A novel inner ear monitoring system for evaluating ototoxicity of gentamicin eardrops in guinea pigs.
OBJECTIVE
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.


METHODS
Prospective study.


METHODS
Guinea pigs were treated with 50 microL saline (n = 10) and 50 microL 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.


RESULTS
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.


CONCLUSIONS
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.
Institute of Toxicology, College of Medicine, National Taiwan University, Taipei, Taiwan.
Ting-Hua
TH
Yang
Shing-Hwa
SH
Liu
Yi-Ho
YH
Young
D000287:Administration, Topical; D000818:Animals; D003051:Cochlea / Q000187:drug effects / Q000503:physiopathology; D007758:Ear, Inner / Q000187:drug effects* / Q000503:physiopathology; D004576:Electromyography; D005072:Evoked Potentials, Auditory / Q000187:drug effects; D005839:Gentamicins / Q000008:administration & dosage / Q000633:toxicity*; D006168:Guinea Pigs; D034381:Hearing Loss / Q000139:chemically induced* / Q000503:physiopathology; D008991:Monitoring, Physiologic / Q000295:instrumentation*; D011446:Prospective Studies; D018709:Statistics, Nonparametric; D014722:Vestibule, Labyrinth / Q000187:drug effects / Q000503:physiopathology
D005839:Gentamicins