ZK 91296, an anticonvulsant beta-carboline which lacks muscle relaxant properties.

ZK 91296, a newly synthesised beta-carboline with partial agonistic activity at the benzodiazepine receptor raised the threshold current necessary to elicit electroconvulsions in mice. This effect was dose-dependent and could be reversed by Ro 15-1788. ZK 91296 antagonised the anticonvulsant action of diazepam, but potentiated that of phenobarbitone. ZK 91296 protected mice from DMCM-induced seizures with high potency, this effect being benzodiazepine specific. In mutant rats exhibiting an increased muscle tone of the hindlimbs, ZK 91296 was devoid of muscle relaxant effect and antagonised the muscle relaxant action of both diazepam and phenobarbitone. The latter effect could be blocked by Ro 15-1788. The results suggest that the actions of ZK 91296 are only partly due to its partial agonistic properties at the benzodiazepine receptor.