The action of the neurotransmitter acetylcholine is mediated through two types of receptors, the ionotrophic nicotinic receptors and the metabotrophic muscarinic receptors. The muscarinic receptors belong to the superfamily of 7-TM G-protein-coupled receptors. Five subtypes of muscarinic receptors have been cloned and named m1-m5.The m1 receptors are the most abundant muscarinic subtype in the cortex and striatum. m1 receptors were also localized in the myenteric plexus where they function as autoreceptors to enhance the release of Ach from the nerves.
