The limbs of salamanders can regenerate even if their nerves are irradiated, provided that some other non-irradiated tissue reaches the site of amputation. This conclusion is reached by repetition of an earlier experiment, which yielded contradictory results. The experimental design does not demonstrate any radiosensitivity of nerves, but indicates that very few non-irradiated cells suffice to initiate regeneration. On the basis of this conclusion and other unconfirmed experiments, the possibility is considered that irradiated cells can recover their ability to regenerate.

a n d D e p a r t m e n t of Genetics, University of B i r m i n g h a m , England ABSTRACTIt is well known that prior local irradiation inhibits the ability of larval salamanders to regenerate an amputated limb, and that implantation of various non-irradiated tissues at the site of amputation restores this ability. Neither wounds in the irradiated region, nor wounds in the non-irradiated shoulder, promote regeneration. A superficial slit i n the skin stretching from non-irradiated tissue to the irradiated site of amputation, however, restores the ability to regenerate. It is presumed that non-irradiated cells migrate down the slit during wound-healing and are thus present at the site of amputation and stimulate regeneration.Transection of the nerve roots following local irradiation of the limb permits a regrowth of non-irradiated axons into the irradiated limb. Such limbs recover both sensory and motor co-ordination and the ability to regenerate. Non-irradiated sections of nervous tracts (axons, Schwann cells and connective tissue sheaths) also promote regeneration when transplanted into irradiated limbs.Since a nerve supply is almost always needed for limb regeneration, yet an irradiated nerve is sufficient for this purpose, no special sensitivity of nerves to x-rays is implied by these experiments. The normal function, regrowth and trophic effects of axons appear to be unimpaired by exposing the entire neuron to doses of irradiation that inhibit limb regeneration.