Initial pattern of outer hair cell death in rat cochlea after exposure to impulse noise

Objective: To observe the initial pattern of outer hair cell（OHC）death in rat cochlea after exposure to impulse noise.Methods: Rats were exposed to 100 pars of impulse noise（3 seconds interval between each pair） at 154 dB SPL.Before and three times（10 min,3 h,and 6 h） 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）.The specimens were examined under a fluorescence microscope for assessment of OHC damage.Results: Morphological examination of OHC nuclei revealed some slightly nuclear condensation and fragmentation in the damaged cochlear region in the animals 10 min after the noise exposure.There were a few swollen nuclei and loss of OHC nuclei could be seen 3 h after the noise exposure.The cochlear lesion expanded containing many missing OHCs and seriously shrunken nuclei 6 h after the noise exposure.（Conclusions: The） results of the study indicate that apoptosis of OHCs takes place extremely rapid after the impulse noise exposure.The necrosis of OHCs is secondary to apoptosis.OHC apoptosis is a quick process.The early expansion of cochlear lesion is contributed primarily by apoptosis.