Santarelli Rosamaria, Carraro Luigi, Conti Guido, Capello Massimo, Plourde Gilles, Arslan Edoardo
Audiology and Phoniatric Service, Department of Medical and Surgical Specialities, University of Padua, Via Giustiniani 2, I-35128 Padua, Italy.
Brain Res. 2003 May 30;973(2):240-51. doi: 10.1016/s0006-8993(03)02520-4.
Auditory steady-state responses (SSRs) are believed to result from superimposition of middle latency responses (MLRs) evoked by individual stimuli during repetitive stimulation. Our previous studies showed that besides linear addition of MLRs, other phenomena, mainly related to the adaptive properties of neural sources, interact in a complex way to generate the SSRs recorded from the temporal cortex of awake rats. The aim of this study was to evaluate the effects of the inhalational general anesthetic, isoflurane, on MLRs and SSRs at several repetition rates (30-60 Hz) recorded from the temporal cortex of rats. Auditory evoked potentials were obtained by means of epidural electrodes in the awake condition and during anesthesia at three isoflurane concentrations (0.38, 0.76 and 1.13 vol.% in oxygen). MLR latency significantly increased during anesthesia in a concentration-dependent manner, while MLR amplitude, even when significantly attenuated with respect to the mean awake baseline value, failed to correlate with isoflurane concentration. SSRs decreased in amplitude and increased in phase during anesthesia in a concentration-dependent manner and the anesthetic-induced decrease of SSR amplitude appeared to be higher than the corresponding MLR attenuation. SSR prediction curves synthesized by linear addition of MLRs failed to predict SSRs in both amplitude and phase. Moreover, phase discrepancies proved to be higher during anesthesia. Our results suggest that MLRs and SSRs recorded from the temporal cortex of the rat exhibit differential sensitivity to isoflurane and that isoflurane could enhance the role of rate-dependent effects in SSR generation.
听觉稳态反应（SSRs）被认为是由重复刺激期间单个刺激诱发的中潜伏期反应（MLRs）叠加产生的。我们之前的研究表明，除了MLRs的线性叠加外，其他现象（主要与神经源的适应性特性有关）以复杂的方式相互作用，从而产生从清醒大鼠颞叶皮质记录到的SSRs。本研究的目的是评估吸入性全身麻醉药异氟烷对从大鼠颞叶皮质记录到的几种重复率（30 - 60 Hz）下的MLRs和SSRs的影响。在清醒状态下以及在三种异氟烷浓度（氧气中分别为0.38、0.76和1.13体积%）的麻醉过程中，通过硬膜外电极获得听觉诱发电位。麻醉期间，MLR潜伏期以浓度依赖的方式显著增加，而MLR波幅即使相对于清醒时的平均基线值显著衰减，也与异氟烷浓度无关。麻醉期间，SSRs波幅以浓度依赖的方式降低，相位增加，并且麻醉引起的SSRs波幅降低似乎高于相应的MLR衰减。通过MLRs线性叠加合成的SSRs预测曲线在波幅和相位上均无法预测SSRs。此外，麻醉期间相位差异更大。我们的结果表明，从大鼠颞叶皮质记录到的MLRs和SSRs对异氟烷表现出不同的敏感性，并且异氟烷可能增强了速率依赖性效应在SSRs产生中的作用。
