Time-course of the effect of dietaryl-tryptophan on plasma cortisol levels in rainbow troutOncorhynchus mykiss

Abstract

SUMMARYIsolated juvenile rainbow trout were fed a feed supplemented with l-tryptophan (TRP) for 3, 7 or 28 days, after which they were either sampled directly (undisturbed) or subjected to a standardised stressor prior to sampling. Controls (stressed and undisturbed) received the same feed but without any supplementary TRP. Stress resulted in a significant elevation of plasma [cortisol] in fish fed control feed and in fish fed TRP-supplemented feed for 3 and 28 days. However, fish fed TRP-supplemented feed for 7 days did not show any significant elevation of plasma [cortisol] in response to stress. Plasma levels of adrenocorticotropin followed the same general pattern as cortisol. Plasma and brain [TRP] were elevated in fish fed TRP-supplemented feed. The amino acid TRP is the precursor of the monoamine neurotransmitter serotonin (5-hydroxytryptamine, 5-HT) and the brain 5-HT system is known to be involved in the control of the hypothalamic-pituitary-interrenal (HPI) axis. Fish fed TRP-supplemented feed showed elevated levels of 5-hydroxyindoleacetic acid (5-HIAA, a major 5-HT metabolite) in the hypothalamus and optic tectum. However, TRP treatment did not appear to result in any effects on brain dopaminergic activity and the effects on brain norepinephric activity do not support a role of norepinephrine in mediating the effects of TRP on HPI axis reactivity in rainbow trout.

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

“…For example, dietary Trp affected 5-HT turnover significantly in the hypothalamus (7) and optic tectum (8) 1 d post Trp treatment, whereas this effect of dietary Trp was expressed less in the brain stem and telencephalon. Moreover, Basic et al (15) showed that Trp treatment tended to enhance hypothalamic 5-HT 1 d post Trp, and that this effect was not present 10 d post Trp treatment.…”

“…Dietary manipulations have been used as tool to investigate the involvement of brain 5-HT in behaviour, mood and cognition in humans (3) . Such manipulations have also been shown to affect the endocrine and behavioural response to stress in comparative vertebrate models (4)(5)(6)(7)(8) . Many of these effects have been attributed to the immediate precursor of 5-HT, the essential amino acid tryptophan (Trp), which enters the brain from the circulation in competition with other large amino acids (LNAA) (9) .…”

“…To do this, Atlantic salmon were given feed containing one, two or three times the Trp content in normal feed for 1 week, a treatment period that has repeatedly been shown to induce behavioural and neuroendocrine changes in several fish species (4)(5)(6)(7)(8)15,16) . Following TRP treatment, the effects on plasma cortisol and 5-HT in the hypothalamus and telencephalon were investigated (8 and 21 d post Trp treatment) in response to standardised acute crowding stress.…”

Effects of the Dietary Tryptophan and Aspartate on the Immune Response of Meagre (Argyrosomus regius) after Stress

“…Functional amino acids could be used to design balanced aquafeeds to enhance the efficiency and profitability of global aquaculture production [9]. Furthermore, we tested the same dosages and administration time that those used previously in other fish species [17][18][19][20][21][22].…”

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“…Hseu et al, 2003 found that dietary supplementation of L-tryptophan in juveniles rainbow trout diet leads to inhibit aggression behavior. Hoglund, Sorensen, Bakke, Nilsson, & Øverli, 2007 also revealed that L-tryptophan reduce cannibalism and stress induced anorexia in juvenile grouper and Lepage, Vilehez, Pottinger and Winberg, (2003) showed that it prevents stress induced cortisol surge. In contrast, Krol, Flisiak, Urbanowicz, and Ulikowski, (2014) reported that the tryptophan supplementation had no significant effect on growth or survival of Silurus glanis.…”