Differential effects of dopamine receptor antagonists on the sexual behavior of male rats

In the present experiments, the dose-response effects of the dopamine (DA) receptor antagonists haloperidol, pimozide, clozapine, sulpiride, and metoclopramide, were assessed on patterns of copulatory behavior in intact, sexually active male rats with a high level of sexual experience and performance. The typical neuroleptics haloperidol (0.01-0.5 mg/kg) and pimozide (0.1-5.0 mg/kg) dose-dependently delayed the initiation of copulation and reduced the number of intromissions that preceded ejaculation. The atypical neuroleptics clozapine (0.1-5.0 mg/kg), and sulpiride (0.1-5.0 mg/kg) dose-dependently delayed the initiation of copulation but had no effect on copulatory behavior once it was initiated. In contrast, metoclopramide dose-dependently reduced ejaculation but had no effect on the ability of rats to initiate copulation. These experiments suggest that aspects of copulatory behavior in male rats are affected differently by DA antagonists depending upon their site of action in the brain. Blockade of mesolimbic DA receptors by typical and atypical neuroleptics may delay the initiation of copulation, whereas blockade of mesostriatal DA receptors by typical neuroleptics and metoclopramide may decrease the ejaculation threshold.