Chen Guang-Di, Decker Brandon, Krishnan Muthaiah Vijaya Prakash, Sheppard Adam, Salvi Richard
Center for Hearing and Deafness, State University of New York at Buffalo, 137 Cary Hall, 3435 Main Street, Buffalo, NY 14214, USA.
Center for Hearing and Deafness, State University of New York at Buffalo, 137 Cary Hall, 3435 Main Street, Buffalo, NY 14214, USA.
Hear Res. 2014 Nov;317:1-8. doi: 10.1016/j.heares.2014.08.004. Epub 2014 Sep 9.
Noise-induced hearing loss (NIHL) initially increases with exposure duration, but eventually reaches an asymptotic threshold shift (ATS) once the exposure duration exceeds 18-24 h. Equations for predicting the ATS have been developed for several species, but not for rats, even though this species is extensively used in noise exposure research. To fill this void, we exposed rats to narrowband noise (NBN, 16-20 kHz) for 5 weeks starting at 80 dB SPL in the first week and then increasing the level by 6 dB per week to a final level of 104 dB SPL. Auditory brainstem responses (ABR) were recorded before, during, and following the exposure to determine the amount of hearing loss. The noise induced threshold shift to continuous long-term exposure, defined as compound threshold shift (CTS), within and above 16-20 kHz increased with noise level at the rate of 1.82 dB threshold shift per dB of noise level (NL) above a critical level (C) of 77.2 dB SPL i.e. CTS = 1.82(NL-77.2). The normalized amplitude of the largest ABR peak measured at 100 dB SPL decreased at the rate of 3.1% per dB of NL above the critical level of 76.9 dB SPL, i.e., %ABR Reduction = 3.1%(NL-76.9). ABR thresholds measured >30 days post-exposure only partially recovered resulting in a permanent threshold shift of 30-40 dB along with severe hair cell loss in the basal, high-frequency region of the cochlea. In the rat, CTS increases with noise level with a slope similar to humans and chinchillas. The critical level (C) in the rat is similar to that of humans, but higher than that of chinchillas.
噪声性听力损失（NIHL）最初会随着暴露时长的增加而加重，但一旦暴露时长超过18 - 24小时，最终会达到一个渐近阈值偏移（ATS）。已经为多个物种开发了预测ATS的方程，但尚未针对大鼠开发，尽管该物种在噪声暴露研究中被广泛使用。为了填补这一空白，我们让大鼠暴露于窄带噪声（NBN，16 - 20 kHz）中5周，第一周从80 dB SPL开始，然后每周将声级提高6 dB，直至最终达到104 dB SPL。在暴露前、暴露期间和暴露后记录听觉脑干反应（ABR），以确定听力损失的程度。在16 - 20 kHz及以上频率范围内，噪声诱导的连续长期暴露阈值偏移，即复合阈值偏移（CTS），随着噪声水平的增加而增加，在高于77.2 dB SPL的临界水平（C）时，每增加1 dB噪声水平（NL），阈值偏移增加1.82 dB，即CTS = 1.82（NL - 77.2）。在100 dB SPL下测量的最大ABR峰值的归一化幅度，在高于76.9 dB SPL的临界水平时，每增加1 dB NL，以3.1%的速率下降，即ABR降低百分比 = 3.1%（NL - 76.9）。暴露后30天以上测量的ABR阈值仅部分恢复，导致永久性阈值偏移30 - 40 dB，同时耳蜗基部高频区域出现严重的毛细胞损失。在大鼠中，CTS随噪声水平增加，其斜率与人类和毛丝鼠相似。大鼠的临界水平（C）与人类相似，但高于毛丝鼠。
