G protein-coupled receptors (GPRs), also known as seven transmembrane receptors, heptahelical receptors or 7TM receptors, comprise a superfamily of proteins that play a role in many different stimulus-response pathways. G protein coupled receptors translate extracellular signals into intracellular signals (G protein activation) and they respond to a variety of signaling molecules, such as hormones and neurotransmitters. GPR123 (G protein-coupled receptor 123) is a 1,279 amino acid multi-pass membrane protein belonging to the G-protein coupled receptor 2 family and LN-TM7 subfamily. Existing as two alternatively spliced isoforms, GPR123 functions as an orphan receptor that is expressed in adult and fetal brain, and in adult spinal cord. The gene encoding GPR123 maps to human chromosome 10q26.3 and mouse chromosome 7 F4.