This is the 2007 version. Click here for the 2017 chapter 02 table of contents.

Acetylcholine

The first transmitter discovered was acetylcholine, pronounced either assiteel-KOH-leen or a-SEE-tyl-koh-leen. The chemical name is abbreviated ACh. It is a combination of choline and acetic acid, distributed widely in the brain and involved in many important brain systems called cholinergic (kohleen-URGE-ik) pathways.

What is ACh? AChE?

Like other transmitters, acetylcholine must somehow be destroyed or taken up from the synaptic cleft once it does its job. Acetylcholinesterase, abbreviated AChE, is responsible for this. It breaks ACh into the components choline and acetic acid, neither of which is active at the synapse. The choline is absorbed back into the presynaptic cell, made into ACh, and stored again in the vesicles. As noted earlier, in the list of ways to alter transmitter levels at the synapse, this is called re-uptake of a transmitter.

How do most insecticides work?

AChE is "knocked out" by chemicals called cholinesterase (kohleen-ESTER-ase) inhibitors. When cholinesterase is inhibited, ACh builds up at the synapses, causing disordered nerve activity. Read the fine print on the label of any insecticide and you will probably see the words "cholinesterase inhibitor." For insects, the effect on ACh-using neurons is fatal.

Why might it be incredibly foolish to spray these around our homes and businesses?

Cholinesterase inhibitors are commonly sprayed around households, businesses, and schools in order to control pests like cockroaches. This is unnecessary (bait trays provide a safe and effective alternative). I humbly predict that within 50 or 100 years this practice will be regarded as incredibly foolish, given that acetylcholine is one of dominant transmitters in humans as well as insects. Problems with cholinergic pathways are linked to Alzheimer's Syndrome and a variety of other disorders.

One common insecticide targeting acetylcholine is malathion (mal-a-THY-on). Communities in the southeastern United States spray it freely to combat mosquitoes. Our hometown paper published a photograph of small children playing in the fog behind a truck spraying malathion. Supposedly malathion is harmless to humans, although many Californians objected to large-scale aerial spraying of malathion during an invasion of Med Flies in prime fruit-growing areas.


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