THE REGENERATION OF AXONS THROUGH NORMAL AND REVERSED PERIPHERAL-NERVE GRAFTS

The effect of proximo-distal orientation of peripheral nerve grafts up on axonal regeneration has been investigated using the sciatic nerve o f the rat as a model. To test the hypothesis that the presence of nerv e branches within a graft will cause misdirection of axons in normally oriented grafts but not in reversed grafts, all grafts studied contai ned branches. Qualitative electron microscopic examination of graft ul trastructure revealed no differences in nerve structure related to gra ft orientation. In most normally oriented grafts, branches persisted u p to 12 months after surgery. These branches contained axons which ter minated at the end of the branch. In all reverse oriented grafts, and in a small number of normally oriented ones, the branches could not be seen after two or more months of regeneration. Axons sprouting outsid e of the epineurium of the graft caused the branch to be incorporated into the nerve structure. Axon counts in the distal stump of grafted n erves after twelve months recovery revealed that normally oriented gra fts with persistent branches led to poorer peripheral regeneration, es pecially of unmyelinated fibers. The results indicate that regeneratio n of axons to their peripheral targets may be facilitated by reversing the graft orientation.