ENHANCED APPETITIVE CONDITIONING FOLLOWING REPEATED PRETREATMENT WITHD-AMPHETAMINE

The behavioural response to psychomotor stimulants is augmented with r epeated exposure to these drugs. Enhanced stimulated dopamine overflow within the nucleus accumbens and amygdala has been found to accompany this behavioural sensitization. In the present experiment, rats recei ved 2 mg/kg d-amphetamine or 1 ml/kg physiological saline once per day for 5 days. Five days later, a behavioural assay confirmed that prior repeated d-amphetamine treatment markedly enhanced the locomotor acti vating effects of a d-amphetamine (0.5 mg/kg, i.p) challenge. Training on a Pavlovian conditioning task began six days subsequently. In Stag e 1, a stimulus (light or tone, S-) was presented negatively correlate d with a sucrose reward. In Stage 2, presentation of the alternative c ounterbalanced stimulus (light or tone, S+) was paired with the availa bility of a 10% sucrose solution. There were no differences between th e two groups in their response to the the S-stimulus. However, sensiti zed animals showed a selective enhancement in the acquisition of condi tioned responding to S+, relative to vehicle-injected controls. No dif ferences in behaviour were recorded during the prestimulus periods, no r during presentations of sucrose. Levels of activity within the opera nt chamber extraneous to alcove approach were also similar in both gro ups of animals. The conditioned instrumental efficacy of S+, relative to S- was assessed in Stage 3, in which stimulus availability was made contingent on a novel lever-pressing response. Both groups showed a s imilar preference for the S+ over the S- stimulus. Hence, rats sensiti zed by prior repeated d-amphetamine showed enhanced appetitive Pavlovi an conditioning, without subsequent effect on conditioned reward effic acy. These data are discussed in light of possible changes in mesoamyg daloid dopamine functioning. Behav Pharmacol 1998; 9:299-308 (C) 1998 Lippincott-Raven Publishers.