Demonstration of nuclear ³H-estradiol binding in hypothalamus and amygdala of female, androgenized-female, and male rats

Radioactivity levels in nuclear and supernatant fractions of tissues of adult gonadectomized normal female rats, females androgenized by an s.c. injection of 1.25 mg testosterone propionate on day 5, and male rats, were determined 1 h after i.v.³H-estradiol administration. High regional specificity among nuclear fractions of brain areas was observed, with the preoptic-anterior hypothalamic area (POA-AH), median eminence-basal hypothalamus (ME-BH), and amygdala having far higher nuclear binding than other brain areas in all groups. In all groups, nuclear binding was receptor-mediated in POA-AH, ME-BH, amygdala, dorsal hypothalamus, and the pre-hypothalamic area, as demonstrated by competitive inhibition with diethylstilbestrol (DES). Also, at this time period there were no differences between male and female rats in DES-blockable radioactivity levels of either nuclear or supernatant fractions in any brain area or pituitary. DES-blockable, nuclear radioactivity levels in POA-AH, ME-BH and uteri were lower in androgenized than in normal females, but the percent of the total tissue radioactivity present in the nuclei did not differ between groups for any tissue. The present demonstration of nuclear estradiol binding in several brain areas of the male is consistent with a physiological role of estrogen in the male.