Axons amplify somatic incomplete spikes into uniform amplitudes in mouse cortical pyramidal neurons.
BACKGROUND
Action potentials are the essential unit of neuronal encoding. Somatic sequential spikes in the central nervous system appear various in amplitudes. To be effective neuronal codes, these spikes should be propagated to axonal terminals where they activate the synapses and drive postsynaptic neurons. It remains unclear whether these effective neuronal codes are based on spike timing orders and/or amplitudes.


RESULTS
We investigated this fundamental issue by simultaneously recording the axon versus soma of identical neurons and presynaptic vs. postsynaptic neurons in the cortical slices. The axons enable somatic spikes in low amplitude be enlarged, which activate synaptic transmission in consistent patterns. This facilitation in the propagation of sequential spikes through the axons is mechanistically founded by the short refractory periods, large currents and high opening probability of axonal voltage-gated sodium channels.


CONCLUSIONS
An amplification of somatic incomplete spikes into axonal complete ones makes sequential spikes to activate consistent synaptic transmission. Therefore, neuronal encoding is likely based on spike timing order, instead of graded analogues.
Chen
Na
N
State Key Lab for Brain and Cognitive Sciences, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China.
Yu
Jiandong
J
Qian
Hao
H
Ge
Rongjing
R
Wang
Jin-Hui
JH
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D001369:Axons / Q000502:physiology*; D002540:Cerebral Cortex / Q000166:cytology*; D003198:Computer Simulation; D051379:Mice; D009474:Neurons / Q000166:cytology / Q000378:metabolism*; D017966:Pyramidal Cells / Q000166:cytology*