Background Incentives to promote drinking (“happy hour”) can encourage faster rates of alcohol consumption, especially in women. Sex differences in drinking dynamics may underlie differential health vulnerabilities relating to alcohol in women versus men. Herein, we used operant procedures to model the happy hour effect and gain insight into the alcohol drinking dynamics of male and female rats. Methods Adult male and female Wistar rats underwent operant training to promote voluntary drinking of 10% (w/v) alcohol (8 rats/sex). We tested how drinking patterns changed after manipulating the effort required for alcohol (fixed ratio, FR), as well as the length of time in which rats had access to alcohol (self-administration session length). Rats were tested twice within the 12 h of the dark cycle, first at 2 h (early phase of the dark cycle, “early sessions”) and then again at 10 h into the dark cycle (late phase of the dark cycle, “late sessions”) with an 8-h break between the two sessions in the home cage. Results Adult females consumed significantly more alcohol (g/kg) than males in the 30-min sessions with the FR1 schedule of reinforcement when tested late in the dark cycle. Front-loading of alcohol was the primary factor driving higher consumption in females. Changing the schedule of reinforcement from FR1 to FR3 reduced total consumption. Notably, this manipulation had minimal effect on front-loading behavior in females, whereas front-loading behavior was significantly reduced in males when more effort was required to access alcohol. Compressing drinking access to 15 min to model a happy hour drove up front-loading behavior, generating alcohol drinking patterns in males that were similar to patterns in females (faster drinking and higher intake). Conclusions This strategy could be useful for exploring sex differences in the neural mechanisms underlying alcohol drinking and related health vulnerabilities. Our findings also highlight the importance of the time of testing for detecting sex differences in drinking behavior.

Alcohol can have more detrimental effects on mental health in women, even when intake is comparable or higher in men. This may relate to a differential pattern of drinking, e.g., how rapidly alcohol is consumed. We used operant procedures to gain insight into sex differences in the drinking dynamics of rats. Adult male and female Wistar rats underwent operant training to promote voluntary drinking of 10% (w/v) alcohol (8 rats/sex). We tested how drinking patterns changed after manipulating the effort required for alcohol (fixed ratio, FR), as well as the length of time in which animals had access to alcohol (self-administration session length). Rats were tested twice within the 12 hours of the dark cycle, at 2 hours (early sessions) and 10 hours into the dark cycle (late sessions). As expected, adult females consumed significantly more alcohol than males in the 30-minute sessions with the FR1 paradigm. Alcohol consumption within females was higher in the late sessions compared to early sessions, whereas this difference was not found within males. Front-loading of alcohol (heavier drinking in the first five minutes of the session) was the primary factor underlying higher consumption in females, and this sex difference was accentuated in the late sessions. Increasing the effort required from FR1 to FR3 reduced alcohol drinking in both sexes. Front-loading behavior remained in females in both early and late sessions, whereas males exhibited minimal front-loading behavior only in the early sessions. Compressing drinking access to 15-minutes drove up front-loading behavior, producing total alcohol intake levels that were comparable in both sexes. This strategy could be useful for exploring sex differences in the effect of voluntary alcohol drinking on the brain. Our findings also highlight the importance of the time of testing for detecting sex differences in drinking behavior.