Acetylcholine is an ester of acetic acid and choline with chemical formula CH3COOCH2CH2N+(CH3)3. This structure is reflected in the systematic name, 2-(acetyloxy)-N,N,N-trimethylethanaminium. Acetylcholine (ACh) was first identified in 1914 by Henry Hallett Dale for its actions on heart tissue. It was confirmed as a neurotransmitter by Otto Loewi who initially gave it the name vagusstoff because it was released from the vagus nerve. Both received the 1936 Nobel Prize in Physiology or Medicine for their work. Later work showed that when acetylcholine binds to acetylcholine receptors on striated muscle fibers, it opens channels in the membrane. Sodium ions then enter the muscle cell, stimulating muscle contraction. Acetylcholine is also used in the brain, where it tends to cause excitatory actions. The glands that receive impulses from the parasympathetic part of the autonomic nervous system are also stimulated in the same way. Acetylcholine is synthesized in certain neurons by the enzyme choline acetyltransferase from the compounds choline and acetyl-CoA. Organic mercurial compounds have a high affinity for sulfhydryl groups, which attributes to its effect on enzyme dysfunction of choline acetyl transferase. This inhibition may lead to acetylcholine deficiency, and can have consequences on motor function. Normally, the enzyme acetylcholinesterase converts acetylcholine into the inactive metabolites choline and acetate. The devastating effects of nerve agents (in bioterrorism, Sarin gas for example) are due to their inhibition of this enzyme, resulting in continuous stimulation of the muscles, glands and central nervous system. Certain insecticides are effective because they inhibit this enzyme in insects. On the other hand, since a shortage of acetylcholine in the brain has been associated with Alzheimer's disease, some drugs that inhibit acetylcholinesterase are used in the treatment of that disease
Release sites Acetylcholine is released in the autonomic nervous system: pre- and post-ganglionic parasympathetic neurons preganglionic sympathetic neurons (and also postganglionic sudomotor neurons, i.e., the ones that control sweating)
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