Characteristics of exaggerated sexual behavior induced by electrical stimulation of the medial preoptic area in male rats.

Twenty-two sexually experienced male rats were implanted with lateral preoptic (LPO) and medial preoptic (MPO) electrodes. Following surgery, the 22 MPO and 18 LPO electrodes were screened for the induction of stimulation-bound copulation in the presence of estrus females. Stimulation through 5 of the MPO electrodes induced highly exaggerated, stimulation-bound sexual behaviou. Ten MPO electrodes produced escape behavior, 2 electrodes aggression and one electrode induced sexual behavior intermingled with aggression. The tips of all the electrodes which effected exaggerated copulation were located within a small preoptic region, less than 1 mm lateral to the midline. LPO electrodes had either inhibitory effects on mating behavior or none at all. The increase in copulatory activity by MPO electrodes' stimulation was expressed in a great enhancement in the number of ejaculations, and marked decreases in the latency to ejaculation, the post-ejaculatory refractory period, and in the number of intromissions preceding an ejaculation. It is concluded that the electrical stimulation affected both the sexual arousal mechanism and the intromission-ejaculation mechanism involved in mating behavior.