Lack of proliferative response in denervated, reamputated limb regenerates of larval Ambystoma.

This paper describes the response of early four-digit regenerates of axolotls to reamputation and denervation. Reamputation of innervated regenerates led to sharp increases in 3H-thymidine labeling index (LI) and mitotic index (MI) on days 2-5 post-reamputation. This resembles the response of innervated limbs following initial amputation. Regenerates that were denervated at the time of reamputation exhibited no proliferative response through day 5. This is in marked contrast to denervated, original amputation limb stumps, in which LI and MI rise for several days (as in innervated stumps) before falling to background levels. Although myelin was scarce near the level of reamputation, the lack of proliferation cannot be explained solely on that basis. The results are consistent with the possibility that the "neurotrophic factor" that causes stump and blastema cell mitosis is not present in unamputated limbs but is made in response to amputation.