Chronologic changes of nitric oxide concentration in the cochlear lateral wall and its role in noise-induced permanent threshold shift.
OBJECTIVE
The objective of this study was to investigate the chronologic changes of nitric oxide (NO) concentration in the cochlear lateral wall and to explore its possible role in permanent threshold shift (PTS) after intense noise exposure.


METHODS
Seventeen guinea pigs were subjected to a single continuous exposure to broadband white noise at 105 +/- 2 dB sound pressure level (SPL) for 40 hours and were divided into four groups according to various postnoise recovery periods. Another 12 guinea pigs were not exposed to noise and served as controls. The hearing status of all animals was evaluated with auditory brainstem responses (ABR) evoked by condensation "click" sounds. ABR were recorded both prior to noise exposure and immediately before killing the animal. After death, NO concentration in the cochlear lateral wall was directly measured with an NO/ozone chemiluminescence technique.


RESULTS
An approximately 1.7-fold increase in NO concentration was observed immediately postnoise exposure, which persisted for up to 28 days. The threshold of ABR elevation (mean, 30 dB SPL) peaked immediately after cessation of noise exposure and gradually resolved to a PTS (mean, 14.5 dB SPL) 56 days after noise exposure when NO concentration had returned to its prenoise exposure level.


CONCLUSIONS
Noise-induced threshold shift, which resolved to a mild PTS, can be partially attributed to NO elevation in the cochlear lateral wall. Our results revealed a nonlinear correlation between ABR recovery and depletion of NO, indicating that the mechanisms of NO changes in the cochlear lateral wall may be more complicated than previously conceived and that other pathophysiologic mechanisms may also play important roles in noise-induced PTS.
Chen
Yuh-Shyang
YS
Department of Otolaryngology, College of Medicine, National Taiwan University, Taipei, Taiwan.
Tseng
Fen-Yu
FY
Lin
Kai-Nan
KN
Yang
Ting-Hua
TH
Lin-Shiau
Shoei Yn
SY
Hsu
Chuan-Jen
CJ
D000818:Animals; D001309:Auditory Threshold / Q000187:drug effects*; D003051:Cochlea / Q000378:metabolism*; D016057:Evoked Potentials, Auditory, Brain Stem / Q000502:physiology; D006168:Guinea Pigs; D008297:Male; D009569:Nitric Oxide / Q000378:metabolism*; D009622:Noise / Q000009:adverse effects; D013997:Time Factors
D009569:Nitric Oxide