Training in the two mouse discrimination procedures was similar to that described previously (Vann et al., 2009). Briefly, each mouse was placed in a standard operant conditioning chamber with two response manipulanda (two levers for Experiment 1 and two nose poke apertures for Experiment 2). Mice were trained to respond on one of the two manipulanda following administration of THC and to respond on the other manipulanda following vehicle injection according to a fixed ratio 10 (FR10) reinforcement schedule, under which 10 consecutive responses on the correct (drug-appropriate) manipulandum resulted in delivery of a small dipper of milk (Experiment 1) or a food pellet (Experiment 2). The training dose of THC was 5.6 mg/kg in both experiments. Responses on the incorrect manipulandum reset the ratio requirement on the correct manipulandum. Daily injections were administered on a double alternation sequence of THC and vehicle (e.g., drug, drug, vehicle, vehicle). For both studies, daily 15 min training sessions were held Monday-Friday until the mice consistently met two criteria: (1) the first completed FR10 was on the correct manipulandum and (2) ≥ 80%
