The night before sample collection, the microdialysis probe with a 1-mm active membrane (CMA7, Harvard Apparatus, Holliston, MA) was inserted into the NAc under isoflurane anesthesia (Webster Veterinary, Devens, MA) at an overnight perfusion rate of aCSF at 0.5 µl/min. On the test day, the flow rate was increased to 1.5 µl/min for 1 hr until sample collection every 10 min. There were four baseline samples followed by 0.2 µl microinjections of aCSF and 0.6 µg CP376395. Microinjection of the CRF-R1 antagonist occurred 10 min before 3 hr into the dark cycle, mimicking microinjection procedures when two-bottle choice was given (Hwa et al. 2014 ). Dopamine was measured by HPLC by electrochemical detection (Miczek et al. 2011 (link)). A stabilizing agent of 20 mM phosphate buffer with 25 mM EDTA was added to 15 µl dialysate samples. A cation-exchange column (Capcell Pak SCX, 1.5mm × 250mm, 5 µm I.D, Shiseido, Tokyo, Japan) separated dopamine at 30°C and a flow rate of 0.2 ml/min. The mobile phase consisted of 150 mM ammonium acetate, 50 mM citric acid, 27 µM EDTA, 10% MeOH, and 1% acetonitrile with pH adjusted to 4.6. Dopamine concentrations were determined by using standard curves with known amounts of dopamine in a range of 0.125–0.5 pg. The limit of detection was 2 fg under these conditions with a 10.5% recovery rate.