Differential involvement of dopamine receptor subtypes in the acquisition of Pavlovian sign-tracking and goal-tracking responses.

Previous work has identified that different forms of Pavlovian conditioned approach, sign-tracking and goal-tracking, are governed by distinct neurochemical mechanisms when compared in animals predisposed to learning one form vs. the other. The present study aimed to investigate whether these are also neurochemically distinct processes in a population of animals capable of developing either response when this is manipulated via the use of distinct conditioned stimuli (CS). Rats were trained on one of two Pavlovian conditioning procedures in which the CS was either a lever, which elicits sign-tracking, or an auditory click, which elicits goal-tracking. The differential involvement of dopamine D1- and D2-receptors (D1R; D2R) in the acquisition of approach types was investigated via systemic administration of antagonists selective to one or both receptor subtypes during Pavlovian training. Results indicate that dopaminergic signalling is important for the acquisition of both sign-tracking and goal-tracking responses. However, whilst development of sign-tracking to a lever depends on activity at both D1R and D2R, development of goal-tracking in response to a click was shown to depend only on activity at D1R. We suggest that the importance of D1R activity in both sign- and goal-tracking acquisition reflects a general role in learning Pavlovian associations, which aligns with data implicating dopamine in prediction error processes. In contrast, the selective involvement of D2R activity in sign-tracking acquisition may reflect its importance in motivational processes such as incentive salience attribution.