Androgen receptor immunoreactivity in somatostatin neurons of the periventricular nucleus but not in the bed nucleus of the stria terminalis in male rats.

Somatostatin (SS) is a neuropeptide responsible for the inhibition of growth hormone (GH) release from the anterior pituitary. The existence of sexual dimorphism in the pattern of GH secretion in several mammalian species strongly suggests a role of sex steroids in the regulation of GH release. It has been recently demonstrated that SS mRNA levels are decreased by gonadectomy in male rats while administration of testosterone reversed the postgonadectomy decrease in hypothalamic SS mRNA levels. The mechanism(s) by which androgens regulate somatostatin neurons are unknown at this time. Both direct and indirect pathways have been suggested. In this study, double-labeling immunocytochemistry was used to address the question of whether SS neurons have androgen receptors in adult male rats. About 70-75% of SS-immunoreactive (-ir) neurons in the periventricular hypothalamic nucleus possess androgen receptors and this co-localization persists throughout the rostrocaudal extent of this nucleus. In the bed nucleus of the stria terminalis, no SS-ir neurons were shown to have androgen receptors. These results suggest that androgens may directly exert their effect upon SS neurons in the periventricular nucleus.