The serotonergic system in Tetrahymena pyriformis.

Assays were performed to determine the presence of serotonin (5-hydroxytryptamine) in Tetrahymena pyriformis GL in two different media using two different assay procedures. Serotonin was present in quantities consistent with those observed in other varieties of protozoa. The serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA) was also present, suggesting that the enzyme, monoamine oxidase (MAO), provides for serotonin deamination. Inhibition of MAO in Tetrahymena was apparent due to resulting accumulation of serotonin and decreased levels of 5-HIAA. The data suggest that serotonin mediates a functional role in Tetrahymena pyriformis GL and that its metabolism may be relevant to such functions.