Protein extraction was performed as previously described . Both the STZ- and vehicle-treated mice were killed under anesthesia with pentobarbital sodium. The hippocampi and cortices were isolated from three mice in each group, and mixed separately for the two groups. Two-DE analysis was repeated in triplicate. In brief, mouse hippocampal samples were homogenized in lysis buffer [7 M urea, 2 M thiourea, 5% CHAPS, 2% immobilized pH gradient (IPG) buffer (GE Healthcare UK Ltd., Buckinghamshire, UK), 50 mM 2-ME, 2.5 μg/ml DNase I, and 2.5 μg/ml RNase A]. Solubilized extracts were centrifuged at 15,000 ×g for 30 min, and the supernatant was used for further analysis.