Steroid receptors in the rat hippocampus: a note to the methodology of their binding assay

Differential and age-dependent effects of maternal deprivation on the hypothalamic-pituitary-adrenal axis of brown norway rats from youth to senescence

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.

Localization of the Glucocorticoid Receptor in Rat Brain Mitochondria

The distribution of glucocorticoid receptor in subcellular fractions of brain cortex and hippocampus, two regions rich in glucocorticoid receptor, has revealed its presence in nuclei, cytosol, mitochondria, synaptosomes, and synaptosomal mitochondria. The identification of glucocorticoid receptor has been accomplished both by Western blotting using antibodies recognizing the carboxy and the amino terminus of the glucocorticoid receptor and by immunogold electron microscopy using the same anti-glucocorticoid receptor antibodies. Antibody-glucocorticoid receptor interaction is abolished by preincubation of each antibody with its competing peptide. In addition to the intact 95-kDa glucocorticoid receptor in all fractions, lower molecular weight glucocorticoid receptor fragments have been also detected by Western blotting. The presence of glucocorticoid receptor in brain mitochondria supports the concept of a direct action of glucocorticoids on mitochondrial gene transcription, parallel to the established primary actions of the hormones on nuclear gene transcription, as a mechanism of coordinate regulation of respiratory enzyme biosynthesis by steroid hormones.

Prenatal stress in rats: effects on plasma corticosterone, hippocampal glucocorticoid receptors, and maze performance

The present experiments were designed to investigate the effects of maternal stress on cognitive and endocrine parameters in the adult offspring. Pregnant rats were stressed daily during the last week of pregnancy (days 15-19) by restraint, and the performance of their offspring in the Morris water maze was recorded. Plasma corticosterone levels after swimming and the status of hippocampal glucocorticoid receptors (GRs) were determined. During acquisition of the task, prenatally stressed (PS) males - but not females - showed longer escape latencies than non-stressed controls when swimming in cold (10 degrees C) but not in warm (20 degrees C) water. This sex- and prenatal stress-specific difference was even more pronounced during reversal learning of the task. In contrast, PS females - but not males - had higher basal corticosterone levels and a lower density of hippocampal corticosteroid receptors than non-stressed controls. In all animals irrespective of treatment, swimming in the water maze causes an increase of corticosterone that was smaller on day 8 of swimming than on day 1. After swimming in cold water, the rise in corticosterone levels in females was steeper and returned faster to baseline values than after swimming in warm water. A similar pattern could be seen in PS females when compared to their non-stressed controls. The data suggest that prenatal stress impairs spatial learning in males but not in females. Basal and stress-induced increases in corticosterone levels, however, were altered in PS females and not in PS males; i.e., prenatal stress-induced changes in corticosterone secretion were not paralleled by prenatal stress-induced deficits in spatial learning.

Distinct specificity for corticosteroid binding sites in amphibian cytosol, neuronal membranes, and plasma

To address mechanisms of corticosteroid action, one needs tools for distinguishing between the major classes of corticosteroid binding sites: neuronal membrane-associated receptors, intracellular ligand-activated transcription factors, and corticosteroid binding globulins (CBG) in plasma. We characterized the binding parameters for three classes of binding sites in an amphibian, Ambystoma tigrinum, and found that each class had a distinct pharmacological specificity. Equilibrium saturation and kinetic experiments indicated that [3H]corticosterone binds to neuronal membranes with high affinity (Kd approximately 0.37 nM). Aldosterone and two synthetic ligands for mammalian intracellular receptors, dexamethasone and RU486, displayed low affinity for brain membrane sites. In cytosol prepared from brain and liver, [3H]corticosterone bound to a single class of receptors with high affinity (Kd approximately 0.75 and 4.69 nM, respectively) and the rank order potencies for steroid inhibition of [3H]corticosterone binding was RU486 > dexamethasone approximately = corticosterone > aldosterone. In kidney and skin cytosol, [3H]corticosterone binding was best fit with a model having a high-affinity and a lower-affinity site; these sites are not consistent with the pharmacology of mammalian Type I (MR) and Type II (GR) receptors. [3H]Corticosterone also bound to presumed CBG in plasma with high affinity (Kd approximately 2.7 nM), but dexamethasone and androgens bound to plasma CBG with equivalently high affinity. These data demonstrate that pharmacological specificity can be a useful tool for distinguishing corticosteroid binding to different classes of binding sites. These data also indicate that there may be marked species differences in the specificity of corticosteroid binding sites.