Hormone sensitivity of muscle activation in the sexually dimorphic SNB/BC neuromuscular system of the rat.

Rat penile reflexes are mediated in part by motoneurons in the sexually dimorphic spinal nucleus of the bulbocavernosus (SNB) and a muscle it innervates, the bulbocavernosus (BC). Recruitment in the M-wave component of electromyographic recording in the SNB/BC neuromuscular circuit is sensitive to testosterone and estradiol. To localize the site of the hormonal effect, we recorded muscle activity in a reduced preparation that isolated the peripheral structures involved in generating an M-wave. Castration reduced recruitment amplitude and increased response latency, and treatment with estradiol or the non-aromatizable androgen dihydrotestosterone prevented these changes. Dihydrotestosterone, but not estradiol, maintained BC muscle mass. These results indicate that functional changes in the SNB/BC circuit can result in part from hormonal sensitivity in the neuromuscular periphery and are independent of muscle mass.