Validation Of Hair Corticosterone As An Endogenous Bio-Marker Of Chronic Stress In Rodents

Corticosterone is the primary glucocorticoid steroid which plays important roles in energy metabolism and responses to physiological and psychological stressors. Endogenous corticosterone in rodent's hair would be a potential biomarker to assess the response of the hypothalamus-pituitary-adrenal axis to chronic stress. However, currently unknown is whether hair corticosterone is associated with endogenous corticosterone in blood and brain.The present study aimed to develop an enhanced assay for determination of endogenous corticosterone in blood, brain and hair, and to examine associations of hair corticosterone with blood and brain corticosterone under basal condition and association with blood corticosterone under chronic stressful condition. Hair at the back and blood samples were collected from non-stressed and stressed rodents, and prefrontal lobe and thalamus from non-stressed rodents. Chronic stress exerted on mice was 30-day repeated social defeat. The analyses were done using high performance liquid chromatography tandem mass spectrometry with atmospheric pressure chemical ionization in positive mode.Results revealed that limits of detection and quantification were 0.2 and 0.5 ng/ml for rat's blood, and 0.5 and 1.0 pg/mg for rat's hair and brain, and 1.25 and 2.50 ng/ml (or pg/mg) for mouse's blood (or hair). Recovery ranged from 84.2 to 108.0%. The intra- and inter-day coefficients of variation were less than 10%. Correlation of hair corticosterone with blood corticosterone was significant in both mice and rats, but correlations with corticosterone in prefrontal lobe and thalamus were not significant in rats. Both hair and blood corticosterone were significantly higher in physiological stressed rats and repeated social defeat stressed mice compared with controls. These results indicated that hair corticosterone is possibly a reliable endogenous biomarker of chronic stress in rodents.