Convulsant effect of Ro 5-4864, a peripheral type benzodiazepine, on the baboon (Papio papio)

The effects of Ro 5-4864, a 1,4-benzodiazepine with a high affinity for the peripheral-type benzodiazepine (Bz) binding site, were investigated in the baboon (Papio papio), which is genetically predisposed to epilepsy. A proconvulsant effect of low doses (1-3 mg/kg, i.v.) of Ro 5-4864 was observed by studying its effect on the photic responses induced by intermittent light stimulation in non-photosensitive baboons. Higher doses of Ro 5-4864 (10 mg/kg, i.v.) were overtly convulsant. The Bzs clonazepam and diazepam blocked these convulsant actions of Ro 5-4864 whereas neither Ro 15-1788, an antagonist of central Bz binding sites, nor PK 11 195, an antagonist of peripheral Bz binding sites, had any effect. It thus appeared that the convulsant effect of Ro 5-4864 was not mediated by Bz binding sites of either the central or the peripheral type. It is possible that Ro 5-4864 exerts its convulsant action at the picrotoxin site of the central Bz receptor - gamma-aminobutyric acid receptor-chloride ionophore complex.