Muscarinic acetylcholine receptor M4 is an Acetylcholine Receptor. Unlike muscarinic receptor M2, the M4 receptor is not involved in smooth muscle contraction. The clinical relevance of this receptor is unknown. However, mouse studies have linked it 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. ESTs have been isolated from human breast and eye libraries.
