NUCLEUS ACCUMBENS SHELL AND CORE DOPAMINE MODIFICATIONS DURING OPERANT RESPONDING FOR SUCROSE

Natural and pharmacological rewarding primary stimuli potentiated mesolimbic dopamine (DA) transmission. Stimuli conditioned (CS) to these rewards (food, sex, drugs of abuse) (US), are essential to support the motivated behaviour, and it is well known that drugs-CSs increased mesolimbic DA. Much discrepancies exist about the impact of food-CSs on nucleus accumbens (NAc) DA. In particular it has been reported that after classical conditioning paradigm, NAc-shell DA shows responsiveness to food US, but it is unresponsive to food-CS, while NAc-core DA is both affected by food-CS and US. The aim of our study was to clarify the role of NAc DA in the responsiveness to CS and to US using a self-administration paradigm (FR1 and FR5). Coupling the microdialysis technique to this paradigm we have studied DA transmission in NAc-shell and core during: 1)sucrose pellets seeking behavior, 2)conditioned cues exposure and 3)non-contingent presentation of sucrose pellets. The main finding of our study was that NAc-shell DA has been activated not only by the conditioned cues but also by food after the instrumental conditioning, and that when both stimuli are presented in the same moment the increase of DA is strengthened and prolonged. We also found that during the acquisition process DA in the shell, but not in the core, increased in parallel to the progress of the training process. We can conclude that DA in the NAc-shell plays an important role on the acquisition and expression of motivated behavior in food consumption.