Brain corticosteroid receptor gene expression and neuroendocrine dynamics during aging

The present study examined the stress responsiveness of the hypothalamic-pituitary-adrenal axis in relation to the properties of corticosteroid receptors in the brain and pituitary in old (30 months) and young (3 months) male Brown Norway rats. The data demonstrate that circulating ACTH rather than the corticosteroid plasma level was elevated under basal conditions and following stress. Furthermore, a reduction of mineralocorticoid receptor (MR) number in the hippocampus and of glucocorticoid receptor (GR) number in the hypothalamus and the pituitary correspond to increased neuroendocrine responsiveness and negative feedback following stress. The changes in receptor binding do not parallel the changes in the amount of MR and GR mRNA measured with in situ hybridization. This suggests that the processing rather than the receptor gene expression is affected in senescence.