[Changes of filamentous-actin at different stages of apoptotic and necrotic hair cells in rat cochleas induced by noise exposure].
OBJECTIVE
To observe the changes of filamentous-actin (F-actin) during process of apoptosis and necrosis in hair cells, and investigate the early mark for hair cells pathology following noise exposure.


METHODS
Twenty young SD rats were used in present study. The animals were randomly assigned into two groups, 10 animals were exposed noise and the remaining without exposure to noise served as normal control. The animals were exposed to a narrow band noise at 110 dB SPL for 8 hours. Immediately after exposure to continuous nose, the animals were exposed to 75 pairs of impulse noise at 155 dB SPL. The auditory brainstem response (ABR) thrush olds of both ears elicited by tone bursts at 5, 10 and 20 kHz were measured before, immediately and 2-week after the noise exposure. Animals were sacrificed and cochleae were quickly removed from the skull. Following fixation, whole specimens comprising the basilar membrane with Corti organ were separated from the modiolus. The organs of Corti were double stained with propidium iodide (PI), a DNA intercalating fluorescent probe used to visualize the morphologic viability of hair cell nuclei, and FITC-labeled phalloidin, a F-actin intercalating fluorescent probe used to visualize the morphologic viability of cuticular plate and the stereocilia in the hair cells. Each organ of Corti was thoroughly examined using fluorescence microscopy.


RESULTS
The animals of test group exhibited a significant elevation of ABR threshold shifts at all tested frequencies after noise exposure immediately and 2-week. There was no detectable F-actin change in both the corresponding cuticular plates and the stereocilia in the OHCs undergoing necrosis. OHCs with slightly increased PI fluorescence and a relatively normal nuclear morphology exhibited normal level of F-actin activity. In the OHCs with mild nuclear condensation (about 3/4 of the normal size) exhibited normal or a slight increased F-actin fluorescence staining. In the OHCs with moderate or severe nuclear condensation (about 1/2 or 1/4 of the normal size), the reduction in F-actin staining was observed. Finally, in the areas where no detectable nuclear staining was present, the reduction in F-actin staining was more severely or absent.


CONCLUSIONS
These results suggest that compare with the change of F-actin, nuclear morphology and staining is the early mark for necrotic and apoptotic hair cells pathology following noise exposure. A biphasic change in F-actin may exist during apoptosis, an initial polymerization and a subsequent depolymerization, but F-actin may be not a necessary component of the process of necrosis in the noise-damaged OHCs.
Yang
Weiping
W
Institute of Otolaryngology, General Hospital of PLA, Beijing, China. yangwp2002@yahoo.com
D000199:Actins / Q000378:metabolism*; D000818:Animals; D017209:Apoptosis; D003051:Cochlea / Q000378:metabolism / Q000473:pathology; D006198:Hair Cells, Auditory / Q000378:metabolism / Q000473:pathology; D006317:Hearing Loss, Noise-Induced / Q000378:metabolism* / Q000473:pathology*; D009336:Necrosis; D051381:Rats; D017207:Rats, Sprague-Dawley
D000199:Actins