GPR139 is a G protein-coupled receptor thought to act on the Gq/11 pathway and whose endogenous agonists are thought to be L-Trp and L-Phe (aromatic amino acids) and also ACTH/alpha-MSH-related peptides. It has putative functions in regulating locomotion, metabolism and addiction and may be relevant to dysfunction of these processes in Parkinson's disease, diabetes and hyperalgesia. In immunohistochemistry, GPR139 has membranous positivity in the striatum, hypothalamus, pituitary, thalamus and habenula in the central nervous system and is nearly absent in peripheral tissues (endometrium and smooth muscle may stain). References: Basic Clin Pharmacol Toxicol. 2019;00:1–12, DOI: 10.1111/bcpt.13263; Neurochem Int. 2017 Jan; 102: 105–113, PMID: 27916541