Toluene ototoxicity in rats: Assessment of the frequency of hearing deficit by electrocochleography

To identify the frequency range most sensitive to toluene-induced auditory damage, the auditory function of adult Long-Evans rats exposed to 1750 ppm of toluene (6 h/day, 5 days/week, 4 weeks), was tested by recording auditor y-evoked potentials directly from the round window of the cochlea. The pres ent electrocochleographic findings do not support a specific mid- to high-f requency loss of auditory sensitivity. On the contrary, the electrophysiolo gic data, obtained for audiometric frequencies ranging from 2 to 32 kHz, sh owed a hearing deficit not only in the mid-frequency region (12-16 kHz), bu t also in the mid-low-frequency region (3-4 kHz). Actually, the effect of t oluene was independent of the frequency in our experimental conditions. His tological analysis was consistent with electrophysiologic data because a br oad loss of outer hair cells occurred in both mid- and mid-apical coil of t he organ of Corti. (C) 1999 Elsevier Science Inc. All rights reserved.