Cocaine and caffeine: conditioned place preference, locomotor activity, and additivity.

Conditioned place preference (CPP) was employed to clarify the reinforcing and locomotor stimulating effects of several doses of cocaine and caffeine (0.32, 1.0, 3.2, 5.6, and 10.0 mg/kg) and to explore the possibility of additive effects between the two drugs. Additionally, the hypothesis that the reinforcing effects of psychostimulants are mediated by the same systems that control psychostimulant-induced locomotor activity was examined by conducting correlational studies between drug-induced locomotor activity and time spent in the drug-conditioned compartments. Several doses of cocaine (1.0, 3.0, 5.6, 10.0 mg/kg), and caffeine (0.32, 1.0, 3.2, 5.6, 10.0) were found to condition place preference and stimulate locomotor activity. A combination of low doses (0.32 mg/kg) of each drug appeared to be additive. A positive relationship between locomotor activity observed during conditioning and time spent in the conditioned compartment during testing was found for cocaine but not caffeine or the low-dose combination of cocaine and caffeine.