Rationale: The paraventricular nucleus of the thalamus (PVT) has been shown to mediate cue-motivated behaviors, such as sign- and goal-tracking, as well as reinstatement of drug-seeking behavior. However, the role of the PVT in mediating individual variation in cue-induced drug-seeking behavior remains unknown.
Objectives: This study aimed to determine if inactivation of the PVT differentially mediates cue-induced drug-seeking behavior in sign-trackers and goal-trackers.
Methods: Rats were characterized as sign-trackers (STs) or goal-trackers (GTs) based on their Pavlovian conditioned approach behavior. Rats were then exposed to 15 days of cocaine self-administration, followed by a 2-week forced abstinence period and then extinction training. Rats then underwent tests for cue-induced reinstatement and general locomotor activity, prior to which they received an infusion of either saline (control) or baclofen/muscimol (B/M) to inactivate the PVT.
Results: Relative to control animals of the same phenotype, GTs show a robust increase in cue-induced drug-seeking behavior following PVT inactivation, whereas the behavior of STs was not affected. PVT inactivation did not affect locomotor activity in either phenotype.
Conclusion: In GTs, the PVT appears to inhibit the expression of drug-seeking, presumably by attenuating the incentive value of the drug cue. Thus, inactivation of the PVT releases this inhibition in GTs, resulting in an increase in cue-induced drug-seeking behavior. PVT inactivation did not affect cue-induced drug-seeking behavior in STs, suggesting that the role of the PVT in encoding the incentive motivational value of drug cues differs between STs and GTs.
Keywords: Cocaine; Goal-tracker; Individual variation; Paraventricular nucleus of the thalamus; Reinstatement; Relapse; Reward cue; Sign-tracker.