ROLE OF PERINATAL ESTROGENS IN SEXUAL-DIFFERENTIATION OF THE INHIBITION OF LORDOSIS BY EXOGENOUS CHOLECYSTOKININ

Microinjections of sulphated cholecystokinin octapeptide (sCCK-8) into the ventromedial nucleus of the hypothalamus inhibit lordosis behavio r in receptive female rats. This effect of sCCK-8 seems to differentia te under the control of gonadal steroids shortly after birth. Neonatal ly castrated males and normal females show similar responses, while an drogenized females are less sensitive to sCCK-8. The current study inv estigated estrogen's role on the differentiation of the response to sC CK-8. On the day of birth male rat pups were castrated, given sham sur geries, or implanted with the antiestrogen tamoxifen or the aromatase inhibitor androst-1, 4, 6-triene-3, 17-dione (ATD). Females were impla nted with testosterone propionate or tamoxifen, or given sham surgerie s. Implants were removed 10 days later. As adults, rats were tested fo r female sexual behavior after microinjections of sCCK-8 into the vent romedial nucleus of the hypothalamus. Neonatally castrated males, ATD- treated males, and control females showed profound inhibition of lordo sis behavior after sCCK-8. These results suggest that elimination of e strogen postnatally prevents defeminization of the reproductive circui try that responds to sCCK-8.