PREPUBERTAL TESTOSTERONE TREATMENT OF FEMALE RATS - DEFEMINIZATION OFBEHAVIORAL AND ENDOCRINE FUNCTION IN ADULTHOOD

This study assesed the capacity of testosterone (T) administered well after the neonatal ''critical'' period to permanently sexually differe ntiate reproductive function. Females received T filled or empty Silas tic capsules during days 15-30 of age and vaginal cyclicity, ovarian w eight and appearance, lordosis and preceptive behaviors, mounting beha vior, and the gonadotropin response to estrogen and progesterone were measured in adulthood. T-treated females (plasma levels of 0.66 ng T/m l) showed constant vaginal estrus from the day of vaginal opening and small, polyfollicular ovaries. Proceptive behaviors were dramatically reduced whether or not the ovaries were present after day 15 of age, b ut lordosis behavior was not affected. Exposure to T for 5-6 h was ine ffective. Compared to controls, T-treated females had dramatically red uced plasma FSH and LH surges. No effects were observed on mounting be havior, phallus size, or body weights. These results suggest that andr ogen at approximately male levels can act on neural substrates well be yond the neonatal period to permanently defeminize endocrine and behav ioral function in the female rat.