EFFECTS OF SEX STEROIDS ON SENSORY AND MOTOR SPINAL MECHANISMS

The male copulatory pattern uses muscles in the penis for erection and penile insertion, the lower trunk for pelvic thrusting, and the sex a ccesory organs for seminal emission. Organization of the nuclei contro lling penile muscles is achieved through cell growth, dendritic arbori zation, and synaptogenesis, actions dependent on androgen but not estr ogen. Testosterone (T) and dihydrotestosterone (DHT) but not estradiol (E2), stimulate pelvic thrusting vigor by synchronizing discharge of motoneurons innervating pelvic muscles. Pelvic thrusting rhythmicity, regulated by spinal interneurons, is produced in female rabbits by E2 or T but not by DHT. Reflex contraction of the seminal vesicles, due t o penile insertion, is facilitated by androgen presumably by its effec t on preganglionic neurons of the hypogastric nerve, located in the do rsal commissural nucleus.