The influence of serotonin and p-chlorophenylalanine on locomotor activity of Drosophila melanogaster.

Two hours after injection of serotonin into 3-day-old virgin females of Drosophila melanogaster, a significant dose-dependent increase in locomotor activity was observed. Since this stimulating effect can be produced either by serotonin or by some of its derivatives that might have formed during these two hours, the fate of injected [3H]-serotonin in the organism of Drosophila was traced by means of thin layer chromatography. The only metabolite found appeared to be N-acetylserotonin. Its formation was rather intense immediately after injection of [3H]-serotonin, and its excretion was rapid enough to make it undetectable at the end of the second hour, when more than 50% of the injected [3H]-serotonin still remained and was being absorbed by tissues. Thus, the increase in locomotor activity observed two hours after injection should be wholly attributed to serotonin, while the rather long latency might be related to some effect of N-acetylserotonin. p-Chlorophenylalanine, an inhibitor of tryptophan-5-hydroxylase, both injected or administered with food, led to increases in locomotor activity level and to some decreases in serotonin content in the heads of flies. The effect of p-chlorophenylalanine on locomotor activity in Drosophila seems to be non-specific in relation to serotoninergic mechanisms of its regulation.