The effects of cholecystokinin (CCK-8) on dopamine-containing nerve terminals in the caudate nucleus and nucleus accumbens of the anesthetized rat: an in vivo electrochemical study

The action of cholecystokinin (CCK) on presynaptic function of dopaminergic nerve terminals has been the subject of much debate in the literature. In efforts to resolve some of the reported ambiguities, high speed in vivo electrochemical recordings were carried out in the caudate nucleus and nucleus accumbens of the urethane anesthetized rat, to determine effects of locally applied sulfated (CCK-8S) and unsulfated (CCK-8US) CCK octapeptide. Locally-applied CCK-8S and CCK-8US caused no increase in the baseline electrochemical signals recorded from either brain region. However, locally applied CCK-8S potentiated the potassium-evoked overflow of dopamine (DA) into the extracellular space in both the caudate and nucleus accumbens. In contrast, pressure ejection of CCK-8US produced no significant effects on the potassium-evoked overflow of DA in either structure. These data support a facilitatory effect of CCK-8S on potassium-evoked overflow from DA-containing nerve terminals in the urethane anesthetized rat that is likely mediated through a peripheral type CCK receptor.