In vivo microdialysis

The intracranial guide cannula implantation surgery and microdialysis procedures are the same as we reported previously [25]. Briefly, two guide cannulae (CMA Microdialysis AB, Solna, Sweden) were implanted into NAc (AP +1.7; ML ±1.7; DV −5.8 mm with 6° angled away from the midline) for in vivo brain microdialysis. After 7 days of recovery from surgery, a probe was inserted into the NAc 12 h before experiments began. On the experimental day, dialysis buffer was perfused through the probe (2.0 μL/min) via a syringe pump. To prevent DA degradation, dialysis samples were collected every 20 min into 10 μL of 0.1 M perchloric acid. After 2 h of baseline collection, animals received either vehicle, increasing concentrations of BINA (0.01–100 µm) perfused locally into the NAc, or two systemic doses of heroin (0.25 and 1.0 mg/kg, s.c.). After collection, all samples were frozen at −80 °C until analysis. Dialysate DA and glutamate were measured using high-pressure liquid chromatography with electrochemical and fluorometric detection, as reported previously [26]. After microdialysis experiments, rats were anesthetized with a high dose of pentobarbital (>100 mg/kg i.p.) and perfused transcardially with 0.9% saline followed by 10% formalin. Brains were removed and placed in 10% formalin for histological verification of microdialysis probe locations.