Abstract
This study was designed to investigate the effects of acoustic deprivation and stimulation following acoustic trauma.
Symmetrical bilateral cochlear lesions were produced in 33 chinchillas by exposure to a high intensity pure tone (117dBSPL, 2kHz) for 15 minutes. Cochlear thresholds were derived from the cochlear action potentials (CAP) taken prior to and one day after exposure. Then the incudo-malleolar complex of one side was removed so that one cochlea was normally stimulated during the recovery period, while the other was deprived of sound. After a period of one to twelve weeks the OAP's on the non-deprived (nonoperated) side were measured. Hair cell damage in the acoustically deprived cochlea was assessed with scanning electron microscopy. In order to quantify the degree of damage to the sensory epithelium, a hair cell damage scale was implemented based on stereociliary integrity.
The control group consisted of six chinchillas with unilateral ossiculectomy but no sound exposure, and four which received sound exposure only. The cochleas of these animals also were analyzed by scanning electron microscopy.
The most significant result of this study was that the cochleas with acoustic deprivation during the recovery period sustained a higher degree of damage than the acoustically stimulated cochleas.
Another result was that symmetrical cochlear lesions could be produced by strict monitoring of sound pressure balance in both middle ear cavities. Finally, careful ossiculectomy did not affect cochlear morphology.
