Caffeine and nicotine: differential effects on ambulation, rearing and wheelrunning.

Male Sprague Dawley rats were tested for open field ambulation and rearing, and for wheelrunning, following repeated injections of either caffeine or nicotine, given according to a Latin Square design. Caffeine enhanced ambulation and rearing at 5 and 15 mg/kg, IP, and increased wheelrunning with 15 and 45 mg/kg. Nicotine (0.63 mg/kg) also enhanced ambulation, but not rearing, and depressed wheelrunning during the first 20 min of testing. Caffeine's enhancement of wheelrunning was not significant during the first two drug administrations. Results suggest that caffeine and nicotine affect activity via different neuropharmacological mechanisms. Previous experience with these drugs may modulate animals' reactivity to them.