HALOPERIDOL DIFFERENTIALLY AFFECTS REINFORCEMENT AND MOTIVATIONAL PROCESSES IN RATS RUNNING AN ALLEY FOR INTRAVENOUS HEROIN

The role of drug-paired environmental stimuli in opiate self-administr ation was investigated by exposing animals to discrete cues that were predictive of the availability or unavailability of heroin reinforceme nt. Rats were trained to traverse a straight arm runway for a reinforc ement consisting of a single 0.1 mg/kg intravenous infusion of heroin delivered upon entrance to the goal box. On each trial, one of two dis criminative olfactory stimuli (orange and almond) was used: one which signaled the availability of heroin in the goal box (S+), and one whic h signaled its absence (S-). The effect of dopamine (DA) receptor anta gonism on reinforcement and motivational processes was investigated by pretreating subjects with 0.0, 0.15 or 0.30 mg/kg of the DA receptor antagonist drug, haloperidol. Haloperidol had no effect on operant run way performance (i.e. goal time) in any condition. However, 24 h later , on the first posttreatment trial, those haloperidol animals that rec eived heroin in the goal box on the previous trial (i.e. the S+ condit ion) ran reliably more slowly than subjects that received vehicle on t he previous S+ trial. These results suggest that haloperidol does not affect the motivational properties of stimuli which predict the availa bility of heroin, while it does diminish the reinforcing effects of ac tually receiving heroin.