Noise Induced Hair Cell Loss During the Sensitive Period of Developing Rat Pup Cochlea

Abstract

The mammalian inner ear is very susceptible to acoustic overstimulation, especially around the time when cochlear elements enter their final stages of maturation. During the past decade, a supra-normal period of sensitivity to acoustic trauma during development has been reported for several mammalian species, such as hamsters, guinea pigs, mice, rats (Falk et al., 1974; Bock and Saunders, 1977; Lenoir et al., 1979; Henry, 1984; and others) and was also hypothesized for humans (Douek et al., 1976). However, there is no study which deals with numerous age graded series of developing subjects from the morphological aspect. Known experimental data are based mainly on electrophysiological methods. In this report we present a light microscopic study of numerical hair cell loss during the sensitive period in low frequency pure tone stimulated immature rats compared with young adults 110 days old at the time of sound exposure. White Sprague-Dawley rats were utilized in this experiment, since the identical strain was chosen for verifying the sensitive period by recording the compound action potential and by means of a different histological technique by Lenoir et al. (1979) and Lenoir and Pujol (1980). Timing of the sensitive period, quantitative aspects, and distribution of hair cell degeneration are discussed in this paper.