ArticlesComparison of Toluene-Induced and Styrene-Induced Hearing Losses
Section snippets
Animals
Male Long–Evans rats (450–500 g, 4 months old) were purchased from Janvier Laboratories (Le Genest, France). The rats (n = 96) were housed in individual cages (350 × 180 × 184 mm) with steam-cleaned pinewood bedding one month before the start of the experiments. Food (UAR Cie. France, reference A04 10) and tap water were available ad libitum. Temperature in the animal quarters was 22 ± 1°C and the humidity ranged from 50 to 55%. Lights (fluorescent lighting) were on from 0700 to 1900 h. No
Electrophysiological Data
Figure 1A shows the PTS values obtained 6 weeks after the toluene exposure. The auditory threshold shifts increase significantly [F(5, 42) = 11.30, p < 0.0001] as a function of the concentrations of the solvent. For instance, a 23-dB shift was obtained with 2000 ppm at 16 kHz, 14 dB at 1750 ppm at 16–20 kHz, and only 4 dB at 20 kHz with 1500 ppm. In the same manner, there is a significant frequency effect [F(9, 378) = 10.75, p < 0.0001] and a significant interaction effect [F(45, 378) = 3.48, p
Discussion
The present study confirms that both toluene and styrene exposures can cause permanent hearing losses in the Long–Evans adult rat (Figs.1A and 1B). The electrophysiological data show that toluene produces a hearing deficit in the vicinity of the 16-kHz area. In the same manner, concentrations of 850 ppm and 1000 ppm styrene cause hearing losses positioned at a similar tonotopic location. For instance, a 22.5-dB PTS was obtained with a 2000-ppm concentration of toluene, whereas a 20-dB and 35-dB
Conclusion
Both toluene and styrene are industrial solvents that can severely damage the auditory function in adult Long–Evans rats. If both solvents cause auditory threshold shifts in mid (16 kHz) and mid-low (4 kHz) frequency regions, high styrene concentrations (>1000 ppm) are capable of causing frequency-independent hearing losses. The cochlea and more specifically the outer hair cells seem to be the preferential targets of these solvents. Based on the electrophysiological and histological data
Acknowledgements
The authors thank Dr. Morata for helpful critiques of the manuscript. They also thank C. Barthélémy (N/PE), M. Roure (N/PE); P. Bonnet (N/TIE), and S. Veissière (N/TMPC) for their technical assistance. A special thanks to M. Grzebyk, who carried out the statistical analyses, and J.P. Dalens (N/TTDC), who helped the authors with the illustrations.
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