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Caffeine potentiates the discriminative-stimulus effects of nicotine in rats
Maciej Gasior1, Maria Jaszyna, Patrik Munzar
1National Institute on Drug Abuse, Intramural Research Program, National Institutes of Health, Baltimore, MD 21224, USA. mgasior@mclean.harvard.edu
Rationale:
Caffeine and nicotine are the main psychoactive ingredients of coffee and tobacco, respectively, with a high frequency of concurrent use in humans.
Objectives:
The aim of the present study was to examine the interaction of caffeine and nicotine in rats trained to discriminate nicotine from saline.
Methods:
Two groups of male Sprague-Dawley rats ( n=8 per group) were trained to discriminate 0.4 mg/kg nicotine, SC, from saline under a fixed ratio schedule of food presentation. One group of rats was chronically exposed to caffeine (1.0 mg/ml) dissolved in their drinking water whereas the other group was exposed to tap water. Effects of IP injections of caffeine on nicotine-lever selection were subsequently examined. In separate groups of rats exposed to the same caffeine-drinking or water-drinking regimen, effects of caffeine pretreatment on nicotine plasma levels were evaluated.
Results:
Although caffeine (1.0-30.0 mg/kg) did not generalize to nicotine when administered alone, it markedly potentiated discriminative-stimulus effects of the threshold dose of nicotine (0.05 mg/kg) in both water- and caffeine-drinking rats. Nicotine plasma levels were, however, not affected by acute or chronic caffeine exposure.
Conclusions:
Caffeine appears to enhance the discriminative-stimulus effects of the threshold dose of nicotine by a pharmacodynamic rather than a pharmacokinetic interaction. This suggests that caffeine consumption may be a contributing factor in the onset, maintenance of and relapse to tobacco dependence.