A biphasic regulation of receptor mRNA expressions for growth hormone, glucocorticoid and mineralocorticoid in the rat dentate gyrus during acute stress

Acute stress increases circulating ACTH and glucocorticoid levels. The hipp ocampus (HIP) is a target of such stress hormones as glucocorticoid and it also expresses receptors for growth hormone (GH), particularly in the denta te gyms (DG). In order to understand the interactions between glucocorticoi ds and functions of GH in HIP during acute stress, the mRNA levels for GH r eceptor (GHR), glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) were investigated in DG in rats exposed to restraint stress in the wat er (RSW). Using in situ hybridization histochemistry (ISHH), high level exp ressions of GHR mRNA were detected in DG. These were clown-regulated by 14% after 0.5 h of RSW and then up-regulated by 38% over the initial level aft er 4 h of RSW. This biphasic enhancement of GHR mRNA expression in DG follo wed the elevation of plasma glucocorticoid levels and paralleled with bipha sic expressions of mRNAs for GR and MR in DG. Although circulating GPI leve ls did not show any correlation with the hippocampal GHR mRNA expression, a drenalectomy (ADX) decreased GHR mRNA expression in DG, and the dexamethaso ne treatment (DEX; 20 mu g/100 mu l, i.p.i of ADX rats rapidly increased th e GHR mRNA expression in DG. These results have suggested that the GHR mRNA expression in the DG is regulated, at least in part, by glucocorticoids an d that GH may be involved in responses of the DG to acute stress. (C) 2000 Elsevier Science B.V. All rights reserved.