2.3 Serum corticosterone detection
The concentration of serum corticosterone was measured by ELISA assay kits (R&D Systems, Inc., Minneapolis, MN, USA) according to the manufacturer’s protocol. The limit of detection for corticosterone concentration was 0.39 ng/ml. The intra-assay and inter-assay coefficients of variation for corticosterone were 5.0 and 7.2%, respectively.