Dietary tryptophan intervention counteracts stress-induced transcriptional changes in a teleost fish HPI axis during inflammation

Immune nutrition is currently used to enhance fish health by incorporating functional ingredients into aquafeeds. This study aimed to investigate the connections between tryptophan nutrition and the network that regulates the communication pathways between neuroendocrine and immune systems in European seabass (Dicentrarchus labrax). When tryptophan was supplemented in the diet of unstressed fish, it induced changes in the hypothalamic-pituitary-interrenal axis response to stress. Tryptophan-mediated effects were observed in the expression of anti-inflammatory cytokines and glucocorticoid receptors. Tryptophan supplementation decreased pro-opiomelanocortin b-like levels, that are related with adrenocorticotropic hormone and cortisol secretion. When stressed fish fed a tryptophan-supplemented diet were subjected to an inflammatory stimulus, plasma cortisol levels decreased and the expression of genes involved in the neuroendocrine response was altered. Modulatory effects of tryptophan dietary intervention on molecular patterns seem to be mediated by altered patterns in serotonergic activity.