Department of Biomedical Engineering, Center for Hearing Research, Boston University, Boston, MA, 02215, USA.
J Assoc Res Otolaryngol. 2012 Apr;13(2):249-267. doi: 10.1007/s10162-011-0300-5. Epub 2011 Dec 13.
The lateral superior olive (LSO) is a brainstem nucleus that is classically understood to encode binaural information in high-frequency sounds. Previous studies have shown that LSO cells are sensitive to envelope interaural time difference in sinusoidally amplitude-modulated (SAM) tones (Joris and Yin, J Neurophysiol 73:1043-1062, 1995; Joris, J Neurophysiol 76:2137-2156, 1996) and that a subpopulation of LSO neurons exhibit low-threshold potassium currents mediated by Kv1 channels (Barnes-Davies et al., Eur J Neurosci 19:325-333, 2004). It has also been shown that in many LSO cells the average response rate to ipsilateral SAM tones decreases with modulation frequency above a few hundred Hertz (Joris and Yin, J Neurophysiol 79:253-269, 1998). This low-pass feature is not directly inherited from the inputs to the LSO since the response rate of these input neurons changes little with increasing modulation frequency. In the current study, an LSO cell model is developed to investigate mechanisms consistent with the responses described above, notably the emergent rate decrease with increasing frequency. The mechanisms explored included the effects of after-hyperpolarization (AHP) channels, the dynamics of low-threshold potassium channels (KLT), and the effects of background inhibition. In the model, AHP channels alone were not sufficient to induce the observed rate decrease at high modulation frequencies. The model also suggests that the background inhibition alone, possibly from the medial nucleus of the trapezoid body, can account for the small rate decrease seen in some LSO neurons, but could not explain the large rate decrease seen in other LSO neurons at high modulation frequencies. In contrast, both the small and large rate decreases were replicated when KLT channels were included in the LSO neuron model. These results support the conclusion that KLT channels may play a major role in the large rate decreases seen in some units and that background inhibition may be a contributing factor, a factor that could be adequate for small decreases.
外侧上橄榄核（LSO）是一种脑干核团，经典地理解为在高频声音中编码双耳信息。先前的研究表明，LSO 细胞对正弦波幅度调制（SAM）音调的包络耳间时间差敏感（Joris 和 Yin，J Neurophysiol 73:1043-1062, 1995; Joris, J Neurophysiol 76:2137-2156, 1996），并且 LSO 神经元的亚群表现出由 Kv1 通道介导的低阈值钾电流（Barnes-Davies 等人，Eur J Neurosci 19:325-333, 2004）。还表明，在许多 LSO 细胞中，同侧 SAM 音调的平均反应率随调制频率高于几百赫兹而降低（Joris 和 Yin，J Neurophysiol 79:253-269, 1998）。这种低通特征不是直接从 LSO 的输入继承而来的，因为这些输入神经元的反应率随调制频率的增加变化很小。在当前的研究中，开发了一个 LSO 细胞模型来研究与上述反应一致的机制，特别是随着频率的增加出现的突发率降低。探索的机制包括后超极化（AHP）通道的影响、低阈值钾通道（KLT）的动力学以及背景抑制的影响。在该模型中，单独的 AHP 通道不足以在高调制频率下引起观察到的反应率降低。该模型还表明，单独的背景抑制（可能来自梯形体的内侧核）可以解释在一些 LSO 神经元中观察到的小反应率降低，但不能解释在其他 LSO 神经元中在高调制频率下观察到的大反应率降低。相反，当 KLT 通道被包括在 LSO 神经元模型中时，小和大的反应率降低都得到了复制。这些结果支持了这样的结论，即 KLT 通道可能在一些单位中观察到的大反应率降低中起主要作用，并且背景抑制可能是一个促成因素，对于小的降低，该因素可能足够。
