HPLC/RIA Analysis of Biologically Active Peptide, Methionine Enkephalin, in the Brain of Seizure-Susceptible El Mouse

Abstract

Biologically active peptide, methionine enkephalin (ME) except cross-reactive substances from methionine enkephalin-like immunoreactivity, was quantified by a technique of high performance liquid chromatography coupled with radioimmunoassay in the brain of El mice (seizure-susceptible strain) to elucidate the relation between seizures and the opioid system. The El mice were divided into El (+) and El (o) depending on whether stimulated or not. The El (+) mice were tossed-up from 28 days after birth, first exhibited abortive seizures at 50 days of age and developed generalized convulsions after 75 days. The ME content in 25-day-old El mice was significantly decreased in the hippocampus and septal area, as compared with the corresponding regions in ddY mice (seizure-nonsusceptible strain; the mother strain of El). This content in both 50-dayold El (+) and El (o) mice was significantly reduced in the septal area and cerebral cortex. It was further shown that the ME content in both 150-day-old El (+) during interictal periods and El (o) mice was markedly decreased in the septal area, cerebral cortex and striatum. The decrease of ME in the El mouse brain was generally compatible with our previous studies concerning the up-regulation of opioid delta receptors in this species. These results suggest that the reduction of endogenous ME could be involved in the pathouenesis of seizures in the El mouse.