Microdialysis testing occurred inside four separate operant chambers located inside foam-insulated isolation units that minimized noise and other environmental stimuli (Coulbourn Instruments, Whitehall, click here PA, USA). The operant chambers (28 × 18 × 19 cm) were

equipped with a fan and a house light. The ceiling of the isolation unit had a small opening that allowed for unobstructed passage of the microdialysis probe tubing into the operant chamber. The operant chambers had grid floors with a plastic tray underneath filled with beta chip. Probes were assembled according to previously reported methods (Sorge et al., 2005). They consisted of 20-μm-diameter polyethylene (PE) tubing (70–75 cm long; Plastics-One, Roanoke, VA, USA) with one end connected to the stainless steel

shaft of a dual-channel liquid swivel (HRS Scientific, Montreal, QC, Canada). The swivel was located on top of the isolation unit and was connected to a variable speed electric syringe infusion pump (Harvard Apparatus, South Natick, MA, USA). Dialysate was collected from the outlet of the probe into 0.5-mL Eppendorf tubes (Sigma–Aldrich). The other end of the PE tubing was attached to a probe tip consisting of 26-gauge stainless steel tubing, 22 mm in length (Fisher Scientific, Nepean, Selleck Anticancer Compound Library ON, Canada) and a 2.5-mm-long semi-permeable membrane (280 μm OD, 220 μm ID, with a molecular weight cutoff of 13 000; Fisher Scientific). The outer end membrane was occluded with epoxy syringe glue (Henkel, Mississauga, ON, Canada) to create a closed system for the flow of dialysate. Small-diameter fused silica tubing (Polymicro Technologies, Pheonix, AZ, USA) extended into the probe 0.5 mm from the glued tip of the semi-permeable membrane. A stainless steel collar was screwed onto the

cannula to secure the probe. Ten days following minipump implantation, rats were anesthetized and microdialysis probes were lowered into each guide cannula 5 h before dialysate sampling began. When lowered, the probe extended 3.0 mm beyond the guide cannula RG7420 directing the probe tip and membrane towards the center of the NAcc. Artificial cerebrospinal fluid (aCSF; in mm: Na+, 145; K+, 2.7; Ca2+, 1.2; Mg2+, 1.0; Cl−, 150; ascorbate, 0.2; and Na2HPO4, 2; pH 7.4 ± 0.1; Sigma) was perfused through the probe during a period of 5 h to prevent occlusion and stabilize the baseline, at a rate of 1.0 μL/min. Following this period, six baseline dialysate samples were collected. Each sample was collected for 10 min at a flow rate of 1.0 μL/min (resulting in 10 μL of dialysate per sample). Samples were immediately placed on dry ice and stored at −80 °C. After baseline, rats were administered AMPH (0.25 mg/kg IP) and another 12 samples were collected every 10 min for a period of 2 h.