Time-course of the effect of dietary L-tryptophan on plasma cortisol levels in rainbow trout Oncorhynchus mykiss.
Isolated 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.
Lepage
Olivier
O
Department of Comparative Physiology, Uppsala University, Norbyvägen 18A, SE-752 36, Sweden.
Vílchez
Inmaculada Molina
IM
Pottinger
Tom G
TG
Winberg
Svante
S
D000324:Adrenocorticotropic Hormone / Q000378:metabolism; D000818:Animals; D001923:Brain Chemistry; D004032:Diet; D006854:Hydrocortisone / Q000097:blood*; D006897:Hydroxyindoleacetic Acid / Q000378:metabolism; D017686:Oncorhynchus mykiss / Q000097:blood / Q000378:metabolism*; D013312:Stress, Physiological / Q000503:physiopathology*; D013997:Time Factors; D014364:Tryptophan / Q000378:metabolism*
D006897:Hydroxyindoleacetic Acid; D014364:Tryptophan; D000324:Adrenocorticotropic Hormone; D006854:Hydrocortisone