DRD3 and Parkinson disease: Dopamine D3 receptor (D3R) has been explored as a potential drug target for the treatment of schizophrenia, Parkinson’s disease (PD), addiction, anxiety, depression, etc. D3R is a class A GPCR and belongs to the dopamine D2-like receptor family, which couples to the inhibitory Gαi/o [23] and is distributed both in the periphery and the brain [24].