Voltage-gated sodium channel expression in rat spiral ganglion neurons

The spiral ganglion neurons (SGN) provide the afferent innervation of the hair cells in the organ of Corti and relay auditory information from the inner ear to the brain. Voltage-gated sodium channels (NaV) initiate and propagate action potentials that encode this sensory information but little is known regarding the subtypes expressed in these cells. We have used RT-PCR and immunohistochemistry to study the compliment and anatomical distribution of NaV channels in rodent SGN. NaV1.1, NaV1.6 and NaV1.7 were all detected at the mRNA level. Fluorescence or streptavidin–horseradish peroxidase immunohistochemistry extended these findings, demonstrating predominant localisation of NaV1.6 and NaV1.7 on SGN cell bodies and NaV1.1 on axonal processes. Dual labelling with peripherin demonstrated higher NaV1.6 and NaV1.7 expression on Type I rather than Type II neurons. These results provide evidence for selective expression and variations in the distribution of VGSC in the rodent SGN, which may guide further studies into afferent function in the auditory pathway and therapeutic approaches for diseases such as hearing loss and tinnitus.