Cochlear function after selective spiral ganglion cells degeneration induced by ouabain.

BACKGROUND

Ouabain, a cardiac glycoside that specifically binds to Na/K-ATPase and inhibits its activity, was applied to gerbils to develop a method for studying auditory neuropathy.

METHODS

Ouabain was applied to the round window of the cochlea in each gerbil by using a piece of gelfoam with 3 microl or 24 microl (1 mmol/L) ouabain solution. The changes of the threshold of auditory brainstem response, cochlear function round window electrocochleography, as well as the morphological changes of the spiral ganglion cells of the cochlea were observed after application of ouabain for 24 hours or 96 hours.

RESULTS

In ouabain treated gerbils, auditory brainstem response and compound action potential thresholds showed either elevation or no response at all. However, the thresholds of cochlear microphonic and distortion product otoacoustic emissions were not affected. Degeneration and necrosis of some spiral ganglion cells in ears with applications of ouabain (24 hours, 3 microl, 1 mmol/L; 96 hours, 24 microl, 1 mmol/L ouabain). The number of spiral ganglion cells was decreased (24 hours, 3 microl, 1 mmol/L ouabain) or near to a total loss (96 hours, 24 microl, 1 mmol/L ouabain).

CONCLUSIONS

These results indicate a high degree of independence between the spiral ganglion cells and the outer hair cell systems in the cochlear transduction mechanism. The method used in this study would provide a valuable tool for studying auditory neuropathy.