Betaine receptor that functions as a ligand-gated non-selective monovalent cation channel in mechanosensory neurons to maintain basal levels of locomotion. The channel is permeable to Na(+) and K(+) but not to Ba(2+) or Ca(2+) ions. Elicits current in response to betaine, very weak current in response to choline, virtually no current in response to acetylcholine and nicotine, and no current in response to glycine and GABA. Expressed in the body wall muscles that are arranged into four longitudinal bundles, some mechanosensory neurons, the head muscles and multiple interneurons. Not expressed in motor neurons (at protein level). Not expressed in embryos and L1 stage but expressed from L2 stage to adulthood in the body wall muscles (at protein level). Mutant worms are morphologically similar to the wild-type but exhibit mild swimming defects and are lethargic with their movement being interrupted by frequent pauses when crawling on a food-free environment (PubMed:24212673). On the same environment, in other occasions they display decreased rates of spontaneous reversal and steering, and slightly increased average speed (PubMed:23950710). Homozygotes are fully resistant to monepantel but heterozygotes are partially affected by the drug with reduced fertility and slightly impaired movement. Suppresses snf-3 mutant phenotype growth defects. Elicits no current in response to the broad-spectrum antiparasitic medicine ivermectin. This channel is allosterically sensitive to monepantel, an anthelmintic of the amino-acetonitrile derivatives (AADs) class, leading to muscle paralysis upon treatment with monepantel. Belongs to the ligand-gated ion channel (TC 1.A.9) family. Acetylcholine receptor (TC 1.A.9.1) subfamily.