Numerous studies have shown that a diet rich in tryptophan (trp) has suppressive effects on aggressive behavior and post-stress plasma cortisol concentrations in vertebrates. These effects are thought to be mediated by the brain serotoninergic system. The rate of serotonin (5-HT) biosynthesis is limited by the availability of trp but only in neurons of the raphe nuclei that predominantly express the isoform TPH2 (trp hydroxylase enzyme). In the periphery as in brain areas that express TPH1 synthesis, 5HT is not limited by the availability of trp. There are factors that influence the influx of trp to the brain e.g. acute stress. Studies in mammals demonstrate that only a minor fraction of trp is used for 5HT synthesis while the remainder enters the kynurenic pathway. The first phase of the pathway is catalyzed by the hepatic enzyme TDO and the extrahepatic enzyme IDO enzymes induced by glucocorticoids and proinflammatory cytokines; Chronic stress and infections may therefore divert available trp to the kynurenic pathway and thereby lower 5HT synthesis. Dietary fatty acids influence proinflammatory cytokines and the metabolic fate of trp. In this review, we study the effects of trp supplementation on behavior and neuroendocrinology.
Year: 2019
Nationality: Norway
Download the document