Plastic Changes in Lumbar Locomotor Networks after a Partial Spinal Cord Injury in Cats

Abstract

After an incomplete spinal cord injury (SCI), we know that plastic reorganization occurs in supraspinal structures with residual descending tracts. However, our knowledge about spinal plasticity is rather limited. Our recent studies point to changes within the spinal cord below the lesion. After a lateral left hemisection (T10), cats recovered stepping with both hindlimbs within 3 weeks. After a complete section (T13) in these cats, bilateral stepping was seen on the next day, a skill usually acquired after several weeks of treadmill training. This indicates that durable plastic changes occurred below the lesion. However, because sensory feedback entrains the stepping rhythm, it is difficult to reveal central pattern generator (CPG) adaptation. Here, we investigated whether lumbar segments of cats with a chronic hemisection were able to generate fictive locomotion-that is, without phasic sensory feedback as monitored by five muscle nerves in each hindlimb. With a chronic left hemisection, the number of muscle nerves displaying locomotor bursts was larger on the left than on the right. In addition, transmission of cutaneous reflexes was relatively facilitated on the left. Later during the acute experiment, a complete spinalization (T13) was performed and clonidine was injected to induce rhythmic activities. There were still more muscle nerves displaying locomotor bursts on the left. The results demonstrate that spinal networks were indeed modified after a hemisection with a clear asymmetry between left and right in the capacity to generate locomotion. Plastic changes in CPG and reflex transmission below the lesion are thus involved in the stepping recovery after an incomplete SCI.

Hindlimb motor responses to unilateral brain injury: spinal cord encoding and left-right asymmetry

“…They demonstrated that a hemicerebellar lesion causes lasting changes in spinal cord functions manifested as the ipsilesional hindlimb flexion and that the hindlimb postural asymmetry (HL-PA) is retained after complete spinal transection. Consistently, monosynaptic and polysynaptic reflexes are enhanced on the ipsilateral side after lateral hemisection of the spinal cord, and this change is sustained after complete spinal transection performed caudally to the hemisection level ( Hultborn and Malmsten, 1983 a , b ; Malmsten, 1983 ; Frigon et al , 2009 ; Rossignol and Frigon, 2011 ; Gossard et al , 2015 ). The HL-PA is an attractive animal model to unravel mechanisms of pathological ‘spinal memory’, which may underlie asymmetric motor deficits including hemiplegia and hemiparesis.…”

Rehabilitation Strategies after Spinal Cord Injury: Inquiry into the Mechanisms of Success and Failure

“…132 Although the concept of a CPG for locomotion is generally accepted in both animals and humans, 33,133 its interneuronal composition is only partly described and little is known about the effects of SCI and step-training on spinal interneurons, particularly in primates. 134 Recent electrophysiological data support the concept that trainingdependent plasticity does indeed occur within the CPG, [135][136][137] as well as in reflex pathways 13,14 and muscle spindles. 15 The specific nature of the changes in CPG interneurons is unknown and warrants further investigation in both animals and humans (Fig.…”

Current Principles of Motor Control, with Special Reference to Vertebrate Locomotion

“…The Rossignol laboratory designed an elegant way of showing that the spinal CPG itself is subject to plasticity (38,157,176,193,325). They hemisected the spinal cord at lower thoracic level, and bilateral locomotor activity rapidly recovered.…”