Evolutionary conservation of glucocorticoids and corticotropin releasing hormone: behavioral and physiological adaptations.

Glucocorticoids and corticotropin releasing hormone (CRH) underlie the physiology of change and adaptation. Both the steroid and peptide are quite ancient. The genes that underlie the production of these information molecules stretch back millions of years. The regulatory mechanisms of glucocorticoids have both restraining and enhancing capabilities on CRH gene expression. While restraint of CRH by glucocorticoids is a fundamental physiological feature of limiting CRH expression from over-use and exhaustion, CRH is also enhanced by glucocorticoids at both the level of extra-hypothalamic CRH sites and at the level of the placenta and fetal programming in the brain. This latter function of glucocorticoids increasing CRH gene expression underlies the physiology of change that underlies diverse adaptive functions.