ABSTRACT
Forelimbs of juvenile axolotls do not regenerate when amputated in a previously irradiated region. They usually do regenerate, however, if they have also been denervated shortly after irradiation and well before amputation. Five series of experiments are reported which define the conditions permitting this paradoxical regeneration.
Crushing the nerves of the brachial plexus proved a satisfactory means of causing temporary denervation. Shielding any region of the arm or shoulder, during an irradiation that preceded such denervation, permits regeneration to occur at a region which was initially irradiated. Lengths of brachial nerve implanted into an irradiated arm also support its regeneration.
It is concluded that temporary denervation (including Wallerian degeneration and the regrowth of axons) mobilizes cells in a shielded region of the arm. These cells migrate both proximally and distally, so that some come to occupy the site of amputation. Schwann cells of the myelin sheath are identified as the cells most likely to behave in this way. It thus seems probable that those non-irradiated Schwann cells which occupy a generally irradiated limb-stump can form the exclusive source of a mesenchymal blastema and the various internal tissues of the regenerate.
