The muscarinic cholinergic receptors belong to a larger family of G protein-coupled receptors. The functional diversity of these receptors is defined by the binding of acetylcholine to these receptors and includes cellular responses such as adenylate cyclase inhibition, phosphoinositide degeneration, and postassium channel mediation. Muscarinic receptors influence many effects of acetylcholine in the central and peripheral nervous system. The clinical implications of this receptor are unknown, however, mouse studies link its function to adenylyl cyclase inhibition. Muscarinic acetylcholine receptor M4 has been reported to be expressed in many regions of the rat brain, particularly the striatum and hippocampus.
