Dopamine D2 Modulation of Sign and Goal Tracking in Rats.

In Pavlovian conditioning, sign- and goal-tracking behaviors represent different approaches towards the conditioned stimulus. These behavioral patterns have been associated with predictive or incentive properties of the conditioned stimulus, with a crucial involvement of the mesolimbic dopamine system. As it is possible that sign tracking behavior is more sensitive to dopamine modulation, we evaluated the dopamine-dependence of sign- and goal-tracking behavior. We assessed responses to both a D2 agonist and an antagonist, and tested performance in a behavioral paradigm known to activate dopamine projections and in an animal model that affects mesolimbic and mesocortical function. Sign trackers displayed a greater sensitivity to a D2 agonist and smaller prepulse inhibition of the acoustic startle response than goal trackers, suggesting a reduced inhibitory ability. In addition, a neonatal ventral hippocampal lesion resulted in the loss of incentive salience of cues in sign trackers. Overall, these data indicate that sign-tracking behavior is more heavily controlled by dopamine than goal tracking.