Hair cell damage after continuous and interrupted pure tone overstimulation: a scanning electron microscopic study in the guinea pig.

In our earlier investigations [Fredelius et al., Hear. Res. 30, 157-167 (1987)] acoustic trauma was studied after continuous 3.85-kHz pure tone exposures of different intensities and durations. In the present investigation, the importance of the introduction of a break during longer 3.85-kHz pure tone exposures was studied. Female pigmented guinea pigs were exposed to 108, 114, or 120 dB SPL for 6 h with or without a 1-h break after the first 3 h. Four weeks after exposure the cochleas were prepared for scanning electron microscopy and the resulting hair cell damage was evaluated according to a 4-grade damage scale. Significant differences could be demonstrated in the hair cell damage in the animals exposed to continuous acoustic overstimulation and those exposed to intermittent overstimulation. The importance of rest periods to decrease hair cell damage during long periods of acoustic overstimulation was clearly demonstrated.