Extracellular dopamine in the anterior nucleus accumbens is distinctly affected by ventral tegmental area administration of cholecystokinin and apomorphine: data from in vivo voltammetry.

The interaction of cholecystokinin (CCK) and dopamine (DA) in the mesolimbic system was investigated. The study focused on DAergic cells not containing colocalized CCK projecting from the ventral tegmental area (VTA) to the anterior nucleus accumbens (NA). Differential pulse voltammetry in pargyline pretreated and anesthetized rats was used to measure extracellular DA in the anterior NA following microinjection of apomorphine either alone or in combination with CCK-8s into the VTA. In agreement with an earlier study there was a dose-dependent increase in the DA signal in the anterior NA after microinjection of CCK-8s into the VTA. Apomorphine microinjected into the VTA produced a biphasic effect on extracellular DA in the anterior NA with an increase from basal levels of approximately 50% by 1 ng, whereas 10 ng was ineffective and 100 ng apomorphine caused a slight decrease in the DA signal. Apomorphine (1 ng) microinjected together with 1 ng CCK-8s produced an increase in the DA signal to approximately 180% of the baseline value, whereas the combination of 1 ng apomorphine and 100 ng CCK-8s was ineffective. When 100 ng apomorphine were microinjected in combination with either 1 ng or 100 ng CCK-8s, the DA signal in the anterior NA was unchanged. These results suggest that low doses of apomorphine injected into the VTA synergistically influence the effects of CCK-8s on extracellular DA in the anterior NA, whereas higher doses of apomorphine suppress the effect of CCK-8s on DAergic cells projecting to the anterior NA.