Action of anticonvulsants on hippocampal slices in Mg-free medium

The effects of six prototype anticonvulsant drugs were investigated on epileptiform field potential discharges evoked in hippocampal slices of rats by removing magnesium ions from the perfusion fluid in order to reveal a possible interaction with N-methyl-D-aspartate (NMDA) receptor activation. All drugs reduced the multiple discharges with the following order of potency: midazolam greater than carbamazepine = phenytoin = phenobarbital greater than ethosuximide = valproate. They had a stronger depressant effect on the later population spikes but none of them abolished the epileptiform discharge. These effects can be explained by known mechanisms of action of the anticonvulsants tested and lend no support for a specific interaction with NMDA receptors.