Unpleasant and anticonflict effects of nicotine observed by conditioned taste aversion and hypertonic NaCl solution...

Effects of subcutaneously (s.c.) administered nicotine on preference for 0.1% saccharin solution and rejection for hypertonic (2%) NaCl solution were investigated in water-deprived mice. The results were compared with those after s.c. administration of methamphetamine, caffeine and morphine. When nicotine 0.3 and 1 mg/kg, methamphetamine 0.5, 1 and 2 mg/kg, and caffeine 30 mg/kg were administered to mice immediately after intake of the saccharin solution, they exhibited a significant decrease in the preference for saccharin solution on the next day (namely conditioned aversion), even though no drug administration was carried out. However, 2.5-10 mg/kg of morphine produced no marked change in the preference. Daily administration for 5 days of nicotine 1 mg/kg, methamphetamine 2 mg/kg, caffeine 30 mg/kg, and morphine 10 mg/kg did not produce any marked change in the individual drug effects on the conditioned taste aversion. On the other hand, rejection for the hypertonic NaCl solution was significantly attenuated when nicotine 0.3 mg/kg was administered prior to the experiment, probably showing an anticonflict effect. Caffeine 10 mg/kg, and morphine 2.5 and 5 mg/kg also attenuated the rejection for hypertonic NaCl solution. In contrast, methamphetamine 0.25-2 mg/kg enhanced the rejection in a dose-dependent manner. The present results suggest that, in spite of the same dose, nicotine shows both unpleasant and anticonflict (antianxiety) effects dependent on the environmental situation such as stimulus, timing of the drug administration etc. Furthermore, it is notable that the effects of nicotine observed in our experiments were similar to those of caffeine.