OPRL1 and depressive symptom measurement: The protein encoded by OPRL1 is a member of the 7 transmembrane G protein-coupled receptor family, which acts as a receptor for endogenous nociceptin/orphanin FQ and is involved in a variety of biological functions and the regulation of neurobehavioral behaviours, including depression, anxiety, learning, memory, motor activity and drug dependence and addiction40–43.