Restoration of the copulatory pelvic thrusting pattern in castrated male rats by the intracerebral implantation of androgen.

The characteristics of duration, vigour, frequency and rhythmicity of pelvic thrusting during copulation were studied by an accelerometric technique in 25 male rats before castration and following restoration of sexual behavior by local implants of testosterone propionate (TP) in the medial preoptic area (mPOA). Twenty-one Ss displayed the complete copulatory pattern during the control tests. Implantation of TP in the mPOA restored mounting activity after castration in 14 out of 21 Ss and only six of them "ejaculated." Spinal cord structures involved in pelvic thrusting of castrated Ss implanted with TP were presumably not exposed to circulating androgen since the sexual accessories were atrophic; in spite of this, only modest differences were found in the characteristics of pelvic thrusting, i.e., an increase in the duration of the mounting trains of the TP implanted Ss. Present data suggest that activation of mPOA-anterior hypothalamic neurons would not only affect limbic and cortical areas related to sexual arousal through their ascending connections but would also modulate through descending pathways, the activity of lower spinal structures involved in copulation.