Origin of AP in electrocochleogram as ivestigated by microelectrode technique

为了解声刺激诱发复合AP的来源，将电刺激（EAP）作用于豚鼠耳蜗，在听神经干记录复合AP。EAP由少量负电位组成。正常耳蜗潜伏期小于1 ms的第一负电位（N1电位）振幅迅速增大，动态范围为6dB。在卡那霉素皮下注射损伤的耳蜗中，N1电位的生长反应与正常耳蜗相同。这说明N1电位来源于电流刺激耳蜗神经的电位。就相对于刺激强度的阈值而言，与声学刺激存在差异。电刺激时，刺激频率越低，N1电位阈值越低，第二负电位（N2电位）潜伏期随刺激强度的不同在1 ~ 2 msec之间。正常耳蜗N_2电位振幅增长缓慢。卡那霉素损伤耳蜗，振幅的线性增长反应消失。结果表明，N_2电位起源于电声效应，而声刺激诱发的N_1电位既表现毛细胞的敏感性，又表现耳蜗神经的敏感性，因此N_1电位往往不表现耳蜗神经的敏感性。在听力正常的豚鼠中使用圆窗刺激，结果表明，静脉注射利多卡因和阿司匹林降低了耳蜗神经纤维以及毛细胞的敏感性。

Compound AP evoked by electrical stimuli (EAP) applied to the cochlea in guinea pigs were recorded in the auditory nerve trunk to know origin of compound ap by acoustic stimuli. EAP consisted of a few negative potentials. In normal cochleas the amplitude of the first negative potential (N1 potential) with latency of less 1 msec rapidly grew and its dynaimic range was 6 dB. In cochleas damaged with kanamycin s.c., the growth response of the N1 potential was the same as that in normal cochleas. This showed that the N1 potential originated from potential of cochlear nerve stimulated by electrical current. As far as threshold with respect to stimulus intensity is concerned, there is a difference to acoustic stimulation. With electrical stimulation the lower the stimulus frequency was, the lower the threshold of the N1 potential was.The latency of the second negative potential (N2 potential) for electrical stimulation was between 1 and 2 msec depending on stimulus strength. In normal cochleas the amplitude of the N2 potential grew slowly. In cochleas damaged with kanamycin the linear growth response of the amplitude was lost. From these findings N2 potential was identified as electrophonic effect in origin.Since the N1 potential evoked by acoustic stimulation shows sensitivities of both hair cells and cochlear nerve, the potential always doesn't show the sensitivity of cochlear nerve. Using round-window stimulation in normally hearing guinea pigs, it was shown that intravenously injected Lidocaine and Aspirin decreased the sensitivities of cochlear nerve fibres in addition to hair cells.