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a deadly alkaloid from various mushrooms, e.g., Amanita muscaria (the fly agaric), and also from rotten fish. See also muscarinic receptors.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.
A toxin with neurologic effects, first isolated from Amanita muscaria (fly agaric) and also present in some species of Hebeloma and Inocybe. The quaternary trimethylammonium salt of 2-methyl-3-hydroxy-5-(aminomethyl)tetrahydrofuran, it is a cholinergic substance whose pharmacologic effects resemble those of acetylcholine and postganglionic parasympathetic stimulation (cardiac inhibition, vasodilation, salivation, lacrimation, bronchoconstriction, gastrointestinal stimulation).
Farlex Partner Medical Dictionary © Farlex 2012
A highly toxic alkaloid, C9H20NO2, found in fly agaric and certain other mushrooms. When ingested, it binds to acetylcholine receptors and thus stimulates the parasympathetic nervous system.
mus′ca·rin′ic (-rĭn′ĭk) adj.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.
muscarineToxicology A small alkaloid in some poison mushrooms; it is structurally similar to acetylcholine, and puts the parasympathetic nervous system in 'overdrive' Antidote Atropine. See Mushrooms.
McGraw-Hill Concise Dictionary of Modern Medicine. © 2002 by The McGraw-Hill Companies, Inc.
A toxin with neurologic effects, first isolated from Amanita muscaria (fly agaric) and also present in some species of Hebeloma and Inocybe. It is a cholinergic substance with pharmacologic effects that include cardiac inhibition, vasodilation, salivation, lacrimation, bronchoconstriction, and gastrointestinal stimulation.
Medical Dictionary for the Health Professions and Nursing © Farlex 2012
muscarineA poison produced by the mushroom Amanita muscaria . Muscaarine is chemically related to acetylcholine
Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005
muscarinea poisonous alkaloid occurring in certain mushrooms.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005
A neurotransmitter substance with special excitatory properties of all preganglionic autonomic neurons, all parasympathetic postganglionic neurons and a few postganglionic sympathetic neurons. Acetylcholine is synthesized and liberated by the action of the enzyme choline acetyltranferase from the compounds choline and acetyl coenzyme A (acetyl CoA) which occurs in all cholinergic neurons. ACh exists only momentarily after its formation, being hydrolysed by the enzyme acetylcholinesterase which is present in the neurons of cholinergic nerves throughout their entire lengths and at neuromuscular junctions: this process is essential for proper muscle function as otherwise the accumulation of ACh would result in continuous stimulation of the muscles, glands and central nervous system. Alternatively a shortage of ACh has devastating effect (e.g. myasthenia gravis). ACh binds to acetylcholine receptors on skeletal muscle fibres. Sodium enters the muscle fibre membrane, which leads to a depolarization of the membrane and muscle contraction. There are two main types of acetylcholine receptors (cholinergic receptors): muscarinic receptors, which are stimulated by muscarine and ACh, belong to a family of G proteins coupled receptors and are situated in parasympathetically innervated structures (e.g. the iris and ciliary body); and nicotine receptors, which are stimulated by nicotine and ACh, are ligand-gated receptors and are situated in striated muscles (e.g. the extraocular muscles). Cholinergic receptors are found in the sympathetic and parasympathetic nervous systems, in the brain and spinal cord. The action of ACh can be either blocked or stimulated by drugs: Anticholinesterase drugs (e.g. neostigmine) inhibit acetylcholinesterase and prolong the action of acetylcholine whereas antimuscarinic drugs (also referred to as anticholinergics or parasympatholytics) such as atropine, cyclopentolate, homatropine, hyoscine and tropicamide inhibit the action of acetylcholine at muscarinic receptors. Other drugs mimic the action of ACh, they are known as parasympathomimetics (e.g. pilocarpine). See cholinergic; cycloplegia; miotics; mydriatic; neurotransmitter; nicotine; synapse; autonomic nervous system.
1. Causing mydriasis of the pupil. 2. A drug which produces mydriasis. Mydriatics are used to carry out a thorough inspection of the fundus and lens, especially in elderly patients in whom the pupils are usually smaller. However, in older people it must be ascertained that the patient does not have glaucoma. There are two classes of mydriatics: (1) antimuscarinic (parasympatholytic, anticholinergic, atropine-like) drugs which antagonize the action of acetylcholine at muscarinic receptors in the ciliary muscle, such as atropine, cyclopentolate, homatropine, hyoscine (scopolamine) and tropicamide. Antimuscarinic drugs produce cycloplegia as well. (2) sympathomimetic (adrenergic stimulating) drugs which directly or indirectly stimulate the dilator pupillae muscle which is innervated by the sympathetic division of the autonomic nervous system. These include cocaine, ephedrine hydrochloride, adrenaline (epinephrine), naphazoline and phenylephrine hydrochloride. See adrenergic receptors; cholinergic; cycloplegia; miotics; dilator pupillae muscle; mydriasis; pupil light reflex; sympathomimetic.
Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann