Differentiation of muscarinic cholinergic receptor subtypes in human cortex and pons: implications for anti-motion sickness therapy.

Radioligand binding studies were used to analyze muscarinic cholinergic receptor subtypes in human cortex and pons. Muscarinic cholinergic receptors were labeled by 3H-quinuclidinyl benzilate (3H-QNB). Scopolamine was equipotent in both brain regions and did not discriminate subtypes of 3H-QNB binding. By contrast, the M1 selective antagonist pirenzepine was approximately 33-fold more potent in human cortex than pons. Carbachol, a putative M2 selective agonist, was more than 100-fold more potent in human pons than cortex. These results demonstrate that the human pons contains a relatively large proportion of carbachol sensitive muscarinic cholinergic receptors. Drugs targeted to this subpopulation of muscarinic cholinergic receptors may prove to be effective anti-motion sickness agents with less side effects than scopolamine.