Abstracts

Loss of function mutations in voltage-gated sodium channels (VGSC) have been linked to epilepsy in humans, but the mechanisms underlying hyperexcitability remain unclear. One possibility for this unexpected seizure phenotype is a compensatory dysregulation of other sodium channel subunits expressed in brain., To evaluate this hypothesis, we examined two VGSC knockout mouse models with spontaneous seizures: one heterozygous for deletion of the Scn2a gene and the other homozygous for knockout of Scn1b. Quantitative RT-PCR was performed in triplicate on RNA from whole brain and selected brain regions from at least 4 pairs of mutant and wild-type littermate controls to compare transcript levels of all known brain VGSC subunit genes (Scn1a, 2a, 3a, 5a, 8a, and 1b-4b)., As expected, in each model we found that the disrupted gene had correspondingly decreased levels of mRNA expression ([sim]65% of wild-type in Scn2aKO/+ and 0% in Scn1bKO/KO mice). In addition, in both models, we found that the expression levels of other VGSC genes did not fall outside of the range of normal biological variation (among wildtype mice on the same strain background) with the exception of Scn5a. This TTX-insensitive VGSC was previously shown in our laboratory to be expressed at low levels in restricted limbic structures of the wild type brain. We found a consistent increase in Scn5a in the B1KO/+ and B1KO/KO mutant whole brain samples, as well as a highly variable increase in the Scn2a KO/+ forebrain samples compared to wildtype littermates., This result demonstrates that deficiency of VGSC alpha and beta subunit genes may lead to dysregulation of other pore forming subunit family members in the developing epileptic brain. These preliminary results in conjunction with cellular resolution analyses may help to define the network contributing to the seizure phenotype in these models., (Supported by an Epilepsy Foundation Pre-Doctoral Research Training Fellowship (SE), and the Wilson Medical Research Foundation (LI [amp] JN).)