Some effects of d-amphetamine, caffeine, nicotine and cocaine on schedule-controlled responding of the mouse

The effects of d-amphetamine (0.03-10.0 mg/kg), caffeine (0.3-100.0 mg/kg), nicotine (0.003-10.0 mg/kg) and cocaine (0.03-56.0 mg/kg) were compared on responding maintained under three different schedules of food presentation in mice. Cumulative doses of d-amphetamine, nicotine and cocaine only decreased responding maintained under fixed-ratio 30 response, fixed-interval 60-sec and fixed-interval 60-sec schedules with a punishment contingency (suppressed responding). In most cases there was an inverse relationship between the ED50 (dose which decreased responding by 50%) for the drug and the rate of responding maintained under each schedule. The exceptions were, with both d-amphetamine and cocaine the ED50 for suppressed responding was smaller than that for non-suppressed fixed-interval responding, and with nicotine the ED50 for fixed-ratio responding was smaller than that for fixed-interval responding. In contrast, intermediate doses of caffeine increased suppressed responding, had little effect on fixed-interval responding and decreased fixed-ratio responding. This difference in profile of effect over the range of conditions studied, suggests that the behavioral effects of psychomotor stimulants can be used to examine potential differences in the mechanisms of action of each drug. Such findings may aid in the understanding of the relationships between the neuropharmacological and behavioral effects of psychomotor stimulant drugs.