Orphan G-protein coupled receptor. Constitutively activates the G(s)-alpha/cAMP signaling pathway (PubMed:28827538). Shows a reciprocal regulatory interaction with the melatonin receptor MTNR1B most likely through receptor heteromerization (PubMed:28827538). May be involved in the regulation of food intake and body weight (By similarity). Forms heterodimer with MTNR1B (PubMed:28827538). Interacts with ARRB1 and ARRB2 in a spontaneous and agonist-independent manner; leading to the internalization of GPR61 in the endosomal compartment (PubMed:28827538). Colocalizes with ARRB2/beta-arrestin-2 in the endosome (PubMed:28827538). Expressed in brain; detected in frontal and temporal lobes, occipital pole, amygdala and hippocampus (PubMed:11690637, PubMed:29226084). Also expressed in testis (PubMed:11690637, PubMed:29226084) and T cells, B cells, and monocyte (PubMed:29226084). Low expression in many other tissues (PubMed:11690637, PubMed:29226084). Widely expressed in the hippocampus (at protein level). Belongs to the G-protein coupled receptor 1 family.