Training-induced plasticity in rats with cervical spinal cord injury: Effects and side effects

Kinematic analyses reveal impaired locomotion following injury of the motor cortex in mice

Brain injury in the motor cortex can result in deleterious functional deficits of skilled and fine motor functions. However, in contrast to humans, the destruction of cortex and its descending fibers has been thought not to cause remarkable deficits in simple locomotion in quadropedal animals. In the present study, we aimed to investigate in detail how lesion of the sensorimotor cortex affected locomotion ability in mice using the KinemaTracer system, a novel video-based kinematic analyzer. We found that traumatic injury to the left sensorimotor cortex induced several apparent deficits in the movement of contralesional right limbs during treadmill locomotion. The step length of right limbs decreased, and the speed in the forward direction was abrogated in the swing phase. The coordinates and angle of each joint were also changed after the injury. Some of the abnormal values in these parameters gradually recovered near the control level. The number of cFos-expressing neurons following locomotion significantly decreased in the right side of the spinal cord in injured mice, suggesting a role for cortex and descending fibers in locomotion. In contrast, interlimb coordination did not change remarkably even after the injury, supporting the notion that the basic locomotor pattern was determined by intraspinal neural circuits. These results indicate that the motor cortex and its descending fibers regulate several aspects of fine limb movement during locomotion. Our findings provide practical parameters to assess motor deficits and recovery following cortical injury in mice.

Anti-Nogo-A and training: can one plus one equal three?

Following spinal cord injury (SCI) the adult central nervous system (CNS) has a limited but substantial capacity for repair and plastic reorganisation. The degree of reorganisation is determined by a number of factors such as the extent and location of the lesion, the remaining circuit activity within the CNS and the age at injury. However, even in the best cases this spontaneous reorganisation does not lead to full recovery of the affected behaviour but instead often results in a functionally successful but compensatory strategy. Current SCI research focuses on enhancing fibre tract (re-)growth and recovery processes. Two currently promising approaches are the neutralisation of CNS growth inhibitory factors, and rehabilitative training of remaining networks. Independently, both approaches can lead to substantial functional recovery and anatomical reorganisation. In this review we focus on Nogo-A, a neurite growth inhibitory protein present in the adult CNS, and its role in regenerative and plastic growth following SCI. We then discuss the efforts of rehabilitative training and the potential combination of the two therapies.

Chondroitinase ABC promotes recovery of adaptive limb movements and enhances axonal growth caudal to a spinal hemisection

A number of studies have shown that chondroitinase ABC (Ch'ase ABC) digestion of inhibitory chondroitin sulfate glycosaminoglycans significantly enhances axonal growth and recovery in rodents following spinal cord injury (SCI). Further, our group has shown improved recovery following SCI in the larger cat model. The purpose of the current study was to determine whether intraspinal delivery of Ch'ase ABC, following T10 hemisections in adult cats, enhances adaptive movement features during a skilled locomotor task and/or promotes plasticity of spinal and supraspinal circuitry. Here, we show that Ch'ase ABC enhanced crossing of a peg walkway post-SCI and significantly improved ipsilateral hindlimb trajectories and integration into a functional forelimb-hindlimb coordination pattern. Recovery of these complex movements was associated with significant increases in neurofilament immunoreactivity immediately below the SCI in the ipsilateral white (p = 0.033) and contralateral gray matter (p = 0.003). Further, the rubrospinal tract is critical in the normal cat during skilled movements that require accurate paw placements and trajectories like those seen during peg walkway crossing. Rubrospinal connections were assessed following Fluoro-Gold injections, caudal to the hemisection. Significantly more retrogradely labeled right (axotomized) red nucleus (RN) neurons were seen in Ch'ase ABC-treated (23%) compared with control-treated cats (8%; p = 0.032) indicating that a larger number of RN neurons in Ch'ase ABC-treated cats had axons below the lesion level. Thus, following SCI, Ch'ase ABC may facilitate axonal growth at the spinal level, enhance adaptive features of locomotion, and affect plasticity of rubrospinal circuitry known to support adaptive behaviors in the normal cat.

Rehabilitative training and plasticity following spinal cord injury

Rehabilitative training is currently one of the most successful treatments to promote functional recovery following spinal cord injury. Nevertheless, there are many unanswered questions including the most effective and beneficial design, and the mechanisms underlying the training effects on motor recovery. Furthermore, rehabilitative training will certainly be combined with pharmacological treatments developed to promote the "repair" of the injured spinal cord. Thus, insight into training-induced mechanisms will be of great importance to fine tune such combined treatments. In this review we address current challenges of rehabilitative training and mechanisms involved in promoting motor recovery with the focus on animal models. These challenges suggest that although rehabilitative training appears to be a relatively straight forward treatment approach, more research is needed to optimize its effect on functional outcome in order to enhance our chances of success when combining pharmacological treatments promoting axonal growth and rehabilitative training in the clinic.