Reinnervation of the ventral root L7 from ventral horn neurons following intramedullary axotomy in adult cats.

Through small longitudinal incisions in the ventral funiculus of the adult cat spinal cord the intramedullary portions of motoraxons forming the L7 ventral root were divided. The animals were sacrificed by glutaraldehyde-perfusion 1-15 weeks postoperatively. In some cases this was preceded by HRP injection into large L7 ventral horn neurons. Sections from the lesioned ventral funiculus and the denervated ventral root L7 were examined by light and electron microscopy. During the first postoperative month increasing numbers of unmyelinated and thinly myelinated large-diameter axons coursed through the lesion and entered the denervated ventral root. Occasional neuroma-like formations were also found in the lesion area. After 5 weeks survival clusters of regenerating axons reached the distal end of the L7 ventral root. Light microscopic examination of Vibratome sections from HRP-injected animals showed that at least some regenerated axons come from large neurons, presumably alpha-motoneurons, in the ventral horn motor nuclei. Most of the examined labeled regenerated axons reached the CNS/PNS junction of the ventral root but a few followed a grossly aberrant course and/or terminated within the lesion. These observations show that regeneration of large-diameter axons through a CNS-lesion is possible. Both the intrinsic regenerative capacity of the axotomized neurons and the presence of a denervated ventral root in the immediate vicinity are likely to be contributing factors with respect to this example of successful CNS axon regeneration.