A modeling study of spinal motoneuron recruitment regulated by ionic channels during fictive locomotion
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A modeling study of spinal motoneuron recruitment regulated by ionic channels during fictive locomotion Qiang Zhang 1 & Yue Dai 1,2 Received: 31 January 2020 / Revised: 31 July 2020 / Accepted: 6 August 2020 # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract During fictive locomotion cat lumbar motoneurons exhibit changes in membrane proprieties including a decrease in voltage threshold (Vth), afterhyperpolarization (AHP) and input resistance (Rin) and an increase in non-linear membrane property. The impact of these changes on the motoneuron recruitment remains unknown. Using modeling approach we investigated the channel mechanism regulating the motoneuron recruitment. Three types of motoneuron pools including slow (S), fatigue-resistant (FR) and fast-fatigable (FF) motoneurons were constructed based on the membrane proprieties of cat lumbar motoneurons. The transient sodium (NaT), persistent sodium (NaP), delayed-rectifier potassium [K(DR)], Ca2+-dependent K+ [K(AHP)] and Ltype calcium (CaL) channels were included in the models. Simulation results showed that (1) Strengthening synaptic inputs increased the number of recruitments in all three types of motoneurons following the size principle. (2) Increasing NaT or NaP or decreasing K(DR) or K(AHP) lowered rheobase of spike generation thus increased recruitment of motoneuron pools. (3) Decreasing Rin reduced recruitment in all three types of motoneurons. (4) The FF-type motoneuron pool, followed by FR- and S-type, were the most sensitive to increase of synaptic inputs, reduction of Rin, upregulation of NaT and NaP, and downregulation of K(DR) and K(AHP). (5) Increasing CaL enhanced overall discharge rate of motoneuron pools with little effect on the recruitment. Simulation results suggested that modulation of ionic channels altered the output of motoneuron pools with either modulating the number of recruited motoneurons or regulating the overall discharge rate of motoneuron pools. Multiple channels contributed to the recruitment of motoneurons with interaction of excitatory and inhibitory synaptic inputs during walking. Keywords Modeling . Motoneuron recruitment . Motor control . Neuromodulation
1 Introduction Locomotion in mammals is generated by spinal cord network known as central pattern generator (CPG). This network can be simplified as a two-level CPG including separate half-center rhythm generator (RG) and pattern formation (PF) (Mccrea et al. 2007). The CPG controls the motoneuron pools that regulate flexor and extensor (Mccrea et al. 2007; Rybak et al. 2006). Action Editor: Steve I. Perlmutter * Yue Dai [email protected] 1
Shanghai Key Laboratory of Multidimensional Information Processing, School of Communication and Electronic Engineering, East China Normal University, Shanghai 200241, China
2
Key Laboratory of Adolescent Health Assessment and Exercise Intervention of Ministry of Education, School of Physical Education and Health Care, East China Normal University, Shanghai 200241, China
Motoneuron pool recruitment is a
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