Physiological actions of putative neuropeptides in the nematode Ascaris suum

Neuropeptide-like immunoreactivity has a widespread distribution in the nematode nervous system (Sithigorngul et al. 1990) and sequences of more than 150 neuropeptides have been predicted from the genomes of C. elegans (Nelson et al. 1998; Nathoo et al. 2001). Here we report a preliminary assessment of the biological activity of six of these on the somatic muscle of the parasitic nematode A. suum. Three of these are encoded by flp (FMRFamide-like peptides) genes and three by nlp (neuropeptide-like precursor) genes. Two of the latter show some sequence similarity to myomodulin, and one to buccalin, molluscan neuropeptides.The effect of the peptides on the body wall muscle of A. suum was determined using an in vitro preparation of dorsal muscle strips as described by Trim et al. (1997). A 1 cm section of muscle was placed in an organ bath attached to an isometric transducer and perfused with artificial perienteric fluid (composition (mM): NaCl 67, sodium acetate 67, MgCl2 5.6, CaCl2 3, KCl 3, Tris-Cl 5; pH 7.6). The excitatory neuromuscular junction transmitter acetylcholine (ACh; 10 µM) was added for 1 min and then washed out. This elicited a rapid and reversible contraction. This was repeated twice to obtain contractions of reproducible amplitude. Subsequently the neuropeptide was added to the preparation 2 min prior to ACh, and the amplitude of the contraction to ACh in the presence of the peptide was expressed as a percentage of the average amplitude of the three contractions prior to the addition of neuropeptide. None of the neuropeptides had a marked effect on basal muscle tension. However, three had a potent effect on the contraction elicited by ACh, with two acting as inhibitors and one as a potentiator. The results are summarised in Table 1.In conclusion, all three of the RF-amide neuropeptides had potent effects, and one of the myomodulin-like peptides had a weak inhibitory action. Further studies are in progress to assess the activity of these peptides in C. elegans.