Selective strengthening of conditioned behaviors that occur during periods of amphetamine exposure

Abstract

Exposure to psychomotor stimulants, during conditioning sessions, can lead to a persistent increase in the strength of conditioned behaviors and the effects of conditioned stimuli, which can be detected in subsequent drug-free periods. It is possible that the effects are selective for the behaviors and stimuli conditioned during drug exposure. The present study was designed to test this prediction. Animals were trained to discriminate two sets of stimuli. For each set, lever pressing during the presentation of one stimulus (S+) was reinforced and responding during the presentation of the other stimulus (S-) had no programmed consequences. Following an initial acquisition phase, training with one set of stimuli continued during sessions of amphetamine exposure, whereas training with the second set continued during saline exposure (20 intermixed sessions). The findings of subsequent drug-free choice tests showed that the drug history selectively enhanced the propensity of animals to engage in the drug-assigned behavior relative to the saline-assigned behavior. This change in behavior was evident in S+, but not S- trials and was potentially mediated by an acute effect of amphetamine on stimulus conditioning. The findings provide novel evidence that the facilitative effects of coincident conditioning and acute psychomotor stimulant exposure can be selective for the stimuli and behaviors conditioned during the drug exposure. These findings are relevant to hypotheses regarding the etiology of drug addiction. © 2007 Nature Publishing Group All rights reserved.