Orphan receptor. May be a receptor for RFamide-family neuropeptides such as NPFF and NPAF, which are analgesic in vivo. May regulate nociceptor function and/or development, including the sensation or modulation of pain (By similarity). Activated by the antimalarial drug chloroquine. Mediates chloroquine-induced itch, in a histamine-independent manner. Expressed exclusively in dorsal root ganglia and nodose ganglia. Expressed in a subset of sensory neurons that includes nociceptors. Expressed in the subclass of non-peptidergic sensory neurons that are IB4(+) and VR1(-). Belongs to the G-protein coupled receptor 1 family. Mas subfamily.