Statistical Analysis

Analysis of variance with repeated measures was used when appropriate to determine possible group effects and interactions. Experimental group (genotype, two levels: WT and KO) was used as a between subjects factor and time, nose-poke hole (active/inactive), cue (with/without), condition (naïve/abstinent) were used as within-subject factors. Newman–Keuls tests for multiple comparisons post hoc analysis was performed when required. All results are expressed as mean±SEM. Differences were considered significant at p<0.05. Statistical tests were performed with Statistica 9.0 (StatSoft, Tulsa, OK, USA).

See Supplementary Information for extended details of animals, CB1 immunohistochemistry, drugs, catheters, apparatus, surgery for cocaine self-administration, cocaine intravenous self-administration basal training, T-maze, in vivo microdialysis for DA release in freely moving mice and ex vivo electrophysiology.