Although the use of sipper tube access for reinforcement rather than discrete delivery introduces drinking efficiency as a possible confound, we did not observe differing efficiencies between the lines, meaning that this was an unlikely source of line differences in discounting behavior. However, the HAP mice did generally consume more reinforcer than the LAP mice in spite of lower adjusted amounts. The most reasonable explanation for this result is the larger number of total trials, as well as forced trials completed by the high-alcohol drinkers as compared to the low drinkers. When we assessed reinforcer access time only on nonforced trials, we again observed no line differences.
