CIRCULATING GONADAL-STEROID HORMONES REGULATE ESTROGEN-RECEPTOR MESSENGER-RNA IN THE MALE-RAT FOREBRAIN

In male rats, the conversion of testosterone to estrogen via aromatiza tion is a critical step in a number of androgen-mediated functions, es pecially reproductive behavior. Within the central nervous system (CNS ), locally formed estrogen binds to its cognate estrogen receptor prot ein. Little is known about what factors regulate the expression of est rogen receptors in the male rat CNS. This study examined whether circu lating male gonadal steroid hormones have a role in the regulation of estrogen receptor mRNA in brain regions critical for the expression of male reproductive behavior. Male rats were gonadectomized or sham ope rated, and 3 days later were sacrificed. Their brains were fixed by pe rfusion, frozen, and sectioned. Tissue sections were hybridized to an S-35-labeled 850 base cDNA probe, complementary primarily to the stero id binding domain of the estrogen receptor mRNA. Following post-hybrid ization washes, slides were dipped in photographic emulsion and expose d for 2 weeks. Estrogen receptor mRNA-containing neurons were observed in all brain regions previously shown by steroid hormone autoradiogra phy to concentrate estrogen. Gonadectomy did not alter the number of e strogen receptor mRNA-producing neurons, but did produce a two-fold in crease in the relative amount of estrogen receptor mRNA per cell in th e medial preoptic nucleus, periventricular preoptic area, and bed nucl eus of the stria terminalis. This study shows that circulating gonadal steroids down-regulate steady state levels of estrogen receptor mRNA within specific brain regions, and thereby have the potential to regul ate the sensitivity of particular target regions in the CNS to estroge n.