Chromatographic and immunological characterisation of neuropeptide Y-like and pancreatic polypeptide-like peptides from the nematode Ascaris suum

Ascaris suum Informs Extrasynaptic Volume Transmission in Nematodes

Neural circuit synaptic connectivities (the connectome) provide the anatomical foundation for our understanding of nematode nervous system function. However, other nonsynaptic routes of communication are known in invertebrates including extrasynaptic volume transmission (EVT), which enables short- and/or long-range communication in the absence of synaptic connections. Although EVT has been highlighted as a facet of Caenorhabditis elegans neurosignaling, no experimental evidence identifies body cavity fluid (pseudocoelomic fluid; PCF) as a vehicle for either neuropeptide or biogenic amine transmission. In the parasitic nematode Ascaris suum, FMRFamide-like peptides encoded on flp-18 potently stimulate female reproductive organs but are expressed in cells that are anatomically distant from the reproductive organ, with no known synaptic connections to this tissue. Here we investigate nonsynaptic neuropeptide signaling in nematodes mediated by the body cavity fluid. Our data show that (i) A. suum PCF (As-PCF) contains a catalog of neuropeptides including FMRFamide-like peptides and neuropeptide-like proteins, (ii) the A. suum FMRFamide-like peptide As-FLP-18A dominates the As-PCF peptidome, (iii) As-PCF potently modulates nematode reproductive muscle function ex vivo, mirroring the effects of synthetic FLP-18 peptides, (iv) As-PCF activates the C. elegans FLP-18 receptors NPR-4 and -5, (v) As-PCF alters C. elegans behavior, and (vi) FLP-18 and FLP-18 receptors display pan-phylum distribution in nematodes. This study provides the first direct experimental evidence to support an extrasynaptic volume route for neuropeptide transmission in nematodes. These data indicate nonsynaptic signaling within the nematode functional connectome and are particularly pertinent to receptor deorphanization approaches underpinning drug discovery programs for nematode pathogens.

The ovijector of Ascaris suum: multiple response types revealed by Caenorhabditis elegans FMRFamide-related peptides

Caenorhabditis elegans possesses 22 FMRFamide-like peptide (flp) genes predicted to encode 60 different FMRFamide-related peptides with a range of C-terminal signatures. Peptides from five flp genes (1, 6, 8, 9 and 14) are known to modulate the ovijector of Ascaris suum in vitro. This study examines the physiological effects of peptides from the remaining 17 flp genes such that the variety of FMRFamide-related peptide-induced ovijector response types can be delineated. Five categories of response were identified according to the pattern of changes in contractile behaviour and baseline tension. Peptides encoded on 16 flp genes (1, 2, 3, 4, 6, 7, 9, 10, 11, 12, 13, 14, 15, 16, 17 and 20) had qualitatively similar inhibitory (response type 1) actions, with the lowest activity thresholds (1 nM) recorded for peptides with FIRFamide or FLRFamide C-terminal signatures. Peptides encoded on four flp genes (2, 18, 19 and 21), and on the A. suum afp-1 gene, had excitatory actions on the ovijector (response type 2), with PGVLRFamides having the lowest activity threshold (1 nM). An flp-2 peptide (LRGEPIRFamide) induced a transient contraction of the ovijector (activity threshold, 10nM) that was designated response type 3. Response type 4 comprised a transient contraction followed by an extended period of inactivity and was observed with peptides encoded on flp-5 (AGAKFIRFamide, APKPKFIRFamide), flp-8 (KNEFIRFamide) and flp-22 (SPSAKWMRFamide). SPSAKWMRFamide was the most potent peptide tested with an activity threshold of 0.1 nM. A single peptide (AMRNALVRFamide; activity threshold 0.1 microM), encoded on flp-11, induced response type 5, a shortening of the ovijector coupled with an increase in contraction frequency. Although most flp genes encode structurally related peptides that trigger one of the five ovijector response types, flp-2 and flp-11 co-encode FMRFamide-related peptides that induce distinct responses. Within the ovijector of A. suum FaRPs play a complex role involving at least five receptor subtypes or signalling pathways.

Neuromuscular transmission in nematode parasites and antinematodal drug action

Some anthelmintic drugs interfere selectively with nematode neuromuscular transmission. These drugs include: the nicotinic agonists, e.g. levamisole, the gamma-amino butyric acid agonist piperazine, and the avermectins which open Cl- channels. The physiology and pharmacology of neuromuscular transmission in nematodes is reviewed and the actions of antinematodal drugs which interfere with the transmission described. The results of experiments on the large porcine-intestinal nematode parasite, Ascaris suum, form the basis of the account presented but experiments on other nematodes suggest that these observations may be generalized. Results of some experiments on the small free living nematode Caenorhabditis elegans are also included.