VARIATIONS IN COCAINE SELF-ADMINISTRATION BY INBRED RAT STRAINS UNDERA PROGRESSIVE-RATIO SCHEDULE

This study investigated the influence of genetics on extent of cocaine taking in rats that were self-administering cocaine under a progressi ve-ratio schedule. Fischer 344, ACI and Brown Norway rats Mere subject s because previous genetic studies on dopamine receptor loci have indi cated that these are genetically divergent strains. All subjects were assessed for acquisition and stability of cocaine self-administration under a progressive ratio schedule. Subsequently, a dose-effect curve for cocaine self-administration was determined for each strain. Fische r 344 rats maintained a higher average breaking point than did the ACI or Brown Norway strains. In addition, dopamine receptor antagonists d ifferentially reduced the ability of cocaine to serve as a reinforcer across the three strains. The D-1-selective dopamine receptor antagoni st, SCH 23390, and the D-2/D-3-selective dopamine receptor antagonist, eticlopride, were significantly more effective in reducing the self-a dministration of cocaine in Brown Norway rats than for the other two s trains. The results of this study demonstrate that genetic differences may play an important role in determining responding under progressiv e-ratio schedules for cocaine, possibly due to differences in the rein forcing efficacy of cocaine.