DEVELOPMENT OF MESSENGER-RNAS FOR GLUCOCORTICOID AND MINERALOCORTICOID RECEPTORS IN RAT HIPPOCAMPUS

The hippocampus plays an important role in mediating glucocorticoid ef fects on the brain. Glucocorticoids are also implicated in neurogenesi s and aged-related neuronal death in the hippocampus. The effects of g lucocorticoids in the hippocampus are elicited through two receptors w ith high-affinity for corticosterone, the glucocorticoid receptor (GR) and the mineralocorticoid receptor (MR). In this study, we used a sen sitive RNase protection assay to quantify the ontogeny of GR mRNA and MR mRNA in hippocampus from embryonic day 18 (E18) to postnatal day 60 (P60). GR mRNA and MR mRNA are expressed at approximately equal level s in the E18 hippocampus. However, by birth, the level of MR mRNA is t hree-fold that of GR mRNA and remains elevated up to P60. The levels o f both mRNAs increase gradually during the period of postnatal neuroge nesis after which they markedly increase to adult levels. In addition, the levels of hippocampal MR mRNA are the same in male and female rat s, whereas the levels of GR mRNA are significantly higher in the P60 f emale rat hippocampus, but not in younger female rats. Our data on the development of mRNA levels do not parallel the levels of glucocortico id and mineralocorticoid receptors as reported in a number of binding studies. Therefore, our studies, when considered together with previou s reports, suggest that posttranscriptional mechanisms play a major ro le in regulating the levels of glucocorticoid-binding sites in the hip pocampus.