PRESENCE IN AND EFFECTS OF PINEAL INDOLEAMINES AT VERY-LOW LEVEL OF PHYLOGENY

The unicellular organism Tetrahymena contains serotonin and is able to take up the hormone from its milieu. The serotonin content of the cel l changes as a function of the presence of foreign exogenous hormones. This indicates a possible role of serotonin as a chemical mediator. E xogenous serotonin stimulates the RNA synthesis of Tetrahymena, and it was the only one among the hormones studied which kept the RNA level durably high. Serotonin stimulates phagocytosis and growth of Tetrahym ena, and its precursors also stimulate growth. Serotonin can imprint T etrahymena, and as a consequence of this the effect of the hormone inc reases in the case of further encounters. Treatment with serotonin-rel ated molecules soon after imprinting can reduce the effect of imprinti ng. Melatonin can contract the pigment cells of Planaria; however, its precursors serotonin and tryptamine can do this more intensely. Both melatonin and serotonin can influence the regeneration of Planaria, wi th effects which differ when different phenomena are studied. Evolutio nary theories are discussed.