Aggression and repeated alcohol drinking-in-the-dark: dissecting subtypes in outbred mice.

RATIONALE: Repeated bouts of alcohol consumption increase the risk for developing alcohol use disorders and influence social dynamics, including aggression. Intermittent, weekly binge-like drinking-in-the-dark (DID) can escalate such intake in mice, potentially altering the trajectory of adaptive social behaviors. OBJECTIVE: To examine individual patterns of alcohol intake over repeated weeks of DID with corresponding measures of offensive aggression in outbred Swiss Webster (CFW) resident mice. METHODS: CFW resident male mice were given 2 h of access to either water or 16% ethanol (w/v) for three days, followed by 4 h of access on day four. This DID protocol was implemented over nine consecutive weeks. Offensive aggression was assessed throughout the experiment, with aggression tests occurring in a neutral arena 20 h after the cessation of the weekly 4-h access session while mice were no longer intoxicated. Measures of total alcohol intake (i.e., g/kg) and the frequency of attacks (i.e., biting), were collected over each week. Intake patterns were subsequently visualized using Gaussian mixture modeling. RESULTS: A subset of CFW mice significantly escalate their alcohol intake across weeks, with group means reaching ~ 4 g/kg in 4 h by Week 9. Offensive aggression appears to be maintained in higher alcohol-drinkers relative to lower alcohol-drinkers. CONCLUSION: Repeated bouts of drinking and aggression testing in outbred mice reveal individual differences in alcohol intake that align with individual differences in aggression. Such trait-like differences reveal a subset of individuals with a vulnerability to consume more alcohol and to engage in offensive aggression while not intoxicated.