Spontaneous activity of auditory-nerve fibers: Insights into Stochastic processes at ribbon synapses
Spontaneous activity of auditory-nerve fibers: Insights into Stochastic processes at ribbon synapses
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DOI：
10.1523/jneurosci.1512-07.2007
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发表时间：
2007-08-01
影响因子：
5.3
通讯作者：
Brown, Mel
中科院分区：
文献类型：
--
作者：
Heil, Peter;Neubauer, Heinrich;Brown, Mel
在一些感觉系统中，刺激表示从分级膜电位到随机尖峰序列的转换是由带状突触执行的。在哺乳动物听觉系统中，绝大多数初级传入听觉神经（AN）纤维的尖峰特征主要由单个内毛细胞（IHC）中的单个带状突触决定，从而为突触的运作提供了一个独特的窗口。在这里，我们检查了当 IHC 膜电位可以被认为是恒定的并且产生 AN 纤维活动的过程可以被认为是静止的条件下，即在没有听觉刺激的情况下，猫 AN 纤维的尖峰间期 (ISI) 的分布。这种自发活动通常被认为是由纤维的耐火特性修改的兴奋性泊松点过程引起的，但在这里我们表明情况并非如此。相反，ISI 分布要好一到两个数量级，并且非常准确地描述为均匀随机激励过程（发射机释放事件）的结果，其中事件间隔时间的分布是形状因子为 2 的指数分布和阿伽玛分布的混合，两者都具有相同的尺度参数。尽管尺度参数随纤维而变化，但混合物中指数分布区间和伽玛分布区间的比例以及耐火特性可以被认为是恒定的。这表明所有带状突触以相似的方式运作，可能只是以不同的速率运作。我们的发现也为更好地理解在该突触处发起的时变刺激的尖峰序列表示，以及听觉通路中时间编码的基础知识迈出了重要的一步。
In several sensory systems, the conversion of the representation of stimuli from graded membrane potentials into stochastic spike trains is performed by ribbon synapses. In the mammalian auditory system, the spiking characteristics of the vast majority of primary afferent auditory-nerve (AN) fibers are determined primarily by a single ribbon synapse in a single inner hair cell (IHC), and thus provide a unique window into the operation of the synapse. Here, we examine the distributions of interspike intervals (ISIs) of cat AN fibers under conditions when the IHC membrane potential can be considered constant and the processes generating AN fiber activity can be considered stationary, namely in the absence of auditory stimulation. Such spontaneous activity is commonly thought to result from an excitatory Poisson point process modified by the refractory properties of the fiber, but here we show that this cannot be the case. Rather, the ISI distributions are one to two orders of magnitude better and very accurately described as a result of a homogeneous stochastic process of excitation (transmitter release events) in which the distribution of interevent times is a mixture of an exponential and agamma distribution with shape factor 2, both with the same scale parameter. Whereas the scale parameter varies across fibers, the proportions of exponentially and gamma distributed intervals in the mixture, and the refractory properties, can be considered constant. This suggests that all of the ribbon synapses operate in a similar manner, possibly just at different rates. Our findings also constitute an essential step toward a better understanding of the spike-train representation of time-varying stimuli initiated at this synapse, and thus of the fundamentals of temporal coding in the auditory pathway.