Dietary l-tryptophan leaves a lasting impression on the brain and the stress response

• Published in: British Journal of Nutrition
• Main Authors: Höglund, Erik, Øverli, Øyvind, Åberg Andersson, Madelene, Silva, Patricia Isabel da Mota E., Laursen, Danielle Caroline, Moltesen, Maria M, Krogdahl, Åshild, Schjolden, Joachim, Winberg, Svante, Vindas, Marco A., Mayer, Ian, Hillestad, Marie
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2017
• Subjects: l-Tryptophan; 5-HIAA 5-hydroxyindoleacetic acid; 5-HT 5-hydroxytryptamine (serotonin); HPI hypothalamic–pituitary–interrenal; SSRI supplementation and serotonin reuptake inhibitors; Trp tryptophan; Long-term effects; Monoamines; Atlantic salmon
• Online Access: https://orbit.dtu.dk/en/publications/4665771e-fd29-418a-a2c5-cb4826296be4; https://doi.org/10.1017/S0007114517001428; https://backend.orbit.dtu.dk/ws/files/133199371/Publishers_version.pdf

Comparative models suggest that effects of dietary tryptophan (Trp) on brain serotonin (5-hydroxytryptamine; 5-HT) neurochemistry and stress responsiveness are present throughout the vertebrate lineage. Moreover, hypothalamic 5-HT seems to play a central role in control of the neuroendocrine stress axis in all vertebrates. Still, recent fish studies suggest long-term effects of dietary Trp on stress responsiveness, which are independent of hypothalamic 5-HT. Here, we investigated if dietary Trp treatment may result in long-lasting effects on stress responsiveness, including changes in plasma cortisol levels and 5-HT neurochemistry in the telencephalon and hypothalamus of Atlantic salmon. Fish were fed diets containing one, two or three times the Trp content in normal feed for 1 week. Subsequently, fish were reintroduced to control feed and were exposed to acute crowding stress for 1 h, 8 and 21 d post Trp treatment. Generally, acute crowding resulted in lower plasma cortisol levels in fish treated with 3×Trp compared with 1×Trp- and 2×Trp-treated fish. The same general pattern was reflected in telencephalic 5-HTergic turnover, for which 3×Trp-treated fish showed decreased values compared with 2×Trp-treated fish. These long-term effects on post-stress plasma cortisol levels and concomitant 5-HT turnover in the telencephalon lends further support to the fact that the extrahypothalamic control of the neuroendocrine stress response is conserved within the vertebrate lineage. Moreover, they indicate that trophic/structural effects in the brain underlie the effects of dietary Trp treatment on stress reactivity.