title: HPLC/RIA analysis of bioactive methionine enkephalin content in the seizure-susceptible El mouse brain.
abstract: We previously reported a deficit of methionine enkephalin-like immunoreactivity (ME-LI), in the cerebral cortex, septal area, hippocampus, and striatum and the abnormal metabolism of opioid peptides in the hippocampus and striatum of seizure-susceptible El mice, which are involved in the pathogenesis of seizures. However, these findings suggest that the ME-LI does not necessarily reflect the bioactive methionine enkephalin (ME). Herein, we measured the biologically active peptide, ME excluding cross-reactive substances by using HPLC coupled with radioimmunoassay to clarify the abnormal function of enkephalinergic neurons in the El mouse brain. The ME content in 25-day-old El mice that had no seizures was significantly decreased in the hippocampus and septal area, as compared with corresponding regions in ddY mice (seizure-nonsusceptible; the mother strain of El). At the age of 50 days when El mice displayed abortive seizures, this content in both stimulated El[s] and nonstimulated El[ns] was significantly reduced in the septal area and cerebral cortex. At the age of 150 days when El mice exhibit tonic-clonic seizures, this content in both El[s] and El[ns] was significantly reduced in the septal area, cerebral cortex and striatum. These findings were generally compatible with our previous findings. This study further supports our hypothesis that a deficit of anticonvulsant endogenous ME, in the cerebral cortex, septal area, and hippocampus of seizure-susceptible El mice play an important role in the pathogenesis of seizures.
authors.affiliation: Department of Neuropsychiatry, Osaka City University Medical School, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Koide
authors.forename: H
authors.initials: H
authors.lastname: Onishi
authors.forename: M
authors.initials: M
authors.lastname: Katayama
authors.forename: T
authors.initials: T
authors.lastname: Kai
authors.forename: S
authors.initials: S
authors.lastname: Yamagami
mesh_terms: D000818:Animals; D001923:Brain Chemistry / Q000502:physiology*; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D004198:Disease Susceptibility; D004744:Enkephalin, Methionine / Q000032:analysis*; D051379:Mice; D008818:Mice, Neurologic Mutants; D009474:Neurons / Q000737:chemistry; D011863:Radioimmunoassay; D012016:Reference Values; D012640:Seizures / Q000378:metabolism*
chemical_list: D004744:Enkephalin, Methionine