The Occurrence and Distribution of 5-Hydroxytryptamine in Hymenolepis diminuta and H. nana

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Abstract
The presence of 5-HT [5-hydroxytryptamine] in H. diminuta and H. nana was detected by 2 biochemical methods and as yellow fluorescence in a histochemical method. In H. diminuta, 5-HT was found in a concentration of approximately 1.2 .mu.g/g; this amount did not vary significantly in worms aged 6-18 days or more or in various regions of the worm. In H. nana, 5-HT was found in a concentration of 1.8 .mu.g/g. It was histochemically localized in H. diminuta and H. nana in a pattern similar to that of acetylcholinesterase previously described in these 2 cestodes and it may be the opposing neurotransmitter to acetylcholine. The lack of 5-HT in the vestigial rostellum of H. diminuta may be correlated with loss of function of this organ.