Evidence for involvement of midbrain central gray in cholinergic mediation of female sexual receptivity in rats.

Experiments were designed to determine the role of the midbrain central gray (MCG) in facilitation of lordosis by cholinergic agonists. In Experiment 1, estradiol-treated female rats received microinjections of carbachol into the MCG and showed a dose-related behavioral facilitation to the agonist. In Experiment 2, MCG injections of oxotremorine (OXO), a selective muscarinic receptor agonist, yielded a dose-related facilitation; this was blocked by systemic pretreatment with scopolamine (SCOP), a muscarinic antagonist. In Experiment 3, MCG-lesion animals were injected unilaterally with OXO intraventricularly following contralateral injection of SCOP or vehicle. Females with MCG damage displayed significantly less facilitation than sham-lesion animals. Pretreatment with SCOP abolished lordosis facilitation in both groups. In addition, after treatment with estradiol and progesterone, sham-lesion females showed more receptivity than MCG-lesion females. Systemic injection of SCOP produced a significant decline in lordosis for both groups. On the basis of these data, it is suggested that the MCG plays an important role in the cholinergic mediation of female sexual receptivity.