Mensh B D, Patterson M C, Whitehead M L, Lonsbury-Martin B L, Martin G K
Division of Neuroscience and Medical Scientist Training Program, Baylor College of Medicine, Houston, Texas.
Hear Res. 1993 Oct;70(1):50-64. doi: 10.1016/0378-5955(93)90051-2.
An important issue in understanding the development of noise-induced hearing loss is whether prior acoustic overstimulation alters the susceptibility of the cochlea to further damage. The present work was designed to establish a model of activity-dependent changes in the susceptibility of the cochlea to acoustic overstimulation by regularly exposing the ear to a low-frequency pure tone. As a quantitative index of cochlear function, 2f1-f2 distortion-product otoacoustic emissions (DPOAEs) were monitored systematically over time in three groups of rabbits, with each group experiencing a unique paradigm that incorporated repeated exposure to the low-frequency tone. Common to each rabbit's exposure protocol was that a given experimental session consisted of two exposure episodes, separated by a 40-min period. Experimental sessions were repeated three times, with 2- to 3-day recovery periods interposed between sessions. The rate of decrement in DPOAE amplitude over a prescribed time period was utilized as a measure of susceptibility to the acoustic trauma. The overall results indicated that ears were more susceptible to exposure 40 mins after the first exposure of a session than they were initially. A series of control experiments indicated that the robustness of the acoustic middle-ear reflex (AMR) did not change between the exposure episodes. Consequently, changes in the AMR could not account for the increased susceptibility seen following the first exposure. However, in awake rabbits with stronger AMRs, higher pure-tone exposure levels were needed to produce increased susceptibility to the second exposure. After 2-3 days of intersession recovery, susceptibility to the effects of excessive sound returned close to its original baseline level. The outcome of these studies demonstrated a reduced capacity for the ear to resist the harmful effects of exposure to a moderately intense tone, which was repeated twice over a brief 40-min period, but little change in susceptibility when identical exposures were repeated over longer intersession intervals of several days.
在理解噪声性听力损失的发展过程中，一个重要问题是先前的声学过度刺激是否会改变耳蜗对进一步损伤的易感性。本研究旨在通过定期让耳朵暴露于低频纯音，建立一个耳蜗对声学过度刺激易感性的活动依赖性变化模型。作为耳蜗功能的定量指标，在三组兔子中系统地监测了随时间变化的2f1-f2畸变产物耳声发射（DPOAE），每组经历一种独特的模式，包括重复暴露于低频音调。每只兔子的暴露方案的共同点是，给定的实验时段由两个暴露阶段组成，中间间隔40分钟。实验时段重复三次，各时段之间插入2至3天的恢复期。在规定时间段内DPOAE振幅的下降速率被用作衡量对声损伤易感性的指标。总体结果表明，在一个时段的首次暴露后40分钟，耳朵比最初更容易受到暴露影响。一系列对照实验表明，在暴露阶段之间，中耳声反射（AMR）的强度没有变化。因此，AMR的变化不能解释首次暴露后观察到的易感性增加。然而，在AMR较强的清醒兔子中，需要更高的纯音暴露水平才能使第二次暴露的易感性增加。经过2至3天的时段间恢复后，对过度声音影响的易感性恢复到接近其原始基线水平。这些研究结果表明，耳朵抵抗适度强度音调暴露有害影响的能力降低，这种暴露在短暂的40分钟内重复两次，但当在几天的较长时段间间隔重复相同暴露时，易感性变化很小。
