DRD2 and Parkinson disease: This, for instance, provides the rationale for the use of A2AR antagonists in PD, which increase the therapeutic index of L-DOPA.71,72 Second, GPCR heteromerization determines potential pharmacodynamic differences between exogenous compounds, such as the A2AR antagonist SCH442416, with its preferential binding to the presynaptic A1R-A2AR versus postsynaptic A2AR-D2R heterotetramers.