Muscarinic acetylcholine receptor

Muscarinic acetylcholine receptors, or muscarinic receptors (mAChRs), are acetylcholine receptors that form G protein-coupled receptors 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.

Subtypes
There are five muscarinic acetylcholine receptor subtypes:
 * M1 receptors, also known as simply mAChRs
 * M2 receptors
 * M3 receptors
 * M4 receptors
 * M5 receptors

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 β2 adrenergic receptors.

In 2020, a small Sweden study confirmed these results in two different patient cohorts. The study assessed patients with moderate ME who met the Canadian and international consensus criteria for ME, plus the Systemic Exertion Intolerance Disease criteria, and found that the majority of patients had raised blood plasma concentration of β1 and β2 adrenergic receptor autoantibodies, and M3 and M4 muscarinic receptor autoantibodies. Levels in cerebral spinal fluid levels were normal. Only 25% of healthy controls had raised autoantibody levels. These findings supported the autoimmune hypothesis for a subset of patients.

Notable studies

 * 2016, Antibodies to β adrenergic and muscarinic cholinergic receptors in patients with Chronic Fatigue Syndrome - (Full text)
 * 2020, Autoantibodies to beta-adrenergic and muscarinic cholinergic receptors in Myalgic Encephalomyelitis (ME) patients – A validation study in plasma and cerebrospinal fluid from two Swedish cohorts - (Full text)

Articles and blogs

 * 2015, Autobodies found in a subset of CFS patients - #MEAction

Learn more

 * Muscarinic receptors - autonomic neurons - Oxford Academic Press
 * Targeting Muscarinic Acetylcholine Receptors for the Treatment of Psychiatric and Neurological Disorders (2019)