Influence of a conditioned light stimulus on cocaine self-administration in rats

Rationale: A number of studies have suggested that the continued presentati on of stimuli associated with cocaine may contribute to drug-seeking and dr ug-taking. The influence of conditioned stimuli on the maintenance of self- administration has not, however, been systematically investigated. Objectiv es: This study was designed to determine whether omission of a stimulus tha t had been paired with self-administered cocaine would influence the mainte nance of cocaine self-administration and whether the effect was dependent o n cocaine dose or session length. Methods: During self-administration train ing, self-administered cocaine infusions were always paired with the illumi nation of a light. On test days, self-administered cocaine was delivered ei ther with or without the cocaine-associated cue. For one group of rats, res ponding maintained by cocaine (0.50 mg/kg per infusion) was measured during daily 18-h sessions. For other groups, responding maintained by additional doses of cocaine (0.125, 0.25, or 1.0 mg/kg per infusion) was measured dur ing daily 18-h sessions. For a final group, daily test sessions (4-5 h) pro duced the dose-effect curve (0.015-1.0 mg/kg per infusion) by repeatedly re ducing the cocaine dose from a starting dose of 1.0 mg/kg per infusion. Res ults: Removal of the light cue decreased cocaine self-administration. The m agnitude of this effect was dependent on the dose of self-administered coca ine and on the test session duration. Greater decrements in responding were produced as session length increased or when low doses of cocaine were sel f-administered. Conclusions: These findings demonstrate that in the absence of a cocaine-associated stimulus, cocaine self-administration is attenuate d and that maintenance of cocaine self-administration is maximally affected by the presence or absence of the conditioned stimulus when the self-admin istered dose is low and/or when session duration is long.