Orphan G-protein coupled receptor. Constitutively activates the G(s)-alpha/cAMP signaling pathway (By similarity). Shows a reciprocal regulatory interaction with the melatonin receptor MTNR1B most likely through receptor heteromerization (By similarity). May be involved in the regulation of food intake and body weight (PubMed:21971119). Forms heterodimer with MTNR1B. Interacts with ARRB1 and ARRB2 in a spontaneous and agonist-independent manner; leading to the internalization of GPR61 in the endosomal compartment (By similarity). Colocalizes with ARRB2/beta-arrestin-2 in the endosome (By similarity). Predominantly expressed in the brain and testes, with relatively lower expression observed in the eye, adrenal gland and pituitary gland. Deficient mice exhibit obesity associated with hyperphagia. Belongs to the G-protein coupled receptor 1 family.