A validation of a new method to analyze corticosterone in the hair of rats and its application to the study of chronic stress

Short-term and long-term changes in the hypothalamic–pituitary-adrenocortical (HPA) axis are nowadays assessed by measuring glucocorticoids (GC) concentration in plasma, feces, urine and saliva but with huge limitations. Hair is also a potentially useful technique but there is no current validated procedure for determining long-term activity of this system in laboratory animals such as rodents. Hence, we developed and validated a specific hair corticosterone extraction and RIA assay procedure; we assessed the sex variation in male and female rats and we subjected several groups of rats to two different chronic stress methods (IMO and CUS) and to ACTH challenge test. The RIA assay showed a sensitivity of 0.6 pg/mg with a recovery of 97.5% ± 6.1. The total plasma corticosterone was higher in female than in male rats but they had the same concentration of active corticosterone in the hair. The animals submitted to IMO and to CUS had higher corticosterone concentration compared to controls after 12 days of stress. Moreover, the ACTH challenge test demonstrated that hair is a better medium to differentiate the severity of stressors on HPA axis than food intake or body and adrenal weight. This new validated procedure is simple, not invasive and could be useful in many experimental contexts involving the study of stress, endocrinology and neuroscience fields, but also for monitoring chronic stress that might be associated with experimental manipulations.