Korean J Otolaryngol-Head Neck Surg.  1999 Dec;42(12):1490-1496.

Histopathologic Changes of Cochlea and Hearing Threshold Changes according to Duration of Noise-Exposure in the Rat

• Kim BH
• Kang SH
• Lim DJ
• Lee BY
• Lee YB

Abstract

BACKGROUND AND OBJECTIVES
The degree of noise induced hearing loss was determined principally according to the level and duration of noise and patient's state. The purpose of this study was to investigate the cochlear histopathology and hearing threshold immediately after noise exposure according to duration of noise exposure, and finally to draw relationship between the cochlear pathology and hearing threshold. MATERIALS AND METHOD: Each group of animals (6 ears) has been exposed for 10 minutes, 1 hour, 2 hours, 3 hours, 4 hours, 24 hours and 48 hours to an octave band of noise with a center frequency of 4000 Hz and a sound pressure level of 110 dB. After noise exposure, the hearing thresholds of the subjects were determined with auditory brainstem response (ABR) and immediately their inner ear were fixed and observed with transmission electron microscopy (TEM).
RESULTS
ABR thresholds were increased according to lengthening of duration of noise exposure. TEM findings of outer hair cells, Deiters' cells and ganglion cells showed more severe degeneration according to lengthening of duration of noise exposure. Damages of all kinds of cells appeared almost at the same time.
CONCLUSION
Through the foregone study, cochlear pathology was proportioned to increased hearing threshold, and the damages of outer hair cells and ganglion cells appeared almost at the same time. It seems that not only damages of outer hair cells, but also damages of ganglion cells contribute to early hearing threshold shift during continuous intense noise exposure.

Keyword

Noise exposure; Outer hair cell; Ganglion cell

MeSH Terms

Animals
Cochlea*
Ear, Inner
Evoked Potentials, Auditory, Brain Stem
Ganglion Cysts
Hair
Hearing Loss
Hearing*
Microscopy, Electron, Transmission
Noise
Pathology
Rats*