2.6. Conditioned place preference (CPP)

An operant behavioral paradigm designed to test the rewarding effects of drugs was used as a screening tool for abuse potential. CPP was conducted in three phases: preconditioning, conditioning, and test day. During the pre-conditioning phase, mice were introduced to the activity boxes for 30 minutes and allowed access to both chambers through an opening in a partition separating the two. The left and right sides of the activity box were lined with horizontal or vertical black and white striped patterns respectively, and the time spent in each chamber recorded by computer. Mice showing a baseline preference for one chamber over another (spending >18 minutes on one side) were not used. During conditioning (3 days), mice were administered vehicle in the morning and placed in one side of the activity box with a closed partition for 30 minutes (vehicle paired chamber). In the afternoon, mice were administered drug (MCC22 or morphine at 10mg/kg, i.p.) and placed in the opposite chamber for an additional 30 minutes (drug paired chamber). On test day, mice were placed in the activity boxes with access to both chambers in the absence of any drug administration.