Death mode of outer hair cells in chinchilla cochlea after exposure to difference levels of intense noise / 解放军医学杂志

ABSTRACT

Objective To quantitatively analyze the occurrence of apoptotic and necrotic outer hair cells (OHCs) and to evaluate the changes of these parameters with time after noise exposure. Methods Chinchillas were exposed to a narrow band noise at either 104 or 108 dB SPL for 1 hour. The animals were executed and dissected at either 1, 4 and 30 days after the noise exposure and the cochleas were collected for detection of OHC death mode. The apoptotic and necrotic OHCs were distinguished by examining the OHC nuclear morphology and confirmed by staining for caspase 3 activity or TUNEL assay. ABR thresholds for click stimuli were used to monitor changes in auditory function. Results The number of apoptotic cells were significantly greater than those of necrotic cells shortly after the noise exposure at day 1 for the 104 dB group, day1 and day4 for 108 dB group ( P =0 01, P =0 03, P =0 01) and the difference between the number of apoptotic cells and necrotic cells became statistically insignificant at day 4 and day 30 for the 104 dB group and day 30 for 108 dB group ( P =0 67, P =0 29, P =0 52). By day 30, apoptotic and necrotic pathologies continued, although in small quantity in both 104 dB group and 108 dB group. Conclusions The results of the study indicated that the early expansion of cochlear lesion is contributed primarily by apoptosis, whereas the later stage of lesion expansion is likely contributed equally by apoptosis and necrosis. The death of OHCs not only takes place during a noise exposure, but also continues for at least 30 days after noise exposure