FMRFamide-like neuropeptides (PubMed:14555955, PubMed:23658528). Ligand to G-protein coupled receptor npr-1 (PubMed:14555955). Involved in modulating locomotion quiescence during the sleep-like state called lethargus which occurs during molting between larval and adult stages, acting via npr-1 (PubMed:23764289). Together with flp-1, plays a homeostatic role by acting on the GABAergic neural transmission at neuromuscular junctions to prevent overexcitation of the locomotor circuit (PubMed:23658528). Plays a role in the navigational capacity of sperm and the targeting of sperm derived from males to the fertilization site in the uterus of hermaphrodites (PubMed:28662030). SVPGVLRF-amide: Excites muscle tension. Activates the G-protein coupled receptor npr-1 more effectively than other flp-18 peptides (PubMed:14555955). Inhibits the activity of dissected pharyngeal myogenic muscle system. Expressed in head neurons and weakly in ventral nerve cord (PubMed:23658528). Expressed in the interneurons AVA, AIY and RIG, the motor neuron RIM and the pharyngeal neurons M2 and M3 (PubMed:14555955). EMPGVLRF-amide: Expressed in cholinergic pharyngeal motoneurons M2 and M3 (PubMed:16187307). May be processed by convertase egl-3. Belongs to the FARP (FMRFamide related peptide) family. Activity as ligand to G-protein coupled receptor npr-1 might depend on a neomorphic gain-of-function sensitivity of the receptor npr-1 associated with the Bristol N2 strains.