An imidazodiazepine derivative, Ro 15-1788, behaves as a weak partial agonist in the crossed extensor reflex

The antagonistic and intrinsic activity of an imidazodiazepine derivative, Ro 15-1788, was manifested on the crossed extensor reflex. Ro 15-1788 antagonized the depressant effect of diazepam and shifted the dose-response curve of diazepam to the right in a parallel manner but could not reverse the depression produced by either phenobarbital or chlorpromazine. Ro 15-1788 also antagonized the enhancement produced by ethyl-beta-carboline-3-carboxylate. When administered alone, Ro 15-1788 showed a weak depressant effect. Thus, Ro 15-1788 seems to be a partial agonist on the benzodiazepine receptors with weak intrinsic activity and pharmacological properties differing from those of ethyl-beta-carboline-3-carboxylate.