Sites of action of testosterone in the brain of the female primate.

Thaw-mount autoradiography was used to map target neurons for tritiated steroids in the brains of ovariectomized rhesus monkeys. In five females, studies were performed 60 min after the administration of 3H-estradiol. Of these, two females were pretreated for five days with daily injections of 2 mg testosterone propionate, one female was pretreated with daily injections of 2 mg dihydrotestosterone propionate, and two females were pretreated with oil vehicle. For comparison, two additional females were administered 3H-testosterone and were killed 30 min later. Following 3H-estradiol administration in females pretreated with oil, there were numerous labeled neurons in the medial preoptic nucleus (n.), anterior hypothalamic area, ventromedial hypothalamic n., arcuate n., bed n. of stria terminalis, lateral septal n., and regions of the amygdala. In females pretreated with testosterone propionate, labeling was virtually abolished in all these areas with the exceptions of the lateral septal n. and arcuate n., presumably because estradiol formed from testosterone competed with 3H-estradiol for estrogen-binding sites. Pretreatment with dihydrotestosterone propionate had no effect on the labeling following the administration of 3H-estradiol. Areas where labeling was blocked, therefore, represent regions where testosterone acted as an estrogen, and it would appear that regional differences in the activity of aromatizing enzymes determine which estrogen target sites in the brain can interact with estrogenic metabolites of testosterone in female primates.