Input Signal Patterns Dominate a Plasticity of Spike-Onset Location at Cortical Pyramid Neurons through Local VGSCs

Abstract

Synaptic signals drive the neurons to fire sequential spikes as digital codes. Short-term pulses initiate a spike at the axonal hillock, and physiological signals may initiate digital spikes at the soma. The regulation, mechanism and impact for spike-onset relocation between subcellular compartments remain unknown, which we investigated by simultaneously recording the soma and axon of pyramidal neurons in cortical slices. By analyzing the abilities of firing spikes, the time phases of spike-onset and the relocations of spike-initiation at these two compartments, we have found that long-time steady depolarization induces sequential spikes at the soma, but fluctuated one induces spikes at the axon. The soma in response to long-time pulses shows low thresholds and short refractory periods, or vice versa. Compared with axonal voltage-gated sodium channels (VGSC), somatic VGSCs in response to a pre-depolarization appear less inactivated and easily reactivated. Based on these VGSC features, the location of spike-onset simulated in NEURON model is consistent with the experiments. The patterns of input signals dominate spike initiations at the axon or soma of cortical pyramidal neurons through influencing local VGSC function. The plasticity of spike-onset location allows the neurons to program the brain codes economically. [This study is supported by the National Award for Outstanding Young Scientist (30325021), National Basic Research Program (2011CB504405) and Natural Science Foundation China (30870517, 30990261 and 81171033) to JHW].