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. These dopamine signals conform to traditional reward-prediction error signals and have been shown to diminish with time. Here we examined if the diminishing dopamine signal in the nucleus accumbens core 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 (100 mM), or the GABA agonists baclofen and muscimol (0.5 mM baclofen/0.05 mM muscimol) into the nucleus accumbens core or the dorsal lateral striatum. Dopamine antagonism within the nucleus accumbens core attenuated sign-tracking, whereas reversible inactivation did not affect sign-tracking but increased non-specific food cup checking behaviors. Neither drug in the dorsal lateral striatum affected sign-tracking behavior. Critically, extended training did not alter these effects. Though extended experience with an incentive stimulus may reduce cue-evoked dopamine in the nucleus accumbens core, this does not alter the function of 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. Abbreviations DLS dorsal lateral striatum GT goal-tracker IN intermediate responder NAcC nucleus accumbens core ST sign-tracker