The effects of caffeine on alcohol oral self-administration behavior in rats

Caffeine and alcohol are some of the most commonly used psychoactive substances in the world, and are often used concomitantly. However, little is known about the effect of caffeine on alcohol consumption. Here, our aim was to investigate the co-exposure of alcohol mixed with caffeine in self-administration. Thirty-two male and thirty-two female Wistar rats were randomly divided into the following groups: control, caffeine (0.25 mg/mL), alcohol (10% v/v) and alcohol mixed with caffeine. After one week of training, the animals underwent self-administration for 21 days (1 h per day) in a fixed ratio of 1 (FR1). The forced swimming test (FST) was performed before the training phase and 24 h after the last self-administration session to verify abstinence-induced depressive-like behaviors. Our results showed that all rats consumed a lower volume of alcohol-containing solution than control solution, and that the presence of caffeine did not influence this parameter. Females consumed less volume of alcohol solution than males but the average dose was similar. Females that self-administered alcohol mixed with caffeine presented a higher immobility in the FST than males that self-administered the same solution. These results support the conclusion that moderate doses of caffeine such as the ones from our study (approximately 7-8 mg/kg/day) do not influence alcohol consumption. Additionally, females might be more susceptible than males to depressive-like effects caused by the abstinence of the use of these substances in combination.