BLOC1S4 and Parkinson disease: In the present study, we uniquely combined our PPN cholinergic DREADD-PD rat model with positron emission tomography (PET) brain scans, utilizing the DR2/3 ligand [11C]PHNO, to test our hypothesis that the CNO-induced motor improvement is due to PPN cholinergic-induced DA release from nigrostriatal DAergic terminals in the striatum.