Neuronal populations capable of regeneration following a combined treatment in rats with spinal cord transection.

Axonal regeneration after spinal cord injury (SCI) in adult mammals is limited by inhibitors associated with myelin and the glial scar. To overcome these inhibitors, a combined approach will be required. We have previously demonstrated that, following complete SCI in rats, a combination of bridging the lesion with Schwann cell (SC)-filled guidance channels, olfactory ensheathing glia implantation, and chondroitinase ABC delivery promoted regeneration of serotonergic fibers into the lumbar spinal cord. In addition, this combined treatment significantly improved locomotor recovery. To complement these findings, we repeated this combined treatment to assess whether fibers other than serotonergic axons were able to regenerate into the caudal spinal cord. In this experiment, we injected the retrograde tracer FluoroGold (FG) into the spinal cord caudal to a complete transection in a control and a treated group. FG-positive cells rostral to the lesion and in the brainstem of animals in the treated group showed that axons were able to regenerate across the SC bridge and into the caudal spinal cord. Treated rats had labeled cells in the reticulospinal nuclei, vestibular nuclei, and the raphe nucleus as well as in the spinal cord. Cell numbers were highest in the thoracic spinal cord and the lateral vestibular nucleus. Determining the mechanisms for the superior capability of these cell populations to regenerate may provide valuable clues in the design of future treatment approaches.