G protein-coupled receptors (GPCRs) are the largest family of genes in animal genomes and represent more than 2% of genes in humans and C. elegans. These evolutionarily conserved seven-transmembrane proteins transduce a diverse range of signals. In view of their pivotal role in cell signaling, it is perhaps surprising that decades of genetic analysis in C. elegans, and recent genome-wide RNAi screens, have identified very few GPCR mutants. Therefore, we screened all GPCRs predicted to bind either small-molecule neurotransmitters or neuropeptides by using RNAi and quantitative behavioral assays. This shows that C16D6.2, C25G6.5, C26F1.6, F35G8.1, F41E7.3, and F59C12.2 are likely to be involved in reproduction, whereas C15B12.5, C10C6.2, C24A8.4, F15A8.5, F59D12.1, T02E9.1, and T05A1.1 have a role in locomotion. Gene deletions for F35G8.1 and T05A1.1 resulted in the same phenotype as that seen with RNAi. As some GPCRs may be resistant to RNAi, or may result in abnormalities not screened for here, the actual proportion of nonredundant receptors with an assayable function is probably greater. Strikingly, most phenotypes were observed for NPY-like receptors that may bind neuropeptides. This is consistent with the known actions of neuropeptides on the body wall muscle and reproductive tract in nematodes.
Visceral hypersensitivity is an important clinical feature associated with irritable bowel syndrome which in some patients has been linked to prior infection. Here we employ an animal model in which transient infection leads to persistent gut dysfunction to investigate the role of altered 5-HT metabolism upon afferent mechanosensensitivity in the post-infected gut. Jejunal segments isolated from Trichinella spiralis-infected mice were used to assess 5-HT metabolism whilst afferent activity in T. spiralis-infected mice was studied by extracellular recordings from jejunal mesenteric afferent bundles and patch clamp recordings of isolated nodose ganglion neurons (NGNs). During acute infection, intestinal 5-HT content and release increased, 5-HT turnover decreased and afferent discharge in response to mechanical stimulation was attenuated. By day 28 post infection (PI), 5-HT turnover had normalized, but 5-HT content and release were still elevated. This was associated with afferent mechano-hypersensitivity, which persisted for 8 weeks PI and was susceptible to 5-HT 3 receptor blockade. NGNs from post-infected animals were more excitable than controls but their current densities in response to 2-methyl-5-HT were lower. T. spiralis infection increased mucosal 5-HT bioavailability and affected the spontaneous activity and mechanosensitivity of gastrointestinal sensory nerves. This involved an initial hyposensitivity occurring during acute infection followed by long-term hypersensitivity in the post-infectious period that was in part mediated by 5-HT acting via 5-HT 3 receptors. Functional down-regulation of 5-HT 3 receptors also occurs in the post-infected animals, which may represent an adaptive response to increased mucosal 5-HT bioavailability.
The ATP-gated P2X7 receptor (P2X7R) was shown to be an important mediator of inflammation and inflammatory pain through its regulation of IL-1β processing and release. Trichinella spiralis-infected mice develop a postinflammatory visceral hypersensitivity that is reminiscent of the clinical features associated with postinfectious irritable bowel syndrome. In this study, we used P2X7R knockout mice (P2X7R−/−) to investigate the role of P2X7R activation in the in vivo production of IL-1β and the development of postinflammatory visceral hypersensitivity in the T. spiralis-infected mouse. During acute nematode infection, IL-1β–containing cells and P2X7R expression were increased in the jejunum of wild-type (WT) mice. Peritoneal and serum IL-1β levels were also increased, which was indicative of elevated IL-1β release. However, in the P2X7R−/− animals, we found that infection had no effect upon intracellular, plasma, or peritoneal IL-1β levels. Conversely, infection augmented peritoneal TNF-α levels in both WT and P2X7R−/− animals. Infection was also associated with a P2X7R-dependent increase in extracellular peritoneal lactate dehydrogenase, and it triggered immunological changes in both strains. Jejunal afferent fiber mechanosensitivity was assessed in uninfected and postinfected WT and P2X7R−/− animals. Postinfected WT animals developed an augmented afferent fiber response to mechanical stimuli; however, this did not develop in postinfected P2X7R−/− animals. Therefore, our results demonstrated that P2X7Rs play a pivotal role in intestinal inflammation and are a trigger for the development of visceral hypersensitivity.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.