Anatomical characterisation of voltage gated sodium channels in the mammalian cochlear nerve spiral ganglia

Abstract

Introduction. There is evidence that Voltage Gated Sodium Channels (VGSC) may represent novel therapeutic targets for treatment of certain types of tinnitus and hearing loss. It is also known that the different VGSC types vary in their affinity for differing VGSC blockers. Parallels have been drawn with certain types of tinnitus, chronic pain and epilepsy (1) These conditions are thought to arise from pathological VGSC activity (2) There has also been empirical interest in the use of VGSC blockers as tinnitolytics, with the best known of these being intravenous lignocaine.Aim. The aim of this study was first begin to characterise VGSCs in the mammalian cochlear nerve spiral ganglion.Method. After sacrifice, guinea pigs were perfused with heparin and then 2% paraformaldehyde. The bony matrix of the cochleae was decalcified in buffer containing EGTA (8%). Decalcified tissues were embedded; frozen and 20‐micron cryosections were made through the cochleae. Immunocytochemistry was then carried out using antibodies that selectively bind to individual sodium channel α‐subunits. Sections were then analysed and photographed using either an epifluorescence or a confocal microscope.Results and Conclusions. Sodium channel type 1.6 and 1.7 were shown to be expressed in the cochlear nerve spiral ganglion. Further work is being carried out to see if there are changes in the expression of these VGSC after ototrauma. These findings may help us to target our therapy to treat certain types of tinnitus and hearing loss.References 1 Smith P.F., Darlington C.L. (2005) Drug treatments for subjective tinnitus: serendipitous discovery versus rational drug design. Curr. Opin. Investig. Drugs.6, 712–7162 Taylor C.P., Meldrum B.S. (1995) Na+ channels as targets for neuroprotective drugs. Trends. Pharmacol. Sci. 16, 309–315