Effects of intra-amygdala R(+) 7-OH-DPAT on intra-accumbens d-amphetamine-associated learning - II. Instrumental conditioning

Rats were trained to associate an initially neutral conditioned stimulus (C S) with a response-independent, intra-accumbens infusion of d-amphetamine ( the unconditioned stimulus; US). Elsewhere, we have reported that as a resu lt of this training. presentations of the CS alone elicited a conditioned r esponse consisting of increased locomotor activity and that acquisition of this conditioned response was enhanced by post-session, intra-amygdala infu sion of the dopamine D-3 receptor preferring agonist, R(+) 7-OH-DPAT. Here, in this same group of animals, we have examined the conditioned rewarding properties of the drug-associated CS by determining its ability to support the acquisition of a novel instrumental response in the absence of drug rew ard. Thus, rats were presented with two novel levers. Presentation of the d rug-associated CS was made continent upon depression of one of the levers ( CR lever), while responding upon the other lever (NCR lever) had no program med consequences. Preferential responding upon the lever delivering the dru g-associated CS was observed despite a 6-week interval between CS-US traini ng and the conditioned reward test. Intra-accumbens administration of d-amp hetamine (0-20 mu g) increased the control over behaviour exerted by the CS . increasing CR, but not NCR lever responding. In contrast, rats that recei ved three pairings of an intra-accumbens infusion of d-amphetamine in combi nation with intra-amygdala infusion of R(+) 7-OH-DPAT, 3 weeks prior to tes ting, displayed similar rates of response upon both levers and were insensi tive to the potentiation of responding for conditioned reward following int raaccumbens d-amphetamine. However, intra-accumbens IZ-amphetamine stimulat ed locomotor activity in a similar dose-related manner in both groups. In t his way, rats that had received intra-accumbens infusion of d-amphetamine i n combination with intra-amygdala infusion of R(+) 7-OH-DPAT appeared exact ly like control group rats, for which the CS had been paired with intra-acc umbens d-amphetamine on a negative basis only. A locomotor activity test in dicated that one behavioural consequence of intra-amygdala administration o f R(+) 7-OH-DPAT was the reduction of the unconditioned locomotor response resulting from intra-accumbens administration of d-amphetamine. Hence, the present data demonstrate that the conditioned rewarding properties of a dru g-associated CS are specific to the CS-US association and are relatively in sensitive to decay over time. However, the rewarding properties of a drug-a ssociated CS were selectively abolished following activation of amygdala D- 3 receptors during presentation of the drug reward. Potential explanations for this effect are discussed, including the possibility that intra-amygdal a R(+) 7-OH-DPAT reduced the incentive value of the US.