The effects of short noise exposures in the guinea pig.

Guinea pigs have been exposed to 20 kHz at 120 dB SPL for exposure durations of 7.5, 6.5, 5.0, and 3.25-min and killed either 3 or 12 weeks post-exposure. One series of guinea pigs exposed for 30-min had cochlear potentials recorded 3 weeks post-exposure. The damage was assessed by surface preparations and quantified as percentage hair cell loss per segment in every row, total number of outer, and inner hair cells missing and the area of total outer hair cell damage. A significantly smaller number of ears were found to be damaged after the shortest exposures, but no significant differences could be detected in the amounts of damage when all the series were compared. Myelinated nerve fibre degeneration had increased after the longer post-exposure interval, but no such differences were observed in the sensory hair cell degeneration.