ADORA2A and Parkinson disease: Adenosine A2A receptors in striatum are selectively localized on GABAergic output neurons of the striatopallidal pathway.3 Increase in GABA release from the globus pallidus after 6-hydroxydopamine injection into the medial forebrain bundle was reversed by systemic injection with istradefylline in rats.18 This study (6002-009) demonstrated the efficacy and safety of istradefylline in Japanese PD subjects.