Previously, it has been shown that α2-AR antagonists improve tremor and rigidity in the reserpinized rat [83], have a potent effect on levodopa-induced dyskinesia in a PD monkey model [84,85,86], and can extend the anti-parkinsonian effect of levodopa in MPTP-treated monkeys [87,88]. This evidence concerns the gene ADORA2A and Parkinson disease.