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Psychopharmacology (Berl). 2009 Mar;202(4):699-709. doi: 10.1007/s00213-008-1353-y. Epub 2008 Oct 11.

Effects of prior amphetamine exposure on approach strategy in appetitive Pavlovian conditioning in rats.

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Department of Psychology, Behavioral and Cellular Neuroscience Program, Texas A&M University, College Station, TX 77843-4235, USA.



Pavlovian conditioning with a discrete reward-predictive visual cue can elicit two classes of behaviors: "sign-tracking" (approach toward and contact with the cue) and "goal-tracking" (approach toward the site of reward delivery). Sign-tracking has been proposed to be linked to behavioral disorders involving compulsive reward-seeking, such as addiction. Prior exposure to psychostimulant drugs of abuse can facilitate reward-seeking behaviors through enhancements in incentive salience attribution. Thus, it was predicted that a sensitizing regimen of amphetamine exposure would increase sign-tracking behavior.


The purpose of these experiments was to determine how a regimen of exposure to amphetamine affects subsequent sign-tracking behavior.


Male Long-Evans rats were given daily injections of d-amphetamine (2.0 mg/kg) or saline for 5 days, then given a 7-day drug-free period followed by testing in a Pavlovian conditioning task. In experiment 1, rats were presented with a visual cue (simultaneous illumination of a light and extension of a lever) located either to the left or right of a centrally located food trough. One cue (CS+) was always followed by food delivery, whereas the other (CS-) was not. In experiment 2, rats were tested in a nondiscriminative (CS+ only) version of the task.


In both experiments, amphetamine-exposed rats showed less sign-tracking and more goal-tracking compared to saline controls.


Contrary to predictions, prior amphetamine exposure decreased sign-tracking and increased goal-tracking behavior. However, these results do support the hypothesis that psychostimulant exposure and incentive sensitization enhance behavior directed toward reward-proximal cues at the expense of reward-distal cues.

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