Combined effects of a simultaneous exposure to noise and toluene on hearing function

To study the combined effects of noise and toluene on auditory function, three experimental groups of Long-Evans adult rats were used. The first group was exposed to toluene (2000 ppm, 6 h/day, 5 days/week, 4 weeks), the second group to an octave band of noise centered at 8 kHz (92 dB SPL), and the last group to a simultaneous exposure to toluene and noise. Auditory function was tested by recording brainstem (inferior colliculus) auditory-evoked potentials. The auditory deficit induced by the combined exposure exceeded the summated losses caused by toluene alone and by noise alone within the range (2-32 kHz) of test frequencies. The nature of the cochlear damage induced by noise alone (injured stereocilia) or by toluene alone (outer hair cells loss) is different.