Differential effects of injection regimen on behavioral responses to cocaine

Locomotor behavior was measured in mice receiving IP cocaine at 5, 10, 20, or 40 mg/kg. then with 5, 5, 10, and 20 mg/kg at 10-min intervals. In the single-dose treatment, mice received a single dose of cocaine at a time corresponding to the equivalent cumulative dose, with saline injections at other times. The single-injection treatment was similar, but saline injections were omitted. Locomotor activity was measured across each 10-min interval. Mice were retested 6 weeks later and 1 day after that. Dose-response curves were similar for all three treatments on the first test, but diverged markedly on subsequent tests. Significant locomotor sensitization occurred at the higher doses on the second test, particularly in the treatments receiving single cocaine injections. On the third test, convulsions occurred at 40 mg/kg, but only in the singly dosed treatments. The results demonstrate that injection parameters can modify both the behavioral and toxic effects of cocaine.