two conditioning subgroups, GRID + or GRID−, and exposed to a Pavlovian differential conditioning procedure. On alternating days, mice in the GRID + group received an injection of ethanol (2 g/kg, i.p.) immediately before a 5-min session on the grid floor (CS + sessions). On intervening days, these mice received saline immediately before exposure to the wire mesh floor (CS-sessions). Conversely, mice in the GRID− group received ethanol paired with the wire mesh floor and saline paired with the grid floor. During conditioning trials, all mice had access to only one of the two compartments of the apparatus. The dose of ethanol (2 g/kg) was chosen because it produces a strong preference for the paired tactile stimuli (Chester and Cunningham, 1998). The 5-min session duration was chosen based on previous studies showing that it produced a stronger CPP with ethanol than did longer session durations (Cunningham and Prather, 1992). For the 30-min test session, all mice received saline. Both compartments of each box were available for exploration during the test session.
