Abstracts

Rationale: BDNF-TrkB signaling is implicated in experimental seizure and epilepsy. However, the downstream signaling mechanism of epileptogenesis from TrkB receptor activation is still controversial and whether it progresses through the PLCγ, NShc, or both is unclear.Therefore, the aim of this study is to examine whether N-Shc is involved in kainic acid (KA)-induced epileptiform activity. Methods: We used 4 to 8 weeks old homozygous N-Shc deficient mice (N-Shc -/-) and C57BL6 mice as a wild type control (N-Shc +/+) . (1) 5 μl of K252a (1 μM) or vehicle (0.1% DMSO) were injected to the lateral ventricle of wild type mice stereotactically(i.c.v). 30 minutes after the K252a or DMSO injection, KA (30 mg/kg, i.p.) was administered, and the behavior seizures were monitored and were scored by Racine seizure scale. (2) The mice (N-Shc +/+, N-Shc-/-) received a administration of KA (30 mg/kg, i.p.). Then the behavior seizures were monitored. At 1 day and 7 days after the seizure induction by KA, the brain was fixed with 4% paraformaldehyde and cut into 10-μm coronal sections with a cryostat. And Nissl stein was performed for evaluate neurotoxicity induced by KA. Neuronal cell death was quantified in the CA1 and CA3 regions of the dorsal hippocampus. (3) The mice were anaesthetized and the hippocampal electrodes were implanted stereotacticaly. 7 days after surgery , the mice were connected through a cable to a digital EEG system. The baseline hippocampal EEG was recorded for at least 30 min. Thereafter, behavior seizures were induced by KA administration (30 mg/kg, i.p.) in each mouse. EEGs were registered continuously for 2 hours after the KA treatment. The epileptiform discharge, spikes and sharp waves (high-amplitude > 2× baseline, frequency;> 5Hz) were calculated and expressed as a mean frequency. Results: We show that pre-treating wild type mice with the TrkB inhibitor K252a significantly reduced the severity of KA-induced seizures(maximam seizure scale: K252a group 1.67±2.08; 0.1% DMSO group 5.0±1.0, p=0.04), suggesting that TrkB-mediated signaling is crucial for the KA-induced seizure. Moreover, we show that a significant reduction of both the seizure scale(maximum seizure scale: NShc +/+ mice, 5.21±0.98; NShc-/- mice, 3.27±1.79, p=0.001) and the frequency of epileptiform discharge in the hippocampus(epileptiform discharge: NShc+/+ mice, 5642.8±1210 times/h; NShc-/- mice,1046±971 times/h, p<0.001) of N-Shc deficient mice as compared with the control mice. The KA-induced selective neuronal cell loss in the CA3 area of the hippocampus was also inhibited in the N-Shc deficient mice. These results suggest that N-Shc is essentially involved in the KA-induced epileptiform activity. Conclusions: We propose that the N-Shc-mediated signaling pathway would provide a potential target for the development of novel therapeutic drugs and/or approaches in the treatment of epilepsy.