Involvement of the lateral mesencephalic tegmentum in copulatory behavior of male rats: neuron activity in freely moving animals.

Single unit activity was recorded from the lateral mesencephalic tegmentum (LMT) during free copulatory activity by male rats. Twenty-four (89%) of 27 units showed changes in the firing rate during at least one of the three phases of copulatory behavior: pursuit of the female, pelvic thrusting and genital grooming. The activity of 16 units (59%) increased during pursuit of the female, and the activity of 3 units (11%) increased markedly during pelvic thrusting accompanied by intromission. In contrast, 6 units (22%) were suppressed during thrusting with intromission. Whereas the activity of 10 units (37%) increased during genital grooming, 7 units (26%) were suppressed below the baseline during this behavior. The specific firing patterns of the LMT units that are correlated with the particular copulatory movements are a strong indication that the LMT may have an important function in the execution of male copulatory behavior. Some LMT units may mediate sensory information from the genitals that is needed to display a series of copulatory movements. Other units may be more directly related to reflex-like copulatory movements.