Effects of CCK8 and of the CCKB-selective agonist BC264 on extracellular dopamine content in the anterior and posterior nucleus accumbens: a microdialysis study in freely moving rats.

The effects of the local administration of cholecystokinin octapeptide (CCK8) in the posterior nucleus accumbens (N. Acc.) and of BC264 (a selective CCKB agonist) in the anterior N. Acc. on dopamine (DA) neurotransmission were studied in awake rats. Microdialysis was used to quantify the extracellular contents of DA and its two metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA). In the posterior N. Acc., a perfusion of 10(-5) M CCK8 for 40 min (i.e. 25 pmol) increased the extracellular levels of DA, DOPAC and HVA. In contrast, 10(-4) M BC264 perfused for 40 min (i.e. 350 pmol) into the anterior N. Acc. reduced extracellular DA but did not modify DOPAC and HVA levels. These findings suggest that the CCK-DA interactions are different in various regions of the N. Acc. and emphasize the functional heterogeneity of the N. Acc., issuing in part from its particular DA innervation (mixed CCK-DA terminals only in the posterior region) but also from the distribution of the CCK fibers and binding sites in this nucleus. This microdialysis study, using perfusions of CCK compounds in the N. Acc. of freely moving rats, shows that the CCK system might play an important regulatory role in limbic DA function.