Acute stress increases circulating ACTH and glucocorticoid levels. The hippocampus (HIP) is a target of such stress hormones as glucocorticoid and it also expresses receptors for growth hormone (GH), particularly in the dentate gyms (DG). In order to understand the interactions between glucocorticoids and functions of GH in HIP during acute stress, the mRNA levels for GH receptor (GHR), glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) were investigated in DG in rats exposed to restraint stress in the water (RSW). Using in situ hybridization histochemistry (ISHH), high level expressions of GHR mRNA were detected in DG. These were down-regulated by 14% after 0.5 h of RSW and then up-regulated by 38% over the initial level after 4 h of RSW. This biphasic enhancement of GHR mRNA expression in DG followed the elevation of plasma glucocorticoid levels and paralleled with biphasic expressions of mRNAs for GR and MR in DG. Although circulating GH levels did not show any correlation with the hippocampal GHR mRNA expression, adrenalectomy (ADX) decreased GHR mRNA expression in DG, and the dexamethasone treatment (DEX; 20 microg/100 microl, i.p.) of ADX rats rapidly increased the 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 and that GH may be involved in responses of the DG to acute stress.