Concomitant Caffeine Increases Binge Consumption of Ethanol in Adolescent and Adult Mice, But Produces Additive Motor Stimulation Only in Adolescent Animals.

BACKGROUND Binge co-consumption of highly caffeinated energy drinks with alcohol (ethanol [EtOH]) has become a common practice among adolescents/young adults and has been associated with an increased incidence of hazardous behaviors. Animal models are critical in advancing our understanding the neurobehavioral consequences of this form of binge drinking. Surprisingly, virtually no work has explored caffeine and EtOH co-consumption or its long-term consequences in adolescent animals. The primary objective of the current study was to extend a previously established mouse model of voluntary binge caffeine and EtOH co-consumption to explore adolescent consumption and responses compared to adults. METHODS Adolescent and adult male C57BL/6J mice had daily limited access to caffeine (0.03% w/v), EtOH (20% v/v), a combined EtOH/caffeine solution, or water for 14 days via the binge-like drinking paradigm, drinking-in-the-dark (DID). Home cage locomotor activity was measured during DID in a subset of mice. Following DID, all mice rested for 18 days so that adolescents reached adulthood, whereupon all mice underwent 7 days of continuous access 2-bottle choice drinking for 10% (v/v) EtOH or water. RESULTS Co-consumption with caffeine significantly increased EtOH intake and resultant blood ethanol concentrations in both adolescent and adult mice. In addition, adolescent mice exhibited a uniquely robust locomotor stimulant response to caffeine and EtOH co-consumption. Later EtOH intake and preference was not influenced, however, by prior fluid consumption history via DID. CONCLUSIONS Together with findings from the human literature, our results suggest that caffeine co-consumption may positively influence binge alcohol consumption in adolescents/young adults. Importantly, this age group may be particularly sensitive to the additive stimulant effects of caffeinated alcohol consumption, an effect which may be related to the high incidence of associated negative outcomes in this population. These observations are particularly concerning considering the heightened plasticity of the adolescent brain.