Kanamycin induced ototoxicity in the laboratory rat. A comparative morphological and audiometric study.

Two comparative experiments on the behavioural, audiometric and histological effects of kanamycin-induced cochleotoxicity in the Wistar rat are reported. In the first experiment kanamycin 400-1,500 mg/kg/day was injected subcutaneously for 20 days and the morphological damage to the organ of Corti assessed. In the second experiment the progression of damage to the organ of Corti was examined in animals given kanamycin 700 mg/kg/day for 4-20 days. Behavioural audiometric studies of threshold shift were undertaken throughout both experiments. In the first study, all the animals were killed after a recovery period of 20 days from the last injection, i.e., day 40, and in the second study groups of animals were killed at 4-day intervals between days 4 and 20 of dosing. One cochlea from each animal was critical point-dried, dissected to expose the organ of Corti and examined by scanning electron microscopy. A vertical section through the contralateral cochlea was examined by light microscopy. The results of the morphological examination of the cochleas were collated with the behavioural audiometry. The morphological damage to the organ of Corti followed a stereotyped pattern of degeneration, the extent of which appeared to be determined both by the number and concentration of the kanamycin administrations. The collateral audiometric examinations indicated that extensive damage had taken place before a shift in the behavioural auditory threshold could be detected by observation of the Preyer reflex.