Dopaminergic and opiate agonists and antagonists differentially decrease multiple schedule responding maintained by sucrose/ethanol and sucrose.

Similar neurobiological mechanisms are hypothesized to influence ethanol- and food-related reinforcement processes. This study examined the ability of compounds with dopaminergic or opiate activity to selectively alter responding maintained by a sucrose/ethanol solution in comparison to a sucrose solution. Long-Evans rats were trained to press a lever using 5% sucrose/10% ethanol and 5% sucrose as the reinforcers on a multiple Fixed Ratio 4 Fixed Ratio 4 schedule of reinforcement. When stable responding was established, the effects of intraperitoneally administered amphetamine (0.0-3.0 mg/kg), haloperidol (0.0-1.0 mg/kg), morphine (0.0-10.0 mg/kg), and naloxone (0.0-10.0 mg/kg) were examined on total session reinforcer presentation and presentation of each reinforcer within individual multiple schedule components. Prior to drug treatment, the total number of reinforcer presentations of the sucrose/ethanol solution was significantly greater than sucrose reinforcer presentations, suggesting the sucrose/ethanol solution was a more efficacious reinforcer. All agents administered decreased responding maintained by sucrose/ethanol and sucrose. The dose-effect curves for sucrose/ethanol were shifted to the left compared to sucrose, suggesting that although the compounds did not selectively impact sucrose/ethanol-maintained responding, sucrose/ethanol-maintained responding was more sensitive to the effects of these compounds.