After ablation of 2 mm of spinal cord in the postbrachial region in larvae of Ambystoma maculatum studies were made on the reconstitution of the cord and the return of function posterior to the ablation level. Healing of the cord at anterior and posterior transection surfaces involves migration of ependymal cells to close the open central canal and movement of cells of the gray matter over the cut surface. Dilation of the central canal occurs at each transection level to form a terminal vesicle. Its wall is made up of ependyma, cells from the gray matter and an outer layer of white matter. Anterior and posterior terminal vesicles gradually increase in length bringing about a slow advance of their tips across the ablation gap, the anterior vesicle moving more rapidly than the posterior. Nerve fibers growing out from the white matter of each terminal vesicle extend across the ablation gap and eventually join the wall of the opposite vesicle. Thus are formed bridges of intracentral fibers between anterior and posterior vesicles. Broad nerve fiber bridges become the white matter of the reconstituted spinal cord. Continued advance of the terminal vesicles across the ablation region results finally in the union of the two vesicles, restoring the continuity of the spinal cord. Recovery of the use of hind limbs for walking and of trunk and tail muscles for swimming is correlated with the extent to which nerve fiber bridges have been established, but does not involve a complete fusion of terminal vesicles. All larvae which walked normally and the majority of those which swam normally possessed fiber bridges with an average diameter of at least 0.05 mm.
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Butler et al. (1965) studied this question.