Brain dopamine (DA) systems are known to be important in regulation of behavior conditioned to
appetitive stimuli. Nevertheless, despite a large body of evidence showing behavioral deficits in the
operant conditioning paradigm produced by DA receptor blockade, there have been relatively few
studies directly assessing behavioral changes in classical conditioning paradigm under this drug
treatment. By employing an appetitive Pavlovian conditioning task, the present work investigated the
effects of selective D1
and D2
receptor antagonists on the expression and acquisition of the conditioned
orienting response (COR) and food-cup approach. SCH23390 (0, 0.05, and 0.10 mg/kg) and raclopride
(0, 0.1, and 0.2 mg/kg) were administered via an intra-peritoneal route in a between-group design. Data
from Experiment 1 showed that both SCH23390 and raclopride suppressed expression of the COR and
food-cup approach, but only the impairment produced by raclopride reached a significant level. In
Experiment 2, with SCH23390 being administered during the acquisition phase, the suppressed COR
was completely restored in a subsequent (24 h later) drug-free session. In contrast, the suppressed COR
in raclopride-pretreated groups was only partially restored. These findings support the view that the
DA system plays a role in the neural substrates underlying this appetitive conditioning. In addition, D2
receptors are more likely involved in the modulation of learning process of the COR than D1
receptors.
