Toluene exposure affects the functional activity of the outer hair cells

Rats were exposed to toluene by inhalation (1400 ppm, 16 h/d, 8 days) and the auditory brainstem response (ABR) and distortion product otoacoustic emissions (DPOEs) were used as measures of the auditory sensitivity. These measurements were made before the exposure to toluene, 3 and 5 days after the start of the exposure and 4 days after the end of the exposure. To quantify the repeated DPOE data the area under the curve of the DPOE amplitudes versus the stimuli levels was calculated and used for statistical analysis. Results demonstrate that 3 days of toluene exposure tended to lower DPOE amplitudes and elevate ABR thresholds. Similarly after 5 days of exposure significantly lower DPOE amplitudes were observed at most frequencies along with elevated ABR thresholds. At 4 days post-exposure DPOE amplitudes were greatly diminished at all frequencies and the ABR thresholds were raised by about 40 dB between 1.6 and 20 kHz. These results show a parallel shift between ABR thresholds and DPOE amplitudes during toluene exposure. Furthermore, the results from the DPOE measurements indicate that mainly the outer hair cells are adversely affected by toluene exposure.