One week after jugular catheter surgery, the rats were assigned to self-administer either saline or 1.0 mg/kg/inf cocaine. Rats were tested for self-administration for ten test sessions, during which responses to the active alternative resulted in i.v. injections of cocaine (or saline) according to a fixed ratio 1 (FR1) schedule of reinforcement followed by a 30 s timeout period. Infusions were accompanied by a 5 s illumination of the stimulus light above the active snout-poke hole, and the house light was extinguished for the duration of the time-out period. Snout-poke responses to the inactive alternative resulted in no programmed consequences. Session durations were 2 h. Following testing, catheters were flushed and rats were returned to the colony room. The criterion for acquisition of cocaine self-administration was an average of ten infusions per day (< 10 % of animals tested for self-administration were excluded from the experiment due to failure of acquisition of self-administration).
Following self-administration, rats were counterbalanced according to performance and assigned to 1 or 7 d withdrawal groups. For collection of tissue after 1 d of withdrawal (cocaine, n = 7; saline, n = 7), brains were harvested 24 h after the last day of self-administration testing. Rats were sacrificed by rapid decapitation, and brains were removed and sliced into 1-mm-thick sections using a brain matrix, and 2-mm-diameter tissue punches targeted at the NAc shell subregion were collected and rapidly frozen on dry ice. For animals undergoing 7 d of withdrawal (cocaine, n = 7; saline, n = 7), tissue was collected after the rats were returned to their home cages and left undisturbed for one week following the last day of cocaine-self administration.
For animals tested for acute exposure to cocaine, rats were sacrificed 1 h following the last self-administration session (cocaine, n = 5; saline, n = 6). In re-exposure to self-administration experiments, rats were returned to their colony rooms and left undisturbed for 7 d. Rats were subsequently retested for a single self-administration session (2 h self-administration) in an identical manner as in previous self-administration sessions, and sacrificed 24 h after the re-exposure test (saline, n = 6; cocaine, n = 6). Brains were harvested in a manner identical to those described above.
Following self-administration, rats were counterbalanced according to performance and assigned to 1 or 7 d withdrawal groups. For collection of tissue after 1 d of withdrawal (cocaine, n = 7; saline, n = 7), brains were harvested 24 h after the last day of self-administration testing. Rats were sacrificed by rapid decapitation, and brains were removed and sliced into 1-mm-thick sections using a brain matrix, and 2-mm-diameter tissue punches targeted at the NAc shell subregion were collected and rapidly frozen on dry ice. For animals undergoing 7 d of withdrawal (cocaine, n = 7; saline, n = 7), tissue was collected after the rats were returned to their home cages and left undisturbed for one week following the last day of cocaine-self administration.
For animals tested for acute exposure to cocaine, rats were sacrificed 1 h following the last self-administration session (cocaine, n = 5; saline, n = 6). In re-exposure to self-administration experiments, rats were returned to their colony rooms and left undisturbed for 7 d. Rats were subsequently retested for a single self-administration session (2 h self-administration) in an identical manner as in previous self-administration sessions, and sacrificed 24 h after the re-exposure test (saline, n = 6; cocaine, n = 6). Brains were harvested in a manner identical to those described above.
