The effect of cocaine on rotarod performance in male C57BL/6J mice

There is surprisingly little research examining the effect of cocaine on motor learning. Given that changes in motor activity can confound behavioral assays of learning and memory a direct assessment of cocaine on motor learning seems warranted. The present study was conducted to examine the effect of cocaine on motor learning using an accelerating rotarod test in adult male C57BL/6J mice. Mice were given an injection of either saline or cocaine (10 mg/kg, i.p.) for 6 consecutive days prior to rotarod training (Pre-exposure). In the first phase of training (Phase I), mice were given an injection of either saline or cocaine 10 min prior to the start of each day's training on the rotarod for 6 consecutive days. In the second phase (Phase II), half the animals continued to receive the same drug during training, while the other half were switched from saline to cocaine or from cocaine to saline. All mice exhibited motor learning as evidenced by an increased latency to fall across days. Animals that received cocaine injections exhibited significantly longer latencies to fall on days 3-6 compared to those mice receiving saline. This enhanced performance was lost when cocaine-injected animals were switched to saline on day 7. It is hypothesized that the performance enhancing effects of cocaine are due to the increased stamina and/or psychomotor stimulation and not the result of enhanced motor learning as the increment in performance was lost when the drug was discontinued.