Distribution of the voltage gated sodium channel Na(v)1.3-like immunoreactivity in the adult rat central nervous system.

Voltage-gated sodium channels are transmembrane proteins responsible for the initiation and propagation of action potentials. One subtype, Na(v)1.3 (brain type III) is tetrodotoxin sensitive and fast inactivated. Na(v)1.3 has been shown to be expressed at low levels in the adult rat, but to be upregulated after sciatic nerve axotomy in the dorsal root ganglia. In the present study, we used immunohistochemistry to look at the distribution of Na(v)1.3 in the adult rat central nervous system. We used a polyclonal antibody, raised against residues 511-524. This epitope corresponds to the sequence located in the intracellular loop between domains I and II of Na(v)1.3 and is specific for this sodium channel subtype. We found Na(v)1.3-like immunoreactivity (-LI) neurons in the cerebral cortex, hippocampal formation, colliculi, and mesencephalic reticular formation. Na(v)1.3-LI was observed in fiber tracts such as the corpus callosum, anterior commissure, corticofugal fibers, lateral lemniscus, and cerebellar peduncles. Na(v)1.3-LI was particularly intense in sensory nerve tracts such as the mesencephalic trigeminal tract, vestibulospinal tract, or spinal trigeminal tract. In the spinal cord, Na(v)1.3-LI was intense throughout the white matter and the dorsal roots. In the spinal cord grey matter, Na(v)1.3-LI fibers terminate in the deep laminae of the dorsal horn and in the ventral horn. Na(v)1.3-LI was also found in motoneurons as well as in ventral roots. This study shows that Na(v)1.3 is present at the protein level in the adult rat.