Altered transporter‐mediated neocortical GABA release in Rasmussen encephalitis

Abstract

To learn whether epileptic seizures in Rasmussen encephalitis (RE) may be promoted by insufficient γ-aminobutyric acid (GABA) release. (3) H-GABA was released from neocortical synaptosomes through transporter reversal following intrasynaptosomal Na(+) accumulation by veratridine that prevents inactivation of Na(+) channels. Tissues of three RE patients were compared with those of nine non-RE. In RE, the release was markedly reduced. In non-RE, the extracellular Ca(2+) concentration ([Ca(2+) ]e ) was inversely related to the amount of release. In RE, the percental decline of additional release upon Cae 2+ withdrawal was linked with the presurgical duration of epilepsy. Permanent opening of Na(+) channels by veratridine resembles maximal frequency of action potentials corresponding to epileptic seizures. These are preceded by a fall in [Ca(2+) ]e . Zero [Ca(2+) ]e increased release through the Na(+) /Ca(2+) exchanger additionally elevating intrasynaptosomal Na(+) . This enhanced GABA release probably reflects an antiseizure mechanism. In RE, the additional release gets lost over epilepsy duration.