Yarden-Rabinowitz Yasmin, Yarom Yosef
Department of Neurobiology, Silberman Institute of Life Sciences and Edmond & Lily Safra Center for Brain Sciences (ELSC), The Hebrew University, 91904, Jerusalem, Israel.
J Physiol. 2017 Sep 1;595(17):5945-5963. doi: 10.1113/JP274115. Epub 2017 Jul 26.
Cerebellar nuclei (CN) neurons can be classified into four groups according to their action potential (AP) waveform, corresponding to four types of neurons previously characterized. Half of the APs are generated by excitatory events, suggesting that excitatory inputs play a key role in generating CN outputs. Analysis of post-synaptic potentials reveals that the probability of excitatory inputs generating an AP is 0.1. The input from climbing fibre collaterals is characterized by a pair of synaptic potentials with a distinct interpair interval of 4.5 ms. The probability of climbing fibre collaterals initiating an AP in CN neurons is 0.15.
It is commonly agreed that the main function of the cerebellar system is to provide well-timed signals used for the execution of motor commands or prediction of sensory inputs. This function is manifested as a temporal sequence of spiking that should be expressed in the cerebellar nuclei (CN) projection neurons. Whether spiking activity is generated by excitation or release from inhibition is still a hotly debated issue. In an attempt to resolve this debate, we recorded intracellularly from CN neurons in anaesthetized mice and performed an analysis of synaptic activity that yielded a number of important observations. First, we demonstrate that CN neurons can be classified into four groups. Second, shape-index plots of the excitatory events suggest that they are distributed over the entire dendritic tree. Third, the rise time of excitatory events is linearly related to amplitude, suggesting that all excitatory events contribute equally to the generation of action potentials (APs). Fourth, we identified a temporal pattern of spontaneous excitatory events that represent climbing fibre inputs and confirm the results by direct stimulation and analysis on harmaline-evoked activity. Finally, we demonstrate that the probability of excitatory inputs generating an AP is 0.1 yet half of the APs are generated by excitatory events. Moreover, the probability of a presumably spontaneous climbing fibre input generating an AP is higher, reaching a mean population value of 0.15. In view of these results, the mode of synaptic integration at the level of the CN should be re-considered.
小脑核（CN）神经元可根据其动作电位（AP）波形分为四组，这与先前鉴定的四种神经元类型相对应。一半的动作电位由兴奋性事件产生，这表明兴奋性输入在产生CN输出中起关键作用。对突触后电位的分析表明，兴奋性输入产生动作电位的概率为0.1。攀缘纤维侧支的输入特征是一对突触电位，其独特的成对间隔为4.5毫秒。攀缘纤维侧支在CN神经元中引发动作电位的概率为0.15。
人们普遍认为，小脑系统的主要功能是提供用于执行运动指令或预测感觉输入的适时信号。该功能表现为一连串的尖峰放电，应在小脑核（CN）投射神经元中体现。尖峰放电活动是由兴奋产生还是由抑制释放产生，仍然是一个备受争议的问题。为了解决这一争议，我们在麻醉小鼠的CN神经元中进行了细胞内记录，并对突触活动进行了分析，得出了一些重要发现。首先，我们证明CN神经元可分为四组。其次，兴奋性事件的形状指数图表明它们分布在整个树突树上。第三，兴奋性事件的上升时间与幅度呈线性相关，这表明所有兴奋性事件对动作电位（AP）的产生贡献相同。第四，我们确定了代表攀缘纤维输入的自发兴奋性事件的时间模式，并通过对harmaline诱发活动的直接刺激和分析证实了结果。最后，我们证明兴奋性输入产生动作电位的概率为0.1，但一半的动作电位由兴奋性事件产生。此外，推测为自发的攀缘纤维输入产生动作电位的概率更高，平均群体值达到0.15。鉴于这些结果，应重新考虑CN水平的突触整合模式。
