Anticonflict effect of caffeine: investigation by punishment and hypertonic NaCl solution procedures in mice

Anticonflict effects of caffeine and diazepam were investigated by two procedures in water-deprived mice; punishment procedure in which the water drinking was suppressed by an electric foot shock, and hypertonic NaCl solution procedure in which the mouse was given 2% NaCl solution in place of tap water to suppress the drinking. Single administration of caffeine (1, 3, 10 and 30 mg/kg) and diazepam (0.25, 0.5, 1 and 2 mg/kg), and combined administration of caffeine (10 mg/kg) plus diazepam (1 mg/kg) were conducted. The mouse's drinking behavior was measured for 40 min immediately after each drug administration. Diazepam 0.25 mg/kg in the punishment procedure, and caffeine 30 mg/kg and diazepam 2 mg/kg in the hypertonic NaCl solution procedure were ineffective to significantly disinhibit the suppressed drinking. However, the other doses of caffeine and diazepam significantly disinhibited the suppressed drinking in both procedures. When the combined administration of caffeine and diazepam was carried out, no enhancement of the effect was observed as compared with those of the single administration of the individual drugs. The present results suggest that caffeine possesses an anticonflict effect at certain doses, although it is pharmacologically different from benzodiazepine anxiolytics.