Figure 1.

Timeline of cocaine self-administration and voltammetric recordings. A, Our experimental design yielded four groups: (1) rats that self-administered a single cocaine infusion with no prior cocaine experience [single injection (no history), black], (2) rats that performed 5 d of cocaine self-administration [cocaine, green], (3) rats that performed cocaine self-administration followed by a 14 or 60 d abstinence and were subsequently allowed to self-administer a single injection of saline [cocaine + abstinence, blue], and (4) rats that performed cocaine self-administration followed by a 14 or 60 d abstinence and were subsequently re-exposed to a single self-administered injection of cocaine (re-exposure, red). B, Number of reinforcers earned relative to day of acquisition. Lack of error post-acquisition reflects the session limit of 40 injections being reached by all rats. Inset, Average number of self-administration sessions before acquisition criteria were met. C, Over the course of cocaine self-administration rats escalate in rate of cocaine intake over days. ***p < 0.001 versus day 1. Error bars indicate ± SEM.