The effects of common input characteristics and discharge rate on synchronization in rat hypoglossal motoneurones.
The effects of common input characteristics and discharge rate on synchronization in rat hypoglossal motoneurones.
复制标题
常见输入特征和放电速率对大鼠舌下运动神经元同步的影响。
DOI：
10.1113/jphysiol.2001.013097
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发表时间：
2002
期刊：
影响因子：
--
通讯作者：
Powers,RK
中科院分区：
文献类型：
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作者：
Türker,KS;Powers,RK
一对同时活跃的运动神经元之间的同步放电被认为是由这对神经元共享的突触输入的尖峰触发效应引起的。虽然有一些量化的指标，已被开发来估计这种常见的输入的强度，仍然有一些争论是否运动神经元放电率影响这些指标的值。本研究的目的是测试运动神经元放电率对这些同步化指标的影响，使用已知的共同输入。为了实现这一目标，我们引起了重复放电大鼠舌下神经运动神经元相结合的阈上注入电流步骤叠加噪声模仿突触驱动可能发生在生理激活。在不同的试验中改变电流阶跃的幅度，以实现5至22 Hz的放电速率。我们首先检查了放电速率对单个EPSP的尖峰触发功效的影响。运动神经元更响应于大的EPSPs在低速率时，他们的背景放电率是相对较低的，引起一个额外的尖峰的EPSPs的概率随着放电率的增加而下降。然而，对于小的高频EPSP，发现了相反的依赖性。然后，我们比较了在几次试验中获得的放电记录，在这些试验中，相同的EPSP序列被反复应用于相同的细胞在不同的背景放电率下放电。这种“共同输入”对运动神经元放电概率的影响是通过编制不同时间同一细胞放电之间的互相关直方图（CCHi s）来确定的。共同的输入诱导同步放电，引起了大的中央峰的CCHists。放电速率和同步水平之间的关系根据所使用的同步指数和共同EPSP的幅度而变化。当大的EPSP被用作公共输入时，同步尖峰的归一化概率随着放电率的增加而下降，无论使用何种归一化方法。相反，当共同输入由大量的小EPSP组成，类似于运动神经元的生理激活过程中可能发生的，不同的同步化指数表现出积极的，消极的或没有依赖于背景放电率。通过低频序列（E）中的放电次数或两个序列（S）中的放电总数对同步尖峰的数量进行标准化的指数显示出对背景放电率没有依赖性，因此可能最适合于在背景放电率范围内量化运动神经元的同步性。
Synchronous discharges between a pair of concurrently active motoneurones are thought to arise from the spike‐triggering effects of synaptic inputs shared by the pair. Although there are a number of quantitative indices that have been developed to estimate the strength of this common input, there is still some debate as to whether motoneurone discharge rate affects the values of these indices. The aim of the present study was to test the effects of motoneurone discharge rate on these synchronization indices using known common inputs. To achieve this aim we elicited repetitive discharge in rat hypoglossal motoneurones by combining a suprathreshold injected current step with superimposed noise to mimic the synaptic drive likely to occur during physiological activation. The amplitude of the current step was varied in different trials to achieve discharge rates from 5 to 22 Hz. We first examined the effect of discharge rate on the spike‐triggering efficacy of individual EPSPs. Motoneurones were more responsive to large EPSPs delivered at a low rate when their background discharge rate was relatively low and the probability of the EPSPs evoking an extra spike decreased with increasing discharge rate. However, the opposite dependence was found for small, high‐frequency EPSPs. We then compared the discharge records obtained in several trials in which the same EPSP train was applied repeatedly to the same cell firing at different background discharge rates. The effect of this ‘common input’ on motoneurone discharge probability was determined by compiling cross‐correlation histograms (CCHists) between the discharges of the same cell at different times. The common inputs induced synchronous discharge that gave rise to large central peaks in the CCHists. The relationship between the discharge rate and the level of synchronization changed depending on the synchronization indices used and the amplitude of the common EPSPs. When large EPSPs were used as the common input, the normalized probability of synchronous spikes declined as the discharge rate increased, regardless of the method of normalization used. In contrast, when the common input was composed of a large number of small EPSPs, similar to that likely to occur during physiological activation of motoneurones, different synchronization indices exhibited a positive, a negative or no dependence on the background discharge rate. Indices based on normalizing the number of synchronous spikes by either the number of discharges in the lower frequency train (E), or by the total number of discharges in both trains (S) showed no dependence on background discharge rate and therefore may be the most suitable for quantifying motoneurone synchrony over a range of background discharge rates.