Changes in F-actin labeling in the outer hair cell and the Deiters cell in the chinchilla cochlea following noise exposure

It has been found that 'conditioning' noise exposures can render the inner ear more resistant to traumatic noise exposures. To explore the possible mechanisms underlying this phenomenon, filamentous actin (F-actin), labeled by rhodamine-phalloidin, was examined in the chinchilla cochlea using confocal fluorescence microscopy. The conditioning noise was 0.5 kHz octave band noise (OBN) at 90 dB SPL for 6 h/day and the high-level noise was the same noise but at 105 dB SPL for 4 h. A variety of pathological changes were found in the chinchilla cochlea after exposure to noise. Subjects exposed to conditioning noise (1 day or 10 days) and only high-level noise showed an increase in F-actin labeling than unexposed controls. By contrast, subjects who had 5 days quiet after the 10-day conditioning exposure exhibited a decrease in F-actin labeling. Interestingly, subjects exposed to high-level noise with prior 10-day conditioning exposure also showed a decrease in F- actin labeling in the cuticular plate and the stereocilia. The F-actin decreases in the stereocilia and the cuticular plates may decrease the mechanical rigidity of the organ of Corti. A more pliable organ of Corti may have reduced the possibility of fracture or ripping of cell junctions during the motion of the basilar membrane induced by acoustic overstimulation.