REGULATION OF GLUCOCORTICOID RECEPTOR AND MINERALOCORTICOID RECEPTOR MESSENGER RIBONUCLEIC-ACIDS BY SELECTIVE AGONISTS IN THE RAT HIPPOCAMPUS

Adrenal steroids can have prodigious effects on the structure, functio n, and survival of hippocampal neurons. In the rat hippocampus, the ac tions of adrenal steroids are mediated by two receptor types, the gluc ocorticoid receptor (GR) and the mineralocorticoid receptor (MR). Usin g in situ hybridization, we have examined the regulation of the messen ger RNAs (mRNAs) encoding the glucocorticoid and mineralocorticoid rec eptors, by aldosterone, which acts selectively through MR, and by RU28 362, which acts selectively through GR. Our results demonstrate that t here is autoregulation of each receptor subtype, such that activation of GR regulates GR mRNA levels and MR activation regulates MR mRNA exp ression. In addition, there is evidence that aldosterone, acting throu gh MR, can affect the expression of GR mRNA. The extent to which a spe cific agonist can produce a significant change in the expression of a particular steroid receptor mRNA varies between the different subfield s of the hippocampus.