Niven J E, Burrows M
Department of Zoology, University of Cambridge, Cambridge CB2 3EJ, United Kingdom.
J Neurosci. 2003 Aug 20;23(20):7461-9. doi: 10.1523/JNEUROSCI.23-20-07461.2003.
Short-term synaptic depression is an important component of computation within neural networks, but little is known of its contribution to information processing during synaptically generated spike trains. We analyzed short-term synaptic depression at a synapse between two identified motoneurons innervating the hind leg of the locust: the FETi-FlTi synapse (fast extensor tibiae-flexor tibiae). Brief electrical stimulation of a single hind leg proprioceptor, the lump receptor (LR), led to prolonged sequences of spikes in FETi, similar in number and frequency to those during natural kicking movements. Depression at the FETi-FlTi synapse during LR-evoked spike bursts was compared quantitatively to that during antidromic spike trains evoked by electrical stimulation of FETi in the extensor tibiae muscle, and by modeling. The magnitude of the short-term depression was significantly greater during LR-evoked spike trains. On the basis of the model parameters required to fit the depression, the FETi-FlTi synapse is predominantly used for transmitting the timing of the onset of FETi spiking rather than its spike rate. During LR-evoked spike trains, there was a rapid reduction in presynaptic spike width that did not occur during antidromic spike trains under physiological calcium concentrations. This produced a concomitant reduction in the amplitude of the FlTi EPSP, suggesting that it contributed to the differences between the two stimulation regimes. Differences in the short-term depression between synaptically evoked and antidromic spike trains emphasize that the properties of synaptic information transfer are dependent on the in vivo conditions at the synapse and may not be reproduced by in vitro spike trains.
短期突触抑制是神经网络计算的重要组成部分，但对于其在突触产生的尖峰序列期间对信息处理的贡献却知之甚少。我们分析了蝗虫后肢两个已鉴定的运动神经元之间突触处的短期突触抑制：FETi-FlTi突触（快速胫节伸肌-胫节屈肌）。对单个后肢本体感受器（肿块感受器，LR）进行短暂电刺激，会导致FETi中出现延长的尖峰序列，其数量和频率与自然踢腿运动期间的相似。在LR诱发的尖峰爆发期间，对FETi-FlTi突触处的抑制与通过电刺激胫节伸肌中的FETi诱发的逆向尖峰序列期间以及通过建模得到的抑制进行了定量比较。在LR诱发的尖峰序列期间，短期抑制的幅度明显更大。根据拟合抑制所需的模型参数，FETi-FlTi突触主要用于传递FETi尖峰开始的时间，而不是其尖峰频率。在LR诱发的尖峰序列期间，突触前尖峰宽度迅速减小，而在生理钙浓度下的逆向尖峰序列期间则不会出现这种情况。这导致FlTi兴奋性突触后电位（EPSP）的幅度随之降低，表明这促成了两种刺激方式之间的差异。突触诱发的尖峰序列和逆向尖峰序列之间短期抑制的差异强调，突触信息传递的特性取决于突触处的体内条件，并且可能无法通过体外尖峰序列来再现。
