Depressive disorders: Prevalence, costs, and theories

Abstract

The estimated global cost of mental health conditions, including depressive disorders, was US$2.5 trillion in 2010. According to the World Health Organization (WHO), more than 350 million people of all ages suffer from depression, 10-40 % of them not improving their condition with the current drug therapies, thus contributing to the increased burden of mental disorders. Indeed, prognostics are not encouraging since it is predicted that unipolar depressive disorders will be the first cause of disability-adjusted life years (DALYs) by the year 2030. For these reasons, it is urgent to find new antidepressant drugs that act on other targets rather than the conventional one (monoamine transmission). Having this in mind, this chapter provides a critical review of the theories available to explain the pathogenesis of depressive disorders, namely, those focusing on disturbances of monoamine, glutamate and GABA transmission, changes in the hypothalamic- pituitary-adrenal (HPA) axis, neuroinflammation, neurogenesis and neurotrophic factors, glial pathology, epigenetic mechanisms, and disturbance of the circadian rhythm.