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 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 , FMRFamide-like peptides encoded on 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) PCF (As-PCF) contains a catalog of neuropeptides including FMRFamide-like peptides and neuropeptide-like proteins, (ii) the FMRFamide-like peptide As-FLP-18A dominates the As-PCF peptidome, (iii) As-PCF potently modulates nematode reproductive muscle function , mirroring the effects of synthetic FLP-18 peptides, (iv) As-PCF activates the FLP-18 receptors NPR-4 and -5, (v) As-PCF alters 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.