Acetylcholine

Acetylcholine was first synthesized in 1967, but it’s biochemical signifiance was not known at that time. It was the first neurotransmitter identified and thus holds a central place in the history of neuropharmacology. (p.235)

Acetyhlcholine effect

In 1914, Henry Dale noticed that the effect of applying ACh was similar to stimulating parasympathetic nerves – he observed the slowing of heart activity. Parasympathetic nerves are part of the nervous system that regulates bodily functions when a person is at rest – such as relaxation, digestion and activating metabolism. For instance our resting heart rate is lowest when we are deep asleep.

Dale in 1904, author unknown.

Acetyhlcholine chemical structure

One of its noteworthy features is the positively charged nitrogen atom with four attached methyl groups. This nitrogen is termed a quaternary nitrogen and ACh is thus classified as a quaternary amine. Many other neurotransmitters are also amines but not of this type.

Chemical structure of acetylcholine

The cholinergic synapse illustrating the processes of acetylcholine (ACh) synthesis and metabolism, presynaptic chline uptake, ad vesicular ACh uptake and release. Pre- and postsynaptic ACh receptors and sites of action of some cholinergic drugs are also shown. The table lists important cholinergic receptor agaonists and antagonists.

Receptor subtype Agonists Antagonists
NicotonicNicotine, methylcarbachol, DMPPD-Tubocurarine, gallamine, mecamylamine, hexamethonium,
MuscarinicMuscaline, pilocarpine, oxotremorineAtropine, scopolamine, pirenzepine (M1-selective), AF-DX 116 (M2-selective)

Sources:

Feldman, R. S., Meyer, J. S., & Quenzer, L. F. (1997). Principles of neuropsychopharmacology. Sinauer Associates. (page 235)

Karczmar, A. G. (1993). Brief presentation of the story and present status of studies of the vertebrate cholinergic system. Neuropsychopharmacology, 9(3), 181–199. https://doi.org/10.1038/npp.1993.81

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