Morphological changes to the stereociliary bundles in the guinea pig cochlea after kanamycin treatment

Pigmented guinea pigs were treated with 400 mg/kg of kanamycin for 8 days and sacrificed 13 days later. The upper surface structures of the organ of Corti were studied using high resolution scanning electron microscopy to reveal fine details of stereociliary fusion and damage to the reticular lamina. Outer hair cell stereocilia showed from partial to complete fusion and loss whilst the inner hair cells showed very little evidence of any damage. In particular, the possible effects of kanamycin on the cross-links between the stereocilia have been investigated. The cross-links are found to be present on all outer and inner hair cell bundles which show no fusion of stereocilia. Partially-fused stereocilia which have free tips still possess the upward-pointing links, and the remaining undamaged stereocilia in these bundles possess the normal cross-links. Where fusion occurs along the sides of the stereocilia, the side-to-side links are missing although whether their absence either results in, or else is caused by, the fusion is not known.