Plasma BDNF measurement

Blood samples were drawn and collected with EDTA as the anticoagulant. Samples were drawn at the time of diagnosis, typically about 20 min following induction of anesthesia for resection. Plasma was immediately isolated from the whole blood after it had been centrifuged at 1000 × g for 10 min at 4°C. An additional centrifuge at 1000 × g for 10 min at 4°C was performed to remove platelets, then plasma was immediately stored at −80°C until it was thawed for assay. Plasma BDNF levels were quantified using enzyme-linked immunosorbent assays (ELISA). A Quantikine Human Cytokine Kit (R&D Systems, Minneapolis, MN) and an ELISA reader were used to analyze plasma BDNF levels. All assays were performed in duplicate and expressed as pictogram per milliliter (pg/mL).