Effects of flavonols on emotional behavior and compounds of the serotonergic system: A preclinical systematic review

Serotonin (5-hydroxytryptamine, 5-HT) is a neurotransmitter that regulates multiple psychophysiological functions. An imbalance of 5-HT in the brain can modulate emotional behavior such as depression and anxiety. Substances, such as flavonols, naturally found in some plants and foods have beneficial effects on psychiatric disorders, have been studied. The aim of this systematic review was to investigate the effects of flavonols on morphological, physiological, and cellular aspects of the serotonergic system as well as on some behaviors modulated by this system. Literature searches were performed in the LILACS, Web of Science, Scopus, PubMed and Sigle via Open Grey databases, from which 1725 studies were found. Using a predefined protocol registered on the CAMARADES website, 18 studies were chosen for qualitative synthesis. Internal validity was assessed using the SYRCLE's risk of bias tool. The Kappa index was also measured to analyze agreement among the reviewers. The results of this systematic review showed that flavonols have been reported to modify physiological aspects of the serotonergic system, increasing levels of serotonin and decreasing levels of its metabolite, 5-hydroxyindoleacetic acid (5-HIAA) and promoting antioxidant effects in encephalic regions. Moreover, the results showed that flavonols can also modulate of the serotonergic system, being associated with antidepressant and anxiolytic activities. Additionally, flavonols were found to not have psychostimulant effect; they can, however, reverse damage to locomotor activity. •Flavonols can increase serotonin and decrease 5-hydroxyindoleacetic acid in the brain.•Flavonols are associated with antidepressant and anxiolytic activities.•The flavonols can reverse damage to locomotor activity.