Local vs systemic effects of acoustic trauma on cochlear structure and transport.

Whether certain effects of acoustic trauma on cochlear structure and function were due to local or systemic agents was investigated in the chinchilla. After unilateral ossicular disarticulation, the animals were given a noise exposure known to cause cochlear damage and vessel transport changes in the stria vascularis. The cochleas with disarticulated ossicular chains received an effective exposure well below one that causes pathologic damage. Only the cochleas with intact ossicular chains showed an increase in the permeability of the strial vessels to horseradish peroxidase tracer and manifested strial edema and organ of Corti damage. These results indicate that the effects of acoustic trauma on cochlear structure and strial vessel transport are induced locally, not systemically. In addition, the minimum time of exposure to 120-dB, 700- to 2800-Hz noise that causes massive cochlear damage in the chinchilla was shown to be between five and ten minutes.