Cocaine self-administration in pigeons

Abstract

Pigeons with chronic indwelling intravenous catheters responded under a multiple schedule of food and cocaine presentation. In one component, responding was maintained by food presentation under a fixed-ratio (FR 50) schedule, whereas in the other component, responding was maintained under the same schedule by IV infusions of cocaine (0.03 or 0.1 mg/kg/injection). A 30-s timeout followed each cocaine infusion. Components alternated after 3 presentations of either food or cocaine, and each session was terminated after 18 cocaine infusions or 2 h, whichever occurred first. In general, under baseline conditions, the response rate was higher in the food component than in the drug component. Under control conditions where saline was substituted for cocaine, the response rate gradually decreased across sessions, while food-maintained responding was generally unaffected. Substituting doses lower or higher than the training dose decreased the rate of cocaine-maintained responding. Food-maintained responding only decreased at higher doses of cocaine. When blackout periods were substituted for the food component (Experiment 2), the response rate in the cocaine component decreased and then stabilized at levels well above zero. Saline substitution on this baseline produced a further decrease in the rate of FR responding. In Experiment 3, the effects of pretreatment with haloperidol (0.056 or 0.1 mg/kg) on both food- and cocaine-maintained responding were examined using a multiple schedule similar to that used in Experiment 1. Each dose was given for a period of 7–10 days. In general, haloperidol dose-dependently decreased both the overall rate of cocaine-maintained responding and the percent of available reinforcers obtained, while having little or no effect on food-maintained responding. This research indicates that cocaine can serve as a reinforcing stimulus for maintaining self-administration behavior in pigeons, and that this behavior is sensitive to antagonism by haloperidol.