Cue-induced dopamine release predicts cocaine preference: Positron emission tomography studies in freely moving rodents

Positron emission tomography studies in drug-addicted patients have shown that exposure to drug-related cues increases striatal dopamine, which displaces binding of the D₂ ligand, [¹¹C]-raclopride. However, it is not known if animals will also show cue-induced displacement of [ ¹¹C]-raclopride binding. In this study, we use [¹¹C]- raclopride imaging in awake rodents to capture cue-induced changes in dopamine release associated with the conditioned place preference model of drug craving. Ten animals were conditioned to receive cocaine in a contextually distinct environment from where they received saline. Following conditioning, each animal was tested for preference and then received two separate [¹¹C]- raclopride scans. For each scan, animals were confined to the cocaine and/or the saline-paired environment for the first 25 min of uptake, after which they were anesthetized and scanned. [¹¹C]-raclopride uptake in the saline-paired environment served as a within-animal control for uptake in the cocaine-paired environment. Cocaine produced a significant place preference (p = 0.004) and exposure to the cocaine-paired environment decreased [ ¹¹C]-raclopride binding relative to the saline-paired environment in both the dorsal (20%; p < 0.002) and ventral striatum (22%; p < 0.05). The change in [¹¹C]-raclopride binding correlated with preference in the ventral striatum (R² = 0.87; p = 0.003). In this region, animals who showed little or no preference exhibited little or no change in [ ¹¹C]-raclopride binding in the cocaine-paired environment. This noninvasive procedure of monitoring neurochemical events in freely moving, behaving animals advances preclinical molecular imaging by interrogating the degree to which animal models reflect the human condition on multiple dimensions, both biological and behavioral.