FMRFAMIDE-RELATED PEPTIDES (FARPS) IN NEMATODES - OCCURRENCE AND NEUROMUSCULAR PHYSIOLOGY

The occurrence of classical neurotransmitter molecules and numerous pe ptidic messenger molecules in nematode nervous systems indicate that a lthough structurally simple, nematode nervous systems are chemically c omplex. Thus far, studies on one nematode neuropeptide family, namely the FMRFamide-related peptides (FaRPs), have revealed an unexpected va riety of neuropeptide structures in both free-living and parasitic spe cies. To date 23 nematode FaRPs have been structurally characterized i ncluding 12 from Ascaris suum, 8 from Caenorhabditis elegans, 5 from P anagrellus redivivus and 1 from Haemonchus contortus. Ten FaRP-encodin g genes have been identified in Caenorhabditis elegans. However, the f ull complement of nematode neuronal messengers has yet to be described and unidentified nematode FaRPs await detection. Preliminary characte rization of the actions of nematode neuropeptides on the somatic muscu lature and neurones of A. suum has revealed that these peptidic messen gers have potent and complex effects. Identified complexities include the biphasic effects of KNEFIRFamide/KHEYLRFamide (AF1/2; relaxation o f tone followed by oscillatory contractile activity) and KPNFIRFamide (PF4; rapid relaxation of tone followed by an increase in tone), the d iverse actions of KSAYMRFamide (AF8 or PF3; relaxes dorsal muscles and contracts ventral muscles) and the apparent coupling of the relaxator y effects of SDPNFLRFamide/SADPNFLRFamide (PF1/PF2) to nitric oxide re lease. Indeed, all of the nematode FaRPs which have been tested on som atic muscle strips of A. suum have actions which are clearly physiolog ically distinguishable. Although we are a very long way from understan ding how the actions of these peptides are co-ordinated, not only with those of each other but also with those of the classical transmitter molecules, to control nematode behaviour, their abundance coupled with their diversity of structure and function indicates a hitherto uniden tified sophistication to nematode neuromuscular intergration.