Regeneration in peripheral nerve grafts to the cat spinal cord

Peripheral nervous system grafts have long been known to promote CNS axonal elongation in the rodent. To investigate whether these principles also apply to a higher order animal, more suitable for physiologic studies, we performed autogenous sciatic nerve grafts to the adult cat spinal cord. This report is a brief, initial study of these grafts. In an effort to study both descending and ascending fibers as separately as possible, laminectomies were performed at both thoracic (T2-T9) and lumbar (L2-L4) levels. Aspiration lesions were made in the left side of the cord and the sciatic grafts were introduced. Three cats were studied with standard histological techniques, confirming previous reports of glial scar formation, collagen deposition, and cyst formation at the graft-CNS junction. In 7 other animals, at 146-179 days after the initial operation, the axonal origins were traced retrogradely using horseradish peroxidase and the tetramethyl benzidine technique. Reinnervation of the graft was found by intrinsic spinal cord neurons and dorsal root ganglia neurons. The number of reinnervating neurons was found to be greater than previously reported in the rodent. There was, however, no evidence of regeneration from brainstem nuclei when the grafts were placed at spinal levels where this has been seen in the rat. This may support an absolute maximum for regenerative distances vs a relative one. Although the amount of data was limited, it did support previous reports that peripheral axotomy enhances the regenerative response seen in primary sensory neurons.