Cochlear injuries after exposure to a kurtotic noise and styrene and its protection.
Abstr 30th Midwinter Res Meet 2007 Feb; 30:244
Combined exposure to both noise and aromatic solvents such as styrene is common in many industries. In this study, cochlear electrical responses and injuries of auditory hair cells as well as supporting cells (including cell death) were determined in rats after exposure to a high kurtotic noise and styrene. Protection against the cochlear injuries by antioxidants (N-Acetyl-L-cysteine and idebenone) was also investigated. The noise exposure (10-20 kHz, at a level of 100 dB SPL with 110-dB impact noise [40-ms duration, 1-ms rise and 30 ms fall time, 1/s], 6 hrs per day for 5 days a week for 3 weeks) induced a frequency-dependent permanent threshold shift (PTS) with a maximal level of about 30 dB at 12 kHz. Morphologic examination in some individuals with severe functional loss showed no sign of damage to auditory hair cells (stereocilia) or supporting cells. The styrene exposure attacked Deiter's cells first. For a short-period styrene exposure (7 days, 1/d at a dosage of 800 mg/kg by gavage), the majority of Deiter's cells in the middle turn showed condensed nuclei, but the outer hair cells (OHCs) looked normal. The 3-week styrene exposure (at 400 mg/kg) destroyed almost all of the 3rd row OHCs and some in the 2nd and 1st rows in the middle turn. Surprisingly, there was only a slight PTS (<5 dB) observed at middle frequencies. The combined exposure showed potentiative effect in the middle frequency region where both the noise and styrene showed toxic effects, functionally or structurally. Treatment with N-acetyl-Lcysteine and idebenone significantly protected against the functional loss induced by the noise and styrene. The results indicate that styrene exposure may cause a severe cochlear injury before a hearing loss can be detected. Risk of noise exposure may be significantly increased in the styrene-exposed individuals. The cochlear damage can be partially protected with application of antioxidants.
Noise-exposure; Exposure-levels; Noise-induced-hearing-loss; Noise-exposure; Noise; Hearing; Hearing-disorders; Hearing-loss; Laboratory-animals; Animals; Styrenes
Abstracts of the 30th Midwinter Research Meeting
Washington University, St. Louis