The role of the striated penile muscles of the male rat in seminal plug dislodgement and deposition.

Seminal plugs, which must be tightly adhered to the vaginal walls for optimal fertilization, are disturbed or loosened by copulatory intromissions. In multi-male mating encounters, a male may reduce the sperm delivered by a previous male by dislodging the former male's plug and depositing his own sperm and plug. Recent work has documented that the striated penile muscles are involved in the production of penile erectile cups and flips. This study focused on the effects of penile muscle excision on the ability of male rats to dislodge and deposit tight plugs. Using a radiopaque contrast medium to visualize if a seminal plug was tightly adhered to the vaginal wall, displaced caudally or dislodged, Experiment 1 examined the manner in which plugs were removed during a series of intromissions. The dislodgement process was envisioned as a gradual one beginning with caudal displacement which occurs during the first or second intromission. Following excision of either the bulbocavernosus (BCX) or ischiocavernosus (ICX) muscles in Experiment 2, plug disturbance ability was impaired in 54 percent and 40 percent of BCX and ICX subjects respectively. Ability to deposit tight plugs was impaired in 45 and 20 percent of BCX and ICX subjects respectively.