Canlon B, Fransson A
Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden.
Hear Res. 1995 Apr;84(1-2):112-24. doi: 10.1016/0378-5955(95)00020-5.
Guinea pigs were sound conditioned to a low-level, long-term pure tone stimulus (1 kHz, 81 dB SPL, 24 days) before exposure to a traumatic noise (1 kHz, 105 dB SPL, 72 h). Auditory brainstem response thresholds and distortion product otoacoustic emissions were obtained at selected frequencies before sound conditioning and at day 1, 5, 10, and 15 during sound conditioning as well as on the final 24th day. Auditory brainstem responses at 1 and 2 kHz were not affected at any time during sound conditioning. The amplitude of the distortion product otoacoustic emission showed minor alterations (below 10 dB) at selected frequencies only during the initial stages (day 1, 5, and 10) of sound conditioning in some, but not all the animals. Distortion product amplitudes were similar to control values on the 15th and 24th day of conditioning. Surface preparations of the organ of Corti did not reveal any significant hair cell loss induced by sound conditioning. The effect of a traumatic exposure (1 kHz, 105 dB SPL, 72 h) on a control group and a sound conditioned group was determined. The distortion product otoacoustic emission amplitude measured 4 weeks after the cessation of the traumatic exposure revealed significant differences. The amplitude of the distortion product otoacoustic emission for the control group was depressed at all tested frequencies and at lower frequencies (2.8, 2.1, and 1.75 kHz) the emissions did not show an increase in response to increases in intensity, of the primaries. The sound conditioned group showed increases in distortion product amplitude with increases in the intensity of the primaries for all tested frequencies and statistically significant reductions from the pre-exposure values were not found. Surface preparations from the control group indicated that the traumatic noise exposure affected nearly 100% of the outer hair cells around the 14 mm distance from the round window. The sound conditioned group showed a significantly less (50%) outer hair cell loss than the control group. The sound conditioned group illustrated an altered pattern of damage after subsequent noise trauma. There were two distinct regions of outer hair cell loss, one being around the 16 mm distance and the other around the 12 mm distance from the round window. These results imply that the intrinsic properties of the outer hair cells and/or the organ of Corti have been altered by sound conditioning.
在暴露于创伤性噪声（1kHz，105dB SPL，72小时）之前，将豚鼠对低水平、长期纯音刺激（1kHz，81dB SPL，24天）进行声音条件化训练。在声音条件化训练前以及训练期间的第1、5、10和15天以及最后第24天，在选定频率下获得听觉脑干反应阈值和畸变产物耳声发射。在声音条件化训练期间的任何时候，1kHz和2kHz处的听觉脑干反应均未受到影响。仅在一些（但不是所有）动物声音条件化训练的初始阶段（第1、5和10天），选定频率下畸变产物耳声发射的幅度出现了微小变化（低于10dB）。在训练的第15天和第24天，畸变产物幅度与对照值相似。柯蒂氏器的表面制备未显示声音条件化训练引起任何明显的毛细胞损失。确定了创伤性暴露（1kHz，105dB SPL，72小时）对对照组和声音条件化训练组的影响。在创伤性暴露停止4周后测量的畸变产物耳声发射幅度显示出显著差异。对照组的畸变产物耳声发射幅度在所有测试频率下均降低，并且在较低频率（2.8、2.1和1.75kHz）下，发射对初级频率强度增加没有显示出增加。声音条件化训练组在所有测试频率下，随着初级频率强度的增加，畸变产物幅度增加，并且未发现与暴露前值相比有统计学上的显著降低。对照组的表面制备表明，创伤性噪声暴露影响了距圆窗约14mm距离处近100%的外毛细胞。声音条件化训练组的外毛细胞损失明显少于对照组（50%）。声音条件化训练组在随后的噪声创伤后显示出改变的损伤模式。有两个明显的外毛细胞损失区域，一个在距圆窗约16mm处，另一个在距圆窗约12mm处。这些结果表明，声音条件化训练改变了外毛细胞和/或柯蒂氏器的内在特性。
