P rats are an extremely well-validated rodent model of AUD (Waller et al., 1982; Lumeng and Li, 1986; Gatto et al., 1987; Stewart et al., 1991; McBride and Li, 1998; Bell et al., 2014; McBride et al., 2014; Kampov-Polevoy et al., 2000). One feature that sets these animals apart from other rodent populations that willingly consume alcohol, is their robust seeking phenotype (Czachowski and Samson, 2002). Given this, it was surprising to find that during alcohol seeking/consumption, trial-encoding was weaker in P rats (Fig. 3B). Weaker trial-encoding in P rats did not result in an opportunity cost, as there were no differences in the number of drinking trials or volume of fluid consumed between Wistar and P rats. However, differences in drinking were intentionally minimized across Wistars and P rats, as each animal was selected to control for differences in behavior and, especially, history of alcohol intake (Linsenbardt and Lapish, 2015). Since differences in trial-encoding were not associated with increased seeking or drinking when reinforced with alcohol, it does not likely reflect the motivational salience of the stimuli or more basic features of the stimuli such as its perceived intensity or information required to locate/time the delivery of the reinforcer.
