Fig. 2

Front-loading behavior drives sex differences in alcohol intake on sessions later in the dark cycle. A Rats were placed in operant boxes at 2 h in the dark cycle (“early sessions”) and returned to the home cage after the 30-min session with an FR1 schedule of reinforcement. After 8 h, rats were placed back in the operant boxes at 10 h in the dark cycle (“late sessions”) and returned to the home cage after the 30-min session. B Average of total alcohol intake (g/kg) of early and late sessions (n = 8 / sex); C average of total water intake (ml/kg) in the control group (n = 4 / sex); D early sessions and E late sessions of total alcohol intake per minute in the session, inset: total alcohol intake in the first 5-min bin. FR fixed ratio, h hour, min minutes. B #, higher intake in late sessions compared to early sessions in females, adjusted p < 0.05, and *, higher intake in females compared to males in the late sessions, adjusted p < 0.05; both indicated by Bonferroni’s multiple comparisons test post hoc analysis following a session × sex interaction. D, E White circles, higher intake compared to the average rate of intake of the session in males and females, adjusted ps < 0.05; indicated by Bonferroni’s multiple comparisons test post hoc analysis following a time × alcohol intake interaction. In inset graph of E *, unpaired t-test, p < 0.05. Error bars and shading are shown in SEM. A is created with BioRender.com