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Dietary tryptophan supplementation does not affect growth but increases brain serotonin level and modulates the expression of some liver genes in zebrafish (Danio rerio)

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Abstract

This study aimed at assessing the effects of the dietary tryptophan (Trp) supplementation on growth and feed utilization, brain serotonin content, and expression of selected liver genes (involved in the liver serotonin pathway, protein synthesis degradation, and antioxidant activity) in zebrafish. A growth trial was conducted with zebrafish juveniles fed five experimental isoproteic (40%DM) and isolipidic (8%DM) fishmeal-based diets containing graded levels of Trp: a Trp-non-supplemented diet (diet Trp0, with 0.22% Trp) and four Trp-supplemented diets containing 2–16 times higher Trp content (diets Trp2, Trp4, Trp8, and Trp16 with 0.40, 0.91, 2.02, and 3.34% Trp, respectively). Diets were tested in quadruplicate, with fish being fed twice a day, 6 days a week for 6 weeks to apparent visual satiation. At the end of the trial, growth performance and feed utilization were assessed, and fish from all experimental groups were sampled for whole-body composition analysis. In addition, fish fed low (Trp0), medium (Trp4), and high (Trp16) Trp diets were also sampled for analysis of brain serotonin content and liver gene expression. Tested tryptophan levels did not influence growth performance nor feed intake. However, values of energy and nitrogen retention as well as body energy content indicate a better feed utilization with diets containing around 0.9% and 2.0% DM Trp. Brain serotonin content increased with increasing dietary tryptophan levels. In addition, regarding liver genes, dietary treatment had a modulatory effect on the expression of Htr1aa and Htr2cl1 genes (encoding for serotonin receptors), TPH1a gene (encoding for tryptophan hydroxylase, the rate-limiting enzyme in the synthesis of serotonin from tryptophan), TOR gene (involved in protein synthesis), and Keap1 gene (involved in antioxidant responses).

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Funding

This work was funded by Programa Operacional Mar2020, Portugal 2020 under the project InovFeed (ref. MAR-02.01.01-FEAMP-0111).

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Authors and Affiliations

  1. Department of Biology, Faculty of Sciences, University of Porto, Rua do Campo Alegre, Edifício FC4, 4169-007, Porto, Portugal

    Cláudia Teixeira, Pedro Rodrigues, Luís Oliva Teles, Helena Peres & António Paulo Carvalho

  2. CIIMAR - Interdisciplinary Centre of Marine and Environmental Research, University of Porto, Terminal de Cruzeiros do Porto de Leixões, Av. General Norton de Matos, 4450-208, Matosinhos, Portugal

    Cláudia Teixeira, Pedro Rodrigues, Laura Guimarães, Luís Oliva Teles, Helena Peres & António Paulo Carvalho

  3. Unit of Pharmacology and Therapeutics, Department of Biomedicine, Faculty of Medicine, University of Porto, Alameda Prof. Hernâni Monteiro, 4200-319, Porto, Portugal

    Paula Serrão & Luís Figueira

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  1. Cláudia Teixeira
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  2. Pedro Rodrigues
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  3. Paula Serrão
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  4. Luís Figueira
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  8. António Paulo Carvalho
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Contributions

C.T., H.P., and A.P.C. conceived the study and designed the trial. C.T. and A.P.C. carried out the experiments. C.T., P.R., P.S., and L.F. carried out the chemical, biochemical, and genomic analyses. C.T., H.P., L.G., and L.O.T. analyzed the data. C.T., A.P.C., and L.G. wrote and L.O.T. revised the manuscript.

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Correspondence to Cláudia Teixeira.

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Teixeira, C., Rodrigues, P., Serrão, P. et al. Dietary tryptophan supplementation does not affect growth but increases brain serotonin level and modulates the expression of some liver genes in zebrafish (Danio rerio). Fish Physiol Biochem 47, 1541–1558 (2021). https://doi.org/10.1007/s10695-021-00994-x

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