An animal model of copulatory disorder induced by social stress in male mice: effects of apomorphine and L-dopa.

We investigated the possible role of dopamine receptors in the mediation of copulatory disorder induced by defeat experience in male mice, using L-dopa and apomorphine. To generate the copulatory disorder, male mice were attacked 20 times daily for 5 consecutive days, as intruders in confrontation with an aggressive resident. Following the repeated exposure to defeat, virtually all intruder males failed to display copulatory behavior towards estrous females. Acute injection of apomorphine (25, 50, 75 micrograms/kg, s.c.) significantly increased both the incidence and the frequency of copulatory elements (mounting and intromission) in a dose-dependent manner. The combination of L-dopa with carbidopa, a dopa decarboxylase inhibitor, also increased significantly copulatory behavior, revealing an inverted U-shaped dose-effect curve. In both cases, locomotion and digging frequencies were significantly decreased. This evidence suggests that dopaminergic mechanisms are involved in the mediation of social stress-induced copulatory disorder.