular levels of 5-HT and its metabolite 5-hydroxy-indole acetic acid (5-HIAA) were measured using in vivo microdialysis. The rats received an intravenous (i.v.) infusion of the steroid synthesis-inhibitor metyrapone (150 mg/kg/ml) in order to manipulate circulating corticosterone levels. Three hours later, the monoamine oxidase inhibitor pargyline (15 mg/kg/2 ml i.v.) was administered to produce an accumulation of extracellular 5-HT. Pargyline administration led to a four fold increase in 5-HT levels, while reducing 5-HIAA by 45%. Metyrapone pretreatment blocked the pargyline-induced rise in plasma corticosterone to baseline levels and diminished the pargyline-induced increase in 5-HT, without affecting 5-HIAA levels. Thus, the data suggest that a decrease in availability of corticosterone for its receptors by metyrapone diminished the 5-HT synthesis rate. Since plasma corticosterone levels during this blockade are still low, it is assumed that brain glucocorticoid receptor occupation is reduced, while mineralocorticoid receptors are still substantially occupied. Therefore the present results support the hypothesis that corticosterone through glucocorticoid receptor activation enhances 5-HT synthesis rate and release in the dorsal hippocampus.

In this study a possible role of 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD) in altering the access of corticosteroids to their receptors in the hippocampus is investigated. In vitro, oxidation of corticosterone to 11-dehydrocorticosterone (11-DHC) was demonstrated in hippocampal homogenates. Glycyrrhetinic acid (GE) and carbenoxolone (CBX) were potent inhibitors of 11 beta-HSD activity and did not display affinity for mineralocorticoid (MRs) nor glucocorticoid receptors (GRs). Intracerebroventricular injection of CBX in vivo (ED50 approximately 30 micrograms) decreased oxidative activity in hippocampal homogenates, as demonstrated in vitro. In vitro, in hippocampal slices, cell nuclear retention of tritiated corticosterone, but not aldosterone, was markedly enhanced in the presence of GE, which at a concentration of 20 nM was found to inhibit 11 beta-HSD activity by about 50% in the intact cell preparation. In contrast to the effect on in vitro cell nuclear uptake, in vivo autoradiography revealed that retention of corticosterone in the hippocampal cell nuclei was not affected after intracerebroventricular treatment with CBX. We conclude that hippocampal 11 beta-HSD activity does not alter binding of low amounts of corticosterone to MRs in vivo, but we cannot exclude that the enzyme may modulate access to corticosteroid receptors under certain circumstances.

Maternal deprivation of neonatal rats for 24 h enhances the adrenocortical response to stress and/or adrenocorticotropin hormone (ACTH) stimulation during the stress hyporesponsive period (SHRP). The present study tests the hypothesis that such maternally deprived neonatal male rats show altered hypothalamic-pituitary-adrenal (HPA) regulation not only immediately after deprivation but also in later life. In addition, we found previously that neonatal changes in HPA activity preceded modulation of nigrostriatal dopamine function. Therefore, we also measured dopamine responsiveness in adult rats which were deprived of their mother during infancy. Neonatal male rats were maternally deprived for 24 h at the age of 3 days, whereas rats of the control group were left undisturbed. At 60 days of age deprived and non-deprived rats were decapitated and brain, adrenal glands and thymus were removed. Trunk blood was collected for determination of plasma ACTH, corticosterone and prolactin concentrations using radioimmunoassay procedures. mRNA levels of mineralocorticoid receptors (MRs) and glucocorticoid receptors (GRs), corticotropin-releasing hormone (CRH) mRNA and tyrosine hydroxylase (TH) mRNA were measured in brain sections with in situ hybridization. In a second group of male deprived and non-deprived rats apomorphine-induced stereotypic gnawing behaviour was examined at 60 days of age as a measure for functional activity of the dopamine system. Deprived neonatal rats showed the following characteristics as compared with non-deprived rats: (i) lower basal CRH mRNA concentration in parvocellular neurons of the paraventricular nucleus of the hypothalamus (PVN), while basal plasma ACTH and corticosterone concentrations were significantly elevated. Basal prolactin levels were not different. (ii) Similar hippocampal MR and GR mRNA levels. (iii) Significantly reduced GR mRNA levels in PVN and anterior pituitary. (iv) Significantly enhanced apomorphine-induced stereotypic gnawing behaviour and (v) higher TH mRNA levels in substantia nigra, while no changes were found in the ventral tegmental area (VTA). It is concluded that maternally deprived neonatal male rats display as young adults elevated basal pituitary-adrenal activity and enhanced apomorphine susceptibility.

The interaction between corticosterone and hippocampal 5-HT1A receptor mRNA expression was investigated in male rats. Two days after adrenalectomy, 5-HT1A receptor mRNA was increased in the granule cell layer of the dentate gyrus. Injection of corticosterone led to a significant dose-dependent and transient suppression of 5-HT1A receptor mRNA. The effect of a low dose of corticosterone (50 micrograms/kg) could be blocked by RU 28318, a specific mineralocorticoid receptor antagonist, but not by RU 38486, a glucocorticoid antagonist. The effect of a higher dose of corticosterone (300 micrograms/kg) could be partially blocked by RU 28318, whereas there was no additional effect of RU 38486. These results point to a stringent regulation of hippocampal 5-HT1A receptors by corticosterone that is predominantly mediated by the mineralocorticoid receptor.

Pharmacogenetically selected Wistar rat lines were used to investigate the implication of either high or low responsiveness of the dopamine system for the activity of the hypothalamus-pituitary-adrenal (HPA) axis. As selection criterion the gnawing response induced by the dopamine agonist apomorphine was used. This criterion allows to distinguish apomorphine susceptible (apo-sus) rats which show a vigorous gnawing response from apomorphine unsusceptible (apo-unsus) rats. The present study, using male animals of the 9-12th generation of the two rat lines, revealed the following characteristics of the stress response system: (i) in apo-sus rats under basal conditions corticotrophin-releasing hormone (CRH) mRNA level in the paraventricular nucleus (PVN) and plasma adrenocorticotropin (ACTH) concentration were significantly higher; total corticosterone (B) plasma level was similar but free B level was lower; (ii) exposure to a novel environment resulted in a higher and prolonged plasma ACTH and total B response in the apo-sus rats. Moreover, the elevated free B level was also prolonged; (iii) apo-sus rats had increased CRH-induced pituitary ACTH release and B secretion was also increased, but not as prolonged as during novelty. (iv) In dexamethasone-pretreated rats an intravenous ACTH1-24 injection resulted in a similar plasma B response in rats of both lines; (v) In vitro, ACTH1-24 produced a significantly higher B secretion by adrenocortical cells of apo-sus rats reflecting the higher in vivo ACTH priming of the adrenal glands in these animals. (vi) apo-sus rats had higher body and thymic weight.(ABSTRACT TRUNCATED AT 250 WORDS)