Effects of prolonged kanamycin administration on cochlear anatomy and auditory brainstem response thresholds in chickens.

OBJECTIVE To determine whether regenerated hair cells in the basilar papilla of chickens are resistant to kanamycin monosulfate damage. DESIGN Randomized controlled trial. SUBJECTS Ninety newly hatched Roman chickens. INTERVENTION Chickens were injected with kanamycin monosulfate (200 mg/kg/d) for 10, 13, 17, 20, 25, or 30 days. RESULTS Scanning electron microscopy revealed that hair cells in the proximal 40% of the basilar papilla degenerated and disappeared after 10 days of kanamycin treatment. Following this, hair cell regeneration and repair was apparent. Regeneration and maturation of hair cells within 20 days in chickens that received treatment for 20 days were similar to those in chickens that were treated for 10 days followed by 10 days of recovery. After 25 days of treatment, many regenerated hair cells of mature appearance were reinjured. Regenerated hair cells of immature appearance were not damaged. The auditory brainstem response assay showed that the loss and recovery thresholds in chickens treated with kanamycin for 20 days were similar to those in chickens treated for 10 days followed by 10 days of recovery. There was a loss of auditory brainstem response thresholds in chickens that were treated with kanamycin for more than 20 days. CONCLUSION The immature regenerated hair cells in the basilar papilla of chickens are resistant to kanamycin ototoxic effects; however, this resistance is not seen in mature hair cells following prolonged kanamycin exposure.