Experimental Studies on mechanism underlying noise-induced Rearing disorder.

第一年，分别在100dBSPL、4 kHz纯音暴露10min前、后测定两种纯音刺激的耳蜗微音学(CM)和听神经复合动作电位(CAP)。CM(CM-DP)的2f1-f2失真产物(2f1-f2)输出在暴露后即刻明显减少，然后逐渐恢复。CM-DPS的减少和恢复与CAP的减少和恢复密切相关，这可能表明外毛细胞(OHC)功能的影响在噪声性暂时性阈值漂移的发生中起重要作用。接下来的研究给药水杨酸盐，这是已知干扰毛细胞的机电转导(EMT)，揭示了CM-DPS与声音暴露的不同变化。从这些结果推测，声过刺激影响OHC的机电传导(MET)。在接下来的一年里，我们研究了强声和水杨酸盐的联合效应。通过改变两种制剂的应用顺序，这些效果被改变了。现有的声诱导损伤减弱了水杨酸盐的额外耳毒性，而当水杨酸盐在暴露于声音之前给药时，衰减不会发生。从这些结果推测，MET在耳蜗电传导机制中比EMT占据主导地位。几种动物的耳蜗会意外地记录到自发性电振荡(AC电位)，而不会受到任何声音或药物的影响。对交流电位特性的仔细观察表明，这些电位是由主动机械振动系统在基底膜上特征频率与电位特征频率相对应的区域产生的。

In the first year, cochlear microphonics (CM) in response to two tone stimuli as well as compound action potential (CAP) of the acoustic nerve were measured before and after exposure to 4kHz pure tone at 100dB SPL for 10min. The output of 2f1-f2 distortion product in the CM (CM-DP) were markedly reduced immediately after the exposure and then recovered gradually. The reduction and recovery in CM-DPs closely paralleled with those in the CAP.This may indicate that the affection of the outer hair cell (OHC) function plays an important role in developing the noise induced temporary threshold shift. The following study with administration of salicylate, which was known to interfere the electro-mechanical transduction (EMT) of OHCs, reveled the different alterations of the CM-DPs from those with sound exposure. From these results it is postulated that acoustic overstimulation affects the mechano-electrical transduction (MET) of OHC.In the following year, combined effects of loud sound and salicylate were studied. The effects were altered by changing the order in which the two agents were applied. The existing sound-induced damage attenuated the additional ototoxicity of salicylate, whereas attenuation did not occur when salicylate administration preceded sound exposure. From these results it is postulated that the MET holds dominant position over EMT in the cochlear transduction mechanism.Spontaneous electrical oscillations (AC potentials) were accidentally recorded from the cochlea of several animals without any exposure to sound or drugs. Close observations in the properties of the AC potentials indicated that the potentials were generated by the active mechanical vibration system at the area on the basilar membrane where the characteristic frequency corresponded to that of the potential.