Development of 5-Hydroxytryptophan Decarboxylase in the Brain, Eye and Whole Embryo of Xenopus laevis

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Abstract
5-Hydroxytryptophan decarboxylase activity was measured in whole embryos, lateral eyes, and brains of developing Xenopus laevis. Cl4- 5-hydroxytryptophan precursor was introduced into an in vitro system containing monoamine oxidase inhibitor; and after incubation radioactive 5-hydroxytryptamine product was extracted and read in a liquid scintillation counter. Enzyme activity in whole embryo showed a reduction and elevation around first spontaneous movement, and a continuing increase after hatching. Enzyme activity in the eyes first measured just after hatching falls swiftly after that point and rises again sharply around the time of first active larval swimming. Brain enzyme activity first measured somewhat later after hatching rises sharply around the time of first active larval swimming. These results considered in the light of previous measurements of 5-hydroxy-tryptamine and 5-hydroxyindole-O-methyl-transferase indicate a connection between indole metabolism and the periods of first spontaneous movement, hatching, and first active larval swimming.