Extensive Spontaneous Plasticity of Corticospinal Projections After Primate Spinal Cord Injury

While axonal regeneration after CNS injury is limited, partial injury is frequently accompanied by extensive functional recovery. To investigate mechanisms underlying spontaneous recovery after incomplete spinal cord injury, adult rhesus monkeys underwent C7 spinal cord hemisections, with subsequent analysis of behavioral, electrophysiological and anatomical adaptations. We found remarkable spontaneous plasticity of corticospinal projections, with reconstitution of fully 60% of pre-lesion axon density arising from sprouting of spinal cord midline-crossing axons. This extensive anatomical recovery was associated with improvement in coordinated muscle recruitment, hand function and locomotion. These findings identify what may be the most extensive natural recovery of mammalian axonal projections after nervous system injury observed to date, highlighting an important role for primate models in translational disease research.