Time sequential analysis of the death of rat's cochlear outer hair cells at the early stage after exposure to impulse noise / 解放军医学杂志

ABSTRACT

Objective To observe the space-time patterns of damaged outer hair cells(OHCs) in rat cochlea at the early stage after exposure to impulse noise. Methods Wistar rats were exposed to 100 emissions of impulse noise (3 seconds interval between each emission) at 154 dB SPL. Four times (10 min, 30 min, 3h and 6h) after the noise exposure, the animals were sacrificed and the organs of Corti were processed for detection of OHC death modes. The apoptotic and necrotic OHCs were distinguished by propidium iodide (PI), a fluorescent probe specifically labeling the nuclear DNA. The specimens were examined under a fluorescence microscope for assessment of OHC damage. Results Nuclear chromatin began to shrink as the chromatin condensed around the nuclear periphery. The peripheral chromatin ring condensed into discrete mass. Chromatin masses appeared to bleb off from the nuclear surface, forming apoptotic bodies at 10 min after the noise exposure. There were a few swollen nuclei appeared 30 min after the noise exposure. Loss of OHC nuclei could be seen 3 h after the noise exposure. The cochlear lesion expanded to contain a large number of missing OHCs and seriously shrunken nuclei at 6 h after the noise exposure. Conclusions The results of the study indicate that death of OHCs takes place extremely rapid after the impulse noise exposure. The apoptosis of OHCs precedes necrosis. OHC apoptosis is a quick process. Most of dead outer hair cells were eliminated 6 h after the noise exposure.