OBJECTIVETo explore the pattern of hair cell injury and expression of P53 apoptosis protein in intensive impulse noise injured cochlear hair cells in guinea pigs.

METHODSTwelve adult guinea pigs were exposed to a series of 40 pairs of impulse noise (2 second intervals) at the intensity of 168 dB (SPL). Animals were terminated at 3, 6 and 12 hours after noise exposure, respectively. Cochlear surface preparations were performed with a double staining of FITC-conjugated phalloidin and propidium iodide for the observations of the stereocilia and the nucleus. P53 immunochemical staining was also performed 12 hours post-noise exposure to observe if there was expression of p53 protein in injured hair cells. Results Three hours after noise exposure, the outer hair cells at the end of basal turn and beginning of second turn were destroyed first with a character of nuclear condensation. Six hours post-noise exposure, many hair cells in the center of damage region had nuclear fragmentations, and the damaging area expanded towards to basal turn and apical turn. Twelve hours after noise exposure, the nucleus in most outer hair cells and inner hair cells at the region of damage center were missing. The nuclear condensation and fragmentation were appeared in hair cells in both sides of the center region of degeneration. P53 immunoreactive products were also found in damaged hair cells, not only in the central damage area, but also in the basal turn and the third turn.

CONCLUSIONSIntensive impulse noise resulted in apoptosis of cochlear hair cells that initiated between the end of basal turn and the beginning of second turn. Hair cell degeneration spread to basal and third turn along the basilar membrane. P53 may play an important role in impulse noise induced-hair cell apoptosis.