Cue-induced reinstatement test

The cue-induced reinstatement test occurred immediately following the last extinction training session (e.g. session 18). Rats were counterbalanced into two different drug treatment groups based first on PCA score. Within each group, rats were further counterbalanced based on the number of port entries during self-administration sessions and behavior during the extinction sessions. Treatment groups received either a mixed cocktail of agonists to the GABA-B (baclofen) and GABA-A receptors (muscimol; Sigma-Aldrich, St. Louis, MO), or a saline injection (control group). Baclofen/muscimol (B/M) was given at a dose of 6 pmol/nl and 0.6 pmol/nl respectively, as infusion of this dose into the PVT has previously been shown to affect cocaine-seeking behavior (Browning et al. 2014, Matzeu et al. 2015). Injections occurred in a room adjacent to the testing room and were administered using a standard dual infusion pump (Pump 11 Elite, Harvard Apparatus) with P50 tubing connecting the two 1-μl syringes (Hamilton) to the injector (33 gauge with a 1-mm projection; Plastics One). Injections occurred at a rate of 100 nl/min for two minutes (total of 200 nl volume), and the injector was left in place for an additional two minutes to allow the drug to diffuse away from the injector and throughout the PVT (Browning et al. 2014). Following the injection, the stylet and cap were replaced, and the rat was brought into the testing room and placed into the Med Associates testing chamber. The house light came on one minute after program initiation, and head entries into the active and inactive port were recorded for the duration of the session. During the cue-induced reinstatement test, head entries into the active port resulted in the presentation of the cue-light for 20 seconds (same as in self-administration training), but no cocaine infusion. That is, presentation of the cue-light previously associated with drug delivery acted as a conditioned reinforcer, and entries into the active port were used as a measure of cocaine-seeking behavior. Entries into the inactive port were recorded, but without consequence. Sessions terminated after 45 minutes, and testing occurred between the hours of 15:00 h and 17:00 h.