THE TRANSFER OF RATS FROM A FAMILIAR TO A NOVEL ENVIRONMENT PROLONGS THE INCREASE OF EXTRACELLULAR DOPAMINE EFFLUX INDUCED BY CCK8 IN THE POSTERIOR NUCLEUS-ACCUMBENS

The effects of cholecystokinin octapeptide (CCK8) on extracellular dop amine (DA) and its metabolites, 3,4-dihydroxyphenylacetic acid and hom ovanillic acid, were measured in the nucleus accumbens (N. Ace.), The experiments were carried out using in vivo microdialysis in awake rats submitted, or not, to a novel environment, the four-hole box, The exp loratory behavior of the animals was studied concurrently in these box es and in the elevated plus maze, Without CCK8 treatment, the transfer of animals from their home cages to the four-hole box induced a trans ient increase in DA efflux and also tended to increase its metabolites in the posterior N, Ace. In rats placed in a familiar environment, th e administration of 25 pmol of CCK8 in this region immediately enhance d DA release, with levels rapidly returning to normal at the end of th e perfusion, In contrast, this treatment produced a longer effect in r ats transferred to the four-hole box, since the DA efflux was still in creased 80 min after the removal of CCK8, The intra-accumbal administr ation of CCK8 induced a hypoexploration in the four-hole box, Moreover , an anxiogenic-like effect of CCK8 was found in the elevated plus maz e, only in rats submitted to a novel environment (four-hole box), Thes e data show that (1) the postero-accumbens DA neurons can be activated by environmental changes and (2) that the intensity of the CCK8 effec ts on extracellular DA levels and on anxiety-like responses seems to d epend on the activity of these neurons previous to CCK8 treatment, The prolonged DA release induced by CCK8 in animals placed in a new situa tion could correspond to a biochemical anticipation preparing them to react when faced by another stimulus.