Facilitation of male rat copulatory behavior by electrical stimulation of the medial preoptic area.

Abstract

Abstract Lesion studies have demonstrated that the medial preoptic area (MPO) plays a critical role in male rat copulatory behavior. The present study attempted to better localize the neural elements mediating this behavior pattern and to determine the influence of preoptic area stimulation on particular aspects of copulatory behavior. Monopolar stimulating electrodes were implanted in the medial preoptic-anterior hypothalamic continuum or the lateral preoptic-medial forebrain bundle region. The effects of stimulating a particular locus were measured by comparing each animal's behavior on repeated stimulation and control tests. All measures of copulatory activity taken were facilitated by medial, but not by lateral, preoptic stimulation. The most common change produced by MPO stimulation was a reduction in both the number of mounts and intromissions preceding ejaculation. Short-latency approach and mounting of the female and greatly reduced refractory periods were also seen in two MPO animals. No evidence of a post-stimulation inhibition of copulatory behavior resulting from the stimulation itself was seen in these two animals. Most animals in both the medial and lateral groups learned to self-stimulate (SS) using the same 30-sec trains of stimulation as used in earlier tests of copulatory activity. SS rate, stimulation-bound copulation, and degree of facilitation of ejaculation were positively correlated in MPO, but not in lateral preoptic animals.