Morphogenetic Activities during Planarian Regeneration as influenced by Triethylene Melamine

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Abstract
The action of an anti-neoplastic substance, triethylene melamine (TEM) on the morphogenetic processes of head regeneration in the planarian Planaria vitta has been studied. A description of the normal regeneration is first given. TEM in very low concentrations strongly retards or blocks regeneration of two eyes. Administered continuously, a high toxicity is observed. Exposure to high concentrations for a short time involves severe retardation of regeneration without any mortality. A phase-specificity is observed. TEM in low concentrations only acts in the first phase of regeneration, in higher concentrations in the middle phase too, but no action is encountered in the late phase of regeneration. The phase specificity is not due to a failure of penetration of the substance. TEM strongly affects mitosis of neoblasts, and this is its primary action on the regenerative process. No action on cellular migration was observed. A dissociation between epimorphosis and morphallactic regeneration is possible following treatment with TEM. Differentiation and induction are not directly influenced by TEM, but may be modified as a result of depletion of neoblasts. A competition of the two symmetrical lateral halves for neoblasts is encountered, resulting in animals with only one lateral eye. The phenomenon is quite distinct from cyclopia. Fission as such is unaffected by TEM. The regeneration of the posterior fragments follows the same pattern as the head-pieces. Histological changes following TEM treatment are described. The PAS reaction is depressed after intense treatment with TEM, the intestine being first depleted of PAS-positive material. Respiratory intensity is unaffected by TEM. A partial protection is obtained by pretreatment of the animals with BAL (2:3-dimercaptopropanol). The free amino acids were studied after TEM treatment. Only one change is observed, a highly elevated glutamine reaction. The significance of epimorphosis and morphallaxis, and the respective role played by mitosis and neoblasts in these two modes of regeneration are discussed. Competition and inhibition phenomena during regeneration are briefly discussed.