Effects of exposure‐pattern differences on TTS and hair‐cell destruction in the chinchilla

Chinchillas were exposed to 700–2800‐Hz noise at 105 dB SPL. Group A was exposed for 10 min on 22 occasions half a week (3 or 4 days) apart. Group B was exposed on a “factory” schedule: 22 10‐min exposures given on Monday through Friday for a month. Group C received a 220‐min exposure on a single day. Median TTS's 60 min after exposure, at 1, 2, 4, and 8 kHz, were 10, 12, and 66 dB, respectively. The median number of missing outer hair cells (MOHC) was 59, 99, and 54, respectively; two control animals had 51 mud 60 MOHC. There was no relation between individual differences in TTS and in cochlear damage. Apparently chinchillas can experience a single very severe TTS (more than 60 dB an hour after exposure) with no measurable haircell damage, but a moderately severe exposure, repeated daily without time for complete recovery between exposures, can produce measurable damage. The relative susceptibility of chinchilla and man will be discussed. [Research supported by the National Institute of Neurological and Communicative Disorders and Stroke, Public Health Service.]