Gamma-aminobutyric acid (GABA)

Definition

The principal inhibitory neurotransmitter in the nervous systems of insects, arachnids, and vertebrates. In arthropods, GABA binds to ligand-gated chloride channels (GABA receptors) on postsynaptic membranes, triggering chloride ion influx that hyperpolarizes neurons and suppresses nerve impulse transmission. The GABAergic system is a major target of neurotoxic insecticides including cyclodienes (e.g., dieldrin), phenylpyrazoles (fipronil), and certain botanical compounds.

Etymology

From gamma (third carbon position in the amino acid backbone), amino, butyric (four-carbon chain), and acid.

Example

Fipronil, a phenylpyrazole insecticide, selectively blocks GABA-gated chloride channels in the cockroach Periplaneta americana, causing uncontrolled neuronal excitation, paralysis, and death—an effect reversed by GABA receptor antagonists like picrotoxin.

Synonyms

• GABA
• 4-aminobutanoic acid

Related Terms

• Neurotransmitter
• GABA receptor
• ligand-gated ion channel
• chloride channel
• fipronil
• cyclodiene
• picrotoxin
• Synapse
• hyperpolarization
• insecticide mode of action

Usage Notes

In arthropod neurobiology, distinguishes between GABA_A receptors (ionotropic, fast inhibitory) and metabotropic GABA_B receptors (less characterized in insects). Many insecticides exploit species differences in receptor subunit composition between insects and vertebrates to achieve selective toxicity. Not to be confused with glutamate (excitatory counterpart) or glycine (inhibitory in vertebrates, minor role in insects).