LEVELS OF SERUM STEROIDS, AROMATASE-ACTIVITY, AND ESTROGEN-RECEPTORS IN PREOPTIC AREA, HYPOTHALAMUS, AND AMYGDALA OF B6D2F1 MALE HOUSE MICETHAT DIFFER IN THE DISPLAY OF COPULATORY-BEHAVIOR AFTER CASTRATION

Most male B6D2F1 hybrid house mice continue to copulate after castrati on (continuers), whereas others do not (noncontinuers). Copulation in continuers appears estrogen dependent. Serum testosterone (T), 17 beta -estradiol (E2), and dihydrotestosterone (DHT), as well as aromatase a ctivity (AA) and estrogen receptor (ER) levels in preoptic area (POA), hypothalamus (HYP), and amygdala (AM) were measured to determine if c ontinuers and noncontinuers differ in estrogen physiology. In general, continuers and noncontinuers did not differ in serum steroid levels, AA, or ER levels. Castration reduced AA in the POA, HYP, and AM. Castr ation did not affect nuclear ER levels in the POA and HYP but reduced nuclear ER in AM. The data demonstrate that castrated B6D2F1 male mice continue to be under the influence of circulating nongonadal E2 that is important for copulation.