Lima da Costa D, Erre J P, Charlet de Sauvage R, Popelar J, Aran J M
Laboratoire d'Audiologie Expérimentale et Clinique, Université de Bordeaux II, Hôpital Pellegrin, France.
Exp Brain Res. 1997 Sep;116(2):259-69. doi: 10.1007/pl00005754.
The bioelectrical activity of the cochlea, without any ipsilateral acoustic stimulation, was recorded in awake guinea pigs (GPs) between electrodes chronically implanted at the round window (RW) and the skull. Measuring its power in the band centered around 1.0 kHz (0.5-2.5 kHz) provided an indirect measure of the ensemble background (EBA) activity of the eighth nerve. Contralateral white-noise (CLWN) stimulation reduced this EBA, presumably by activation of medial olivocochlear fibers. The aim of the investigation was to validate measurements of EBA and of its contralateral suppression in order to study the medial efferent function. The first goal was to find the best conditions for recording the EBA in the absence of ipsilateral stimulation and for studying its suppression by contralateral acoustic stimulation, which implies that no noise was generated by the experimental animal. Thus recordings were compared in normal, awake GPs and in GPs under sedation with xylazine, anesthetized with a combination of xylazine and ketamine, and with and without temperature regulation. In order to monitor the effects of sedation and anesthesia, the recordings were analyzed not only in the 0.5- to 2.5-kHz frequency band but also in the other frequency bands, 5-50 Hz, 50-150 Hz, and 150-500 Hz, which presumably include general central and neuromuscular contributions. The results show that sedation with xylazine accompanied by regulation of body temperature does not affect the EBA value nor its contralateral suppression. Nevertheless, anesthesia should be avoided, even with control of body temperature. The second goal of this study was to identify the specific cochlear contribution to the raw RW signal. Thus recordings were performed in normal and deafened animals and analyzed in the frequency band 0.5-2.5 kHz and also in the other frequency bands of 5-50 Hz, 50-150 Hz, and 150-500 Hz. The results indicate that most of the cochlear activity lies in the frequency band 0.5-2.5 kHz, with also some minor contribution coming from the 150- to 500-Hz band. Analysis and comparison of power values in the different conditions indicate that specific cochlear EBA power was about 60 microV2. From a commonly accepted mean background discharge rate of 50 spikes/s (sp/s), the EBA power without CLWN should have been around 4.4 microV2 if the fibers' activity was random. This difference suggests that there is probably some degree of synchrony between individual fibers. There was a reduction of approximately 45% during CLWN stimulation. This suppression might correspond to a reduction in both discharge rate and synchrony of the fibers.
在清醒的豚鼠中，于长期植入在圆窗（RW）和颅骨之间的电极间记录耳蜗的生物电活动，且无任何同侧听觉刺激。测量其在以1.0 kHz（0.5 - 2.5 kHz）为中心的频段内的功率，可间接测量第八神经的总体背景（EBA）活动。对侧白噪声（CLWN）刺激可降低这种EBA，推测是通过激活内侧橄榄耳蜗纤维实现的。本研究的目的是验证EBA及其对侧抑制的测量，以便研究内侧传出功能。首要目标是找到在无同侧刺激时记录EBA以及研究其被对侧听觉刺激抑制的最佳条件，这意味着实验动物不产生噪声。因此，在正常清醒的豚鼠、用赛拉嗪镇静的豚鼠、用赛拉嗪和氯胺酮联合麻醉的豚鼠以及有和没有温度调节的情况下进行记录比较。为监测镇静和麻醉的效果，不仅在0.5 - 2.5 kHz频段，还在其他频段，即5 - 50 Hz、50 - 150 Hz和150 - 500 Hz进行记录分析，这些频段可能包含一般的中枢和神经肌肉成分。结果表明，用赛拉嗪镇静并伴有体温调节不会影响EBA值及其对侧抑制。然而，即使有体温控制，也应避免麻醉。本研究的第二个目标是确定耳蜗对原始RW信号的特定贡献。因此，在正常和致聋动物中进行记录，并在0.5 - 2.5 kHz频段以及5 - 50 Hz、50 - 150 Hz和150 - 500 Hz的其他频段进行分析。结果表明，大多数耳蜗活动位于0.5 - 2.5 kHz频段，150 - 500 Hz频段也有一些微小贡献。对不同条件下功率值的分析和比较表明，特定的耳蜗EBA功率约为60 μV²。从普遍接受的平均背景放电率50个脉冲/秒（sp/s）来看，如果纤维活动是随机的，无CLWN时的EBA功率应该约为4.4 μV²。这种差异表明，各个纤维之间可能存在一定程度的同步性。在CLWN刺激期间，功率降低了约45%。这种抑制可能对应于纤维放电率和同步性的降低。
