The reinnervation of regenerated hair cells in the basilar papilla of chicks after kanamycin ototoxicity.

When newly hatched chicks were injected with kanamycin on 8 successive days, the hair cells were destroyed completely in the area 0.4 to 0.8 mm from the proximal end of the basilar papilla. At this time, and 1 and 7 days following the completion of 10 days of injections, the nerve fibres in the basilar papilla of chicks show no sign of injury. On the first day following 10 days kanamycin administration the regenerated hair cells obtained not only afferent innervation, but also efferent innervation. At 15 days following drug cessation, afferent innervation of the regenerated hair cells was already similar to the controls, and the thresholds measured at this time were significantly better than those at 1 and 7 days. The chalice efferent terminals did not appear until the 60th day of drug cessation. Efferent innervation of the regenerated hair cells also approached maturity at this time. Compared with the half month after the completion of drug injection, the hearing of birds had no evident increase. It was obvious that afferent innervation of the regenerated hair cells was related more to the recovery of hearing than efferent innervation. The regenerated hair cells beginning reinnervation early and maturing were important factors influencing the recovery of the birds' hearing function after kanamycin ototoxicity.