The effect of noise exposure on the aging ear.

The effect of noise exposure on auditory sensitivity and inner ear morphology was compared in aged and young mature mice. Hearing thresholds were obtained by auditory evoked brain stem responses (ABR) before and after noise exposure, and hair cell loss was quantified. The study was done in two parts: first to assess the effect of noise exposure on subjects with presbycusis, and second to assess its effect on aged subjects without measurable presbycusis. In the first experiment C57BL/6 mice, with an age-related hearing loss, were used as a model for presbycusis. C57BL/6 mice exhibiting presbycusis were more susceptible to noise injury than age-matched CBA/Ca mice. In the second experiment CBA/Ca mice were used. These mice retain normal hearing even with advancing age. The aged CBA/Ca mice had the same susceptibility to noise injury as young CBA/Ca mice.