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

The exposure to chronic stressors could have deleterious effects on an animal’s health and well-being and could negatively influence the result of an experimental design. The stress situation involves an activation of the hypothalamic–pituitary–adrenocortical (HPA) axis changes in the adrenocortical secretion of glucocorticoids (GC). Short-term and long-term changes are nowadays assessed by measuring GC concentrations in plasma, feces, urine and saliva but there are clear limitations to each of these approaches. Therefore there is no current non-invasive validated procedure for determining long-term activity of this system in laboratory animals rodents. The aim of the present study was, for the first time, to develop and validate a reliable method for measuring hair corticosterone concentrations in rats. Sprague Dawley rats of 10 weeks were shaved in the morning on their back and collected 200 mg of hair samples. The procedure involved: two isopropanol washes of the samples to remove contaminants, powdering of the washed and dried hair, a 21-h methanol extraction followed by evaporation of the solvent, reconstitution of the extract in phosphate buffer and analysis of the extracted corticosterone by radioimmuneassay (RIA). The sensitivity of the assay was 0.6 pg/mg. The measured recovery was: 97.5% +/- 6.1 and the coefficient of variation of the whole process (extraction + analysis): 7.8%. Therefore this new procedure 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.