Effects of adrenalectomy and of mineralocorticoid receptor/glucocorticoid receptor ligands in female Brown Norway and Fischer 344 rats and f1 hybrids

Our previous studies suggested that the mineralocorticoid receptor (MR) of Brown Norway (BN) male rats is active independently of the presence of its ligands (i.e. constitutively active), and that glucocorticoid receptor (GR)-mediated mechanisms are more efficient in BN than in Fischer 344 (F344) male rats. Such functional differences in corticosteroid receptors led us to compare the effect of adrenalectomy (ADX) and MR/GR-mediated actions (treatments with deoxycorticosterone, DOC and RU 28362, respectively) on female rats from both strains, and, within the framework of a genetic study, to investigate how these differences were inherited in rats of the first generation (F1) born from the crossbreeding between BN and F344 inbred rats. This study extends our previous hypotheses of a constitutive activation of MR and of a greater efficiency of GR in males to females of the BN strain. In both strains, female rats were less sensitive to ADX and to treatments with DOC or RU 28362 than males. Globally, F1 hybrid BNxF344 rats inherited the functional characteristics of MR and GR of BN rats.     

Role of adrenal steroid mineralocorticoid and glucocorticoid receptors in long-term potentiation in the CA1 field of hippocampal slices

We previously demonstrated in the dentate gyrus (DG) of anesthetized and freely behaving rats that both acute as well as chronic administration of corticosterone produces a suppression in long-term potentiation (LTP). In subsequent studies we showed, again in the DG, that activation of the two types of adrenal steroid receptors (mineralocorticoid (MR) and glucocorticoid (GR)) produce biphasic effects on synaptic plasticity; activation of MR produces an enhancement while activation of GR produces a suppression in LTP. In a separate study, we further demonstrated in rats administered the specific GR agonist RU 28362 that high-frequency stimulation, which normally produces LTP, instead produced long-term depression (LTD) in these animals. In the present study we investigated the effects of MR and GR activation by adrenal steroids on synaptic plasticity of the hippocampal CA1 field, but we studied this ex vivo, in a slice preparation. The results indicate that, as in our studies in the DG, adrenal steroids produce biphasic effects: in ADX rats, aldosterone (a specific MR agonist) enhanced while RU 28362 suppressed synaptic plasticity. Unlike the in vivo preparation, however, rarely was LTD observed in the animals receiving RU 28362. Also, ADX itself did not produce noticeable effects on synaptic plasticity. The present results are in agreement with previous studies showing that elevations in corticosterone or an acute episode of experimentally induced stress in vivo causes a suppression in LTP in the hippocampal CA1 field, in vitro.     

Effects of adrenal steroid manipulations and repeated restraint stress on dynorphin mRNA levels and excitatory amino acid receptor binding in hippocampus

Adrenal steroid and stress effects were determined in hippocampus on levels of dynorphin (DYN) mRNA, expressed in dentate gyrus, and excitatory amino acid receptors, measured in Ammon's horn and dentate gyrus. Adrenalectomy (ADX) decreased DYN mRNA levels in dentate gyrus and replacement with aldosterone (ALDO), a specific type I adrenal steroid receptor agonist, prevented the decrease. Ru28362, a specific type II receptor agonist, had no effect. Likewise, kainate receptor binding to the stratum lucidum and hilus region of dorsal hippocampus was decreased after ADX and this decrease was prevented by ALDO but not by Ru28362 treatment. Similar though smaller effects were found for CNQX binding to AMPA receptors but only in the dentate gyrus molecular or infra- and supragranular layers. Although corticosterone (CORT) treatment of intact rats (40 mg/kg for 3 weeks) elevated DYN mRNA levels in dentate gyrus, up to 14 days of daily restraint stress (1 or 6 h/day) had no significant effect. Neither CORT treatment nor repeated restraint stress altered NMDA and non-NMDA glutamate receptors in hippocampus. The results of this study showing ADX-induced decreases of DYN mRNA and CNQX binding in dentate gyrus and decreased kainate binding in mossy fiber terminal regions are consistent with morphological evidence showing that adrenal steroids maintain normal integrity and structure of dentate gyrus neurons and do so via type I adrenal steroid receptors. These same parameters are apparently not sensitive to chronic restraint stress although the effects of other stressors must be examined.     

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.     

Impaired up-regulation of type II corticosteroid receptors in hippocampus of aged rats

Several recent investigations have reported a decline of rat hippocampal corticosteroid-binding receptors (CSRs) with aging. This decline has been proposed to be an initial cause (through disinhibition) of the elevated adrenal steroid secretion that apparently occurs with aging; however, it could instead be an effect of corticoid elevation (through down-regulation). In order to assess the effects of age on CSR biosynthetic capacity in the absence of down-regulatory influences of endogenous corticoids, as well as to study aging changes in CSR plasticity, we examined the up-regulation of hippocampal CSR that follows adrenalectomy (ADX). The rat hippocampus contains at least two types of CSR binding and differential analysis of types I and II CSR was accomplished by selective displacement of [3H]corticosterone with RU-28362, a specific type II agonist. In young (3 months old) Fischer-344 rat hippocampus, up-regulation of type II binding above 2-day ADX baseline was present by 3-7 days and increased still further by 8-10 days post-ADX; type I CSR density did not change significantly between 1 and 10 days post-ADX. However, in aged (24-26 months old) rats, type II CSR up-regulation did not occur over the 10 day post-ADX period. Thus, the age-related impairment of type II up-regulation may reflect an intrinsic deficit in CSR biosynthesis or lability that is independent of the acute endogenous adrenal steroid environment.     

Effects of aldosterone or RU28362 treatment on adrenalectomy-induced cell death in the dentate gyrus of the adult rat

Previous studies have shown that granule cells of the adult dentate gyrus require adrenal steroids for their survival. In order to investigate whether activation of type I or type II adrenal steroid receptors can mediate granule cell survival, we have analyzed the density of pyknotic cells in the granule cell, CA1 and CA3 pyramidal cell layers in Nissl stained hippocampal sections from adult male rats which were either sham operated, adrenalectomized, or adrenalectomized and treated with aldosterone as a specific type I receptor agonist or RU28362 as a specific type II receptor agonist. Aldosterone treatment completely protected the dentate gyrus from adrenalectomy-induced cell death, while treatment with RU28362 resulted in only a partial protection against cell death in this region. These results indicate that type I adrenal steroid receptor activation is sufficient to protect against adrenalectomy-induced cell death.     

The effects of Type I and Type II corticosteroid receptor agonists on exploratory behavior and spatial memory in the Y-maze

We investigated the effects of two adrenal steroid agonists on adrenalectomized (ADX) rats' performance on the Y-maze. The Y-maze was chosen because memory can be assessed quickly and because it is sensitive to various parameters of exploratory behavior and spatial memory performance. Four days after surgery, ADX rats were injected with aldosterone (ALDO, a selective Type I receptor agonist), RU362 (a selective Type II receptor agonist) or sesame vehicle at three different time points (120 min prior to Trial 1, immediately after Trial 1 or 120 min after Trial 1). SHAM-operated rats injected with vehicle were also tested. The results indicate that vehicle-treated ADX rats were impaired on spatial recognition memory compared to SHAM rats. Treatment with ALDO restored spatial recognition memory performance of ADX rats to a level comparable to SHAM-treated rats by acting on acquisition and consolidation, whereas treatment with RU362 did not change the poor spatial recognition memory performance of ADX rats. Discrimination memory was improved only when either agonist was injected prior to the first trial, strongly suggesting a non-selective effect of corticosteroids on discrimination memory such as increasing arousal. A detailed analysis of exploratory behavior showed that both the ALDO- and RU362-treated rats explored the Y-maze more than the ADX and SHAM groups at all periods of the experiment. These results show that the non-specific increase in exploratory behavior induced by replacing corticosteroids targeted at Type I and Type II receptors was used differentially with the ALDO-treated rats learning and consolidating spatial information better than the RU362-treated rats. These data are discussed along with other evidence to suggest that Type II receptors may require the simultaneous occupancy of Type I receptors to affect learning and memory processes.     

Effects of mineralocorticoid and glucocorticoid receptors on long-term potentiation in the CA3 hippocampal field

We have previously shown that the two types of adrenal steroid receptors, mineralocorticoid MR. and glucocorticoid GR. produce opposite effects on long-term potentiation LTP. in the dentate gyrus in vivo. and CA1 hippocampal field in vitro. More specifically, MR activation enhanced and prolonged LTP, whereas GR activation suppressed LTP in these areas and also produced a long-term depression LTD. of the synaptic response. In the present experiment we investigated acute effects of MR and GR activation on LTP induction in the mossy fiber and commissural associational input to the CA3 hippocampal field, since the mechanisms underlying LTP induction in these two pathways differ, the former being N-methyl-D-aspartate receptor NMDAR. independent while the latter being NMDAR-dependent. Rats were either adrenalectomized ADX or adrenally intact. ADX animals were acutely injected with either the specific MR agonist, aldosterone, the specific GR agonist RU 28362 or vehicle. One hour following the injection, the animals were prepared for electrophysiological recording stimulation. Field potential recordings were performed in the radiatum or laconosum moleculare layers of the CA3 field, with stimulation of either the mossy fibers or the commissural associational input from the contralateral hemisphere. We also replicated our previous findings by recording in the dentate gyrus with stimulation of the medial perforant pathway, in the same animals. As observed in our previous study in the dentate gyrus, we found an enhancement and a suppression of LTP with MR and GR activation, respectively. Similarly, for the commissural associational input to CA3, MR activation enhanced LTP, while GR activation reduced it. In contrast, for the mossy fiber input to CA3, neither MR nor GR activation significantly affected LTP induction. These results indicate that adrenal steroids may modulate LTP induction in the hippocampus via an interaction with glutamatergic NMDAR.     

Characterization of Glucocorticoid Type II Receptors in Neuronal and Glial Cultures from Rat Brain

The purpose of this study was to characterize and compare the properties of glucocorticoid Type II receptors in neuronal and astrocyte glial cultures prepared from rat brain. Type II receptors in cytosol prepared from cultured cells were labeled with [³ H]dexamethasone (DEX) at 0°C. The binding was saturable and specific, with a complete displacement by unlabeled DEX or RU 28362 (a pure glucocorticoid). Scatchard analysis of [³ H]DEX binding suggested a single class of receptors with a slightly lower dissociation constant (K_d) in neuronal (1.13 nM) versus astrocyte glial (1.64 nM) cytosol. The number of binding sites (B_max) in astrocyte glial cultures was four times that in neuronal cultures on a per milligram protein basis (120.3 versus 29.3 fmol/mg protein). The presence of Type II receptors in cultured neurons and astrocyte glia was further confirmed by immunofluorescent staining with a monoclonal antibody against this receptor (BuGR-2). The steroid specificity of Type II receptors was studied by examining the displacement of [³ H]DEX binding to cytosol with unlabeled steroids. For both types of cultures, the potency series for competition was RU 28362> DEX> corticosterone> > aldosterone. Switching cultured cells from serum-supplemented to serum-free medium reduced [³ H]DEX binding at low concentrations (0.5 to 5 nM) of the ligand in both types of culture, thus resulting in a decrease in the apparent affinity. This treatment did not, however, have any significant effect on the total number of binding sites. In summary, these results demonstrate that both neuronal and astrocyte glial cells in culture contain specific glucocorticoid Type II receptors, which resemble those seen in the brain and peripheral tissues.     

Acute glucocorticoid pretreatment suppresses stress-induced hypothalamic-pituitary-adrenal axis hormone secretion and expression of corticotropin-releasing hormone hnRNA but does not affect c-fos mRNA or fos protein expression in the paraventricular nucleus of the hypothalamus

Corticosterone regulates both basal and stress-induced hypothalamic-pituitary-adrenal (HPA) axis activity in a negative-feedback fashion. However, the cellular and molecular mechanisms of this negative feedback have yet to be explicitly characterized. By comparing stress-induced c-fos and corticotropin-releasing hormone (CRH) expression in the paraventricular nucleus (PVN), we may be able to determine whether acute glucocorticoid treatment affects the net neural excitatory input to the PVN (represented primarily by c-fos mRNA expression) or directly affects the ability of cells in the PVN to respond to that input (represented primarily by CRH hnRNA expression). In the following studies, we observed the effect of acute glucocorticoid (RU28362) treatment on subsequent HPA axis reactivity by measuring stress-induced plasma hormone concentration [corticosterone and adrenocorticotropic hormone (ACTH)] and gene expression (c-fos and CRH) in the PVN. First, we examined the dose-response relationship between systemically administered RU28362 (1-150 microg/kg, i.p) and suppression of the stress-induced corticosterone response. We then confirmed central nervous system access of the maximally suppressive dose of RU28362 (150 microg/kg) by an ex vivo radioligand binding assay. RU28362 selectively occupied the majority of glucocorticoid receptors in the hippocampus and hypothalamus while having no effect on mineralocorticoid receptors. In separate studies, RU28362 (150 microg/kg) and corticosterone (5 mg/kg) were injected i.p. 1 h before restraint stress. Compared to vehicle-treated controls, rats treated with RU28362 and corticosterone had substantially blunted stress-induced corticosterone and ACTH production, respectively. Furthermore, treatment with RU28362 significantly blunted stress-induced CRH hnRNA expression in the PVN. By contrast, neither RU28362 nor corticosterone treatment had an effect on stress-induced neuronal activation as measured by c-fos mRNA and its protein product in the PVN. This dissociation between c-fos and CRH gene expression suggests that glucocorticoid suppression of HPA activity within this time-frame is not a result of decreased excitatory neural input to the PVN, but instead depends on some direct effect of RU28362 on cells intrinsic to the HPA axis.     

Modulation of presynaptic glucocorticoid receptors on glutamate release from rat hippocampal nerve terminals

In this study, we have examined the role of corticosterone (CORT) in the regulation of neuronal glutamate release using nerve terminals (synaptosomes) isolated from the rat hippocampus. Adult male Sprague‐Dawley rats received either a chronic systemic administration of CORT (daily 25 mg/kg in sesame oil, subcutaneously) or long‐term bilateral adrenalectomy (ADX) (3–4 weeks), and then the release of 4‐aminopyridine (4AP)‐evoked endogenous glutamate and the levels of glucocorticoid receptor (GR) expression from hippocampal nerve terminals were studied. Chronic administration of CORT resulted in a significant increase of 4AP‐evoked glutamate release from hippocampal nerve terminals, whereas ADX reduced 4AP‐evoked glutamate release. In addition, chronic administration of CORT and ADX induced a significant reduction and increase in GR expression in hippocampal synaptosomes, respectively, as detected by Western blots. Furthermore, acute treatment of CORT or dexamethasone facilitated 4AP‐evoked glutamate release from synaptosomes freshly isolated from naïve rat hippocampus and this effect can be significantly prevented by pretreatment of GR antagonist mifepristone, but not by mineralocorticoid receptor (MR) antagonist RU28318. Together, our results strongly support the presence of GRs on presynaptic nerve terminals in the rat hippocampus acting to facilitate the release of neuronal glutamate. Synapse 63:745–751, 2009. © 2009 Wiley‐Liss, Inc.     

Further studies of brain aldosterone binding sites employing new mineralocorticoid and glucocorticoid receptor markers in vitro

We have used synthetic markers of the glucocorticoid (GC) receptor (RU 28362) and of the mineralocorticoid (MC) receptors (RU 26752 and RU 28318) to characterize the specificity of the sites binding aldosterone (ALDO), dexamethasone (DEX) and corticosterone (CORT) in cytosol of hippocampus. The results obtained suggest that ALDO was bound mostly to a MC receptor, as the relative binding affinity (RBA) of the GC receptor marker (and that of the previously studied RU 26988) was negligible for this site, in contrast to the high RBA displayed by RU 26752. DEX was bound for a large part to a GC receptor, as RU 28362 competed for this site, although the MC receptor marker still showed some affinity. An intermediate effect of both marker types was obtained with CORT. RU 28318 was a weak competitor for either the GC or the MC binding site. Thus, RU 28362 and RU 26752 allowed the discrimination of two to three receptors in the hippocampus, similarly to those described in the kidney. Finally, we have demonstrated the usefulness of these synthetic markers in identifying MC binding sites in several brain regions and also in the hippocampus during ontogenetic development.     

Methamphetamine-induced decrease in neural glucocorticoid receptors: relationship to monoamine levels

Methamphetamine (MA) is a potent psychostimulant drug which is neurotoxic to dopamine (DA) and serotonin (5-HT) neurons. It has been previously reported that acute MA administration to adrenalectomized rats produced large dose-related decreases in hippocampal and striatal glucocorticoid receptors (GR). The present study was designed to determine if MA could decrease neural and peripheral GR when administered to adrenal-intact rats using a neurotoxic dosing regimen which produces depletions of brain DA and 5-HT levels. MA (0, 6.25, 12.5 and 25 mg/kg) was administered to adrenal-intact rats every 2 h for a total of 4 doses. Rats were adrenalectomized (ADX0 6 days later and subsequently sacrificed 24 h later. GR and mineralocorticoid receptors (MR) were measured using radioligand binding assays. Tissue levels of 5-HT and DA were measured in order to confirm the neurotoxic effects of MA and also to relate corticosteroid receptor levels to monoamine concentrations. MA produced dose-related decreases in GR levels in the hippocampus, striatum, frontal cortex and hypothalamus. Hippocampal MR were not affected by MA. 5-HT was also decreased in all of these same 4 brain regions, whereas DA was significantly decreased only in the striatum. MA did not decreases GR in cerebellum and similarly had no effect on DA and 5-HT in this region. MA also did not decrease GR or 5-HT levels in the spleen. These results demonstrate that MA produces a decrease in GR in a variety of brain areas, which is related primarily to 5-HT depletions. There is however a certain degree of tissue specificity in the effects of MA on GR and 5-HT levels. MA-induced decreased in neural GR may have important implications for the rewarding and neurotoxic effects of this abused drug.     

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.     

Potentiation of angiotensin II-induced drinking by glucocorticoids is a specific glucocorticoid Type II receptor (GR)-mediated event

Earlier studies showed that pretreatment (3 and 6 h) of rats with the glucocorticoid hormone, dexamethasone, potentiated the drinking response to either central or peripheral administration of angiotensin II (AII). In the present study the specificity and mechanisms of this potentiation were examined. Intraperitoneal (i.p.) injection of rats with the pure glucocorticoid agonist, RU 28362 (0.4-1.6 mg/kg; 3-24 h), resulted in a time- and dose-dependent potentiation of the drinking responses to either peripherally (100 micrograms/kg, s.c.) or centrally (10 ng) injected AII, similar to the effects of dexamethasone. Drinking induced by central injection of carbachol (200 ng) was unaltered by pretreatment with RU 28362, suggesting that potentiation by this compound was specific for AII. The potentiation of AII-induced drinking by either dexamethasone or RU 28362 was completely abolished by pretreatment with the glucocorticoid Type II receptor (GR) antagonist, RU 38486 (2 mg/kg, i.p.), but not by the mineralocorticoid Type I receptor (MR) blocker, mespirenone (2 mg/kg, i.p.). Taken together, these results indicate that the glucocorticoid-induced potentiation of AII-induced drinking is mediated via GR. Associated with the fact that glucocorticoids potentiate AII-induced drinking is the observation that these steroids also potentiate AII-induced urine output. This enhancement of urine output may explain in part the potentiation in drinking behavior. Possible mechanisms are discussed.     

Effects of adrenalectomy and type I or type II glucocorticoid receptor activation on 5-HT1A and 5-HT2 receptor binding and 5-HT transporter mRNA expression in rat brain

We evaluated the effects of adrenalectomy (ADX) and replacement with glucocorticoid receptor agonists on serotonin (5-HT) 5-HT_1A and 5-HT₂ receptor binding in rat brain. 5-HT_1A receptor binding was increased in the CA2–CA4 and the dentate gyrus of the hippocampus 1 week after ADX. This effect was prevented by the systemic administration of aldosterone (10 μg/μl/h) but not by RU28362 (10 μg/μl/h). No significant effect was observed on 5-HT₂ receptor binding in rat cortex. The expression of 5-HT transporter mRNA was unchanged in the raphe nucleus as measured by in situ hybridization.     

Long-Term Selective Down-Regulation of Brain Glucocorticoid Receptors after Neonatal Dexamethasone Treatment in Rats

The development of corticosteroid receptors may be permanently modified by perinatal hormonal influences. Changes in binding characteristics of corticosteroid receptors were examined in rats treated sc. with 1  μg/g dexamethasone (DEX) on postnatal day (PND) 1 and subsequently two more times on PND 3 and 5 in several brain areas. [³H]Corticosterone (CORT) binding capacity (B_max) and affinity (K_d) were determined at 3 weeks old and adult ages by using saturation analysis. The mineralocorticoid type receptor (MR) and the glucocorticoid receptor (GR) sites were measured separately with single point analysis applying a selective glucocorticoid ligand RU 28362 saturating GR. The decrease in CORT binding was due to a selective GR decrement in all structures and the MR concentration was not changed considerably. The basal levels of plasma CORT were not permanently influenced by neonatal DEX. In conclusion, DEX given during the first week of life resulted in long-term and selective down-regulation of GR and this decrement was independent of the actual circulating CORT level.     

Adrenal steroid regulation of neuropeptide Y (NPY) mRNA: differences between dentate hilus and locus coeruleus and arcuate nucleus

Regulation by adrenal steroids of neuropeptide Y (NPY) mRNA was investigated in hilus of the dentate gyrus, arcuate nucleus of hypothalamus and locus coeruleus (LC) of the adult rat brain. Adrenalectomy (ADX) increased NPY mRNA in hilus but decreased NPY mRNA levels in arcuate nucleus and LC. Using a steroid replacement paradigm previously shown to discriminate between Type I and Type II adrenal steroid receptor mediated effects, it was shown that Type I receptor stimulation by aldosterone prevented the ADX-induced increase of NPY mRNA in hilus, whereas Type II receptor stimulation by Ru28362 prevented the ADX-induced decrease in NPY mRNA in arcuate nucleus and LC. The results for hilus are consistent with evidence for a role of Type I receptors in maintaining levels of a number of gene products associated with neurotransmission. The different regulation in hilus from that in arcuate and LC indicate, along with evidence for regulation of NPY expression by insulin, NGF and cyclic AMP and phorbol esters, that the adrenal steroid regulation of NPY gene expression is part of a complex set of regulatory mechanisms that depend on the brain region and cell type.     

Gluco- and mineralocorticoid receptor-mediated regulation of neurotrophic factor gene expression in the dorsal hippocampus and the neocortex of the rat

Gluco- and mineralocorticoid receptors (GR and MR) act via common promoter elements but may exert different effects on gene regulation in various regions of the forebrain. In order to separately analyse the role of GR and MR in the regulation of neurotrophic factor genes and their receptors, we used adrenalectomy and subsequent hormone injections in the rat as a model system. Twenty-four hours after adrenalectomy rats were injected with a single dose of corticosterone (2 and 10 mg/kg), aldosterone (0.5 mg/kg) or the synthetic glucocorticoid agonist RU 28362 (4 mg/kg). Gene expression of basic fibroblast growth factor (bFGF) and its high-affinity receptors [fibroblast growth factor receptor subtypes 1-3 (FGF-R1, FGF-R2, FGF-R3)], as well as brain-derived growth factor (BDNF) and neurotrophin-3 (NT-3) was analysed at 4 h after the hormone injection in CA1-CA4 (cornus of Ammon areas of the hippocampus) and dentate gyrus of the dorsal hippocampus and in neocortex by means of in situ hybridization. We found that bFGF is regulated in CA2, CA3 and dentate gyrus by GR and MR together, and in CA1, CA4 and neocortex by GR alone. FGF-R2 expression in the hippocampus seems to be regulated only by MR, while BDNF expression appears to depend on both receptors. FGF-R1, FGF-R3 and NT-3 were only moderately affected by the hormone activation of GR and MR acting in concert or alone in the various regions. Thus, the present findings suggest that the adrenal cortical system through GR and MR participate in the control of neurotrophic factor signalling in a highly subregion- and cellular-dependent manner.