Social and solitary feeding in natural Caenorhabditis elegans isolates are associated with two alleles of the orphan G-protein-coupled receptor (GPCR) NPR-1: social feeders contain NPR-1 215F, whereas solitary feeders contain NPR-1 215V. Here we identify FMRFamide-related neuropeptides (FaRPs) encoded by the flp-18 and flp-21 genes as NPR-1 ligands and show that these peptides can differentially activate the NPR-1 215F and NPR-1 215V receptors. Multicopy overexpression of flp-21 transformed wild social animals into solitary feeders. Conversely, a flp-21 deletion partially phenocopied the npr-1(null) phenotype, which is consistent with NPR-1 activation by FLP-21 in vivo but also implicates other ligands for NPR-1. Phylogenetic studies indicate that the dominant npr-1 215V allele likely arose from an ancestral npr-1 215F gene in C. elegans. Our data suggest a model in which solitary feeding evolved in an ancestral social strain of C. elegans by a gain-of-function mutation that modified the response of NPR-1 to FLP-18 and FLP-21 ligands.

To navigate O2 gradients, C. elegans can modulate turning rates and speed of movement. Aerotaxis can be reprogrammed by experience or engineered artificially. We propose a model in which prolonged activation of the AQR, PQR, and URX neurons by low O2 switches on previously inactive O2 sensors. This enables aerotaxis to low O2 environments and may encode a "memory" of previous cultivation in low O2.

Our work provides insights into how a complex behavior emerges from simpler behavioral motifs coordinated by a distributed circuit.

More than fifty FMRFamide-like neuropeptides have been identified in nematodes. We addressed the role of a subset of these in the control of nematode feeding by electrophysiological recording of the activity of C. elegans pharynx. AF1 (KNEFIRFamide), AF2 (KHEYLRFamide), AF8 (KSAYMRFamide), and GAKFIRFamide (encoded by the C. elegans genes flp-8, flp-14, flp-6, and flp-5, respectively) increased pharyngeal action potential frequency, in a manner similar to 5-HT. In contrast, SDPNFLRFamide, SADPNFLRFamide, SAEPFGTMRFamide, KPSVRFamide, APEASPFIRFamide, and AQTVRFamide (encoded by the C. elegans genes flp-1; flp-1; flp-3; flp-9; flp-13, and flp-16, respectively) inhibited the pharynx in a manner similar to octopamine. Only three of the neuropeptides had potent effects at low nanomolar concentrations, consistent with a physiological role in pharyngeal regulation. Therefore, we assessed whether these three peptides mediated their actions either directly on the pharynx or indirectly via the neural circuit controlling its activity by comparing actions between wild-type and mutants with deficits in synaptic signaling. Our data support the conclusion that AF1 and SAEPFGTMRFamide regulate the activity of the pharynx indirectly, whereas APEASPFIRFamide exerts its action directly. These results are in agreement with the expression pattern for the genes encoding the neuropeptides (Kim and Li, 1999) as both flp-8 and flp-3 are expressed in extrapharyngeal neurons, whereas flp-13 is expressed in I5, a neuron with synaptic output to the pharyngeal muscle. These results provide the first, direct, functional information on the action of neuropeptides in C. elegans. Furthermore, we provide evidence for a putative inhibitory peptidergic synapse, which is likely to have a role in the control of feeding.

In many items of high voltage plant, a mineral or synthetic oil is used in conjunction with paper as the dielectric medium. However, increasing awareness of the environmental impact of human activity and increasing disposal costs have encouraged researchers to direct their attention to renewable and biodegradable alternatives. Originally used in capacitors, vegetable oils are now finding widespread use in some transformer installations, particularly in the United States. Therefore, it seems prudent to begin systematic investigations of the aging behavior of a number of vegetable based oils and assess their potential for application in high voltage systems. A total of five food grade vegetable oils, an oil specifically formulated for high voltage applications (Envirotemp FR3) and dodecylbenzene (DDB) were aged at various temperatures in air. Their aging behavior was assessed by ultra-violet/visible, infrared and dielectric spectroscopies supplemented with measurements of viscosity. It was found that olive oil offered excellent resistance to aging (comparable to Envirotemp oil), rapeseed oil offered intermediate properties whereas corn and sunflower oil oxidized appreciably after aging. Despite being more prone to oxidation, all the vegetable oils offered dielectric properties which were better than dodecylbenzene and similar to mineral oil.