HPLC chromatograms of intracellular OXY. Neurons were treated in the absence (control) or presence of 10 μM OXY. After incubation for 6 and 24 h, 100-μl intracellular extracts were aliquotted, and 20 μl of each sample was subjected to HPLC analysis. Chromatogram (a) shows the intracellular substances at the different time points (6 and 24 h) that can be detected in the control group. The retention time of intracellular OXY was confirmed by injecting an OXY standard under the same conditions (d). Chromatograms (a) and (d) prove that no endogenous substances would interfere with the peak identification of OXY. The HPLC chromatograms of intracellular OXY are shown by (b) and (c), and the peak area of intracellular OXY was autointegrated as 95,240 (incubation for 6 h) and 47,238 (incubation for 24 h).