Degeneration of spiral ganglion cells in the chinchilla after inner hair cell loss induced by carboplatin.

The anticancer drug carboplatin has been used to generate inner hair cell (IHC) lesions in the cochlea of chinchillas. This has provided a valuable model for the study of the relative roles of IHCs and outer hair cells (OHCs). In the present study, we examined the pathological and temporal relationships between the degeneration of the cochlear IHCs and type I spiral ganglion cells (SGCs). A single intravenous dose of 200 mg/m2 carboplatin produced extensive IHC loss with no apparent effect on the OHCs. The auditory brainstem response threshold was significantly elevated by 2 weeks following treatment and remained stable through 12 weeks. Elevated thresholds were well correlated with morphological lesions. On the other hand, the SGC population progressively decreased from 2 to 12 weeks after treatment, to about half of the control density values. A positive correlation existed between the density of SGC and the number of surviving IHCs. These results indicate that selective damage to IHCs causes a distinct loss of SGCs.