Role of the bulbospongiosus muscles in sexual behavior and fertility in the house mouse.

In two studies we investigated the role of the bulbospongiosus muscles (mBS) in the copulatory behavior, fertility, and ex copula reflexes of B6D2F1/J male mice. In Experiment 1, males had the mBS excised (BSx) or underwent a sham surgical procedure (SHx) and were tested for sexual behavior. BSx males had a significantly higher number of breaks (periods after intromission when the penis leaves the vagina and is reinserted without a dismount) per intromissive mount. On all other copulatory measures, BSx and SHx males were statistically indistinguishable. Vaginal smears taken daily from mated females revealed no effect of the male's condition on the rate of pseudopregnancy, but there was a higher rate of pregnancy in females mated to SHx males. In Experiment 2, males were tested for penile reflexes after midthoracic spinal transection. BSx males showed no intense erections, significantly fewer moderate erections, and significantly fewer clusters (series of reflexes separated by less than 15 sec). The results of the two experiments suggest that in mice the mBS contributes to the penile erection necessary to maintain intromission during thrusting. It also appears that in mice, as in rats, the actions of the mBS in promoting the formation of penile cups contribute substantially to fertilization.