Differential up- and down-regulation of type I and type II receptors for adrenocorticosteroid hormones in mouse brain

Glucocorticoid and mineralocorticoid receptor mRNA expression in squirrel monkey brain

Corticosteroids have been implicated in hippocampal atrophy in patients with severe psychiatric disorders, but little is known about receptor expression for corticosteroids in human or nonhuman primate brain. Both the glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) were surveyed in this study of squirrel monkey brain using in situ hybridization histochemistry. Regions of high GR mRNA levels included CA1 and CA2 of hippocampus, dentate gyrus, paraventricular hypothalamus, lateral geniculate, lateral>medial amygdala, and cerebellum. Western analysis confirmed that GR immunoreactivity in squirrel monkey brain tissue most likely reflects the alpha isoform. Regions of high MR mRNA levels included all hippocampal pyramidal cell fields, dentate gyrus granule cell layer, lateral septum, medial>lateral amygdala, and to a lesser extent, cerebellum. Low levels of MR were also expressed in caudate and putamen. Receptor expression for corticosteroids in deep brain structures and the hippocampal formation was similar to that previously reported in rodents, but GR and MR mRNA were expressed at higher levels in squirrel monkey cerebral cortex. GR expression was evident in all cortical layers, particularly the pyramidal cell-rich layers II/III and V. MR expression was restricted to the more superficial cortical layers, and was only moderately represented in layer V. Laminar patterns were apparent in all regions of cortex for GR expression in squirrel monkeys, but low MR mRNA levels were found in dorsomedial prefrontal cortex (PFC). Different subregional distributions and distinctive laminar patterns suggest specialized functions or coordinated interactions between GR and MR mediated functions in primate PFC.

Distribution of corticosteroid receptors in the rhesus brain: relative absence of glucocorticoid receptors in the hippocampal formation

Chronic stress has been associated with degenerative changes in the rodent and primate hippocampus, presumably mediated in part via neuronal glucocorticoid receptors (GRs). In the rat brain, GRs are widely distributed and are particularly dense in the hippocampus. The distribution of GRs in the primate brain, however, has not been fully characterized. In this study, we used in situ hybridization histochemistry and immunohistochemistry to map the distribution of GR mRNA and GR protein, respectively, in adult rhesus monkeys (Macaca mulatta). In contrast to its well established distribution in the rat brain, GR mRNA was only weakly detected in the dentate gyrus (DG) and Cornu Ammonis (CA) of the macaque hippocampus, whereas it was abundant in the pituitary (PIT), cerebellum (CBL), hypothalamic paraventricular nucleus (PVN), and, to a lesser extent, the neocortex. Immunohistochemical staining indicated a very low density of GR-like immunoreactive cells within the macaque hippocampal formation in contrast to the high density observed within the PVN, prefrontal and entorhinal cortices, and cerebellar cortex. Relative to the low level of GR, mineralocorticoid receptor (MR) mRNA and protein expression were abundant within the DG and CA of the rhesus monkey hippocampal formation. These results indicate that, in the primate, neocortical and hypothalamic areas may be more important targets for GR-mediated effects of glucocorticoids than the hippocampus. Alternatively, it is also possible that glucocorticoid effects are mediated through the MRs present in the hippocampal formation.

[3H]-aldosterone binding sites (type I receptors) in the lateral wall of the cochlea: distribution assessment by quantitative autoradiography

Mineralocorticoids, such as aldosterone, are steroids that enhance Na+ retention and K+ excretion in ion-transporting epithelial tissues through regulation of Na, K-ATPase. Previous studies suggest that aldosterone may regulate labyrinthine ion transport through up-regulation of Na, K-ATPase sites, a process mediated by high-affinity aldosterone (type I) receptors. In the present study, information concerning density and distribution of aldosterone binding sites in cochlear lateral wall tissues was determined by quantitative autoradiography using [3H]-aldosterone and RU-28362, a glucocorticoid agonist that blocks low affinity binding to glucocorticoid (type II) receptors. The results revealed that the distribution of aldosterone binding sites differs among the individual cochlear regions of the lateral wall. The highest level of binding was associated with the stria vascularis and epithelial cells of the spiral prominence. Elevated levels of binding were also observed in stromal cells of the spiral prominence, and to a lesser extent in the spiral ligament. The differential distribution of aldosterone binding sites in the lateral wall resembles the pattern of localization of Na, K-ATPase sites observed in previous studies and is compatible with the idea that mineralocorticoids play a role in the regulation of cochlear cation transport.

Adrenalectomy-induced increase of brain protein synthesis is antagonized by corticosterone replacements in free-moving rats

The autoradiographic method with L-[35S]-methionine was used to determine whether changes in glucocorticoid circulating levels were associated with changes in local rates of protein synthesis in rat brain. Chronic bilateral adrenalectomy induced an increase of methionine incorporation rates into proteins in 60 of the 62 brain regions examined (mean effect, +50%). This effect was confirmed biochemically and quantified by correcting for the relative contribution of methionine derived from protein degradation to the precursor pool for protein synthesis in the whole brain. Acute or chronic administration of corticosterone, at doses that normalize basal levels of adrenocorticotrophic hormone, reversed or prevented the adrenalectomy-induced increase of protein synthesis in most regions. However, in nearly all the regions studied (59 of 62), acute corticosterone administration to sham-operated rats did not change the apparent rate of protein synthesis. These results demonstrate that glucocorticoids exert a generalized inhibitory action on brain protein synthesis, because the stimulatory and persistent effect of adrenalectomy on protein synthesis was antagonized by corticosterone replacements at physiological doses. Thus, the regulation of overall brain protein synthesis by glucocorticoids emphasizes the role of neuroendocrine events on long-term neurochemical processes.

Characterization of mineralocorticoid and glucocorticoid receptors in primate brain

Characteristics of neural corticosteroid receptors were studied in 51 adrenally-intact macaque monkeys using a modification of a corticosteroid receptor assay developed in this laboratory for rodent studies. Using cortisol as a ligand, two receptor subtypes could be distinguished and with similar Kd's to those observed in rodents, as measured with corticosterone. The time course showed maximum binding for mineralocorticoid receptors at 24 h and for glucocorticoid at 4 h. There were regional differences in the number of available binding sites for each receptor type, as well as an inverse correlation between the concentration of cortisol in the blood at the time of death and the number of available binding sites. In general this paper emphasizes the similarities between such receptors in primate and those in other species, similarities that could be detected despite the technical constraints of studying tissue taken from non-adrenalectomized animals.

H-2 gene complex and corticosteroid responsiveness: evidence that the corticosteroid hormone signal transduction pathway in the adult mouse lung is not associated with haplotype-specific responses to corticosteroids

Differential responsiveness to corticosteroids (CORT) has been shown to be related to HLA haplotype. A strong association between the mouse homolog to the human HLA complex, the H-2 complex, and intrauterine responses to CORT have also been demonstrated; haplotype differences alter CORT-induced susceptibility to cleft palate and temporal differences in lung maturation. Since variation in the glucocorticoid receptor (GR) is associated with tissue specific responses to CORT, we hypothesize that haplotype-specific CORT responsiveness may be regulated by H-2 associated modification of GR expression and/or function. Given that H-2 congenic mice are genetically identical except at the H-2 complex on mouse chromosome 17 and the GR structural gene is encoded on chromosome 18, the GR gene is identical in these mice. However, any step in the GR signal transduction pathway may be regulated by gene(s) at or near the H-2 complex and result in haplotype-specific differences in CORT responsiveness. We have investigated differences in qualitative and quantitative characteristics of the adult B10 (H-2b) and B10.A (H-2a) pulmonary GR by Scatchard analysis, immunochemical and biochemical assays. No differences in the GR binding parameters (BMAX and Kd), receptor form and level, or ligand-GR complex binding to glucocorticoid response element (GR-GRE) were detected, leading us to conclude that H-2 associated factors do not regulate the relative intrauterine responses to CORT by modulating the adult GR.(ABSTRACT TRUNCATED AT 250 WORDS)

High affinity aldosterone binding sites (type I receptors) in the mammalian inner ear

The presence of aldosterone (Type 1) binding sites in the mammalian inner ear has been previously suggested by an increase in inner ear Na, K-ATPase ouabain binding sites in response to the administration of aldosterone in vivo (Pitovski et al., 1993). Type I binding sites have now been identified and characterized in the lateral wall of the basal turn of the cochlea and in the ampullae of the semicircular canals of the guinea pig. In the presence of RU 28362, which blocks low-affinity binding of the labeled hormone to Type II sites, [3H]-aldosterone binds to a single class of high-affinity (Type I) sites with Kd values of 34.7 nM in lateral wall of the basal turn of the cochlea and 31.3 nM in the ampullae of the semicircular canals. Bmax is 17.1 fmol/mg dry tissue for the cochlear sample and 17.4 fmol/mg dry tissue for the ampullae, comparable to reported values in renal tissue (17-31 fmol/mg protein). Thus, the results of receptor-binding experimental protocols with [3H]-aldosterone clearly suggest that these inner ear tissues are a target site of mineralocorticoid action.

No aging effect on hippocampal type II glucocorticoid receptors in two inbred mouse strains

We report here on the type II glucocorticoid receptor concentration in the hippocampal cytosol of two inbred strains of mice, C57BL/6J and DBA/2J, aged 2 and 24 months. Glucocorticoid receptors are usually considered as mediating cytotoxic effects of glucocorticoids on hippocampal neurons and modulating hippocampus-dependent behaviors. Either a decrease in glucocorticoid receptors with aging or no effect of aging have been reported previously. In order to test whether strain differences may explain these conflicting results, we have measured, using [3H]RU 28362, the hippocampal glucocorticoid receptor concentrations in two inbred strains of mice showing differential modifications of some hippocampus-dependent behaviors with aging. Our results show that there is neither a strain nor an age effect.

Kainic acid-induced decrease in hippocampal corticosteroid receptors

The potential role of excitatory amino acids in the regulation of brain corticosteroid receptors was examined using systemic administration of kainic acid. Administration of kainic acid (5, 10, and 15 mg/kg) to 24-h adrenalectomized rats that were killed 3 h later produced large, dose-related decreases in glucocorticoid receptors (GR) in hippocampus (23-63%), frontal cortex (22-76%), and striatum (41-49%). Kainic acid did not decrease hypothalamic GR. Hippocampal mineralocorticoid receptors (MR) were also markedly decreased (50-71%) by kainic acid. Significant decreases in corticosteroid receptors could be detected as soon as 1 h after kainic acid (10 mg/kg) administration. Decreases in hippocampal, cortical, and hypothalamic GR as well as hippocampal MR were observed 24 h after administration of kainic acid (10 mg/kg) to adrenalectomized rats. Kainic acid (10 mg/kg) also significantly decreased hippocampal GR and MR as well as GR in the other three brain regions when administered to adrenal-intact rats that were subsequently adrenalectomized and killed 48 h after drug administration. The kainic acid-induced decreases in hippocampal GR and MR binding were due to decreases in the maximum number of binding sites (Bmax) with no change in the apparent affinity (KD). Kainic acid when added in vitro did not displace the GR and MR radioligands from their respective receptors. These studies demonstrate that excitatory amino acids play a prominent role in the regulation of hippocampal corticosteroid receptors. In addition, the data indicate that noncorticosterone factors are involved in corticosteroid receptor plasticity.

Corticosterone regulation of brain and lymphoid corticosteroid receptors

Circulating lymphocytes are often used as a model for brain corticosteroid receptor regulation in clinical disease states, although it is not known if lymphoid receptors are regulated in a similar manner as brain receptors. In the present study the regulation of brain (hippocampus, frontal cortex, hypothalamus and striatum), lymphoid (circulating lymphocytes, spleen and thymus) and pituitary glucocorticoid receptors in response to alterations in circulating corticosterone levels was examined. Seven days following adrenalectomy, type II corticosteroid receptors (i.e. glucocorticoid receptors) were significantly increased in the hippocampus, frontal cortex and hypothalamus, but not in any other tissues. Administration of corticosterone (10 mg/kg) for 7 days significantly decreased type II as well as type I (i.e. mineralocorticoid receptors) receptors in the hippocampus. Type II receptors in the frontal cortex, circulating lymphocytes and spleen were also significantly decreased by chronic corticosterone treatment. Immobilization stress (2 h a day for 5 days) failed to alter receptor density in any of the tissues. These results demonstrate that homologous regulation of corticosteroid receptors by corticosterone does not invariably occur in all tissues and emphasize the complex degree of regulation of these receptors. However, the simultaneous downregulation of both hippocampal and lymphocyte glucocorticoid receptors by corticosterone provides support for the hypothesis that circulating lymphocytes do reflect some aspects of brain glucocorticoid receptor regulation.

Corticosterone regulation of type I and type II adrenal steroid receptors in brain, pituitary, and immune tissue

Type I and Type II adrenal steroid receptor levels were compared in the brain, pituitary and immune system of adrenalectomized rats in the presence or absence of several replacement doses of corticosterone. Six days of adrenalectomy produced an up-regulation of Type II adrenal steroid receptors in the brain and spleen. The lowest replacement dose of corticosterone (equivalent to resting levels of this hormone) blocked this Type II receptor up-regulation, while higher replacement doses of corticosterone were associated with widespread Type I and Type II adrenal steroid receptor down-regulation. However, the dose of corticosterone required for receptor down-regulation varied between tissues. Specifically, hippocampal receptors were most sensitive to corticosterone, whereas pituitary receptors were the least sensitive. All tissues examined, except the pituitary, exhibited a down-regulation of Type II receptors with a high corticosterone replacement dose which approximated acute stress levels of this hormone. In summary, physiologically relevant concentrations of corticosterone were capable of down-regulating Type I and Type II adrenal steroid receptors in multiple brain areas and peripheral immune tissues, including peripheral blood mononuclear cells. In contrast, adrenal steroid receptor levels in the pituitary were relatively insensitive to regulation by corticosterone.

Presence of type I and type II/IB receptors for adrenocorticosteroid hormones in the inner ear

Aldosterone-Type I and dexamethasone-Type II/IB receptor complexes were identified in cytosol prepared from both cochlear and vestibular tissue samples. The specific binding capacity of Type I receptors in the cochlear tissues was approximately equal to that in the vestibular tissues. Likewise, the binding capacity of Type II/IB receptors in the cochlea was approximately equal to that in the vestibular endorgans. Based on the total specific binding measured with dexamethasone, the Type II/IB receptors appeared to outnumber the Type I receptors in cochlear and vestibular tissues by a factor of approximately 2.6; however, when adjustments were made for the probable cross-binding of dexamethasone to Type I receptors, these ratios were decreased to approximately 1.6. The existence of protein receptors for adrenocorticosteroid hormones demonstrated in the present study clearly suggests a mechanism whereby such hormones may directly regulate fluid and ionic gradients in the inner ear.

Treatment of mouse brain cytosol with dextran-coated charcoal and high salt does not reveal a new glucocorticoid binder

Incubation of steroid-free whole mouse brain cytosol from adrenalectomized-ovariectomized mice with saturating concentrations of tritiated dexamethasone was found to label all Type I as well as all Type II adrenocorticosteroid receptors. The quantitative and brain regional distribution of residual dexamethasone binding in cytosols pre-treated with dextran-coated charcoal (DCC) and 300 mM KCl was indistinguishable from that for tritiated aldosterone-Type I receptor complexes under the same conditions. We therefore conclude that the dexamethasone binding sites remaining after DCC and KCl treatment of steroid-free brain cytosol are due to the presence of Type I receptors. The differential sensitivity of Type I and Type II receptors to the DCC/KCl treatment paradigm may be useful in the purification of Type I receptors.

A novel effect of molybdate on the binding of [3H]aldosterone to gel-filtered type I receptors in brain cytosol

Recently we reported that adding molybdate to crude steroid-free cytosol at 0 degree C results in a dose-dependent reduction in the binding of [3H]aldosterone ([3H]ALDO) to Type I adrenocorticosteroid receptors. In the experiments outlined here, we found that addition of molybdate to steroid-free brain cytosol produces a 30-50% increase in the subsequently measured maximal specific binding capacity (BMAX) of [3H]ALDO-Type I receptors if the cytosol is subjected to Sephadex G-25 gel filtration prior to steroid addition. These manipulations were found to have no effect on the equilibrium dissociation constant (Kd) of the receptors. In contrast, when gel filtration of steroid-free cytosol was performed in the absence of molybdate, there was a 2-fold increase in the Kd and over a 50% reduction in the subsequently measured BMAX of [3H]ALDO-Type I receptors. When molybdate was added to this steroid-free cytosol immediately following gel filtration, there was no reduction (or increase) in Type I receptor [3H]ALDO binding capacity compared with non-gel-filtered controls. The addition of as little as 2 mM molybdate to crude steroid-free cytosol was found to stabilize the binding capacity of Type I receptors during exposure to 22 degrees C incubations; however, when gel-filtered steroid-free cytosol was exposed to these conditions at least 10 mM molybdate was required to stabilize Type I receptor binding capacity. Adding the sulfhydryl reducing reagent, dithiothreitol, to the various steroid-free cytosols had little effect on [3H]ALDO-Type I receptor binding.(ABSTRACT TRUNCATED AT 250 WORDS)

Further chemical differentiation of type I and type II adrenocorticosteroid receptors in mouse brain cytosol: evidence for a new class of glucocorticoid receptors

There are at least two classes of intracellular receptors for adrenocorticosteroid hormones in brain. Type I receptors have a high affinity for the naturally occurring gluco- and mineralocorticoids, corticosterone (CORT) and aldosterone (ALDO), respectively, and a very low affinity for synthetic glucocorticoids such as dexamethasone (DEX). type II receptors have a high affinity for the synthetic glucocorticoids, a lower affinity for CORT and a very low affinity for ALDO. In recent studies with mouse brain cytosol we have found a number of other biochemical differences between these two receptor types. In the present study, brain cytosol from adrenalectomized mice was prepared in HEPES buffer and subjected to various potentially inactivating treatments prior to assessment of Type I and Type II receptor specific binding capacity by incubation for 24 h at 0 degrees C with [3H]ALDO +/- [1H]RU 26988 (to prevent or permit the cross-binding of [3H]ALDO to Type II receptors) or [3H]DEX +/- [1H]Prorenone (to prevent or permit the cross-binding of [3H]DEX to Type I receptors), respectively. These studies revealed that 10-20% of the high-affinity (Kd = 3 nM) [3H]DEX specific binding capacity remained even after extensive, high concentration and repeated pretreatments with dextran-coated charcoal (DDC. to remove endogenous sulfhydryl-reducing reagents and other biochemicals). These procedures had little effect on Type I receptors. Further analyses revealed that DCC-resistant [3H]DEX binders were not Type I receptors since they were not saturated by [1H]Prorenone. These binders were also not inactivated by aging steroid-free cytosol at 0 degree C or by treating it with buffers containing 0.3 M KCl. Since these