Cochlear potentials and electron microscopy applied to the study of small cochlear lesions.

Abstract

Many investigators have attempted to define the relations among behavioral auditory thresholds, cochlear potentials and cochlear pathology after excessive exposure to noise. We have observed that some noise exposed chinchillas have fewer missing sensory cells yet lower cochlear potentials than nonexposed controls. By comparing the cochleae of animals with the above characteristics, we found that the noise exposed ear had many misshapen outer hair cells, possible loss of some of the peripherally arranged mitochondria in the same cells and an increase in vesicles, vacuoles and smooth endoplasmic reticulum in the afferent nerve fibers in the region of the organ of Corti from which the low cochlear potentials were recorded. It is clear from these findings that hair cell counts alone do not always give a true indication of the functional status of the cochlea. In describing the permanent anatomical effects of a particular noise exposure on the inner ear, the condition of the cells and nerve fibers which remain after injury must be determined in addition to the number of sensory cells and nerve fibers which were lost.