Origin of renewed spinal ganglia during tail regeneration in urodeles

The source of the cells which form the spinal ganglia within the regenerating urodele tail is not yet indisputably known. Classical and modern experimental approaches trace the spinal cord as the most probable source. The aim of the present study was to further investigate this item by conventional histology, counting of mitotic figures, and estimating the labeling index. The main results can be summarized as follows: (a) The regenerated part of the tail contained only two bilaterally asymmetrical pairs of ganglia, with respect to the rostrocaudal (anterior-posterior) axis. (b) The anterior ganglia were slightly differentiated and appropriately localized; therefore, analysis was performed mainly in the posterior, still developing ganglia. (c) An anatomical continuation between the ventrolateral side of the regenerated spinal cord and the laterally forming spinal ganglion was noticed. There was some indication that many cells migrated out from the spinal cord towards the spinal ganglion, through the ventral root. (d) The mitotic and the labeling index along the regenerated spinal cord exhibited individual peaks near the level of each developing ganglion. The last two observations corroborate and reinforce the prevailing view that the progenitors of the spinal ganglion cells which are formed in the regenerating tail are of spinal cord origin.