Spagnolo PA, Kimes A, Schwandt ML, et al. - Using [¹¹C]raclopride displacement, researchers sought to determine striatal dopamine (DA) release resulting from an intravenous infusion of morphine in healthy, nondependent opioid-experienced participants. They also investigated how DA release is related to morphine-induced subjective effects in these participants. To ensure tolerability, intravenous morphine (10 mg/70 kg) was given to 15 participants in the clinic on session 1. Intravenous morphine and placebo (saline) sessions were then provided to participants without adverse reactions (n = 10), in counterbalanced order, while performing [¹¹C]raclopride positron emission tomography scans. In this study for the first time, in vivo human evidence indicating DA transmission in the ventral striatum is impacted by morphine was presented. They observed clear subjective and physiological effects and a significant decrease in [¹¹C]raclopride nondisplaceable binding potential, especially in the nucleus accumbens and globus pallidus, following administration of morphine. The change in [¹¹C]raclopride nondisplaceable binding potential was approximately 9%.