Early damage in the chinchilla vestibular sensory epithelium from carboplatin.

Carboplatin, a second-generation platinum drug used in the treatment of cancer, can damage the hair cells in the vestibular system; however, little is known about the time course of its vestibulotoxic effects. The present study examined the acute vestibulotoxic effects of carboplatin (50 mg/kg) in the chinchilla. The duration of the nystagmus response evoked by cold caloric stimulation was significantly reduced 6 h following carboplatin treatment and showed a maximum, permanent reduction of approximately 50% by 24 h after injection. Light-microscopic observations at 6 h subsequent to injection revealed swollen afferent dendrites beneath type-I hair cells and the appearance of small vacuoles within the type-I hair cells; these changes were most pronounced in the crista ampullaris of the semicircular canals compared to the maculae of the utricle and saccule. Many mitochondria were swollen and partially depleted of their membranous infoldings. The mitochondrial abnormalities tended to be somewhat more severe in the hair cells than in their afferent terminals. The structural abnormalities in the mitochondria were more severe at 24 h following injection resulting in the appearance of larger and more numerous vacuoles in the hair cells. By 3 days after injection, many type-I hair cells were filled with large vacuoles which often caused severe distortion of the nucleus and disruption of the plasma membrane. Small vacuoles were occasionally observed in type-II hair cells, mainly in the crista ampullaris. These results indicate that the vestibulotoxic effects of carboplatin occur quite rapidly and cause significant disruption of the mitochondria in hair cells and their afferent terminals.