Physiological mechanism underlying the progressive resistance to noise induced hearing loss.
Fiorino-FG; Gratton-MA; Subbanna-M; Bianchi-L; Henderson-D
Il Valsalva 1989 Jan; 54():36-41
The role of the efferent auditory nervous system in the development of cochlear resistance to noise, and the importance of the crossed olivo cochlear bundle (COCB) were studied in chinchillas. Adult chinchillas were made monaural, and the COCB was severed in two. Hearing thresholds of the animals were measured before, during and after noise exposure. Noise exposure consisted of an octave band noise centered at 500 hertz (Hz) at 100 decibels (dB) sound pressure level, for 6 hours a day for 20 consecutive days. The noise exposure produced a relatively flat hearing loss of about 50dB across the audiometric range. At 500 and 1,000Hz, the chinchillas with severed COCB showed essentially the same pattern of results or a general decrease of 20 to 30dB in the amount of hearing loss over the 20 day period. At higher frequencies of 4,000 and 8,000Hz there was a nonsystematic decrease in hearing loss over the 20 days for animals with severed COCB. The authors suggest that the absence of toughening at high frequencies may reflect the lack of dynamic feedback to the basal end of the cochlea in animals with severed COCB. The toughening effect observed at the low frequencies may indicate increased effectiveness of the acoustic reflex at the low and mid frequencies.
NIOSH-Publication; NIOSH-Grant; Noise-induced-hearing-loss; Laboratory-animals; Noise-exposure; Hearing-threshold; Nerve-function
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