Christian Leukel1, Wolfgang Taube2, Jörn Rittweger3, Albert Gollhofer4, Michel Ducos3, Tobias Weber3, Jesper Lundbye-Jensen5. 1. Department of Medicine, Movement and Sport Science, University of Fribourg, Switzerland. Electronic address: christian.leukel@unifr.ch. 2. Department of Medicine, Movement and Sport Science, University of Fribourg, Switzerland. 3. German Aerospace Centre, Institute of Aerospace Medicine, Division Space Physiology, Cologne, Germany. 4. Department of Sport Science, University of Freiburg, Germany. 5. Department of Nutrition, Exercise and Sports, University of Copenhagen, Denmark; Department of Neuroscience and Pharmacology, University of Copenhagen, Denmark.
Abstract
OBJECTIVES: Joint immobilization has previously been shown to modulate corticospinal excitability. The present study investigated changes in the excitability of distinct fractions of the corticospinal pathway by means of conditioning the H-reflex with transcranial magnetic stimulation (TMS) of the primary motor cortex (Hcond). This method allows assessment of transmission in fast (monosynaptic) and slow(er) (polysynaptic) corticospinal pathways. METHODS: 9 subjects underwent 8weeks of unilateral ankle joint immobilization during daytime, 7 subjects served as controls. The measures obtained before and after immobilization included stretch- and H-reflexes assessing excitability of the spinal reflex circuitries, TMS recruitment curves estimating overall changes in corticospinal excitability, and Hcond. RESULTS: TMS recruitment curves showed an overall increase in corticospinal excitability following immobilization. Importantly, Hcond revealed significant facilitation of conditioned reflexes, but only for longer conditioning intervals, suggesting that immobilization increased excitability only of slower, indirect corticospinal pathways. No changes were observed in the control group. Immobilization had no significant effects on spinal reflex measures. CONCLUSIONS: 8weeks of ankle joint immobilization was accompanied by pathway-specific modulation of corticospinal transmission. SIGNIFICANCE: It is particularly interesting that fast corticospinal projections were unaffected as these are involved in controlling many, if not most, movements in humans.
OBJECTIVES: Joint immobilization has previously been shown to modulate corticospinal excitability. The present study investigated changes in the excitability of distinct fractions of the corticospinal pathway by means of conditioning the H-reflex with transcranial magnetic stimulation (TMS) of the primary motor cortex (Hcond). This method allows assessment of transmission in fast (monosynaptic) and slow(er) (polysynaptic) corticospinal pathways. METHODS: 9 subjects underwent 8weeks of unilateral ankle joint immobilization during daytime, 7 subjects served as controls. The measures obtained before and after immobilization included stretch- and H-reflexes assessing excitability of the spinal reflex circuitries, TMS recruitment curves estimating overall changes in corticospinal excitability, and Hcond. RESULTS: TMS recruitment curves showed an overall increase in corticospinal excitability following immobilization. Importantly, Hcond revealed significant facilitation of conditioned reflexes, but only for longer conditioning intervals, suggesting that immobilization increased excitability only of slower, indirect corticospinal pathways. No changes were observed in the control group. Immobilization had no significant effects on spinal reflex measures. CONCLUSIONS: 8weeks of ankle joint immobilization was accompanied by pathway-specific modulation of corticospinal transmission. SIGNIFICANCE: It is particularly interesting that fast corticospinal projections were unaffected as these are involved in controlling many, if not most, movements in humans.
Authors: Hamidollah Hassanlouei; Christopher W Sundberg; Ashleigh E Smith; Andrew Kuplic; Sandra K Hunter Journal: J Appl Physiol (1985) Date: 2017-05-11
Authors: Vianney Rozand; Jonathon W Senefeld; Christopher W Sundberg; Ashleigh E Smith; Sandra K Hunter Journal: J Neurophysiol Date: 2019-05-15 Impact factor: 2.714