The actions of Caenorhabditis elegans neuropeptide-like peptides (NLPs) on body wall muscle of Ascaris suum and pharyngeal muscle of C. elegans.

The actions of six Neuropeptide-like Peptides (NLPs) were investigated on Ascaris suum dorsal body wall muscle and Caenorhabditis elegans pharyngeal muscle. The NLPs tested on A. suum muscle, viz, NLP-1A, NLP-2A and B, had no direct effect on the muscle but all reversibly reduced acetylcholine (ACh)-induced contractions of the muscle, NLP-2A being the most potent, with an IC50 value of 78 microM. NLP-2A also reversibly reduced ACh-induced depolarizations of A. suum muscle resting membrane potential. NLP-1A, NLP-2A, NLP-3C and NLP-10A all increased pharyngeal pumping in C. elegans, NLP-8A weakly inhibited pumping while NLP-2B was inactive. NLP-10A induced a concentration-dependent increase in pumping activity with a threshold of 10-100 nM. Since genes encoding NLPs (nlp genes) are expressed in C. elegans pharyngeal neurons it is likely these peptides play a role in feeding behaviour.