The role of Schwann cells in paradoxical regeneration in the axolotl.

The experiments described here examine further the conditions under which paradoxical regeneration occurs and provide support for the hypothesis that a proximal migration of Schwann cells is responsible for the phenomenon. When only the hand is shielded from irradiation and the limb is denervated, amputation through the forearm or upper arm sometimes results in regeneration. The effects of variation in the time interval between denervation and amputation, the level of amputation and the method and number of denervations on the incidence of regeneration were investigated. The presence or absecce of viable Schwann cells at the amputation plane was deduced from the remyelination of nerves under conditions which do or do not permit paradoxical regeneration. The nerves of totally irradiated and denervated limbs remain unmyelinated following regrowth of axons and such limbs do not regenerate after amputation. When only the hand was shielded from irradiation before the limbs were denervated, the new axons became completely remyelinated and some of these limbs regenerated when amputated. It is suggested that under these conditions Schwann cells can migrate proximally and can then proliferate further to form a blastema, since they would be the only unirradiated tissue present at the amputation plane.