Brain samples were thawed on ice, and a 10% homogenate was prepared. 50 mL of a 0.4 N perchloric acid solution was added to 200 μL of the sample, and samples were gently blown with nitrogen gas before being centrifuged at 13,000 RPM for 60 min. 100 μL of sample was added to a microautosampler vial, blown with nitrogen gas, capped and loaded at 4°C in the autosampler cooling tray. 10 μL of sample was injected into the HPLC system and measured by electrochemical detection.
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