The picrotoxin-like action of a convulsant benzodiazepine, Ro5-3663

The potency and site of action of Ro5-3663 as a GABA antagonist were investigated in the rat cuneate slice in vitro. A Schild plot for Ro5-3663 was clearly non-linear but enabled a pA2 value of 3.97 to be calculated. Combination studies using the 'classical' GABA antagonists bicuculline and picrotoxin indicated that Ro5-3663 acted at a separate site from bicuculline, but may share a common site with picrotoxin.