The Protective Effect of Conditioning on Noise-Induced Hearing Loss Is Frequency-Dependent

We compared the extent of temporary threshold shift (tts) and hair cell loss following high level 4 khz noise exposure with those preconditioned with moderate level 1 and 4 khz octave band noise. fifteen male albino guinea pigs (300- 350 g in weight) were randomly allocated into three groups: those exposed to 4 khz octave band noise at 102 db spl (group 1, n=5); those conditioned with 1 khz octave band noise at 85 db spl, 6 hours per day for 5 days, then exposed to noise (group 2, n=5); those conditioned with 4 khz octave band noise at 85 db spl, then exposed to noise (group 3, n=5). an hour and one week after noise exposure, threshold shifts were evaluated by auditory-evoked brainstem response (abr) and then animals were euthanized for histological evaluation. we found that tts and cochlear damage caused by noise exposure were significantly reduced by 1 khz and 4 khz conditioning (p<0.001). we also showed that 4 khz protocol attenuates noise- induced tts but no significant tts reduction occurred by 1 khz conditioning. both protocol protected noise-induced cochlear damage. we concluded that lower tone conditioning could not protect against higher tone temporary noise-induced hearing loss, thus conditioning is a local acting and frequency-dependent phenomenon.