Once cocaine self-administration was stable rats were anesthetized with xylazine hydrochloride (10mg/kg, i.p.) and ketamine hydrochloride (100mg/kg, i.p.) and placed in a stereotaxic frame. Surgery for electrochemical recordings followed previously described procedures (Phillips et al., 2003a). A microdialysis guide cannula (Locking Intracerebral Guide and Stylet, Bioanalytical Systems, West Lafayette, IL), was implanted above the NAc shell (1.7 mm anterior, 0.8 lateral, coordinates relative to bregma) or NAc core (2.2 mm anterior, 1.5 lateral). Shell placements are within rostral portions of the NAc shell which has greater dopamine concentration (Heidbreder & Feldon, 1998) and negligible noradrenergic input compared to caudal portions (Delfs et al., 1998; Baldo et al., 2003). A bipolar stimulating electrode (tip diameter 0.2 mm, tips spaced 1 mm apart, Plastics One, Roanoke, VA) was lowered to the substantia nigra/VTA, 5.2 mm posterior, 1 mm lateral and 7.8 mm dorsoventral (Paxinos & Watson, 1986). An Ag/AgCl reference electrode was placed in the contralateral hemisphere, approximately 3.6 mm posterior to bregma. The implanted items were permanently affixed to the skull with cranioplastic cement.
