Prepubertal testosterone treatment of female rats: defeminization of behavioral and endocrine function in adulthood.

This study assessed the capacity of testosterone (T) administered well after the neonatal "critical" period to permanently sexually differentiate reproductive function. Females received T filled or empty Silastic capsules during days 15-30 of age and vaginal cyclicity, ovarian weight and appearance, lordosis and proceptive behaviors, mounting behavior, and the gonadotropin response to estrogen and progesterone were measured in adulthood. T-treated females (plasma levels of 0.66 ng T/ml) 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, but lordosis behavior was not affected. Exposure to T for 5-6 h was ineffective. Compared to controls, T-treated females had dramatically reduced plasma FSH and LH surges. No effects were observed on mounting behavior, phallus size, or body weights. These results suggest that androgen at approximately male levels can act on neural substrates well beyond the neonatal period to permanently defeminize endocrine and behavioral function in the female rat.