The CCK-B antagonist CI-988 increases dopamine levels in microdialysate from the rat nucleus accumbens via a tetrodotoxin- and calcium-independent mechanism.

CI-988, a water-soluble, selective cholecystokinin-B antagonist, was perfused through a microdialysis probe into the anterior nucleus accumbens, posterior nucleus accumbens, or caudate nucleus of anesthetized rats. High concentrations of CI-988 produced three- to fivefold increases in dopamine overflow, at all three sites, that were temporally correlated with the CI-988 perfusion and returned to baseline levels upon cessation of CI-988 perfusion. However, the cholecystokinin-A antagonist CAM-1481, and the relatively inactive enantiomer of CI-988, CAM-1241, also increased dopamine overflow in the nucleus accumbens. Furthermore, the ability of CI-988 to increase dopamine overflow persisted in the absence of calcium in the perfusate and was not sensitive to tetrodotoxin treatment. The mechanism by which locally administered CI-988 increases dopamine overflow appears not to be anatomically specific, not selective for one cholecystokinin receptor subtype, and may be nonvesicular.