Dopamine modulates cholecystokinin release in neostriatum.

Peptides of the cholecystokinin family, but mainly the sulphated octapeptide (CCK8), have been found in brain extracts of several species. High amounts are present in axons and nerve endings in the rat neostriatum (caudate-putamen) and a role for cholecystokinin as a neurotransmitter in this functionally important area is possible. We have incubated slices of rat caudate-putamen (CP) to study the release of cholecystokinin-immunoreactivity (CCK-IR) in vitro. The release of CCK-IR was induced by veratridine. It was dependent on the presence of Ca2+ in the incubation medium and was blocked by tetrodotoxin. We now present evidence that dopaminergic agonists added to the slices modulate the veratridine-induced release via different groups of receptors. Receptors which mediate an enhancement of the release of CCK-IR seem to be located on afferent axons and nerve endings and are possibly of the D-2 subtype. Receptors which mediate an attenuation of the release are probably situated on cells intrinsic to the CP. These receptors seem to be coupled to adenylate cyclase and might thus be of the D-1 subtype. There is also evidence that endogenous dopamine when released enhances the secretion of CCK-IR.