The effectiveness of N-acetyl-l-cysteine (l-NAC) in the prevention of severe noise-induced hearing loss

Three groups of chinchillas were exposed to a nonGaussian continuous broadband noise at an Leq = 105 dB SPL, 8 h/d for 5 d. One group (N = 6) received only the noise. A second group (N = 6) received the noise and was additionally treated with l-NAC (325 mg/kg, i.p.). Treatment was administered twice daily for 2 d prior to exposure and for 2 d following the exposure. During exposure the animals received the l-NAC just prior to and immediately after each daily exposure. The third group (N = 4) was exposed to the noise and received saline injections on the same schedule as the l-NAC treated animals. Auditory evoked potential recordings from the inferior colliculus were used to estimate pure tone thresholds and surface preparations of the organ of Corti quantified the sensory cell population. In all three groups PTS exceeded 50 dB at 2.0 kHz and above with severe sensory cell loss in the basal half of the cochlea. There was no statistically significant difference among the three groups in all measures of noise-induced trauma. Treatment with l-NAC did not reduce the trauma produced by a high-level, long duration, broadband noise exposure.