Do antidepressants stabilize mood through actions on the hypothalamic-pituitary-adrenocortical system?

Patients suffering from severe depression often show an increased activity of the hypothalamic-pituitary-adrenocortical (HPA) system, a premature escape from the cortisol suppressant action of dexamethasone, and a number of other neuroendocrine changes. This might be explained by defective glucocorticoid feedback inhibition. Normalization of the hyperactive HPA system occurs during successful antidepressant pharmacotherapy of depressive illness, and this could be achieved by antidepressant-induced increases in the cellular corticosteroid receptors, rendering the HPA system more susceptible to feedback inhibition by cortisol. Both mineralocorticoid- and glucocorticoid-receptor mRNA levels and hormone-binding activities are found to be increased following treatment of different cell lines or animals with antidepressants. Since the timecourse of antidepressant actions on corticosteroid receptors follows more closely that of clinical improvement of depression, antidepressants might elevate mood in depressives through their long-term effects on HPA regulation.