[Cochlear histopathological changes following chronic extracochlear electrical stimulation in kittens].

Histopathological investigation of the cochlea following chronic extracochlear electrical stimulation was carried out in 5 kittens. The auditory nerves were electrically stimulated with round window or tympanic promontory electrodes for periods of 1276-1526 h using charge-balanced biphasic current pulses at charge densities of 1.27-5.73 microC/cm2. geom. phase. The histopathological changes were examined with a light microscope. The findings were as follow: 1. The fixations of round window and tympanic promontory electrodes were very firm. Six round window membranes became thicker in the area which contacted the electrode. One was pushed into the scala tympani and adhered to the spiral lamina of the hook region. 2. There was some outer hair cell loss, mild inner hair cell loss and disappearance of Corti's organ structures in a small area of lower basal turns. 3. Decrease of spiral ganglion cell density was found over a 2% basilar membrane length in 2 stimulated cochleas. 4. There was no change in normal control cochleas. These results indicate that mild histopathological changes occurred even though chronic electrical stimulation was performed with non-invasive extracochlear electrodes. The mechanism behind these changes should be further investigated.