Vestibular ototoxicity of gentamicin assessed by the recording of a short-latency vestibular-evoked response in cats.

The short-latency vestibular-evoked response (VsER) and the auditory brain stem response (ABR) were recorded with scalp electrodes in four cats before, during, and after systemic administration of gentamicin. The VsER was altered and later disappeared in three cats, and in one cat it became asymmetric, typical of a unilateral vestibular lesion. In all cats the ABR was unaffected and remained normal through the end of the experiment 4 months later. Histopathological examination of the temporal bones of three cats showed severe damage to the vestibular end-organ, particularly in the summit of the cristae, but in lesser amounts in the hair cells on the slopes of the cristae and in the maculae. In one cat, the pathological condition was greater in one ear, corresponding to the asymmetry in the VsER records. This new method of inducing and recording the VsER has been demonstrated by the present study to be an effective tool for experimentally assessing vestibular end-organ and nerve function in animal models. Furthermore, these results indicate that the VsER is generated in the vestibular labyrinth, most probably by the cristae of the semicircular canals.