Invertebrate neuroscience has provided a number of very informative model systems that have been extensively utilized in order to define the neurobiological bases of animal behaviours (Sattelle and Buckingham in Invert Neurosci 6:1-3, 2006). Most eminent among these are a number of molluscs, including Aplysia californica, Lymnaea stagnalis and Helix aspersa, crustacean systems such as the crab stomatogastric ganglion and a wide-range of other arthropods. All of these have been elegantly exploited to shed light on the very important phenomenon of the molecular and cellular basis for synaptic regulation that underpins behavioural plasticity. Key to the successful use of these systems has been the ability to study well-defined, relatively simple neuronal circuits that direct and regulate a quantifiable animal behaviour. Here we describe the pharyngeal system of the nematode C. elegans and its utility as a model for defining the genetic basis of behaviour. The circuitry of the nervous system in this animal is uniquely well-defined. Furthermore, the feeding behaviour of the worm is controlled by the activity of the pharynx and this in turn is regulated in a context-dependent manner by a simple nervous system that integrates external signals, e.g. presence or absence of food, and internal signals, e.g. the nutritional status of the animal to direct an appropriate response. The genetics of C. elegans is being effectively exploited to provide novel insight into genes that function to regulate the neuronal network that controls the pharynx. Here we summarise the progress to date and highlight topics for future research. Two main themes emerge. First, although the anatomy of the pharyngeal system is very well-defined, there is a much poorer understanding of its neurochemistry. Second, it is evident that the neurochemistry is remarkably complex for such a simple circuit/behaviour. This suggests that the pharyngeal activity may be subject to exquisitely precise regulation depending on the animal's environment and status. This therefore provides a very tractable genetic model to investigate neural mechanisms for signal integration and synaptic plasticity in a well-defined neuronal network that directs a quantifiable behaviour, feeding.

This review considers the factors involved in the regulation of feeding and metabolism in response to food deprivation using Caenorhabditis elegans as a model organism. Some of the sensory neurons and interneurons involved in food intake are described, together with an overview of pharyngeal pumping. A number of chemical transmitters control feeding in C. elegans including 5-hydroxytryptamine (5-HT, serotonin), acetylcholine, glutamate, dopamine, octopamine, and tyramine. The roles of these transmitters are modified by neuropeptides, including FMRFamide-like peptides (FLPs), neuropeptide-like protein (NLPs), and insulin-like peptides. The precise effects of many of these neuropeptides have yet to be elucidated but increasingly they are being shown to play a role in feeding and metabolism in C. elegans. The regulation of fat stores is complex and appears to involve the expression of a large number of genes, many with mammalian homologues, suggesting that fat regulatory signalling is conserved across phyla. Finally, a brief comparison is made between C. elegans and mammals where for both, despite their evolutionary distance, classical transmitters and neuropeptides have anorectic or orexigenic properties. Thus, there is a rationale to support the argument that an understanding of the molecular and genetic basis of feeding and fat regulation in C. elegans may contribute to efforts aimed at the identification of targets for the treatment of conditions associated with abnormal metabolism and obesity.

BACKGROUNDMacrocyclic lactones are arguably the most successful chemical class with efficacy against parasitic nematodes. Here we investigated the effect of the macrocyclic lactone ivermectin on lipid homeostasis in the plant parasitic nematode Globodera pallida and provide new insight into its mode of action.RESULTSA non‐invasive, non‐destructive, label‐free and chemically selective technique called Coherent anti‐Stokes Raman scattering (CARS) spectroscopy was used to study lipid stores in G. pallida. We optimised the protocol using the free‐living nematode Caenorhabditis elegans and then used CARS to quantify lipid stores in the pre‐parasitic, non‐feeding J2 stage of G. pallida. This revealed a concentration of lipid stores in the posterior region of J2 s within 24 h of hatching which decreased to undetectable levels over the course of 28 days. We tested the effect of ivermectin on J2 viability and lipid stores. Within 24 h, ivermectin paralysed J2 s. Counterintuitively, over the same time‐course ivermectin increased the rate of depletion of J2 lipid, suggesting that in ivermectin‐treated J2 s there is a disconnection between the energy requirements for motility and metabolic rate. This decrease in lipid stores would be predicted to negatively impact on J2 infective potential.CONCLUSIONThese data suggest that the benefit of macrocyclic lactones as seed treatments may be underpinned by a multilevel effect involving both neuromuscular inhibition and acceleration of lipid metabolism. © 2017 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.