Kissane, RWP, Chakrabarty, S orcid.org/0000-0002-4389-8290, Askew, GN orcid.org/0000-0003-1010-4439 et al. (1 more author) (2022) Heterogeneity in form and function of the rat extensor digitorum longus motor unit. Journal of Anatomy, 240 (4). pp. 700-710. ISSN 0021-8782
Abstract
The motor unit comprises a variable number of muscle fibres that connect through myelinated nerve fibres to a motoneuron (MN), the central drivers of activity. At the simplest level of organisation there exist phenotypically distinct MNs that activate corresponding muscle fibre types, but within an individual motor pool there typically exists a mixed population of fast and slow firing MNs, innervating groups of Type II and Type I fibres, respectively. Characterising the heterogeneity across multiple levels of motor unit organisation is critical to understanding changes that occur in response to physiological and pathological perturbations. Through a comprehensive assessment of muscle histology and ex vivo function, mathematical modelling and neuronal tracing, we demonstrate regional heterogeneities at the level of the MN, muscle fibre type composition and oxygen delivery kinetics of the rat extensor digitorum longus (EDL) muscle. Specifically, the EDL contains two phenotypically distinct regions: a relatively oxidative medial and a more glycolytic lateral compartment. Smaller muscle fibres in the medial compartment, in combination with a greater local capillary density, preserve tissue O2 partial pressure (PO2) during modelled activity. Conversely, capillary supply to the lateral compartment is calculated to be insufficient to defend active muscle PO2 but is likely optimised to facilitate metabolite removal. Simulation of in vivo muscle length change and phasic activation suggest that both compartments are able to generate similar net power. However, retrograde tracing demonstrates (counter to previous observations) that a negative relationship between soma size and C-bouton density exists. Finally, we confirm a lack of specificity of SK3 expression to slow MNs. Together, these data provide a reference for heterogeneities across the rat EDL motor unit and re-emphasise the importance of sampling technique.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © 2021 The Authors. Journal of Anatomy published by John Wiley & Sons Ltd on behalf of Anatomical Society. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. |
Keywords: | capillary supply; motoneuron; oxygen modelling; skeletal muscle; work loop |
Dates: |
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Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Biological Sciences (Leeds) > School of Biomedical Sciences (Leeds) |
Funding Information: | Funder Grant number International Foundation for Research in Paraplegia P153 |
Depositing User: | Symplectic Publications |
Date Deposited: | 22 Nov 2021 11:54 |
Last Modified: | 03 Jan 2023 14:47 |
Status: | Published |
Publisher: | Wiley |
Identification Number: | 10.1111/joa.13590 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:180267 |
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