The regulation of cholecystokinin release from rat caudatoputamen in vitro

Cholecystokinin (CCK) is one of the most abundant neuropeptides in the rat caudatoputamen (cp). CCK perikarya innervating cp are thought to originate in neurons in the claustrum/piriform cortex area of the amygdala. Previous studies on the release of CCK from cp have focused on the influence of dopamine agonists. The present study has examined the influence of other neuroactive substances on the release of CCK. The release of CCK from rat cp slices in vitro stimulated by potassium was quantitated with a specific CCK radioimmunoassay. This potassium-stimulated release of CCK was Ca2+-dependent. Maximal stimulation of CCK release was observed at 55 mM potassium. Several lines of evidence indicate that the release of CCK from cp is inhibited by some other substance (or substances) released by a Ca2+-dependent mechanism from cp along with CCK. Release media from cerebral cortex or cp (called 'conditioned media' or CM) inhibits the release of CCK from fresh slices of cp but not from cerebral cortex. The release of dopamine from cp is unaffected by CM from cortex or cp. The identity of the substance in CM which inhibits CCK release from cp is still under investigation, though it appears not to be CCK, dopamine, acetylcholine, somatostatin, leucine enkephalin or gamma-aminobutyric acid.