SUBCORTICAL MULTIPLE-UNIT ACTIVITY CHANGES DURING RAT MALE SEXUAL-BEHAVIOR

Multiple unit activity (MUA) was recorded from the ventral tegmental a rea (VTA) and mesencephalic locomotor region (MLR) during copulatory b ehavior of freely moving male rats. Simultaneous accelerometric record ings of the copulatory pelvic thrusting performed by the male rat were taken to precisely correlate in time the changes in MUA with well def ined elements of copulation. The baseline MUA firing rates recorded in the quiet-alert condition in the VTA and in the MLR were significantl y increased during pursuit of the female by the male; significantly hi gher MUA firing rates were found in the VTA at the 500 ms periods befo re and during the execution of pelvic thrusting in mount, intromission , and ejaculation responses as compared to the baseline, and returned to this value when these responses ended. The maximum MUA firing rate in the MLR was obtained during the execution of pelvic thrusting in ea ch copulatory response, and it remained significantly elevated, as com pared to the baseline, after thrusting and at the postintromission and postejaculatory genital grooming, then decreasing to basal values at the initial part of the postejaculatory interval. The fact that the hi ghest changes in MUA were related to pelvic thrusting suggests a major participation of both structures in the execution of motor copulatory responses. Copyright (C) 1997 Elsevier Science Inc.