The endocannabinoid system in mental disorders: Evidence from human brain studies

Mental disorders have a high prevalence compared with many other health conditions and are the leading cause of disability worldwide. Several studies performed in the last years support the involvement of the endocannabinoid system in the etiopathogenesis of different mental disorders. The present review will summarize the latest information on the role of the endocannabinoid system in psychiatric disorders, specifically depression, anxiety, and schizophrenia. We will focus on the findings from human brain studies regarding alterations in endocannabinoid levels, cannabinoid receptors and endocannabinoid metabolizing enzymes in patients suffering mental disorders. Studies carried out in humans have consistently demonstrated that the endocannabinoid system is fundamental for emotional homeostasis and cognitive function. Thus, deregulation of the different elements that are part of the endocannabinoid system may contribute to the pathophysiology of several mental disorders. However, the results reported are controversial. In this sense, different alterations in gene and/or protein expression of CB1 receptors have been shown depending on the technical approach used or the brain region studied. Despite the current discrepancies regarding cannabinoid receptors changes in depression and schizophrenia, present findings point to the endocannabinoid system as a pivotal neuromodulatory pathway relevant in the pathophysiology of mental disorders.This study was supported by the Spanish Ministry of Economy and Competitiveness (SAF2015-67457-R, MINECO/FEDER), the Plan Estatal de I+D+i 2013-2016, the Instituto de Salud Carlos III-Subdirección General de Evaluación y Fomento de la Investigación, Spanish Ministry of Economy, FEDER (PI13/01529) and the Basque Government (IT616/13). I I-L is a recipient of a Predoctoral Fellowship from the Basque Government. E F-Z is a recipient of a Predoctoral Fellowship from the University of Cantabria. CM is a recipient of a Postdoctoral Marie Skłodowska-Curie Individual Fellowship (H2020-MSCA-IF-2016, ID 747487)