Muscarinerge

Muscarinergic, or muscarinic, refers to the system mediated by muscarinic acetylcholine receptors (mAChRs), a family of G protein–coupled receptors distinct from the nicotinic receptors. The five subtypes, M1 through M5, have varied tissue distribution and signaling.

M2 receptors predominate in the heart, where activation reduces heart rate and contractility. M3 receptors are common in smooth muscle and glands and mediate bronchoconstriction, salivation, lacrimation, sweating, and GI motility. M1, M4, and M5 are abundant in the brain, where they modulate cognitive function, arousal, and dopamine signaling.

Pharmacology: Muscarinic agonists include acetylcholine, muscarine, pilocarpine, and cevimeline; antagonists include atropine and scopolamine. Clinically, muscarinic agonists are used in glaucoma (pilocarpine) and xerostomia (cevimeline). Antimuscarinics treat bradycardia-related conditions, COPD, overactive bladder, and motion sickness.

Toxicology: Overstimulation produces SLUDGE symptoms—salivation, lacrimation, urination, defecation, GI upset, emesis—along with miosis, bronchospasm, and bradycardia. Muscarine poisoning arises from certain mushrooms (e.g., Amanita species). Treatment is with atropine to block muscarinic effects and supportive care.

In research, muscarinic receptors in the CNS, especially M1 and M4, are explored as targets for cognitive disorders and schizophrenia, while peripheral M3 receptors influence glandular secretion and smooth muscle tone.