Effects of Pilocarpine-induced Seizures on the Neuronal Cell Death, Mossy Fiber Sprouting and Neurogensis in the Hippocampus of Mice

Lee, Sang Hyeon; Kook, Ji Hyun; Hwang, Shinae; Kim, Jong Keun; Bae, Choon Sang

Abstract

Present study was performed to delineate the inter-relationship among neuronal death, mossy fiber sprouting (MFS) and neurogenesis in hippocampal formation of pilocarpine-treated mice. Status epilepticus was induced by intraperitoneal administration of 300 mg/kg pilocarpine in male ICR and C57BL/6 mouse. The severity of seizure was evaluated using 5 grades of Racine scales for first 4 hr after pilocarpine injection. Fluro-Jade C (FJC) staing, NeoTimm's staining and immunohistochemistry for BrdU were employed to evaluate neuronal cell death, MFS and neurogenesis, respectively. All animals in the present study induced seizures over grade 3 of Racine scale by pilocarpine injection. ICR mice show higher seizure severity (mean Racine scale; 4.37) than C57BL/6 mice do (mean Racine scale; 3.22), while the latency times for the first seizure over Racine scale grade 3 are from 15 min to 20 min and showed no difference between the 2 strains. In ICR mouse, numerous FJC-positive cells in hilus of hippocampus were detected at 4 h after pilocarpine injection, while they were not detected at that time in C57BL/6 mouse. The number of FJC-positive neuronal cells, which were densely found in the pyramidal layer of CA1, CA3 and hilus polymorphic regions of hippocampus, reached peak at 3 days after injection and then few cells were found at 7 days after injection in both strains. In control animals, BrdU positive cells in dentate subgranular layer which represent the hippocampal neurogenesis were more numerous in C57BL/6 than in ICR. The number of BrdU positive cells significantly increased at 2 days after pilocarpine injection and reached the peak at 8 days after injection and returned to control level at 15 day after injection in both strains. The percent increase of the BrdU positive cell was more prominent in ICR mouse. MFS was found at 2 weeks after the injection and the intensity of MFS was getting strong at 4 weeks after injection. There was no differences in MFS grading between 2 strains. These results suggest that there are some inter-relationships among the seizure severity, hippocampal neuronal cell death and hippocampal neurogenesis, but they don't have any significant relationships with the mossy fiber sprouting from dentate granule cells.