Muscarinic acetylcholine receptor

Muscarinic acetylcholine receptors, or mAChRs, are acetylcholine receptors that form G protein-receptor complexes in the cell membranes of certain neurons and other cells. They play several roles, including acting as the main end-receptor stimulated by acetylcholine released from postganglionic fibers in the parasympathetic nervous system.

Types
There are five muscarinic acetylcholine receptors:
 * M1
 * M2
 * M3
 * M4
 * M5

ME/CFS
In 2015, a relatively large German study found 29% of ME/CFS patients had elevated autoantibodies to M3 and M4 muscarinic acetylcholine receptors, as well as ß2 adrenergic receptors.