Eliciting inflammation enables successful rehabilitative training in chronic spinal cord injury.

Rehabilitative training is one of the most successful therapies to promote motor recovery after spinal cord injury, especially when applied early after injury. Polytrauma and management of other medical complications in the acute post-injury setting often preclude or complicate early rehabilitation. Therefore, interventions that reopen a window of opportunity for effective motor training after chronic injury would have significant therapeutic value. Here, we tested whether this could be achieved in rats with chronic (8 weeks) dorsolateral quadrant sections of the cervical spinal cord (C4) by inducing mild neuroinflammation. We found that systemic injection of a low dose of lipopolysaccharide improved the efficacy of rehabilitative training on forelimb function, as assessed using a single pellet reaching and grasping task. This enhanced recovery was found to be dependent on the training intensity, where a high-intensity paradigm induced the biggest improvements. Importantly, in contrast to training alone, the combination of systemic lipopolysaccharide and high-intensity training restored original function (reparative plasticity) rather than enhancing new motor strategies (compensatory plasticity). Accordingly, electrophysiological and tract-tracing studies demonstrated a recovery in the cortical drive to the affected forelimb muscles and a restructuration of the corticospinal innervation of the cervical spinal cord. Thus, we propose that techniques that can elicit mild neuroinflammation may be used to enhance the efficacy of rehabilitative training after chronic spinal cord injury.