Ototoxicity on cochlear nucleus neurons following systemic application of gentamicin

Conclusion. The gentamicin-induced pathological alteration in the cochlear nucleus is not exclusively a secondary consequence of the damage in the cochlea. Instead, the toxic effect of gentamicin on the cochlear nucleus may occur simultaneously or even earlier than that on the cochlea. Objectives. To investigate the pathological alteration of cochlear nucleus neurons in guinea pigs following systemic application of gentamicin. Materials and methods. Guinea pigs were injected with gentamicin for I day, 3 days, I week, 2 weeks, and 3 weeks, respectively. In gentamicin-treated animals, the hearing function was evaluated by measuring the auditory brainstem response (ABR). The number and cross-sectional area of substance P-positive neurons in the cochlear nucleus were also measured. Results. The threshold of ABR and the number of substance P-positive neurons in the cochlear nucleus were significantly increased after I week and 3 days of injection of gentamicin, respectively. The cross-sectional area of substance P-positive neurons in the cochlear nucleus was significantly reduced after 1-day injection of gentamicin.