The influence of the cochlear efferent system on chronic acoustic trauma.
The role of the olivocochlear bundle (OCB) in modulating noise-induced permanent injury to the auditory periphery was studied by completely sectioning the OCB fibers in chinchillas and exposing the animals while awake to a broad-band noise at 105 dB SPL for 6 h. Outer hair cell (OHC) function was assessed by measuring 2f1-f2 distortion product otoacoustic emissions (DPOAE) at frequencies from 1.2 to 9.6 kHz and cochlear microphonics (CM) at frequencies from 1 to 8 kHz. As a result of de-efferentation, the CM was decreased but the DPOAEs were unchanged in de-efferented ears as compared with efferented control and sham-operated ears. Following noise exposure, the ears that were de-efferented showed significantly more depression of DPOAE input/output functions and greater decrement of CM amplitude. The differences between de-efferented and efferent-innervated ears were evident across all the frequencies. The cochlear lesions of the OHCs reflected by traditional cytocochleograms, however, were minimal in both efferented and de-efferented ears. The results indicate that cochlear de-efferentation decreases the CM in chinchilla and increases the ear's susceptibility to noise-induced permanent hearing damage. More importantly, de-efferentation increases susceptibility at low frequencies as well as high frequencies.
Zheng
X Y
XY
Department of Communicative Disorders and Sciences, State University of New York at Buffalo 14214, USA.
Henderson
D
D
Hu
B H
BH
Ding
D L
DL
McFadden
S L
SL
D000818:Animals; D001306:Auditory Pathways / Q000293:injuries / Q000503:physiopathology; D002682:Chinchilla; D002908:Chronic Disease; D003051:Cochlea / Q000293:injuries / Q000294:innervation* / Q000503:physiopathology*; D003055:Cochlear Microphonic Potentials; D003714:Denervation; D004525:Efferent Pathways / Q000293:injuries / Q000503:physiopathology; D018072:Hair Cells, Auditory, Outer / Q000293:injuries / Q000503:physiopathology; D006317:Hearing Loss, Noise-Induced / Q000209:etiology* / Q000473:pathology / Q000503:physiopathology