Following collection, blood was allowed to settle for 1 h prior to centrifugation. Samples were centrifuged at 3000 × g for 20 min after which serum was removed and stored at -80 °C until analysis. Serum corticosterone (5 μl) was measured using commercial RIA kits (MP Biomedicals, Costa Mesa, CA), as previously described (Bingham and Viau, 2008). Briefly, for corticosterone analysis, the serum samples were diluted 1:100 and 1:200 for basal and stress conditions, respectively, to render hormone detection within the linear part of the standard curve. [125I]-labeled corticosterone was used as trace; the corticosterone antibody cross-reacts slightly with desoxycorticosterone (0.34%) and testosterone and cortisol (0.10%).
