Differential expression of fos family and jun family mRNAs in the rat hypothalamo-pituitary-adrenal axis after immobilization stress.

We aimed to clarify the regulatory mechanism of the hypothalamo-pituitary-adrenal axis that plays key roles in initiating stress responses, as well as the roles of immediate early genes in this process. We investigated the stress-induced activation of fos and jun family proto-oncogenes by means of in situ hybridization histochemistry. Immobilization stress induced c-fos and jun B mRNAs in the parvocellular region of the hypothalamic paraventricular nucleus, the anterior and intermediate lobes of pituitary, and in the adrenal gland after 7 min of immobilization, although no c-fos or jun B mRNAs were detected in these and other organs in control rats. The levels of these mRNAs peaked after 30-60 min of immobilization, then declined. A low level of fos B mRNA appeared at 15-30 min and peaked after 60-90 min. On the contrary, c-jun and jun D mRNAs were constitutively expressed in the paraventricular nucleus and adrenal cortex. These findings indicate that the members of the fos and jun family proto-oncogenes play different roles in the transcriptional regulation of genes involved in the hypothalamo-pituitary-adrenal axis, and that monitoring immediate early genes is a useful method for following stress-induced cellular responses in the neuro-endocrine system.