Lobster locomotor activity as a measure of GABA(A) receptor modulation

Gamma-aminobutyric acid (GABA) is a well-known neurotransmitter. A crustace an behavioural assay was developed for the examination of the effects of a benzodiazepine agonist and an antagonist of GABA(A)-type receptors. Both ad ult and juvenile male and female lobsters, Homarus americanus, were treated with single (or follow-up) empirically determined doses of the agonist, di azepam, one of its metabolites (desmethyldiazepam), the antagonist, N-methy l-beta -carboline-3-carboxamide (MBC), or vehicle alone. The effects of the compounds were monitored in a submerged circular open-held for differences in locomotor activity, which was significantly inhibited by diazepam. Trea tment with MBC following injection of diazepam reversed the latter's effect s on locomotion. These results suggest that benzodiazepines may affect crus tacean GABA receptors in a fashion similar to the GABA(A) type found in the vertebrates, and that they may be involved in the regulation of locomotor behaviour.