At the time of decapitation, blood from each rat was collected in tubes, placed on ice, and was spun in a refrigerated centrifuge. Plasma was separated and stored at −40°C for hormonal measurements by radioimmunoassay. Levels of ACTH, corticosterone (CORT) and prolactin immunoreactivity were assayed from unextracted plasma by using kits from MP Biomedicals (Costa Mesa, CA), DiaSorin Inc. (Stillwater, MN), and Amersham Life Science Inc. (US), respectively. All values were determined in duplicate in a single assay.
