Acetylcholine

Definition

A small-molecule neurotransmitter synthesized from choline and acetate, released at cholinergic synapses to propagate nerve impulses across chemical synapses by binding to nicotinic or muscarinic receptors. In arthropods, it is the primary excitatory transmitter at neuromuscular junctions and central synapses, making it a central target of many insecticides and a key compound in studies of arthropod neurophysiology, behavior, and toxicology.

Etymology

From acetic acid + choline, reflecting its ester structure

Example

Organophosphate insecticides such as malathion and parathion kill insects by irreversibly inhibiting acetylcholinesterase, the enzyme that hydrolyzes acetylcholine at synapses; the resulting accumulation of acetylcholine causes continuous neuronal firing, paralysis, and death.

Synonyms

• ACh

Related Terms

• acetylcholinesterase
• cholinergic
• neuromuscular junction
• Synapse
• Neurotransmitter
• Organophosphate
• nicotinic receptor
• insecticide toxicology

Usage Notes

Distinguished from other arthropod neurotransmitters such as glutamate (excitatory at some neuromuscular junctions), GABA (inhibitory), and octopamine (modulatory). The term 'cholinergic' describes synapses, neurons, or receptors that use acetylcholine. In entomological toxicology, acetylcholine is often discussed in the context of target-site resistance, where mutations in acetylcholinesterase reduce insecticide binding without disrupting normal synaptic function.