Grooming behavior induced by ACTH involves cerebral cholinergic neurons and muscarinic receptors

The grooming behavior induced by intracerebroventricular administration of ACTH was specifically antagonized by the muscarinic receptor antagonists, atropine and scopolamine. The antagonism occurred in a dose-dependent manner with an ED50 of 0.2 mg/kg (i.p.) for atropine, and 0.03 mg/kg (i.p.) for scopolamine. Neither methylscopolamine nor methylatropine, injected intraperitoneally affected grooming induced by ACTH (except for a small inhibition at the largest dose of methylscopolamine), but pronounced inhibition occurred when these drugs were administered intracerebroventricularly. The grooming induced by ACTH was also inhibited by prior intracerebroventricular administration of hemicholinium-3, a cholinergic antagonist that acts presynaptically by inhibiting the uptake of choline and hence, the synthesis of acetylcholine. These data suggest a role for cholinergic neurons and muscarinic receptors in the CNS in grooming behavior induced by ACTH.