Dopamine output in the nucleus accumbens shell is related to the acquisition and the retention of a motivated appetitive behavior in rats

Chronic stress exposure consistently impairs the reactivity to aversive and pleasurable stimuli in rats; these behavioral modifications are associated with a decrease in dopamine output in the nucleus accumbens shell (NAcS). However, when rats that have already acquired an appetitive behavior are exposed to chronic stress, they develop an impaired reactivity to avoidable aversive stimuli while retaining the appetitive behavior. The dissociation between these two behavioral traits was used to study whether the decreased dopaminergic activity in the NAcS was connected to either of the two deficits. Dopamine output was studied through microdialysis as dopamine accumulation following re-uptake inhibition by cocaine. When rats that had previously acquired the appetitive behavior were exposed to chronic stress, they showed a dopaminergic transmission in the NAcS similar to that of controls and significantly higher than that of chronically stressed animals. Thus, dopamine output in the NAcS was consistently associated to the acquisition and maintenance of appetitive behavior, while the expression of a deficit in avoidance appeared to be independent of it.