Assessment of gentamicin-induced vestibulotoxicity by click and galvanic vestibular-evoked myogenic potentials: a guinea pig investigation.
OBJECTIVE
The aim of this investigation carried out with guinea pigs was to study the possible effects of a gentamicin treatment on the saccular macula and on its afferent vestibular ganglion neurons.


METHODS
The gentamicin-induced impairment was analyzed using vestibular-evoked myogenic potentials (VEMPs) elicited by both click and galvanic vestibular stimulations (GVS). Fifty microl of saline or gentamicin solution (40 mg/ml) was dropped over the round window membrane of the right (control) and left (lesion) cochleae, respectively. Four weeks after surgery, the VEMPs elicited with clicks and GVS were evaluated for each animal. Then, the animals were sacrificed in order to perform morphological and anti-Nav1.8 immunocytochemical analyses.


RESULTS
Click- and GVS-VEMPs were obtained in all of the controls, whereas no potentials were obtained from gentamicin-treated animals. Lesions of sensory cells were observed in the saccular macula. In the injured vestibular ganglion, the percentage of voltage-gated sodium channel Nav1.8-like immunoreactive (Nav1.8-LI) neurons was significantly lower (38.9+/-0.7) than that (53.6+/-3.2) calculated in controls.


CONCLUSIONS
Gentamicin-induced impairments of the saccular macula and afferents of guinea pigs can be evaluated by recording both click- and GVS-VEMPs. Both tests provide information on the sacculo-collic reflex pathway and could help a clinical diagnosis of gentamicin intoxication by conventional eardrops in the patient with a perforated eardrum.
Cheng
Po-Wen
PW
Department of Otolaryngology, Far Eastern Memorial Hospital, Taipei, Taiwan.
Lue
June-Horng
JH
Lin
Chi-Te
CT
Day
An-Shiou
AS
Young
Yi-Ho
YH
D000161:Acoustic Stimulation / Q000379:methods; D000818:Animals; D004576:Electromyography / Q000379:methods; D005072:Evoked Potentials, Auditory / Q000187:drug effects*; D007839:Functional Laterality; D005839:Gentamicins; D006168:Guinea Pigs; D062559:NAV1.8 Voltage-Gated Sodium Channel; D009334:Neck Muscles / Q000503:physiopathology; D011930:Reaction Time / Q000187:drug effects; D015222:Sodium Channels / Q000378:metabolism; D015837:Vestibular Diseases / Q000139:chemically induced / Q000473:pathology / Q000503:physiopathology*
D005839:Gentamicins; D062559:NAV1.8 Voltage-Gated Sodium Channel; D015222:Sodium Channels