Electrical match between initial segment and somatodendritic compartment for action potential backpropagation in retinal ganglion cells

by Sarah Goethals, Martijn Christiaan Sierksma, Xavier Nicol, Annabelle Réaux-Le Goazigo, Romain Brette
Abstract:
The action potential of most vertebrate neurons initiates in the axon initial segment (AIS), and is then transmitted to the soma where it is regenerated by somatodendritic sodium channels. For successful transmission, the AIS must produce a strong axial current, so as to depolarize the soma to the threshold for somatic regeneration. Theoretically, this axial current depends on AIS geometry and Na+ conductance density. We measured the axial current of mouse retinal ganglion cells using whole-cell recordings with post-hoc AIS labeling. We found that this current is large, implying high Na+ conductance density, and carries a charge that co-varies with capacitance so as to depolarize the soma by  30 mV. Additionally, we observed that the axial current attenuates strongly with depolarization, consistent with sodium channel inactivation, but temporally broadens so as to preserve the transmitted charge. Thus, the AIS appears to be organized so as to reliably backpropagate the axonal action potential.
Reference:
Sarah Goethals, Martijn Christiaan Sierksma, Xavier Nicol, Annabelle Réaux-Le Goazigo, Romain Brette, 2021. Electrical match between initial segment and somatodendritic compartment for action potential backpropagation in retinal ganglion cells, Journal of Neurophysiology.
Bibtex Entry:
@article{Goethals2021,
author = {Goethals, Sarah and Sierksma, Martijn Christiaan and Nicol, Xavier and R{'e}aux-Le Goazigo, Annabelle and Brette, Romain},
title = {Electrical match between initial segment and somatodendritic compartment for action potential backpropagation in retinal ganglion cells},
journal = {Journal of Neurophysiology},
year = {2021},
doi = {10.1152/jn.00005.2021},
url = {https://www.biorxiv.org/content/10.1101/2020.09.15.297937v2.full.pdf},
abstract = { The action potential of most vertebrate neurons initiates in the axon initial segment (AIS), and is then transmitted to the soma where it is regenerated by somatodendritic sodium channels. For successful transmission, the AIS must produce a strong axial current, so as to depolarize the soma to the threshold for somatic regeneration. Theoretically, this axial current depends on AIS geometry and Na+ conductance density. We measured the axial current of mouse retinal ganglion cells using whole-cell recordings with post-hoc AIS labeling. We found that this current is large, implying high Na+ conductance density, and carries a charge that co-varies with capacitance so as to depolarize the soma by ~30 mV. Additionally, we observed that the axial current attenuates strongly with depolarization, consistent with sodium channel inactivation, but temporally broadens so as to preserve the transmitted charge. Thus, the AIS appears to be organized so as to reliably backpropagate the axonal action potential. }
}