DRD2 and major depressive disorder: Disruptions in the regulation of this system are known to result in numerous disorders, including depression, psychosis, bipolar disorder, general anxiety disorder and Parkinson's disease.1 Neurotransmitters mediate their effects via numerous G protein coupled receptors (GPCRs), which comprise the largest family of human cell surface receptors.2 Herein, we focus on the dopamine D2 receptor (D2R) and its endogenous agonist dopamine – a neurotransmitter with a catecholamine scaffold3 that is also common to other signaling molecules (e.g., adrenaline or noradrenaline).