Ototoxicity of ethanol in the tympanic cleft in animals

This work was undertaken to study the ototoxicity of topically applied ethanol in quantitative terms. Using guinea pigs, ethanol was administered (1) on the round window for 10 min, (2) instilled in the middle ear cavity for 24 hours, and (3) perfused into the cochlear canal (into the scala tympani) at the rat of 10 microliter/min for 10 min. Cochlear microphonics from the electrode on the round window were recorded. The critical concentration (the maximum dilution ratio) of the ethanol that appears to be ototoxic in the experimental condition mentioned above was determined to be (1) 50%, (2) 10%, (3) 0.1% respectively. Using chinchillas, the effect of ethanol with round window application on the Endocochlear Potential (EP) was studied. Simultaneous recording of EP from the 1st and 3rd turn of the cochlea showed a more marked decline in EP in the 1st turn. 70% ethanol caused an irreversible, plateauing decline in EPO, while 35% ethanol caused a reversible decline in EP.