PROGESTERONE MODULATION OF ANDROGEN-DEPENDENT SEXUAL-BEHAVIOR IN MALE-RATS

The present study examines the effects of physiological levels of prog esterone (P) on copulatory behavior in sexually naive male rats. Two w eeks after gonadectomy males were implanted with either empty Silastic capsules (BL) or Silastic capsules containing testosterone (T), P, or both (P + T). When tested with an estrous female, all of the gonadall y intact males (intact) and none of the BL controls exhibited mounting /intromission behaviors. Mounting was observed in 75% of the T-alone m ales. More than half (64%) of the P-alone males and 100% P + T males e xhibited mounting. In most cases, mounting was followed by intromissio n responses. Subsequently, intact and gonadectomized males received da ily injections of the P antagonist RU486 along with hormone treatment. After receiving RU486, only 63% of the intact males and 71% of the T- alone males mounted successfully. The facilitatory effects of P on cop ulatory behavior were completely abolished by RU486 treatment. The pre sent studies provide the first evidence in mammals suggesting that P-d ependent mechanisms influence neurochemical pathways involved in copul ation.