Among the most important decisions an animal makes is whether to engage in active movement and feeding behavior or to become quiescent. The molecular signaling mechanisms underlying this decision remain largely unknown. The nematode Caenorhabditis elegans displays sleep-like quiescence following exposures that result in cellular stress. The neurosecretory ALA neuron is required for this stress-induced recovery quiescence, but the mechanisms by which ALA induces quiescence have been unknown. We report here that quiescence induced by heat stress requires ALA depolarization and release of FMRFamide-like neuropeptides encoded by the flp-13 gene. Optogenetic activation of ALA reduces feeding and locomotion in a FLP-13-dependent manner. Overexpression of flp-13 is sufficient to induce quiescent behavior during normally active periods. We have here identified a major biological role for FMRFamide-like neuropeptides in nematodes, and we suggest that they may function in a similar capacity in other organisms.
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