Data and code for: A Mechanism for Differential Control of Axonal and Dendritic Spiking Underlying Learning in a Cerebellum-like Circuit

In addition to the action potentials used for axonal signaling, many neurons generate dendritic 'spikes' associated with synaptic plasticity. However, in order to control both plasticity and signaling, synaptic inputs must be able to differentially modulate the firing of these two spike types. Here we investigate this issue in the electrosensory lobe (ELL) of weakly electric mormyrid fish, where separate control over axonal and dendritic spikes is essential for the transmission of learned predictive signals from inhibitory interneurons to the output stage of the circuit. Through a combination of experimental and modeling studies, we uncover a novel mechanism by which sensory input selectively modulates the rate of dendritic spiking by adjusting the amplitude of backpropagating axonal action potentials. Interestingly, this mechanism does not require spatially segregated synaptic inputs or dendritic compartmentalization, but relies instead on an electrotonically distant spike initiation site in the axon—a common biophysical feature of neurons.除了用于轴突信号传导的动作电位（action potentials）之外，众多神经元还会产生与突触可塑性（synaptic plasticity）相关的树突尖峰（dendritic spikes）。然而，若要同时调控突触可塑性与信号传导过程，突触输入必须能够差异化调节这两类尖峰的发放活动。本研究以弱电长颌鱼（weakly electric mormyrid fish）的电感觉叶（electrosensory lobe, ELL）为模型体系，对该问题展开探究——在此脑区中，对轴突与树突尖峰的独立调控，是将习得的预测信号从抑制性中间神经元（inhibitory interneurons）传递至环路输出阶段的关键环节。本研究结合实验与建模手段，揭示了一种全新的机制：感觉输入可通过调节反向传播的轴突动作电位（backpropagating axonal action potentials）的振幅，选择性调控树突尖峰的发放频率。值得注意的是，该机制无需依赖空间分隔的突触输入或树突区室化，而是依托于轴突上一处电紧张距离较远的尖峰起始位点（spike initiation site）——这是神经元普遍具备的一类生物物理特征。