Age-related changes in sensitivity of the postpubertal ear to acoustic trauma.

Although the age of the postpubertal mammal is typically ignored in evaluating the damaging effects of noise on the ear, it was shown to account for over 65% of the variability in the mouse. 44 inbred CBA/J mice, ranging in age from 60 (early postpuberty) to 360 days (late middle age), were tested for cochlear AP thresholds at frequencies from 2 to 64 kHz. They were then subjected to 5 min of a 124 dB octave band (12-24 kHz) noise. Although all the mice had similar pre-exposure thresholds, the extent of noise-induced AP threshold elevation and the frequencies most severely affected depended upon the ages of the mice. The youngest subjects had the greatest threshold elevations, being most pronounced at, and 1 octave above, the center frequency of the noise exposure. With increasing age there was a progressively less severe effect. The oldest subjects had cochlear AP threshold elevations which were restricted to a frequency 2 octaves above the exposure frequency.