Muscarine, an alkaloid derived from the poisonous mushroom A. muscaria, mimics the action of acetylcholine at muscarinic receptors. It is often used as a biochemical tool for studying signal transduction. Muscarinic receptors transduce their signals by coupling with G proteins. Five musacarinic receptors (M1-M5) have been identified, M1 and M3 are implicated in Alzheimer’s disease. (+)-Muscarine is the biologically active stereoisomer of muscarine.