DRD2 and Parkinson disease: Similarly, affinity of D2R (Long form) for dopamine agonist and D2R signaling is dramatically reduced upon co-expression and stimulation of A2AR in membrane preparation of rat [133] and sheep striatum [31] due to antagonistic effect on D2R which is exerted by A2AR. This explains why A2AR antagonists increase both the affinity of dopamine for D2R and therapeutic efficacy of L-dopa, which is used in treatment of Parkinson’s disease.