Although most studies have identified damage in the cochlea and semicircular canals as the primary sites of aminoglycoside toxicity, little attention has been devoted to the toxic effects on the otolithic organs. This study aimed to assess the toxic effect of gentamicin eardrops on the inner ear end organs via a novel inner ear monitoring system combined with morphological examination.
Guinea pigs were treated with 50 μL saline (n = 10) and 50 μL gentamicin (40 mg/mL; n = 10) on the right and left round window membranes, respectively. An inner ear monitoring system, including auditory brainstem response (ABR), caloric, ocular vestibular-evoked myogenic potential (oVEMP), and cervical VEMP (cVEMP) tests, was used to assess ototoxicity in guinea pigs at 2 weeks after treatment. The animals were then sacrificed for morphological study via confocal microscopy.
Normal results in ABR, caloric, cVEMP, and oVEMP tests were shown in all saline-treated ears, whereas elevated ABR threshold and absent responses in caloric, oVEMP, and cVEMP tests were noted in all gentamicin-treated ears. The cochlear and vestibular explants harvested from the gentamicin-treated ears revealed substantial loss of hair cells.
The inner ear monitoring system, including ABR, caloric, oVEMP, and cVEMP tests, might help to evaluate toxicity information of the topical eardrops or agents on the inner ear end organs, including cochlea, semicircular canals, utricle, and saccule.