Origin of renewed spinal ganglia during tail regeneration in urodeles

The source of the cells which form the spinal ganglia with in the regenerat ing urodele tail is not yet indisputably known. Classical and modern experi mental approaches trace the spinal cord as the most probable source; The ai m 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 ga nglia 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 regener ated spinal cord and the laterally forming spinal ganglion was noticed. The re was some indication that many cells migrated out from the spinal cord to wards the spinal ganglion, through the ventral root. (d) The mitotic and th e labeling index along the regenerated spinal cord exhibited individual pea ks near the level of each developing ganglion. The last two observations co rroborate and reinforce the prevailing view that the progenitors of the spi nal ganglion cells which are formed in the regenerating tail are of spinal cord origin.