Effects of aging on normal hearing loss and noise-induced threshold shift in albino and pigmented guinea pigs.

In a previous investigation into noise-induced hearing loss by comparing 2-month-old albino with pigmented guinea pigs, albinos displayed significantly greater shifts in cochlear microphonic (CM) threshold and less recovery than the pigmented animals 7 days after noise exposure. The present study compared the responses of 14-month-old albino and pigmented guinea pigs to the same noise parameters used previously. Thresholds for the first detectable elicitation of CM for three pure tones were recorded prior to, at 90 min and at 7 days after a 45-min exposure to 126 dB broadband noise. Before exposure to noise, thresholds for pigmented guinea pigs were 24 dB higher than those in the albinos. Following noise exposure, the pigmented animals showed less than half the amount of threshold shift displayed by the albinos. This change ws attributed to the higher pre-exposure thresholds in the pigmented guinea pigs. Converging lines of evidence suggest that cochlear pigmentation may have both protective and toxic influences on the inner ear.