Cochlear insults from noise, drugs, and genetics

In recent years, cochlear damage has usually been documented by the loss of hair cells as judged from surface preparations; in some reports, small samples have also been taken for radial light or electron microscopic analyses. The present study used three groups of deaf guinea pigs: (1) deafened by kanamycin-ethacrynic acid; (2) deafened by 159-dB-SPL noise; and (3) genetically deaf waltzing guinea pigs. Ears were studied by light microscopy, using serial paraffin sections cut in the plane of the modiolus. In all animals, there is more extensive damage to the organ of Corti than simple hair cell loss, and there is a secondary loss of spiral ganglion cells. Basilar membrane, tectorial membrane, Reissner's membrane, and stria vascularis are not affected. The time course for total organ of Corti loss and spiral ganglion loss is dependent upon the type of deafening but the end results are all similar. [Supported by NIH grants NS-12510 and NS-11647.]