The diffuse distribution of Nav1.2 on mid-axonal regions is a marker for unmyelinated fibers in the central nervous system

Unmyelinated fibers in the central nervous system are known to exist in hippocampal mossy fibers, cerebellar parallel fibers and striatal projection fibers. Previously, we and others reported diffuse distribution of Nav1.2, a voltage-gated sodium channel α-subunit encoded by the SCN2A gene, on unmyelinated striatal projection fibers. Mutations in the SCN2A gene are associated with epilepsies and autism. In this study, we investigated the distribution of Nav1.2 on the unmyelinated fibers in the corpus callosum and stria terminalis by immunohistochemistry and immunoelectron microscopy analysis, suggesting that diffuse localization of Nav1.2 on mid-axonal regions can be a useful marker for unmyelinated fibers.