ESTROGENIC REGULATION OF PROENKEPHALIN MESSENGER-RNA EXPRESSION IN THE VENTROMEDIAL HYPOTHALAMUS OF THE ADULT MALE-RAT

Endogenous opioid peptides and their receptors are regulated by gonada l steroid hormones in the rat hypothalamus. Recent evidence suggests t hat gonadal steroids are capable of regulating the expression of proen kephalin (PE) mRNA in the ventromedial hypothalamus (VMH) of female, b ut not male rats. Therefore, we examined the effect of gonadectomy wit h or without four weeks of hormone treatment on PE mRNA expression in adult male Fisher 344 rats using quantitative in situ hybridization hi stochemistry. Gonadectomy reduced plasma testosterone and dihydrotesto sterone (DHT) levels compared to intact rats, while subsequent estradi ol (E2) or DHT treatment increased plasma E2 and DHT levels, respectiv ely. Furthermore, gonadectomy reduced PE mRNA expression in the VMH, b ut not in the striatum nor the olfactory tubercle compared to intact r ats, and this reduction was prevented in the presence of E2, but not D HT. The results suggest that the activation of estrogen receptors norm ally functions to maintain the level of VMH PE mRNA expression, which is sensitive to hormonal regulation in adult male rats. Thus, gonadal steroid hormones might regulate those reproductive functions which are modulated by PE-derived opioid peptides in the male rat brain.