There has been considerable interest in the role of
dopamine D(3) receptors in appetitive conditioning but few studies have examined their role in aversive conditioning. The present study examined the effect of the
dopamine D(3) receptor-preferring partial agonist
BP 897 (1-(4-(2-naphthoyl-amino)butyl)-4-(2-methoxyhenyl)-1A-piperazine hydrochloride) and the selective
dopamine D(3) receptor antagonist SB-277011A (trans-N-[4-[2-(6-cyano-1,2,3,4-tetrahydroisoquinolin-2-yl)ethyl]syclohexyl]4-quinolininecarboxamide]) on the expression and acquisition of fear conditioning. Rats (N=143) received 3 conditioned stimulus-
shock pairings and then received 15 conditioned stimulus-alone presentations (3 per day) while lever pressing for food. Response suppression was taken as the behavioral measure of fear. Rats showed strong suppression to the conditioned stimulus after it had been paired with
shock and suppression progressively weakened over conditioned stimulus-alone presentations. In experiment 1, rats that received
BP 897 (1.0, 2.0 mg/kg i.p.) or SB-277011A (10.0 mg/kg i.p.) prior to conditioned stimulus-alone presentation sessions showed reduced suppression to the conditioned stimulus as compared to rats that received vehicle or lower doses of
drug (0, 0.1 mg/kg
BP 897; 0, 0.5, 5.0 mg/kg SB-277011A).
Injections of
BP 897 (1.0, 2.0 mg/kg) or SB-277011A (10.0 mg/kg) prior to conditioned stimulus-
shock pairings did not significantly affect subsequent response suppression. Thus,
BP 897 and SB-277011A dose-dependently attenuated the expression but not the acquisition of conditioned fear. These findings suggest that
BP 897 and SB-277011A reduce the control of responding by aversively conditioned stimuli.