Prado-Guitierrez Pavel, Fewster Leonie M, Heasman John M, McKay Colette M, Shepherd Robert K
Department of Otolaryngology, The University of Melbourne, Australia.
Hear Res. 2006 May;215(1-2):47-55. doi: 10.1016/j.heares.2006.03.006. Epub 2006 Apr 27.
We investigated the effect of pulse duration (PD) and interphase-gap (IPG) on the electrically-evoked auditory brain stem response (EABR) and viiith nerve compound action potential (ECAP) of deafened guinea pigs in order to test the hypothesis that the extent of change in these neural responses is affected by the histological status of the auditory nerve. Fifteen guinea pigs were deafened by co-administration of kanamycin and furosemide. Animals were acutely implanted with an 8-band electrode array at 1, 4 or 12 weeks following deafening. EABR and ECAP input/output functions were recorded in response to charge balanced biphasic current pulses. We determined the change in current required to equalize; (i) the EABR amplitude when the duration of the current pulse was doubled (104-208 micros/phase); and (ii) the EABR and ECAP amplitudes when the IPG was increased from 8 to 58 micros using a 104 micros/phase current pulse. Following the completion of each experiment the cochleae were examined quantitatively for spiral ganglion neuron survival. As expected, the current level required to evoke an EABR with equal amplitude was lower when the animal was stimulated with current pulses of 208 compared with 104 micros/phase. Moreover, the current level required to evoke EABR/ECAPs with equal amplitude was lower when current pulses had an IPG of 58 versus 8 micros. Importantly, there was a reduction in the magnitude of this effect with greater neural loss; the reduced efficacy of changing both PD and IPG on these electrically-evoked potentials was statistically correlated with neural survival. These results may provide a tool for investigating the contribution of auditory nerve survival to clinical performance among cochlear implant subjects.
我们研究了脉冲持续时间（PD）和相间间隙（IPG）对致聋豚鼠电诱发听性脑干反应（EABR）和第八对脑神经复合动作电位（ECAP）的影响，以检验以下假设：这些神经反应的变化程度受听神经组织学状态的影响。15只豚鼠通过联合使用卡那霉素和速尿致聋。在致聋后1、4或12周，将动物急性植入8通道电极阵列。记录EABR和ECAP的输入/输出函数，以响应电荷平衡双相电流脉冲。我们确定了使以下各项相等所需的电流变化：（i）当电流脉冲持续时间加倍（104 - 208微秒/相位）时EABR的振幅；以及（ii）当使用104微秒/相位的电流脉冲将IPG从8微秒增加到58微秒时EABR和ECAP的振幅。在每个实验完成后，对耳蜗进行定量检查以确定螺旋神经节神经元的存活情况。正如预期的那样，与104微秒/相位的电流脉冲相比，当用208微秒的电流脉冲刺激动物时，诱发等振幅EABR所需的电流水平更低。此外，当电流脉冲的IPG为58微秒而非8微秒时，诱发等振幅EABR/ECAP所需的电流水平更低。重要的是，随着神经损失增加，这种效应的幅度会降低；改变PD和IPG对这些电诱发电位的效果降低与神经存活在统计学上相关。这些结果可能为研究听神经存活对人工耳蜗植入受试者临床性能的贡献提供一种工具。
