The regeneration of brachial nerves of contralateral origin into denervated fused newt forelimbs Supported by NIH Training Grant 5 TO1 GM 00312-15 and a grant from the Muscular Dystrophy Association of America to Dr. Bruce M. Carlson. Reported earlier in abstract form (Goshgarian, '75a). This material is part of a thesis for the degree of Doctor of Philosophy, University of Michigan.

Abstract

Previous studies involving the end-to-end fusion of the forelimbs of the adult newt have demonstrated that new limbs can regenerate from the transected ends of proximo-distally reversed limb segments. The limb regeneration could only have been initiated by nerve fibers of contralateral origin. The purpose of the present study is to describe histologically the manner in which nerve fibers of contralateral origin regenerate through the junction of fused limbs into the opposite limb. The first sign of nerve regeneration into the opposite limb was observed at eight days post fusion. The nerves crossed over into the opposite, originally denervated limb in a highly dispersed manner. These nerve fibers eventually aggregated, however, either under the skin or within persisting nerve trunks. By 19 days post fusion the nerve fibers had reached the elbow region of the originally denervated limb and by 25 days they were seen at the most proximal extent of the limb. The diameters of the axons seemed smaller than the diameters of regenerating axons observed in non-fused newt forelimbs.