2.7. HPLC analysis of dopamine and its metabolite

Dopamine and metabolites in the striatum were measured by HPLC. Briefly, tissues were sonicated in chilled 0.1 M perchloric acid containing dihydroxybenzylamine as an internal standard. After centrifugation (15,000×g, 30 min, 4 °C), the supernatant was diluted with mobile phase (75 mM of NaH2PO4, 1.7 mM Octane sulfonic acid, 10% methanol, pH 3.0), and 10 μl of sample was isocratically eluted through a 80×4.6 mm C18 column (Waters Associates, Milford, MA) with a flow rate of 1.5 ml/min. Neurochemicals including dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC) were detected by a two-channel electrochemical detector (Waters Associates) at a potential of 1.5 mV. Concentrations were normalized by wet tissue weight.