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Timothy G. Geary, Nikki J. Marks, Aaron G. Maule, Jerry W. Bowman, Susan J. Alexander-Bowman, Tim A. Day, Martha J. Larsen, Teresa M. Kubiak, John P. Davis and David P. Thompson
The Annals of the New York Academy of Sciences 897:212-227
Nematode FaRPs already number >50, with many more yet to be identified. To date, few non-FaRP neuropeptides have been identified in these organisms, even though evidence suggests that other families are present. Clearly, FaRPergic systems must have important functions in nematode neuromuscular control. Although some progress has been made in the characterization of FaRP pharmacology in nematodes, much remains to be learned. Most pharmacological studies have been done with Ascaris suum, because of its large size. In contrast, thanks to the Caenorhabditis elegans genome project, we know most about the FaRP complement of this free-living animal. That essentially all C. elegans FaRPs are active on at least one A. suum neuromuscular system argues for conservation of ligand-receptor recognition features among members of the phylum Nematoda. Structure-activity studies on some nematode FaRPs have revealed regions required for activity; two examples illustrate that SAR "rules" differ considerably among the FaRPs. Second messenger studies, along with experiments on ionic dependence and anatomical requirements for activity, reveal that FaRPs act through many different mechanisms. Although species in the phylum Platyhelminthes (flatworms) apparently utilize fewer FaRPs than nematodes, there are examples of cross-phylum activity of nematode FaRPs. The extent to which other invertebrate FaRPs show cross-phylum activity remains to be determined. How FaRPergic nerves contribute to the control of behavior in nematodes, and are integrated with non-neuropeptidergic systems, also remains to be elucidated.