Abstracts

Rationale: The voltage-gated potassium channel Kv4.2 is a critical regulator of dendritic excitability in the hippocampus, and is crucial for dendritic signal integration. Kv4.2 mRNA and protein expression as well as function are reduced in several genetic and pharmacologically induced rodent models of epilepsy. However, so far it is not known if reduced Kv4.2 is just an epiphenomenon of epilepsy, or if it causes neuronal hyperexcitability and increased seizure susceptibility. Our previous studies suggest that microRNA-induced downregulation of Kv4.2 contributes to seizure development in a mouse model of kainic-acid induced status epilepticus. In the present study, we used Kv4.2 heterozygous mice and adult-onset manipulation of hippocampal Kv4.2 expression in mice to assess Kv4.2’s role in regulating hyperexcitability and neuronal morphology in the brain. Methods: The mice (n=11 per group) were genotyped and western blot and quantitative real-time PCR (qPCR) was performed to confirm the protein and mRNA expression. Seizures were induced using i.p injection of kainic acid. Seizure onset and EEG power was identified by cortical EEG recordings using a wireless EEG system. For Kv4.2 overexpression, 6 -8 weeks old C57BL/6 male mice were injected with lentivirus expressing Kv4.2 or a GFP control using bilateral intra-hippocampal CA1 injections. Results: Western blot and quantitative real-time PCR analyses confirmed a significant reduction of Kv4.2 protein (t-test; p < 0.05) and mRNA levels (t-test; p < 0.05) in the Kv4.2 heterozygous mice compared to WT littermates. EEG analyses, showed that the latency to onset of kainic acid-induced seizures is significantly shortened in Kv4.2 heterozygous mice compared to WT littermates (n = 5, t-test; p < 0.05). In addition, a significant increase in total EEG power was observed. No changes in anxiety behavior or overall activity could be detected. Preliminary studies suggest that CA1 injection of lentivirus overexpressing Kv4.2 delays seizure onset compared to controls. Conclusions: Overall, these results show that Kv4.2 expression levels regulate seizure onset and severity. In the future, manipulation of Kv4.2 expression and function may be used to alter seizure susceptibility in epilepsy. Funding: NIH Grants 1R01NS092705 (C.G.)