A dopamine antagonist blocks vaginocervical stimulation-induced neuronal responses in the rat forebrain.

During mating in rats, the male provides vaginocervical stimulation (VCS) to the female via intromissions. VCS, provided manually, mimics many aspects of mating, including facilitation of lordosis, induction of sexual receptivity, abbreviation of the period of sexual receptivity, and induction of twice-daily prolactin surges, which result in pseudopregnancy. VCS also induces the expression of Fos, the protein product of the immediate early gene c-fos, which has been used as a marker for neurons that are responsive to mating stimuli. Because VCS induces the release of dopamine in the forebrain, as well as phosphorylation of DARPP-32, a phosphoprotein associated with activation of the D(1) subtype of dopamine receptor, we tested the hypothesis that VCS induces Fos expression by acting on the D(1) class of dopamine receptors. Injection of SCH 23390, an antagonist of the D(1) class of dopamine receptors, virtually eliminated VCS-induced Fos expression without affecting constitutive levels of Fos-Immunoreactivity (Fos-IR) in all brain areas in which VCS induced Fos expression. In a follow-up experiment, expression of a second immediate early protein, egr-1, was blocked as well, suggesting that these results are not specific to Fos. Therefore, the results are consistent with the idea that VCS induces dopamine release, causing activation of D(1) dopamine receptors, which in turn, results in neuronal response, as seen by both Fos and egr-1 expression.