Figure 1 shows the average daily ethanol intakes during the first 10 weeks of concurrent access to 10, 20, and 30% ethanol and ethanol intakes during each of the 4 sessions during weeks 7–10. P rats readily acquired ethanol self-administration during the 2nd day of concurrent access to the 3 ethanol solutions (similar to Rodd-Henricks et al., 2002a, b). During the initial 5 weeks of responding, overall ethanol intakes were consistent (3.2 ± 0.2 g/kg for the 4 1-hour sessions; Fig. 1, top panel). Elevated ethanol intakes were observed during week 6, when total daily amount increased 48% (two-tailed t test indicated significant increase from average intake of weeks 3–5; p < .001). Ethanol intakes gradually increased until week 9 (92% increase compared to average intake of weeks 3–5; p < .001) and stabilized between weeks 9–10.
