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Non-uniform upregulation of the autogenic stretch reflex among hindlimb extensors following lateral spinal lesion in the cat

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Abstract

Successful propagation throughout the step cycle is contingent on adequate regulation of whole-limb stiffness by proprioceptive feedback. Following spinal cord injury (SCI), there are changes in the strength and organization of proprioceptive feedback that can result in altered joint stiffness. In this study, we measured changes in autogenic feedback of five hindlimb extensor muscles following chronic low thoracic lateral hemisection (LSH) in decerebrate cats. We present three features of the autogenic stretch reflex obtained using a mechanographic method. Stiffness was a measure of the resistance to stretch during the length change. The dynamic index documented the extent of adaptation or increase of the force response during the hold phase, and the impulse measured the integral of the response from initiation of a stretch to the return to the initial length. The changes took the form of variable and transient increases in the stiffness of vastus (VASTI) group, soleus (SOL), and flexor hallucis longus (FHL), and either increased (VASTI) or decreased adaptation (GAS and PLANT). The stiffness of the gastrocnemius group (GAS) was also variable over time but remained elevated at the final time point. An unexpected finding was that these effects were observed bilaterally. Potential reasons for this finding and possible sources of increased excitability to this muscle group are discussed.

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Acknowledgements

Some of the work reported in this paper comprised part of a dissertation (Kajtaz 2019). The authors would like to acknowledge contributions of Drs. B. Prilutsky, A. Kilshko, and R. Mehta, who generously provided control animals and invaluable expertise. The authors wish to thank Drs. M.A. Lyle, R. Noel, and C. Tuthill for their help with terminal experiments, K.A. Cheffer and W.J.R. O’Steen for their help with survival surgeries, Dr. M.D. Reed and J.M. Nanney for thoughtful comments on the manuscript and graphical assistance, and Darlene Burke for advising on a statistical approach. We also thank Dr. T.C. Cope for valuable discussions on the interpretation of these results.

Funding

This work was supported by the National Institutes of Health NS097781 and Veterans Administration I01RX002316 & B9249S, and the Rebecca F. Hammond Endowment.

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Contributions

The analyses used in this study were designed by EK as part of a larger program of study on spinal cord injury directed by DRH and TRN. Acquisition of data was completed by all authors, data analysis was performed by EK, and all authors contributed to the interpretation. The first draft of the manuscript was written by EK and all authors contributed to subsequent versions of the manuscript. All authors read and approved the final manuscript.

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Correspondence to T. Richard Nichols.

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The authors declare no conflicts of interest.

Ethics approval

All procedures were completed in accordance with the guidelines from the National Institute of Health and protocols approved by the Institutional Animal Care and Use Committee of Georgia Institute of Technology, the University of Louisville, and the Robley Rex VA Medical Center.

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The software was written in Matlab© and is available given a reasonable request.

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Communicated by Winston D. Byblow.

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Kajtaz, E., Montgomery, L.R., McMurtry, S. et al. Non-uniform upregulation of the autogenic stretch reflex among hindlimb extensors following lateral spinal lesion in the cat. Exp Brain Res 239, 2679–2691 (2021). https://doi.org/10.1007/s00221-020-06016-1

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  • DOI: https://doi.org/10.1007/s00221-020-06016-1

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