Defining optimum electrode arrays for multichannel cochlear prostheses; histopathological analysis

The cochlear histopathology of two different deaf animal preparations was studied with light, transmission, and scanning electron microscopy. In one experimental series, cats were deafened by a slow injection of neomycin sulfate into the scala tympani immediately prior to an acute neurophysiological experiment. Brainstem evoked responses (BSER) indicated the loss of hearing was rapid. Histological examination revealed that all hair cells and many supporting elements of the organ of Corti were destroyed, with little decline in numbers of ganglion cells or dendrites. In a second series, cats were deafened slowly by daily intramuscular injections of neomycin. When the neomycin dosage was minimal for effecting complete hearing loss (detected by BSER) and survival times limited, dendrites and ganglion cells were nearly intact. However, in high-dose and/or long-surviving neomycin deafened cats, extensive loss of ganglion cells and dendrites occurs. These deaf animal preparations are suitable for electrophysiological mapping experiments designed to define optimum intracochlear multielectrode arrays, as they model different cochlear pathologies observed in profoundly deaf patients. [Work supported by NIH Contract ♯N01-NS-7-2367, NIH Grant ♯NS-11804, and Hearing Research, Inc.]