THE EFFECTS OF COCAINE ON OPERANT RESPONDING FOR FOOD IN SEVERAL STRAINS OF MICE

The availability of numerous genetically homogenous mouse strains perm its the analysis of genetic influences on behavior and also behavioral sensitivity (responsivity) to drugs of abuse. The current study was c onducted to characterize discriminated operant responding for food in four inbred strains (Balb/cByJ, DBA/2J, C57BL/6J, SJL/J), an Fl Hybrid (C57BL/6xSJL), and one outbred strain (CD I) of mouse. The effect of cocaine on this operant behavior was also examined. Initially, all ani mals were trained to nosepoke for food on a continuous reinforcement s chedule. The minimum response requirement for reinforcement was increa sed every 5 days until the animals were responding on an FR-15 schedul e of reinforcement. All strains increased operant responding as the sc hedule of reinforcement was raised, However, significant differences i n response rate and discrimination learning were observed among the va rious strains of mice. Cocaine administration reduced operant respondi ng for food in Balb/cByJ, C57BL/6J, C57BL/6xSJL/J and CD1 mice at a do se of 15.0 mg/kg, whereas higher doses were required in DBA/2J mice (3 0.0 mg/kg) and SJL/J mice (56.0 mg/kg). These results suggest that ope rant performance and the effect of cocaine on this behavior is differe ntially influenced by genetic make-up.