Selective gating of neuronal activity by intrinsic properties in distinct motor rhythms
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Many neural circuits show fast reconfiguration following altered sensory or modulatory inputs to generate stereotyped outputs. In the motor circuit of Xenopus tadpoles, I study how certain voltage-dependent ionic currents affect firing thresholds and contribute to circuit reconfiguration to generate two distinct motor patterns, swimming and struggling. Firing thresholds of excitatory interneurons [i.e., descending interneurons (dINs)] in the swimming central pattern generator are raised by depolarization due to the inactivation of Na+ currents. In contrast, the thresholds of other types of neurons active in swimming or struggling are raised by hyperpolarization from the activation of fast transient K+ currents. The firing thresholds are then compared with the excitatory synaptic drives, which are revealed by blocking action potentials intracellularly using QX314 during swimming and struggling. During swimming, transient K+ currents lower neuronal excitability and gate out neurons with weak excitation, whereas their inactivation by strong excitation in other neurons increases excitability and enables fast synaptic potentials to drive reliable firing. During struggling, continuous sensory inputs lead to high levels of network excitation. This allows the inactivation of Na+ currents and suppression of dIN activity while inactivating transient K+ currents, recruiting neurons that are not active in swimming. Therefore, differential expression of these currents between neuron types can explain why synaptic strength does not predict firing reliability/intensity during swimming and struggling. These data show that intrinsic properties can override fast synaptic potentials, mediate circuit reconfiguration, and contribute to motor–pattern switching.
Li , W-C 2015 , ' Selective gating of neuronal activity by intrinsic properties in distinct motor rhythms ' , The Journal of Neuroscience , vol. 35 , no. 27 , pp. 9799-9810 . https://doi.org/10.1523/JNEUROSCI.0323-15.2015
The Journal of Neuroscience
Copyright © 2015 Li. This is an Open Access article distributed under the terms of the Creative Commons Attribution License Creative Commons Attribution 4.0 International (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution and reproduction in any medium provided that the original work is properly attributed.
DescriptionThis research has been supported by the Royal Society, Wellcome Trust (089319), and the Biotechnology and Biological Sciences Research Council (BB/L0011X/1). I thank Drs. Steve Soffe, Alan Roberts, Erik Svensson, Hong-Yan Zhang, and Stefan Pulver for commenting on the manuscript.
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