Redistribution of inhibitory force feedback between a long toe flexor and the major ankle extensor muscles following spinal cord injury

• Type of Material: Article
• Authors: Irrum F Niazi, Georgia Institute of Technology; Mark Lyle, Emory University; Aaron Rising, University of Louisville; Dena R Howland, University of Louisville; Richard T Nichols, Georgia Institute of Technology
• Language: English
• Date: 2020-08-01
• Publisher: WILEY
• Publication Version: Author Accepted Manuscript (After Peer Review)
• Copyright Statement: Published 2020. This article is a U.S. Government work and is in the public domain in the USA.
• Final Published Version (URL): http://dx.doi.org/10.1002/jnr.24630
• Title of Journal or Parent Work: JOURNAL OF NEUROSCIENCE RESEARCH
• Volume: 98
• Issue: 8
• Start Page: 1646
• End Page: 1661
• Grant/Funding Information: Research reported in this publication was supported by NIH NINDS F32NS080393 (MAL), NICHD HD32571 (TRN), NINDS NS097781 (DRH, TRN), VA RR&D B9249S (DRH), B7165-R (DRH), B2316-R (DRH, TRN) and Rebecca F. Hammond Endowment (DRH). Disclaimer: The manuscript content is solely the responsibility of the authors and does not necessarily represent the official views of the Department of Veterans Affairs, National Institutes of Health or the United States Government.
• Keywords: spinal reflex; Golgi tendon organs; Neurosciences & Neurology; MECHANICAL ACTIONS; TRICEPS SURAE MUSCLES; CLASP-KNIFE REFLEX; LOW THORACIC HEMISECTION; spinal hemisection; Science & Technology; Life Sciences & Biomedicine; Neurosciences; SOLEUS MUSCLE; HINDLIMB EXTENSORS; HETEROGENIC REFLEXES; spinal circuitry; GROUP IB; LOCOMOTION; CUTANEOUS REFLEXES; feline

Abstract

Inhibitory pathways from Golgi tendon organs project widely between muscles crossing different joints and axes of rotation. Evidence suggests that the strength and distribution of this intermuscular inhibition is dependent on motor task and corresponding signals from the brainstem. The purpose of the present study was to investigate whether this sensory network is altered after spinal cord hemisection as a potential explanation for motor deficits observed after spinal cord injury (SCI). Force feedback was assessed between the long toe flexor and ankle plantarflexor (flexor hallucis longus), and the three major ankle extensors, (combined gastrocnemius, soleus, and plantaris muscles) in the hind limbs of unanesthetized, decerebrate, female cats. Data were collected from animals with intact spinal cords (control) and lateral spinal hemisections (LSHs) including chronic LSH (4–20 weeks), subchronic LSH (2 weeks), and acute LSH. Muscles were stretched individually and in pairwise combinations to measure intermuscular feedback between the toe flexor and each of the ankle extensors. In control animals, three patterns were observed (balanced inhibition between toe flexor and ankle extensors, stronger inhibition from toe flexor to ankle extensor, and vice versa). Following spinal hemisection, only strong inhibition from toe flexors onto ankle extensors was observed independent of survival time. The results suggest immediate and permanent reorganization of force feedback in the injured spinal cord. The altered strength and distribution of force feedback after SCI may be an important future target for rehabilitation.