INVOLVEMENT OF D(2) DOPAMINERGIC RECEPTORS IN THE EMOTIONAL AND MOTIVATIONAL RESPONSES INDUCED BY INJECTION OF CCK-8 IN THE POSTERIOR PART OF THE RAT NUCLEUS-ACCUMBENS

When CCK-8 was injected in the rat posterior nucleus accumbens, where it is in part co-localized with dopamine, a decrease in exploration of the four hole box and the elevated plus maze was observed. In this st udy, a selective destruction of the dopaminergic mesoaccumbens pathway induced by local injection of 6-hydroxydopamine (6-OHDA) in the nucle us accumbens was found to suppress the CCK-8-evoked behavioral effects . Moreover, an ex vivo measurement of the dopaminergic metabolism has been performed after injection of CCK-8 in the posterior nucleus accum bens by electrochemical detection of dopamine and its metabolites extr acted from punches of brain tissue. The results showed that CCK-8 decr eased the turnover of dopamine in the posterior part but not in the an terior part of the nucleus accumbens or in the ventral tegmental area. Furthermore, sulpiride, a selective antagonist for D2 dopamine recept ors, but not SCH 23390, a selective antagonist for D1 dopamine recepto rs, prevented CCK-8-induced behavioral responses. Taken together, thes e results suggest that CCK-8 could be involved in behavioral adaptatio n to situations producing change in emotional and/or motivational stat es through modulation of presynaptic D2 receptor functioning.