INCREASED NUMBER OF VASOPRESSIN NEURONS IN THE SUPRACHIASMATIC NUCLEUS (SCN) OF BISEXUAL ADULT MALE-RATS FOLLOWING PERINATAL TREATMENT WITHTHE AROMATASE BLOCKER ATD

In an earlier article an enlarged subpopulation of vasopressin contain ing neurons was found in the suprachiasmatic nucleus (SCN) of homosexu al men as compared to heterosexuals. The present study investigates th e possibility that the number of vasopressin neurons in the SCN and se xual partner preference behavior in male rats are both influenced by s ex hormones during brain development. For this purpose, we studied gro ups of adult male rats that had been treated either prenatally or pre- and postnatally with the aromatase inhibitor ATD (1,4,6-androstatrien e-3,17-dione) which blocks the aromatization of testosterone to estrad iol, Rats treated with ATD in both pre- and postnatal periods showed ' bisexual' partner preference behavior and appeared to have 59% more va sopressin-expressing neurons in the SCN than the controls. The prenata lly treated rats did not differ from the controls, This observation su pports the hypothesis that the increased number of vasopressin neurons found earlier in the SCN of adult homosexual men might reflect differ ences that took place in the interaction between sex hormones and the brain early in development.