Drug and Alcohol Dependence 251 (2023) 110921 Available online 7 August 2023 0376-8716/© 2023 Elsevier B.V. All rights reserved. Differential consumption of alcohol, caffeine, and caffeinated alcohol by adolescent rats, and effects on post-adolescent gene expression signatures in the nucleus accumbens and orbitofrontal cortex ☆ Shannon M. Thompson a , Ryan J. Rakoczy a , Margot A. Duffy a , Andor J. Kiss b , Matthew S. McMurray a, * a Department of Psychology, Miami University, 90 N. Patterson Ave, Oxford, OH 45056, USA b Center for Bioinformatics and Functional Genomics, Miami University, 700 E. High St, Oxford, OH 45056, USA A R T I C L E INFO Keywords: Alcohol Caffeine Adolescent TruSeq targeted RNA expression TREx ABSTRACT Caffeinated alcoholic beverages (CABs) are widely consumed despite little known about their behavioral and biological effects. Furthermore, CABs are also popular among adolescents, a particularly vulnerable and maturing demographic. In this preliminary study, we compared levels of daily adolescent voluntary consumption of caffeine (0.03%), alcohol (10%), caffeinated alcohol (0.03% + 10%), or vehicle and evaluated the effects of this on mRNA expression in brain regions associated with addiction and known to be affected by each drug. Beginning on postnatal day 30, rats were allowed unrestricted access to gelatin combined with one, both, or neither drug for twenty days. Compared to vehicle-consuming animals, consumption of gelatin was signifcantly attenuated when alcohol was included. The addition of caffeine to alcohol increased alcohol consumption in the early days of access compared to alcohol alone; however, after two weeks, alcohol consumption between these groups reached comparable levels. Compared to animals consuming caffeine alone, combining caffeine with alcohol signifcantly reduced caffeine intake. Targeted mRNA analysis of tissue collected from the nucleus accumbens and orbitofrontal cortex after the consumption period identifed unique patterns of differentially expressed genes between treatment groups, across a broad array of neurotransmitter systems. Of particular note were genes related to a number of solute transporters and serotonergic functions. This preliminary work suggests unique pharmacological and behavioral effects from consuming caffeinated alcohol during adolescence. Since CABs are widely consumed by adolescents, these results suggest that more research into the pharmacological and behavioral effects elicited by CABs is warranted. 1. Introduction Adolescence (~10–20 years old in humans) is a period of increased risk-taking across a range of behaviors, but especially in the consump- tion of alcohol and other drugs. Recent evidence shows that approxi- mately 40% of 18–20-year-olds in the US report consuming alcohol in the past 30 days (Chen and Yoon, 2021). Nationwide, this age group also shows a higher rate of problematic binge drinking (25.6%) than older adults (15.2%; Substance Abuse and Mental Health Services Adminis- tration, 2012, 2015). Even moderate consumption of alcohol during this developmental window can have many consequences, including im- mediate (e.g., drunk driving, arrest, etc.), and those that persist through adulthood (e.g., addiction; Turgeon et al., 2016; Spear, 2018). Since adolescence is a period of rapid brain development, this development may be disturbed by consumption of drugs, thereby affecting behavior across the lifespan. Furthermore, the brain regions that control execu- tive function such as the prefrontal cortex, are among the last to develop (Gogtay et al., 2004). These regions and the behaviors they support are particularly susceptible to developmental insults. Therefore, it is important that we understand the factors that contribute to unhealthy alcohol intake in adolescence, including environmental, behavioral, and pharmacological factors. One understudied factor that may facilitate high levels of alcohol intake is combining alcohol with other drugs. Caffeinated alcoholic ☆ This project was supported by funding from the College of Arts and Science and the Department of Psychology at Miami University. * Corresponding author. E-mail address: mcmurrms@miamioh.edu (M.S. McMurray). Contents lists available at ScienceDirect Drug and Alcohol Dependence journal homepage: www.elsevier.com/locate/drugalcdep https://doi.org/10.1016/j.drugalcdep.2023.110921 Received 13 April 2023; Received in revised form 31 July 2023; Accepted 2 August 2023