The effects of caffeine in the social interaction test and on exploration in rats: comparison with ethanol and clorazepate

The effects of caffeine (20mg/kg) in the holeboard and social interaction tests were compared with those of ethanol (0.4g and dipotassium clorazepate (3mg/kg), following acute administration in one group of rats or after five daily injections in another group. The rats were put in pairs into an unfamiliar arena with high levels of illumination (n = 80), or tested individually in the holeboard (n = 80). Acute caffeine produced no effect on the time spent in social interaction, although it enhanced the number of social contacts, and both genital and total sniffing. Following five injections, caffeine also increased the time spent in social interaction. Acute clorazepate enhanced this time but this effect showed partial tolerance after five injections. Clorazepate also enhanced the number and duration of social contacts, increasing social grooming and genital sniffing, regardless of the duration of the treatment. Ethanol increased the time spent in social interaction following five injections, and increased social grooming. In the holeboard, stimulant effects were observed for caffeine and clorazepate, showing partial tolerance and without any effect on head dipping. In the social interaction test, only a stimulant effect for caffeine was obtained. The results of this study suggest that, under some circumstances, caffeine may enhance social interaction, in a manner similar to standard anxiolytics. Such an effect is potentiated by repeated administration.