Neuroscience

Operation of spinal sensorimotor circuits controlling phase durations during tied-belt and split-belt locomotion after a lateral thoracic hemisection

Ilya A Rybak author has email address
Natalia A Shevtsova
Johannie Audet
Sirine Yassine
Sergey N Markin
Boris I Prilutsky
Alain Frigon author has email address

Department of Neurobiology and Anatomy, College of Medicine, Drexel University, Philadelphia, USA
Department of Pharmacology-Physiology, Faculty of Medicine and Health Sciences, Centre de Recherche du CHUS, Université de Sherbrooke, Sherbrooke, Canada
School of Biological Sciences, Georgia Institute of Technology, Atlanta, USA

https://doi.org/10.7554/eLife.103504.1

Open access
Copyright information

Figures and data

Model of spinal circuits controlling treadmill locomotion.
A. Model of the intact system (“intact model”). The model includes two bilaterally located (left and right) RGs (each is similar to that shown in Rybak et al., 2024, Fig. 3C) coupled by (interacting via) several commissural pathways mediated by genetically identified commissural (V0_D, V0_V, and V3) and ipsilaterally projecting excitatory (V2a) and inhibitory neurons (see text for details). Left and right excitatory supraspinal drives (α_L and α_R) provide activation for the flexor half-centers (F) of the RGs (ipsi- and contralaterally) and some interneuron populations in the model, as well as for the extensor half-centers (E) (γ_L and γ_R ipsilaterally). Two types of feedback (SF-E1 and SF-E2) operating during extensor phases affect (excite), respectively, the ipsilateral F (SF-E1) and E (SF-E2) half-centers, and through V3-E neurons affect contralateral RGs. The SF-E1 feedback depends on the speed of the ipsilateral “belt” (β_L or β_R) and contributes to the extension-to-flexion transition on the ipsilateral side. The SF-E2 feedback activates the ipsilateral E half-center and contributes to “weight support” on the ipsilateral side. The ipsilateral excitatory drives (α_L and α_R) suppress the effects of all ipsilateral feedback inputs by presynaptic inhibition. The detailed description and all model parameters can be found in the preceding paper (Rybak et al., 2024). B. Model of the right-hemisected system. All supraspinal drives on the right side (and their suppression of sensory feedback from the right limb) are eliminated from the schematic shown in A.

Simulation of locomotion on a tied-belt treadmill using the right-hemisected model.
A1 and A2. Changes in the durations of cycle period and extensor/stance and flexor/swing phases during simulated tied-belt locomotion on the left contralesional (A1) and right ipsilesional (A2) sides of the model with an increasing simulated treadmill speed. B1 and B2. The curves from panels A1 and A2 for the hemisected model are superimposed with the corresponding curves obtained from the intact model (modified from Rybak et al., 2024, Fig. 5A)

Simulation of locomotion on a split-belt treadmill using the right-hemisected model in the Left slow/Right fast condition, with the ipsilesional hindlimb stepping on the fast belt.
A1 and A2. Changes in the durations of cycle period and extensor/stance and flexor/swing phases during simulated split-belt locomotion on the left contralesional (A1) and right ipsilesional (A2) sides of the model. B1 and B2. The curves from panels A1 and A2 for the hemisected model are superimposed with the corresponding curves obtained from the intact model (modified from Rybak et al., 2024, Fig. 5A)

Simulation of locomotion on a split-belt treadmill using the right-hemisected model in the Left fast/Right slow conditions, with the ipsilesional hindlimb stepping on the slow belt.
A1 and A2. Changes in the durations of locomotor period and extensor/stance and flexor/swing phases during simulated split-belt locomotion on the left contralesional (A1) and right ipsilesional (A2) sides of the model. B1 and B2. The curves from panels A1 and A2 for the hemisected model are superimposed with the corresponding curves obtained from the intact model (modified from Rybak et al., 2024, Fig. 5A).

Cycle and phase durations before and after a right thoracic lateral hemisection in cats walking on a tied-belt treadmill.
A1 and A2. Changes in the durations of cycle period and stance and swing phases during tied-belt locomotion in intact cats (before hemisection). B1 and B2. The same characteristics obtained from cats 7-8 weeks after a right lateral thoracic hemisection. C1 and C2. The curves from panel B1 and B2 for hemisected cats are superimposed (for comparison) with the corresponding curves (A1 and A2) obtained from intact cats.

Cycle and phase durations before and after a right thoracic lateral hemisection in cats walking on a split-belt treadmill in the Left slow/Right fast condition, with the ipsilesional hindlimb stepping on the fast belt.
A1 and A2. Changes in the durations of cycle period and stance and swing phases during split-belt locomotion in intact cats (before hemisection). B1 and B2. The same characteristics obtained from cats 7-8 weeks after a right lateral thoracic hemisection. C1 and C2. The curves from panel B1 and B2 for injured cats are superimposed (for comparison) with the corresponding curves (A1 and A2) obtained from intact cats.

Cycle and phase durations before and after a right thoracic lateral hemisection in cats walking on a split-belt treadmill in the Left fast/Right slow condition, with the ipsilesional hindlimb stepping on the slow belt.
A1 and A2. Changes in the durations of cycle period and stance and swing phases during split-belt locomotion in intact cats (before hemisection). B1 and B2. The same characteristics obtained from cats 7-8 weeks after a right lateral thoracic hemisection. C1 and C2. The curves from panel B1 and B2 for injured cats are superimposed (for comparison) with the corresponding curves (A1 and A2) obtained from intact cats.

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