The action of seven convulsants as antagonists of the GABA response of Limulus neurons

1. Intracellular recordings were made from neurons in the abdominal ganglia of Limulus polyphemus. GABA was inhibitory on all the neurons tested. 2. Picrotoxinin was approximately equipotent with picrotoxin as a reversible antagonist of the GABA inhibitory response. 3. Picrotin, the inactive component of picrotoxin, reversibly antagonized the GABA inhibitory response but was 19 times less potent than picrotoxinin. 4. Both t-butylbicyclophosphate and tetramethylenedisulphotetramine reversibly antagonized the GABA inhibitory responses, but were 2410 and 2705 times respectively less potent than picrotoxinin. 5. Bicuculline methochloride and p-tolyl silatrane had no blocking action on the GABA inhibitory responses of these neurons.