THE EFFECTS OF PARTIAL IRRADIATION ON TAIL REGENERATION IN ADULT SIREDON MEXICANUM

¹ From the Radiobiology Laboratory, Roswell Park Memorial Institute (New York State Department of Health), Buffalo, NewYork

1. The tails of 115 adult axolotls (Siredon mexicanum) were amputated, and the regenerates that developed were irradiated locally 1 to 2 months later with one or another of the following doses: 1,000 r, 2,000 r, 4,500 r, and 6,000 r. A more proximal amputation, performed a relatively long time (more than 1 year) after irradiation, was followed by the development of only 12 regenerates, all monstrous. Obviously these regenerates developed from the boundary zone, where irradiation of the cellular material had been only partial. In the other 103 animals, regeneration was completely suppressed.

2. The 12 monstrous regenerates were the products of limited regeneration, and represented various types of abnormalities, ranging from narrow paddle-shaped formations with almost normal axial skeletons and spinal cords to small and narrow awl-shaped formations lacking both axial skeletons and spinal cords. Regression of the axial skeleton, which has been observed in previous study in 90 per cent of regenerates of axolotl extremities during the first 100 to 150 days after irradiation, was observed in only one instance in the present study. Pathologic changes in the distal portion of the spinal cord were minor and very similar to such changes in irradiated tails of young axolotls, but ingrowth of the spinal cord in the distal portion of the regenerate did not occur in some cases.

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