Effects of microinjection of the D2 dopamine antagonist raclopride into the ventral tegmental area on ethanol and sucrose self-administration

From previous microinjection studies, a reciprocal feedback between the nuc leus accumbens and the ventral tegmental area (VTA) has been implicated in the reinforcing stimulus actions of ethanol and sucrose. In these studies, the effects of self administration of ethanol or sucrose solutions on maint ained responding were similar when a dopamine antagonist was injected in th e nucleus accumbens or a dopamine agonist was injected into the VTA. Our st udy was performed to determine if the effects on responding that had been o bserved when a dopamine agonist was injected into the nucleus accumbens wou ld occur after an injection of a dopamine antagonist into the VTA. Male, Lo ng-Evans rats were initially trained to lever press using either 10% ethano l or 75% sucrose solutions as the reinforcers. Bilateral guide cannulae wer e implanted to allow microinjection into the VTA of differing doses of the dopamine D2 antagonist, raclopride, Only at the highest dose tested (10 mu g) was any effect observed on responding maintained by either reinforcer. T he effect was minimal and different from that observed after the microinjec tion of a dopamine agonist into the nucleus accumbens. This suggests that e ither the actions of the nucleus accumbens agonist manipulation involved ot her processes or that the level of enhanced dopamine release in the nucleus accumbens from the VTA antagonist injection was not sufficient to mimic th e effect of the nucleus accumbens agonist injections.