Cochlear neuronal degeneration precipitated by experimental blockage of the spiral lamina perforated zone

Abstract

Observation of patterns of neuronal degeneration in cats with cochlear implants has led to the hypothesis that blockage of the spiral lamina perforations (canaliculae perforantes of Schuknecht) by the implant produces localized dendritic degeneration and ganglion cell loss. To test this hypothesis four cats were implanted with 1 × 1 mm squares of polyethylene (PE) film placed directly on the perforated zone (four ears). Four control ears received similar PE squares placed on the scala tympani wall opposite the basilar membrane. Histological examination of the cochleae after 3 months survival time revealed almost total dendritic degeneration and 50%–75% ganglion cell loss in localized regions of the cochlea where the implant fibrous encapsulation could be seen in direct contact with the perforated zone. No neuronal degeneration was observed in the cochleas which showed no fibrous tissue in contact with the perforated zone. These results indicate that the perforated zone is a contact critical area and needs to be avoided by implanted electrodes intended for functional stimulation of the cochlea. [Work supported by NIH.]