Pharmacological and anatomical aspects of cholinergic activation of female sexual behavior

Forebrain infusion of cholinergic agonists activated the sexual response, lordosis, in ovariectomized female rats that had been primed with a low dose of estrogen. Carbachol, an agonist with both muscarinic and nicotinic properties, and oxotremorine, an agonist with a primarily muscarinic action, produced dose-related increases in the frequency of lordosis elicited by stimulus male rats. This facilitation of lordosis was prevented when females were pretreated systemically with atropine or scopolamine, two muscarinic receptor antagonists. These results indicate that the effect of carbachol and oxotremorine on lordosis is mediated by cholinergic muscarinic receptors. The location of these receptors within the brain has not been identified. Ventricular infusion of carbachol was as effective as infusion directly into the medial preoptic area (POA) and more effective than infusion directly into the ventromedial hypothalamus (VMH). Furthermore, when carbachol or oxotremorine was delivered to the POA through cannulae angled to avoid traversing the lateral ventricles, no facilitation of lordosis was observed. These data suggest that muscarinic receptors stimulated by central infusion of cholinergic agonists may not be located in either the POA or the VMH, two regions traditionally implicated in the regulation of lordosis.