Long-lasting contribution of dopamine in the nucleus accumbens core, but not dorsal lateral striatum, to sign-tracking.

The attribution of incentive salience to reward-paired cues is dependent on dopamine release in the nucleus accumbens core (NAcC). These dopamine signals conform to traditional reward-prediction error signals and have been shown to diminish with time. Here we examined whether the diminishing dopamine signal in the NAcC has functional implications for the expression of sign-tracking, a Pavlovian conditioned response indicative of the attribution of incentive salience to reward-paired cues. Food-restricted male Sprague Dawley rats were trained in a Pavlovian paradigm in which an insertable lever predicted delivery of food reward in a nearby food cup. After 7 or 14 training sessions, rats received infusions of saline, the dopamine antagonist flupenthixol, or the GABA agonists baclofen and muscimol into the NAcC or the dorsal lateral striatum (DLS). Dopamine antagonism within the NAcC attenuated sign-tracking, whereas reversible inactivation did not affect sign-tracking but increased non-specific food cup checking behaviors. Neither drug in the DLS affected sign-tracking behavior. Critically, extended training did not alter these effects. Although extended experience with an incentive stimulus may reduce cue-evoked dopamine in the NAcC, this does not remove the dependence on dopamine in this region to promote Pavlovian cue approach nor result in the recruitment of dorsal lateral striatal systems for this behavior. These data support the notion that dopamine within the mesoaccumbal system, but not the nigrostriatal system, contributes critically to incentive motivational processes independent of the length of training.