Pure-tone overstimulation protects surviving avian hair cells from acoustic trauma

It was found that intense pure-tones which damage hair cells in chicks, also result in damage to the tectorial membrane (TM). This study was designed to elucidate the effects of a second pure-tone insult on hair cells which survived a priming pure-tone exposure. Chicks were exposed to a pure-tone of 1.5 kHz at 124 dB SPL. Lesion was found in both TM and hair cells, but the area of damage to the TM was much larger than that to the hair cells. Following this exposure, chicks were exposed to a second intense pure-tone at 2.2 kHz 124 dB SPL. The frequency of the second exposure corresponded to a region where the TM did, but hair cells did not appear to be injured by the first exposure. The second exposure caused significantly less hair cell damage in chicks already exposed to the 1.5 kHz pure-tone than in controls which were not primed with the first exposure. This finding suggests that the first exposure provides a degree of protection for the surviving hair cells, perhaps by uncoupling them from the TM.