Differential biochemical mechanisms mediate locomotor stimulation effects by caffeine and nicotine in rats.

Effects of caffeine and the interactive effects of caffeine and nicotine on locomotor activity in rats were examined in the present study. Other than confirming previous reports that both drugs enhanced locomotion, we have also found that their effects on activity were additive. Meanwhile, results of various biochemical measures have revealed that at the minimum effective doses of caffeine and nicotine which facilitated locomotor activity, only one biochemical system was preferentially influenced by either drug alone. The most significant findings were that caffeine stimulated the release of catecholamines and nicotine decreased the concentrations of tyrosine and tryptophan in brain. The combined effects of caffeine and nicotine on these brain amines were not different from those of each drug alone. Together with the report that caffeine and nicotine had differential actions on different activity measures, the present results support the hypothesis that caffeine and nicotine affect locomotor activity via different neurochemical mechanisms.