EFFECTS OF ADMINISTRATION OF CHOLECYSTOKININ INTO THE VTA ON DA OVERFLOW IN NUCLEUS-ACCUMBENS AND AMYGDALA OF FREELY MOVING RATS

The carboxyterminal octapeptide of cholecystokinin (CCK-8) coexists wi th dopamine (DA) in mesolimbic neurons of the ventral tegmental area ( VTA). In the present study, in vivo microdialysis in freely moving rat s was used to assess the relative effects of sulfated CCK-8 (CCK-8S), unsulfated CCK-8 (CCK-8US) and CCK tetrapeptide (CCK-4), focally injec ted into the VTA, on DA overflow in two mesolimbic DA/CCK-8S terminal regions, the nucleus accumbens and the amygdala. Consistent with elect rophysiological findings, microinjection of CCK-8S, but not CCK-BUS or CCK-4, elicited increases in DA overflow in both terminal regions. In the absence of anatomical evidence of CCK-containing fibers in the VT A region, it seems reasonable to conclude that the modulation of termi nal DA overflow by CCK-8S through actions at the somatodendritic regio n represents a form of autoregulation of these cells. Whereas CCK-8US and CCK-4 are preferential CCK-B receptor agonists, CCK-8S binds non-s electively to CCK-A and CCK-B receptors. Thus, these results implicate CCK-A receptors in the stimulatory effects of CCK-8S on VTA DA neuron s.