Cocaine-Induced Conditioned Place Preference

CPP was assessed using a two-chamber box equipped with infrared beams (Med Associates) as previously described with modifications [38 (link), 45 (link)]. The two compartments exhibited different patterns on the walls and floor, and were separated by a removable guillotine door. On the first day, mice were allowed to freely explore both chambers for 20 min. For the conditioning phase, mice received a saline injection and were confined to one chamber or a drug injection (cocaine, CTEP or cocaine+CTEP) and were confined to the opposite chamber for 20 min. Mice were submitted to 3 saline-paired injections and 3 drug-paired injections in alternate days, resulting in 6 days of conditioning. Conditioning was counterbalanced so that half of the mice received cocaine injections paired to side A and for the other half cocaine was paired to side B. The CPP test was performed 24 h after the last conditioning session and consisted of a drug free session where mice were allowed to freely explore both compartments for 20 min as in the habituation session. Time spent in each compartment was assessed and the data were expressed as the difference between the time spent on the drug-paired side and the saline-paired side. Ten to thirteen mice per group were tested.