Dopaminergic Modulation of Brain Activation Using Simultaneous PET/Pharmacological MRI

Objectives: The overarching goal of this study is to assess the dynamic association between dopamine (DA) D2 receptor (D2R) occupancy measured by positron emission tomography (PET) with \[11C\]raclopride and brain activity inferred by pharmacological magnetic resonance imaging (phMRI) in the human brain, and to assess the relative sensitivity and specificity of the neurovascular coupling for slow (oral) versus rapid (intravenous, IV) stimulant methylphenidate (MP) delivery. Secondary objectives are to assess the associations between behavioral measures (heart and respiration rates and blood pressure, motor and sleep parameters, and neuropsychological testing variables), D2R occupancy and fMRI signals. Study population: 10 healthy males and 10 healthy females 18-55 years old will be included. Test-retest reproducibility studies will be carried out in 5 participants. Design: Double-blind. Participants will undergo simultaneous PET/phMRI, to evaluate dynamic changes in D2R occupancy by DA with \[11C\]raclopride and in blood-oxygenation-level dependent (BOLD) signals, under MP or placebo (PL). The participants will be scanned on 3 different occasions: 1) oral-MP (60 mg) and iv PL (3 cc saline), 2) oral-PL and iv-MP (0.25 mg/kg in 3 cc sterile water) and 3) oral PL and iv PL, which will be carried in different study days with at least 48 hours between them and their order will be randomized across subjects. Participants and researchers will be blind to the nature of the stimulant drug (MP/PL). Outcome parameters: The scale factor between the distribution volume ratio (DVR) and the BOLD signal in the dorsal and ventral striatum for the slow and fast MP challenges.