Impact of Repeated Heavy Ethanol Intoxication During Early Adolescence on Adult Anxiety-Like, Exploratory, Risk Assessment, and Drinking Behaviors in Mice

Abstract

Exceeding binge-level drinking is common among adolescents and is associated with both short- and long-term adverse outcomes. This study evaluated the effects of repeated ethanol-induced intoxication during early adolescence on behavioral outcomes in early adulthood. Male and female C57BL/6J mice (5 weeks old) received intraperitoneal (i.p.) injections of either saline (control) or 3.2 g/kg ethanol (intoxicated). A subset of intoxicated mice had blood collected on days 1 and 4, confirming heavy intoxication ([~]289 mg/dL). At 9 weeks of age, animals were tested in the Light-Dark Box (LDB) and Elevated Plus Maze (EPM) immediately after receiving either saline or 1.2 g/kg ethanol. In the LDB, early adolescence intoxication did not affect anxiety-like behaviors but reduced risk assessment behaviors in males, indicating riskier decision-making. No pretest ethanol effect was observed. In the EPM, pretest ethanol produced an anxiolytic effect, accompanied by increased exploration and a reduction in risk-assessment behaviors, while adolescence intoxication did not yield significant effects. To better characterize behavioral organization beyond discrete measures, we applied Markov chain models to quantify first-order transition probabilities to and from risk-assessment states. This analysis revealed that pretest ethanol markedly reduced the complexity of behavioral structure, especially in the EPM, while adolescent intoxication had no detectable ethological effect. Finally, a separate cohort of controls and intoxicated mice underwent a two-bottle choice Intermittent Overnight Drinking protocol in adulthood. Adolescent ethanol intoxication increased voluntary ethanol intake in females but not in males. These findings highlight long-lasting and sex-specific consequences of early adolescent intoxication on risk-related behaviors and alcohol consumption.