Answer: Muscarine is a chemical that is found in mushrooms that activates muscarinic acetylcholine receptors in the body.
Acetylcholine is an endogenous neurotransmitter that can act at two different classes of acetylcholine receptors, the nicotinic acetylcholine receptor (nAChR) and the muscarinic acetylcholine receptor (mAChR). Acetylcholine is a major neurotransmitter that is utilized by the central nervous system and the peripheral nervous system as the neuromuscular junction.
Muscarine is an endogenous substance that is found in mushrooms. It was first isolated from Amanita muscaria. It is found in high concentrations in mushrooms belonging to the genus Inocybe or Clitocybe at concentrations exceeding 1% (Mushroom poisoning from species of genus Inocybe (fiber head mushroom): a case series with exact species identification)
Muscarine acts as a cholinomimetic, meaning that it acts in the same way as the normal endogenous neurotransmitter acetylcholine. Acetylcholine can act at the ionotropic receptors, which are the nAChRs. The muscarinic acetylcholine receptors, on the other hand, are metabotropic.
Muscarine can be deadly at high concentrations in the blood. Because it acts like acetylcholine, it can cause a sudden decrease in heart rate, similar to robust activation of the vagus nerve, cranial nerve X. Other symptoms include constriction of the pupils, increased salivation, and constriction of the bronchioles with decreased respiratory rate. In the event of muscarine poisoning, quick administration of a muscarinic acetylcholine receptor antagonist such as atropine can serve to reverse the symptoms of poison.