Regional effects of ceruletide, a cholecystokinin-8 analog, on the striatal monoaminergic systems in food-deprived mice.

To clarify the pharmacological mechanism by which ceruletide affects involuntary movements, we used 20-h food-deprived mice to examine the acute effects of ceruletide (600 micrograms/kg, i.p.) on the histochemistry of striatal dopaminergic and serotonergic systems. The latter was unchanged but a reduction in catecholamine fluorescence was seen which was restricted to the ventrolateral (VL) portion of the striatum. Biochemical assays also indicated decreased levels of dopamine (DA) and its metabolites in this restricted region of the striatum with little or no change in noradrenaline, serotonin or their metabolites. In all regions examined, except the dorsomedial part of the mid-striatum, the ratio of dopamine metabolites to dopamine was higher in the ceruletide-treated group than in controls, suggesting increased DA release. Further pharmacological experiments showed that, compared to results in mice receiving only ceruletide: the ceruletide-induced decreases in DA and dihydroxyphenylacetic acid (DOPAC) in VL were less after alpha-methyl-p-tyrosine treatment; ceruletide caused no significant decrease in either DA or DOPAC after pargyline pretreatment, although the low levels of homovanillic acid (HVA) were still further significantly reduced; and the ceruletide-induced decrease of DA was reduced, that of DOPAC was abolished and that of HVA enhanced by nomifensine pretreatment. These results suggested that ceruletide might induce a more rapid degradation of DA in VL and increased efflux of HVA through the blood-brain barrier. This evidence suggests that ceruletide has a regionally specific effect on the striatal dopaminergic system which may relate to the amelioration of involuntary movements.