Upregulated expression of voltage-gated sodium channel Nav1.3 in cortical lesions of patients with focal cortical dysplasia type IIb

Focal cortical dysplasia (FCD) is one of the causes of intractable epilepsy in humans. Cytomegalic neurons, not balloon cells, are considered to be the putative generators of epileptic activity in FCD type IIb (FCDIIb). Voltage-gated sodium channel III alpha-isoforms (Na(v)1.3) play crucial roles in the initiation and propagation of action potentials and are important regulators of neuronal excitability. Here, we examined 12 FCDIIb surgical specimens from patients undergoing surgery for epilepsy and used age-matched normal control cortical tissue (CTX) from 10 autopsy samples as controls. Using reverse transcription-PCR and western blot techniques, we found that the mRNA and protein levels of Na(v)1.3 were clearly upregulated in FCDIIb surgical specimens compared with the controls (CTX). Results of immunohistochemistry analyses demonstrated that Na(v)1.3 immunoreactivity was widely present in FCDIIb lesion tissue; specifically, high levels of Na(v)1.3 immunoreactive proteins were located mainly in cytomegalic neurons of different sizes and shapes, not in balloon cells. Double-labeling studies showed most cytomegalic neurons expressing Na(v)1.3 colabeled with neuronal markers and glutamate receptors-1. Taken together, our results show an upregulation of Na(v)1.3 protein and a specific cellular distribution of Na(v)1.3 proteins in FCDIIb lesion tissue samples, suggesting that Na(v)1.3 may be involved in the generation of epileptic activity in FCDIIb. NeuroReport 23: 407-411 (C) 2012 Wolters Kluwer Health vertical bar Lippincott Williams & Wilkins.