Incomplete spinal cord injury promotes durable functional changes within the spinal locomotor circuitry

Abstract

While walking in a straight path, changes in speed result mainly from adjustments in the duration of the stance phase while the swing phase remains relatively invariant, a basic feature of the spinal central pattern generator (CPG). To produce a broad range of locomotor behaviors, the CPG has to integrate modulatory inputs from the brain and the periphery and alter these swing/stance characteristics. In the present work we raise the issue as to whether the CPG can adapt or reorganize in response to a chronic change of supraspinal inputs, as is the case after spinal cord injury (SCI). Kinematic data obtained from six adult cats walking at different treadmill speeds were collected to calculate the cycle and subphase duration at different stages after a first spinal hemisection at T(10) and after a subsequent complete SCI at T(13) respectively aimed at disconnecting unilaterally and then totally the spinal cord from its supraspinal inputs. The results show, first, that the neural control of locomotion is flexible and responsive to a partial or total loss of supraspinal inputs. Second, we demonstrate that a hemisection induces durable plastic changes within the spinal locomotor circuitry below the lesion. In addition, this study gives new insights into the organization of the spinal CPG for locomotion such that phases of the step cycle (swing, stance) can be independently regulated for adapting to speed and also that the CPGs controlling the left and right hindlimbs can, up to a point, be regulated independently.

Effect of Locomotor Training in Completely Spinalized Cats Previously Submitted to a Spinal Hemisection

“…As illustrated in Figures 6 and 7 (black circles and bars), the HL coupling values and mean AIs of the Untrained Group remained unchanged between the third week after hemisection and spinalization (ANOVA, p Ͼ 0.05). This result is in accordance with our recent study (Martinez et al, 2012) showing that when no training is performed after spinalization, the asymmetries observed after hemisection are maintained after spinalization indicating that the hemisection had promoted spontaneous intraspinal reorganizations.…”

“…The second spinal lesion, this time complete, disrupted the remnant supraspinal inputs to the spinal cord and aimed at revealing the instraspinal changes that occurred between the two lesions. As showed herein and in a recent paper (Martinez et al, 2012), locomotor characteristics observed 3 weeks after hemisection were retained for a long time after spinalization but, interestingly, only on the side of the previous hemisection (left side) while the right HL made adjustments to catch up with the left HL. This retention of changes on the left side indicated that the new mode of functioning observed after hemisection was imprinted within the spinal cord and is imputable to the first iSCI because the locomotor pattern was shown to remain unchanged in spinal animals that were not submitted to a previous partial SCI (Lovely et al, 1990).…”

“…This early reexpression of HL locomotion indicates that the first iSCI has promoted intrinsic changes within the spinal circuitry such that it was already primed to reexpress locomotion at high speeds after the spinalization. One of the most striking recent findings showed that some kinematic changes that occurred between the two spinal lesions were retained for at least 3 weeks after spinalization on the side of the previous hemisection (Martinez et al, 2012). This carryover indicates that mechanisms related to adaptation to the hemisection have imprinted the spinal cord probably in part through the action of remnant supraspinal pathways or persistent spinal changes.…”

“…A spinal hemisection was performed in 9 adult cats at thoracic level 10 (T10) and then a complete spinalization at T13, 3 weeks later (Martinez et al, , 2012. Cats were not trained but only assessed weekly.…”

Accuracy and precision of gait events derived from motion capture in horses during walk and trot

“…Kinematics of the distal limb could be of further potential (Moorman et al, 2012;Olsen et al, 2013). Motion capture and force plates have the potential to aid assessment of deficits in neuro-motor control on a spinal or supraspinal level because spatial and temporal characteristics are primarily controlled through the spinal and supra-spinal neural pathways (Martinez et al, 2012;Rossignol and Frigon, 2011). Classification of movement as normal, or abnormal, can be based on a combination of subjective clinical examination and objective analysis of gait (Keegan et al, 2012;Lord et al, 2013;Wren et al, 2011).…”