Benzodiazepine inhibition of [3H]flunitrazepam binding and caffeine-induced seizures in mice

The median inhibitory and anticonvulsant potencies of seven benzodiazepine (BDZ) agonists and one BDZ antagonist (Ro15-1788) were established by two tests: inhibition of [3H]flunitrazepam receptor binding and prevention of caffeine-induced seizures in mice. The effect of Ro15-1788 on the anticonvulsant potency of diazepam against caffeine-induced seizures was also investigated. The [3H]flunitrazepam receptor binding inhibitory potencies (IC50s) of the BDZ agonists correlate well with their anticonvulsant potencies (ED50s) against caffeine-induced seizures (r = 0.831; P greater than 0.01 and less than 0.05). Ro15-1788 and clonazepam are the most potent inhibitors (IC50s: 1.72 and 1.75 nM, respectively), but differ markedly in their ability to obtund caffeine-induced seizures (ED50s: 43.2 and 0.226 mg/kg, respectively). Although both Ro15-1788 and diazepam are effective against caffeine-induced seizures, when used in combination Ro15-1788 antagonizes the anti-caffeine effect of diazepam. These data indicate that Ro15-1788 is a BDZ partial agonist with low efficacy as well as a potent antagonist.