Postnatal handling alters glucocorticoid, but not mineralocorticoid messenger RNA expression in the hippocampus of adult rats.

Postnatal handling alters hypothalamic-pituitary-adrenal (HPA) responses to stress in the rat. Handling also increases hippocampal glucocorticoid receptor density, and this effect appears to form, in part at least, the basis for the effect of handling on HPA responsiveness to stress. In the present study we have used in situ hybridization techniques to examine the effect of postnatal handling on the expression of glucocorticoid and mineralocorticoid receptor mRNAs in various cell fields of the dorsal hippocampus in adult rats. Grain counting analysis over individual cells showed that postnatal handling significantly increased (40-50%) glucocorticoid receptor mRNA in all hippocampal cell fields. In contrast, handling had no effect on mineralocorticoid receptor mRNA expression. These findings are consistent with the results of receptor binding studies showing that handling increases hippocampal glucocorticoid receptor, but not mineralocorticoid receptor density. Thus, the increase in glucocorticoid receptor binding in handled animals is likely associated with altered rates of receptor biosynthesis. Moreover, the handling effect is quite specific, altering glucocorticoid receptor, but not mineralocorticoid receptor mRNA expression. The mechanism(s) whereby glucocorticoid receptor gene expression is permanently increased by postnatal handling remains to be determined.