DR1 and Parkinson disease: We propose that this effect forms the mechanistic basis for the profound motor defects shown by unilateral lactacystin-lesioned rats and reflects data from other PET imaging studies that also made use of a D2/3 receptor probe, to reveal that DR1 striatal levels are typically elevated in PD patients prior to DA substitution therapy [59, 60], similar to that seen in other animal models of PD [61].