DRD2 and Parkinson disease: Interestingly, the stimulation of A2ARs in A2A-D2 heterodimers positively regulates β-arrestin recruitment to D2Rs, resulting in D2R internalization (Borroto-Escuela et al., 2011; Huang et al., 2013), and the functional coupling of heterodimer receptors is impaired in a rat model of Parkinson’s disease (Fernández-Dueñas et al., 2015).