Szabo T M, Weiss S A, Faber D S, Preuss T
Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
J Neurophysiol. 2006 Apr;95(4):2617-29. doi: 10.1152/jn.01287.2005. Epub 2006 Jan 25.
The teleost Mauthner (M-) cell mediates a sound-evoked escape behavior. A major component of the auditory input is transmitted by large myelinated club endings of the posterior VIIIth nerve. Paradoxically, although nerve stimulations revealed these afferents have mixed electrical and glutamatergic synapses on the M-cell's distal lateral dendrite, paired pre- and postsynaptic recordings indicated most individual connections are chemically silent. To determine the sensory information encoded and the relative contributions of these two transmission modes, M-cell responses to acoustic stimuli in air were recorded intracellularly. Excitatory postsynaptic potentials (EPSPs) evoked by both short 100- to 900-Hz "pips" and longer-lasting amplitude- and frequency-modulated sounds were dominated by fast, repetitive EPSPs superimposed on an underlying slow depolarization. Fast EPSPs 1) have kinetics comparable to presynaptic action potentials, 2) are maximal on the distal lateral dendrite, and 3) are insensitive to GluR antagonists. They presumably are coupling potentials, and power spectral analysis indicated they constitute a high-pass signal that accurately tracks sound frequency and amplitude. The spatial profile of the slow EPSP suggests both proximal and distal dendritic sources, a result supported by predictions of a multicompartmental model and the effects of AMPAR antagonists, which preferentially reduced the proximal component. Thus a second class of afferents generates a portion of the slow EPSP that, with sound stimuli, demonstrate that the dominant mode of transmission at LMCE synapses is electrical. The slow EPSP is a dynamic, low-pass representation of stimulus strength. Accordingly, amplitude and phase information, which are segregated in other systems, are faithfully represented in the M-cell.
硬骨鱼的Mauthner（M-）细胞介导声音诱发的逃避行为。听觉输入的一个主要成分是由第八对脑神经后部的有髓大棒状末梢传递的。矛盾的是，尽管神经刺激显示这些传入神经在M细胞的远端外侧树突上有混合的电突触和谷氨酸能突触，但成对的突触前和突触后记录表明，大多数单个连接在化学上是沉默的。为了确定编码的感觉信息以及这两种传递模式的相对贡献，细胞内记录了M细胞对空气中声刺激的反应。由短的100至900赫兹“尖峰”和持续时间更长的幅度和频率调制声音诱发的兴奋性突触后电位（EPSP），主要由叠加在潜在缓慢去极化上的快速、重复性EPSP主导。快速EPSP 1）具有与突触前动作电位相当的动力学，2）在远端外侧树突上最大，3）对谷氨酸受体拮抗剂不敏感。它们可能是耦合电位，功率谱分析表明它们构成了一个高通信号，能够准确跟踪声音频率和幅度。缓慢EPSP的空间分布表明其来源既有近端树突也有远端树突，这一结果得到了多房室模型预测以及AMPA受体拮抗剂作用的支持，AMPA受体拮抗剂优先降低了近端成分。因此，第二类传入神经产生了一部分缓慢EPSP，在声音刺激下，这表明在大棒状末梢与M细胞突触处的主要传递模式是电传递。缓慢EPSP是刺激强度的动态低通表示。因此，在其他系统中分离的幅度和相位信息在M细胞中得到了如实呈现。
