The Role Of Notch Signaling Pathway In The Medial Temporal Lobe Epilepsy Formation

ObjectiveEstablish mesial temporal lobe epilepsy model in adult mice and investigate the role of Notch signaling during epileptogenesis.MethodsStereotaxically unilateral injection of kainic acid (KA) into the dorsal hippocampus of adult C57BL/6mice. Normal saline for the control group by the same process. Evaluate the models by observing seizures post injection and examining histopathological consequences of hippocampus. Notch intracellular domain (NICD) is the key element of Notch signaling. Western blot was performed, as to detect NICD expression of hippocampus at different time points post injection. Besides, NICD immunofluorescence was used to demonstrate its distribution in hippocampus.Results1. Status epilepticus occurred in91%(62/66) mice after unilateral intrahippocampal KA injection, with6mice die of it. The total success rate was80%(56/70). In saline injection group, no seizure was observed.2. Compared to saline injected mice, in KA injected mice sacrificed3h post-KA injection, H&E staining of both sides of the hippocampus revealed a large number of pyknotic pyramidal cells in CA1, CA3, hilus and dentate gyrus, of which CA3was the most severe. Five days after KA injection, a remarkable cell loss was observed in both sides of the hippocampus in these same areas, with contralateral CA2neurons relatively retained. Five weeks post-KA injection, in the ipsilateral side of the hippocampus neuronal loss was almost completely in CA1and CA3, accompanied with prominent dispersion of the granule cell layer in dentate gyrus, which was consistent with human MTLE. While in the contralateral side neurons were replenished and hippocampus structure was restored.3. In KA injected mice, respectively for3h,16h,24h,3d,5d and1w post injection, the relative NICD expression of ipsilateral hippocampus was1.079±0.101,1.446±0.249(P<0.01),1.334±0.268(P<0.05),1.685±0.390(p<0.01),2.036±0.698(P<0.05),1.257±0.456. Normalized to saline injected mice, n=6mice for each time point and group.4. NICD immunofluorescence in ipsilateral side of KA injected mice was prominently up-regulated at5d post injection, and was predominantly localized in subgranular zone of dentate gyrus. Conclusion1. Establishing mesial temporal lobe epilepsy models in C57BL/6mice by unilateral intrahippocampal kainic acid injection was feasible and reliable.2. Using this model, we found NICD expression, which predominantly localized in subgranular zone of dentate gyrus, was elevated during epileptogenesis in ipsilateral side of hippocampus. This suggests that Notch signaling may have a role during epileptogenesis, but the exact mechanism is yet to be determined.