Benzodiazepine antagonist Ro 15-1788 (flumazepil) attenuates the anticonvulsant activity of diazepam in epileptic fowl

The ability of the imidazobenzodiazepine Ro 15-1788 to displace diazepam from brain membranes in vitro and to antagonize the anticonvulsant activity of diazepam in vivo was determined in epileptic fowl. At doses of 1.0 mg/kg and higher, Ro 15-1788 significantly attenuated the anticonvulsant action of diazepam (1.0 mg/kg) in epileptic chickens. Ro 15-1788 alone exerted no anticonvulsant activity even in doses as high as 10 mg/kg. Specific binding of 10 nM [³H]diazepam to whole homogenate fractions prepared from cerebral hemispheres of epileptic fowl was inhibited by Ro 15-1788 with an IC₅₀ of 8.5 nM and the K_i was determined to be 4.25 nM. These results suggest that Ro 15-1788 competes directly with diazepam for a binding site involved in producing anticonvulsant activity.     

Decreased GAB A, Benzodiazepine, and Picrotoxinin Receptor Binding in Brains of Rats After Cobalt-Induced Epilepsy

In previous studies of experimental and human epilepsy, defects have been shown in the gamma-aminobutyric acid (GABA) receptors. We further investigated the role of the GABA/benzodiazepine/picrotoxinin receptor complex in the epileptic focus and also in other regions of the rat brain. The focus was induced by cobalt implantation to the right motor cortex, and the brains were dissected 16-19 days after the operation. Benzodiazepine (using [3H]flunitrazepam as a ligand; FLU), GABA [3H]muscimol; MUS), and picrotoxinin [( 35S]t-butylbicyclophosphorothionate; TBPS) receptor bindings were measured in different brain areas and the values were compared with glass-implanted controls. In the focal area, the specific receptor binding decreased in the order TBPS greater than FLU greater than MUS. In the perifocal area only TBPS binding decreased, and Scatchard analysis showed a decrease in the number of binding sites (p less than 0.05) without any effect on binding affinity. No change was seen in the binding characteristics of the other areas studied. According to our results, in cobalt-induced epilepsy the GABA/benzodiazepine/picrotoxinin receptor complex is modulated in the focal area; this may lead to a defect in chloride conductance, which in turn induces disturbed control of neuronal activity in the epileptic focus.