A comparative evaluation of the dopamine D2/3 agonist radiotracer [11C]NPA and antagonist [11C]raclopride to measure amphetamine-induced dopamine release in the human striatum

()-N-Propyl-norapomorphine (NPA) is a full dopamine D2/3 receptor agonist, and [11C]NPA is a suitable radiotracer to image D2/3 receptors configured in a state of high affinity for agonists with positron emission tomography (PET). In this study, the vulnerability of the in vivo binding of [11C]NPA to acute fluctuation in synaptic dopamine was assessed with PET in healthy humans and compared with that of the reference D2/3 receptor antagonist radiotracer [11C]raclopride. Ten subjects (eight females and two males) were studied on two separate days, a minimum of 1 week apart, both with [11C]raclopride and [11C]NPA at baseline and after the administration of 0.5 mg kg1 oral d-amphetamine. Kinetic modeling with an arterial input function was used to derive the binding potential relative to nonspecific uptake (BPND) in the ventral striatum (VST), cau