[Hair cell damage and regeneration in the quail cochlea following kanamycin ototoxicity].

Forty-day old quails were given kanamycin (KM) at a dose of 400mg/kg per day for ten days. Evoked potential thresholds induced by both click and tone burst were obtained at 1 day or 1, 2, 3, 4 and 6 weeks respectively after the last injection, and compared with the thresholds of age-matched control animals. The cochlea of the animals was examined by scanning electron microscopy (SEM). The results showed that the application of KM for 10 days produced massive destruction of the basilar papilla at 1 day posttreatment. The damaged region began at the base and extended apically to the position about 50-70% of the total distance along the papilla, with most severe damage in the basal end. The auditory thresholds measured at the same time revealed a significant elevation at 2 and 4 kHz. However, the number of hair cells in the damaged region recovered rapidly with time, and so did the function. By the end of 3 weeks postinjection, almost all the hair cells reappeared in the pathologic region and the function improved further, with nearly normal thresholds at all frequencies but 4kHz. Six weeks after KM treatment, the basilar papilla showed a nearly normal appearance, but there was no further functional improvement at 4kHz, with the threshold shift by 17.5 dB (P < 0.01). The results of the present study demonstrated that structural recovery was faster than functional one.