Noise-induced outer hair cells' dysfunction and cochlear damage in rabbits

الملخص EN

Background : Outer hair cells' (OHCs') dysfunctions as the extent of temporary and permanent threshold shifts (TTS and PTS) and cochlear damage were assessed in rabbits exposed to continuous noise. Methods : Twelve New Zealand white rabbits were studied in noise (N) (n = 6 ; exposed to continuous noise ; 95dB SPL, 500-8000 Hz for 8 h per day during 5 consecutive days) and control (C) (n = 6 ; not exposed to noise).

OHCs' functions were assessed by distortion product otoacoustic emission (DPOAE) level (Ldp) measurements in different periods and comparing TTS and PTS.

Animals were anaesthetized by CO2 ; cochleae were extracted, fixed in 10 % formaldehyde for 48 hours, decalcified by 10 % nitric acid for 24 hours, and dehydrated, embedded, sectioned 5 µm thickness and stained by Hematoxylin and Eosin for light microscopy. Results : The most and least Ldp or TTS or PTS were related to 5888.50 Hz and 588.00 Hz respectively in noise subjected rabbits (P<0.05).

TTS and PTS were decreased up to 17.79 dB and to 16.01 dB respectively.

TTS were more than PTS over all test frequencies, especially at 5888.50 Hz (P < 0.05).

Ldp or TTS or PTS were found to be equal across ears (P > 0.05).

Severely vacuolated OHCs, pyknotic IHCs, swollen SC, and slightly thickened BM were found. Conclusion : Continuous noise extensively led to OHCs' dysfunctions as decreased Ldp (both TTS and PTS) and highly damage to cochlea.