Total ablation of cochlear haircells by perilymphatic perfusion with water

Time course of cochlear injury discharge (excitotoxicity) determined by ABR monitoring of contralateral cochlear events

The dynamics of cochlear excitotoxicity can be monitored from effects on the contralateral ear. After unilateral mechanical ablation of the cochlea (in a mouse model) we observed immediate elevations in auditory brainstem evoked response (ABR) thresholds in the contralateral ear. Threshold elevations peaked at 2-3 h post ablation, and returned to baseline levels after 5-6 h. These contralateral effects are initiated by cochlear afferent injury discharges most likely activating the olivocochlear efferent system. Six hours after cochlear injury, ABR thresholds were fully returned to pre-lesion baseline levels and remained normal for up to 10 days of monitoring. We have confirmed that our cochlear ablation procedure increases short-term activity levels in the auditory brainstem and midbrain using c-fos labelling. The study provides insight into the dynamics of glutamate excitotoxicity, a pathological process directly related to acute tinnitus after acoustic trauma, and more generally implicated in many types of brain injury and neuro-degenerative disease.

Transtympanic Ringer's lactate application in the prevention of cisplatinum-induced ototoxicity in a chinchilla animal model

Objective: Ototoxicity is currently the most frequent dose-limiting side effect of cisplatinum chemotherapy. To date, there is no protocol to prevent dose-related ototoxicity, despite its prevalence and predictability. Previous animal studies have found lactate to be effective in the prevention of cisplatinum-induced ototoxicity. The objective of this study was to test the protective benefits of transtympanic Ringer's lactate in the prevention of cisplatinum-induced ototoxicity.

Study Design: A randomized prospective controlled trial was conducted in an animal model.

Setting: Animal care research facilities of The Montreal Children's Hospital Research Institute.

Subjects and Methods: A total of 44 chinchillas were exposed to systemic cisplatinum injected intraperitoneally in divided cycles to reach the targeted cumulative dosage of 16 mg/kg. Ototopical application of Ringer's lactate solution 0.2 mL twice per day during the chemotherapy cycles was performed. Each animal had one experimental (Ringer's) and one control ear. Distortion product otoacoustic emissions (DPOAEs) were collected for a wide range of frequencies (between 1 and 16 kHz), and scanning electron microscopy was performed to evaluate the protective effects of Ringer's lactate.

Results: Ototopical application of Ringer's lactate solution in our established chinchilla animal model did not provide an otoprotective effect as measured by the DPOAE response and electron microscopy.

Conclusion: In our study, the intratympanic application of Ringer's lactate solution through a tympanostomy ventilation tube did not provide an otoprotective effect. Further studies are needed to better assess the otoprotective or ototoxic effects of Ringer's lactate and other antioxidants on animal and human hearing.