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Dar W. Aspartame-induced cognitive dysfunction: Unveiling role of microglia-mediated neuroinflammation and molecular remediation. Int Immunopharmacol 2024; 135:112295. [PMID: 38776852 DOI: 10.1016/j.intimp.2024.112295] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2024] [Revised: 05/14/2024] [Accepted: 05/16/2024] [Indexed: 05/25/2024]
Abstract
Aspartame, an artificial sweetener, is consumed by millions of people globally. There are multiple reports of aspartame and its metabolites affecting cognitive functions in animal models and humans, which include learning problems, headaches, seizures, migraines, irritable moods, anxiety, depression, and insomnia. These cognitive deficits and associated symptoms are partly attributed to dysregulated excitatory and inhibitory neurotransmitter balance due to aspartate released from aspartame, resulting in an excitotoxic effect in neurons, leading to neuronal damage. However, microglia, a central immunocompetent cell type in brain tissue and a significant player in inflammation can contribute to the impact. Microglia rapidly respond to changes in CNS homeostasis. Aspartame consumption might affect the microglia phenotype directly via methanol-induced toxic effects and indirectly via aspartic acid-mediated excitotoxicity, exacerbating symptoms of cognitive decline. Long-term oral consumption of aspartame thus might change microglia's phenotype from ramified to activated, resulting in chronic or sustained activation, releasing excess pro-inflammatory molecules. This pro-inflammatory surge might lead to the degeneration of healthy neurons and other glial cells, impairing cognition. This review will deliberate on possible links and research gaps that need to be explored concerning aspartame consumption, ecotoxicity and microglia-mediated inflammatory cognitive impairment. The study covers a comprehensive analysis of the impact of aspartame consumption on cognitive function, considering both direct and indirect effects, including the involvement of microglia-mediated neuroinflammation. We also propose a novel intervention strategy involving tryptophan supplementation to mitigate cognitive decline symptoms in individuals with prolonged aspartame consumption, providing a potential solution to address the adverse effects of aspartame on cognitive function.
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Affiliation(s)
- Waseem Dar
- Translational Neurobiology and Disease Modelling Laboratory, Department of Life Sciences, School of Natural Sciences, Shiv Nadar Institution of Eminence, Greater Noida, 201314, India.
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2
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Serotonin deficiency induced after brain maturation rescues consequences of early life adversity. Sci Rep 2021; 11:5368. [PMID: 33686115 PMCID: PMC7940624 DOI: 10.1038/s41598-021-83592-4] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2020] [Accepted: 01/22/2021] [Indexed: 01/31/2023] Open
Abstract
Brain serotonin (5-HT) system dysfunction is implicated in depressive disorders and acute depletion of 5-HT precursor tryptophan has frequently been used to model the influence of 5-HT deficiency on emotion regulation. Tamoxifen (TAM)-induced Cre/loxP-mediated inactivation of the tryptophan hydroxylase-2 gene (Tph2) was used to investigate the effects of provoked 5-HT deficiency in adult mice (Tph2 icKO) previously subjected to maternal separation (MS). The efficiency of Tph2 inactivation was validated by immunohistochemistry and HPLC. The impact of Tph2 icKO in interaction with MS stress (Tph2 icKO × MS) on physiological parameters, emotional behavior and expression of 5-HT system-related marker genes were assessed. Tph2 icKO mice displayed a significant reduction in 5-HT immunoreactive cells and 5-HT concentrations in the rostral raphe region within four weeks following TAM treatment. Tph2 icKO and MS differentially affected food and water intake, locomotor activity as well as panic-like escape behavior. Tph2 icKO prevented the adverse effects of MS stress and altered the expression of the genes previously linked to stress and emotionality. In conclusion, an experimental model was established to study the behavioral and neurobiological consequences of 5-HT deficiency in adulthood in interaction with early-life adversity potentially affecting brain development and the pathogenesis of depressive disorders.
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Lu X, Ce Q, Jin L, Zheng J, Sun M, Tang X, Li D, Sun J. Deoiled sunflower seeds ameliorate depression by promoting the production of monoamine neurotransmitters and inhibiting oxidative stress. Food Funct 2020; 12:573-586. [PMID: 33367360 DOI: 10.1039/d0fo01978j] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
We aimed to evaluate the antidepressant activity of deoiled sunflower seeds (SFS), which are rich in tryptophan, in our mouse model and explored a possible mechanism of action. Male C57BL/6J mice were subjected to chronic unpredictable mild stress (CUMS) and were administered a diet containing SFS as the main protein source. SFS alleviated CUMS-induced depression-like behaviors, compared to the effects of a whey protein-based diet. This effect was related to increases in the levels of serotonin, dopamine, norepinephrine, acetylcholine, and brain-derived neurotrophic factor in SFS-fed mice. These changes accompanied the amelioration of inflammatory abnormalities and oxidative stress. SFS increased the aromatic amino acid levels, and the ratio of tryptophan to neutral amino acids. Furthermore, the antidepressant-like effects of SFS were involved in lipid, nucleotide, and amino acid metabolism. In summary, SFS was found to attenuate depression-like symptoms in mice. These antidepressant effects may be related to the increase in the levels of aromatic amino acids and neurotransmitters, amelioration of oxidative stress and inflammation, and the regulation of the levels of abnormal metabolites to the normal levels.
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Affiliation(s)
- Xiaomeng Lu
- Institute of Nutrition and Health, School of Public Health, Qingdao University, Qingdao 266071, Shandong, China.
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Gasparini CF, Smith RA, Griffiths LR. Genetic and biochemical changes of the serotonergic system in migraine pathobiology. J Headache Pain 2017; 18:20. [PMID: 28194570 PMCID: PMC5307402 DOI: 10.1186/s10194-016-0711-0] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2016] [Accepted: 12/09/2016] [Indexed: 12/23/2022] Open
Abstract
Migraine is a brain disorder characterized by a piercing headache which affects one side of the head, located mainly at the temples and in the area around the eye. Migraine imparts substantial suffering to the family in addition to the sufferer, particularly as it affects three times more women than men and is most prevalent between the ages of 25 and 45, the years of child rearing. Migraine typically occurs in individuals with a genetic predisposition and is aggravated by specific environmental triggers. Attempts to study the biochemistry of migraine began as early as the 1960s and were primarily directed at serotonin metabolism after an increase of 5-hydroxyindoleacetic acid (5-HIAA), the main metabolite of serotonin was observed in urine of migraineurs. Genetic and biochemical studies have primarily focused on the neurotransmitter serotonin, considering receptor binding, transport and synthesis of serotonin and have investigated serotonergic mediators including enzymes, receptors as well as intermediary metabolites. These studies have been mainly assayed in blood, CSF and urine as the most accessible fluids. More recently PET imaging technology integrated with a metabolomics and a systems biology platform are being applied to study serotonergic biology. The general trend observed is that migraine patients have alterations of neurotransmitter metabolism detected in biological fluids with different biochemistry from controls, however the interpretation of the biological significance of these peripheral changes is unresolved. In this review we present the biology of the serotonergic system and metabolic routes for serotonin and discuss results of biochemical studies with regard to alterations in serotonin in brain, cerebrospinal fluid, saliva, platelets, plasma and urine of migraine patients.
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Affiliation(s)
- Claudia Francesca Gasparini
- Menzies Health Institute Queensland, Griffith University Gold Coast, Parklands Drive, Southport, QLD, 4222, Australia
| | - Robert Anthony Smith
- Genomics Research Centre, Institute of Health and Biomedical Innovation, School of Biomedical Sciences, Queensland University of Technology, Musk Ave, Kelvin Grove, QLD, 4059, Australia
| | - Lyn Robyn Griffiths
- Genomics Research Centre, Institute of Health and Biomedical Innovation, School of Biomedical Sciences, Queensland University of Technology, Musk Ave, Kelvin Grove, QLD, 4059, Australia.
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5
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Evidence of an inverse correlation between serotonergic activity and spreading depression propagation in the rat cortex. Brain Res 2017; 1672:29-34. [DOI: 10.1016/j.brainres.2017.07.011] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2017] [Revised: 07/12/2017] [Accepted: 07/14/2017] [Indexed: 11/19/2022]
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Linden M, Helmbold K, Kempf J, Sippas S, Filss C, Langen KJ, Eisert A, Zepf FD. Dietary tryptophan depletion in humans using a simplified two amino acid formula - a pilot study. Food Nutr Res 2016; 60:29272. [PMID: 27989269 PMCID: PMC5165058 DOI: 10.3402/fnr.v60.29272] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2015] [Revised: 09/26/2016] [Accepted: 11/03/2016] [Indexed: 11/14/2022] Open
Abstract
BACKGROUND Acute tryptophan depletion (ATD) is a well-established dietary method in translational brain research used to briefly lower central nervous serotonin (5-hydroxytryptamine (5-HT)) synthesis. A simplified two amino acid ATD formula (ATDPHE/LEU) was developed while reducing the overall amount of amino acids (AAs), with the objective of administration especially in children and adolescents in future studies. OBJECTIVE This study investigated tryptophan (TRP) influx rates across the blood-brain barrier (BBB) after dietary ATDPHE/LEU administration relative to the ATD Moja-De protocol that has been established for use in children and adolescents. DESIGN Seventy-two healthy adults (50% females) were randomized into four groups and administered ATD Moja-De, its TRP-balanced control condition (BAL), ATDPHE/LEU, or its respective control mixture (BALPHE/LEU) in a counterbalanced, double-blind, between-subjects design. Blood samples were collected at baseline and at hourly intervals for 6 h after AA intake. Questionnaires about mood, taste, and challenge tolerance were completed at fixed time points. RESULTS Both challenge mixtures significantly reduced central nervous TRP influx as calculated by Michaelis-Menten kinetics relative to baseline and the respective control conditions with only mild and comparable side effects. A greater decline in TRP influx over the BBB after ATDPHE/LEU administration when compared with ATD Moja-De was detected without group effects for taste, challenge tolerance, and mood. There was unintended initial short increase in plasma TRP concentrations observed after ATDPHE/LEU intake, and a possible redistribution between free and protein-bound TRP triggered by protein synthesis stimulated by the ingested AAs may account for this finding. Moreover, a decline in TRP influx after BALPHE/LEU administration over a 6-h period was observed, and the large amount of PHE in the BALPHE/LEU mixture may be a possible explanation for this particular phenomenon, which could have led to an unexpected increase in displacement of TRP at the BBB in this control condition. CONCLUSIONS This pilot study provides preliminary evidence for the possibility of lowering TRP influx as calculated by Michaelis-Menten kinetics into the brain by using a simplified ATD protocol in humans. The simplified composition of only two AAs, the lower overall AA amount, and the appropriate tolerance are characteristics of the newly developed ATDPHE/LEU protocol. Future studies focusing on the effects of the ATDPHE/LEU protocol and its respective control condition on CSF 5-HIAA concentrations, as well as neurochemical studies in rodents, are needed to further validate this newly developed AA mixture before definite conclusions about its usability in ATD-related research in humans, its specificity, and additional effects can be made.
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Affiliation(s)
- Maike Linden
- Clinic for Child and Adolescent Psychiatry, Psychosomatics and Psychotherapy, RWTH Aachen University, Aachen, Germany.,JARA Translational Brain Medicine, Jülich Aachen Research Alliance, Jülich, Germany
| | - Katrin Helmbold
- Clinic for Child and Adolescent Psychiatry, Psychosomatics and Psychotherapy, RWTH Aachen University, Aachen, Germany.,JARA Translational Brain Medicine, Jülich Aachen Research Alliance, Jülich, Germany
| | - Janina Kempf
- Clinic for Child and Adolescent Psychiatry, Psychosomatics and Psychotherapy, RWTH Aachen University, Aachen, Germany.,JARA Translational Brain Medicine, Jülich Aachen Research Alliance, Jülich, Germany.,Faculty of Arts and Social Sciences, Maastricht University, Maastricht, The Netherlands
| | - Shabnam Sippas
- Clinic for Child and Adolescent Psychiatry, Psychosomatics and Psychotherapy, RWTH Aachen University, Aachen, Germany.,JARA Translational Brain Medicine, Jülich Aachen Research Alliance, Jülich, Germany.,Faculty of Arts and Social Sciences, Maastricht University, Maastricht, The Netherlands
| | - Christian Filss
- Section JARA-Brain, Jülich-Aachen Research Alliance (JARA), Jülich, Germany
| | - Karl-Josef Langen
- Section JARA-Brain, Jülich-Aachen Research Alliance (JARA), Jülich, Germany.,Institute of Neuroscience and Medicine (INM-3, -4, -5), Research Centre Jülich, Jülich, Germany.,Department of Nuclear Medicine, RWTH Aachen University Hospital, Aachen, Germany
| | - Albrecht Eisert
- Department of Pharmacy, RWTH Aachen University, Aachen, Germany
| | - Florian Daniel Zepf
- Clinic for Child and Adolescent Psychiatry, Psychosomatics and Psychotherapy, RWTH Aachen University, Aachen, Germany.,JARA Translational Brain Medicine, Jülich Aachen Research Alliance, Jülich, Germany.,Centre and Discipline of Child and Adolescent Psychiatry, Psychosomatics and Psychotherapy, School of Psychiatry and Clinical Neurosciences & School of Paediatrics and Child Health, Faculty of Medicine, Dentistry and Health Sciences, The University of Western Australia, Perth, Australia.,Specialised Child and Adolescent Mental Health Services (CAMHS), Department of Health in Western Australia, Perth, Australia;
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Eisner P, Klasen M, Wolf D, Zerres K, Eggermann T, Eisert A, Zvyagintsev M, Sarkheil P, Mathiak KA, Zepf F, Mathiak K. Cortico-limbic connectivity in MAOA-L carriers is vulnerable to acute tryptophan depletion. Hum Brain Mapp 2016; 38:1622-1635. [PMID: 27935229 DOI: 10.1002/hbm.23475] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2016] [Revised: 11/09/2016] [Accepted: 11/14/2016] [Indexed: 01/12/2023] Open
Abstract
INTRODUCTION A gene-environment interaction between expression genotypes of the monoamine oxidase A (MAOA) and adverse childhood experience increases the risk of antisocial behavior. However, the neural underpinnings of this interaction remain uninvestigated. A cortico-limbic circuit involving the prefrontal cortex (PFC) and the amygdala is central to the suppression of aggressive impulses and is modulated by serotonin (5-HT). MAOA genotypes may modulate the vulnerability of this circuit and increase the risk for emotion regulation deficits after specific life events. Acute tryptophan depletion (ATD) challenges 5-HT regulation and may identify vulnerable neuronal circuits, contributing to the gene-environment interaction. METHODS Functional magnetic resonance imaging measured the resting-state state activity in 64 healthy males in a double-blind, placebo-controlled study. Cortical maps of amygdala correlation identified the impact of ATD and its interaction with low- (MAOA-L) and high-expression variants (MAOA-H) of MAOA on cortico-limbic connectivity. RESULTS Across all Regions of Interest (ROIs) exhibiting an ATD effect on cortico-limbic connectivity, MAOA-L carriers were more susceptible to ATD than MAOA-H carriers. In particular, the MAOA-L group exhibited a larger reduction of amygdala connectivity with the right prefrontal cortex and a larger increase of amygdala connectivity with the insula and dorsal PCC. CONCLUSION MAOA-L carriers were more susceptable to a central 5-HT challenge in cortico-limbic networks. Such vulnerability of the cortical serotonergic system may contribute to the emergence of antisocial behavior after systemic challenges, observed as gene-environment interaction. Hum Brain Mapp 38:1622-1635, 2017. © 2016 Wiley Periodicals, Inc.
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Affiliation(s)
- Patrick Eisner
- Department of Psychiatry, Psychotherapy, and Psychosomatics, Medical School, RWTH Aachen University, Aachen, Germany.,JARA-Translational Brain Medicine, Aachen, Germany
| | - Martin Klasen
- Department of Psychiatry, Psychotherapy, and Psychosomatics, Medical School, RWTH Aachen University, Aachen, Germany.,JARA-Translational Brain Medicine, Aachen, Germany
| | - Dhana Wolf
- Department of Psychiatry, Psychotherapy, and Psychosomatics, Medical School, RWTH Aachen University, Aachen, Germany.,JARA-Translational Brain Medicine, Aachen, Germany
| | - Klaus Zerres
- Department of Human Genetics, Medical School, RWTH Aachen University, Aachen, Germany
| | - Thomas Eggermann
- Department of Human Genetics, Medical School, RWTH Aachen University, Aachen, Germany
| | - Albrecht Eisert
- Department of Pharmacy, RWTH Aachen University, Aachen, Germany
| | - Mikhail Zvyagintsev
- Department of Psychiatry, Psychotherapy, and Psychosomatics, Medical School, RWTH Aachen University, Aachen, Germany.,JARA-Translational Brain Medicine, Aachen, Germany
| | - Pegah Sarkheil
- Department of Psychiatry, Psychotherapy, and Psychosomatics, Medical School, RWTH Aachen University, Aachen, Germany.,JARA-Translational Brain Medicine, Aachen, Germany
| | - Krystyna A Mathiak
- Department of Psychiatry, Psychotherapy, and Psychosomatics, Medical School, RWTH Aachen University, Aachen, Germany.,JARA-Translational Brain Medicine, Aachen, Germany
| | - Florian Zepf
- Department of Child and Adolescent Psychiatry, School of Psychiatry and Clinical Neurosciences and School of Pediatrics and Child Health; Faculty of Medicine, Dentistry and Health Sciences; The University of Western Australia (M561), Perth, Australia.,Department of Health in Western Australia, Specialized Child and Adolescent Mental Health Services (CAMHS), Perth, Australia
| | - Klaus Mathiak
- Department of Psychiatry, Psychotherapy, and Psychosomatics, Medical School, RWTH Aachen University, Aachen, Germany.,JARA-Translational Brain Medicine, Aachen, Germany
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Hood SD, Bell CJ, Argyropoulos SV, Nutt DJ. Don't panic. A guide to tryptophan depletion with disorder-specific anxiety provocation. J Psychopharmacol 2016; 30:1137-1140. [PMID: 27329165 DOI: 10.1177/0269881116655321] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The 2002 paper "Does 5-HT restrain panic? A tryptophan depletion study in panic disorder patients recovered on paroxetine" by Bell and colleagues - reprinted in this issue of the Journal - reports on a study undertaken in the halcyon days of David Nutt's Psychopharmacology Unit at the University of Bristol, England. In this invited commentary authors of the original work discuss the impact of this paper on the field of acute tryptophan depletion research (especially in the field of clinical anxiety disorders) and the development of disorder-specific anxiogenic provocations over the past decade.
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Affiliation(s)
- S D Hood
- School of Psychiatry & Clinical Neurosciences (M521), University of Western Australia, Perth, WA, Australia
| | - C J Bell
- Mental Health Clinical Research Unit, Department of Psychological Medicine, University of Otago, Christchurch, New Zealand
| | - S V Argyropoulos
- Centre for Neuropsychopharmacology, Division of Brain Sciences, Imperial College London, London, UK
| | - D J Nutt
- Centre for Neuropsychopharmacology, Division of Brain Sciences, Imperial College London, London, UK
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A high-fat diet differentially regulates glutathione phenotypes in the obesity-prone mouse strains DBA/2J, C57BL/6J, and AKR/J. Nutr Res 2016; 36:1316-1324. [PMID: 27866830 DOI: 10.1016/j.nutres.2016.10.004] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2016] [Revised: 10/12/2016] [Accepted: 10/14/2016] [Indexed: 12/12/2022]
Abstract
The ubiquitous tripeptide glutathione (GSH) is a critical component of the endogenous antioxidant defense system. Tissue GSH concentrations and redox status (GSH/GSSG) are genetically controlled, but it is unclear whether interactions between genetic background and diet affect GSH homeostasis. The current study tested the hypothesis that a high-fat diet regulates GSH homeostasis in a manner dependent on genetic background. At 4 months of age, female mice representing 3 obesity-prone inbred strains-C57BL/6J (B6), DBA/2J (D2), and AKR/J (AKR)-were randomly assigned to consume a control (10% energy from fat) or high-fat (62% energy from fat) diet for 10 weeks (n=5/diet per strain). Tissue GSH levels, GSSG levels, and GSH/GSSG were quantified, and hepatic expression of GSH-related enzymes was evaluated by quantitative reverse transcription polymerase chain reaction. The high-fat diet caused a decrease in hepatic GSH/GSSG in D2 mice. In contrast, B6 mice exhibited a decrease in GSSG levels in the liver and kidney, as well as a resultant increase in renal GSH/GSSG. AKR mice also exhibited increased renal GSH/GSSG on a high-fat diet. Finally, the high-fat diet induced a unique gene expression response in D2 mice compared with B6 and AKR. The D2 response was characterized by up-regulation of glutamate-cysteine ligase modifier subunit and down-regulation of glutathione reductase, whereas the B6 and AKR responses were characterized by up-regulation of glutathione peroxidase 1. Two-way analysis of variance analyses confirmed several diet-strain interactions within the GSH system, and linear regression models highlighted relationships between body mass and GSH outcomes as well. Overall, our data indicate that dietary fat regulates the GSH system in a strain-dependent manner.
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Influence of Tryptophan and Serotonin on Mood and Cognition with a Possible Role of the Gut-Brain Axis. Nutrients 2016; 8:nu8010056. [PMID: 26805875 PMCID: PMC4728667 DOI: 10.3390/nu8010056] [Citation(s) in RCA: 437] [Impact Index Per Article: 54.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2015] [Revised: 12/14/2015] [Accepted: 01/11/2016] [Indexed: 12/21/2022] Open
Abstract
The serotonergic system forms a diffuse network within the central nervous system and plays a significant role in the regulation of mood and cognition. Manipulation of tryptophan levels, acutely or chronically, by depletion or supplementation, is an experimental procedure for modifying peripheral and central serotonin levels. These studies have allowed us to establish the role of serotonin in higher order brain function in both preclinical and clinical situations and have precipitated the finding that low brain serotonin levels are associated with poor memory and depressed mood. The gut-brain axis is a bi-directional system between the brain and gastrointestinal tract, linking emotional and cognitive centres of the brain with peripheral functioning of the digestive tract. An influence of gut microbiota on behaviour is becoming increasingly evident, as is the extension to tryptophan and serotonin, producing a possibility that alterations in the gut may be important in the pathophysiology of human central nervous system disorders. In this review we will discuss the effect of manipulating tryptophan on mood and cognition, and discuss a possible influence of the gut-brain axis.
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Serotonergic modulation of resting state default mode network connectivity in healthy women. Amino Acids 2016; 48:1109-1120. [PMID: 26767373 DOI: 10.1007/s00726-015-2137-4] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2015] [Accepted: 11/16/2015] [Indexed: 09/29/2022]
Abstract
The default mode network (DMN) plays a central role in intrinsic thought processes. Altered DMN connectivity has been linked to diminished cerebral serotonin synthesis. Diminished brain serotonin synthesis is further associated with a lack of impulse control and various psychiatric disorders. Here, we investigated the serotonergic modulation of intrinsic functional connectivity (FC) within the DMN in healthy adult females, controlling for the menstrual cycle phase. Eighteen healthy women in the follicular phase (aged 20-31 years) participated in a double-blind controlled cross-over study of serotonin depletion. Acute tryptophan depletion (ATD) and a balanced amino acid load (BAL), used as the control condition, were applied on two separate days of assessment. Neural resting state data using functional magnetic resonance imaging (fMRI) and individual trait impulsivity scores were obtained. ATD compared with BAL significantly reduced FC with the DMN in the precuneus (associated with self-referential thinking) and enhanced FC with the DMN in the frontal cortex (associated with cognitive reasoning). Connectivity differences with the DMN between BAL and ATD in the precentral gyrus were significantly correlated with the magnitude of serotonin depletion. Right medial frontal gyrus and left superior frontal gyrus connectivity differences with the DMN were inversely correlated with trait impulsivity. These findings partially deviate from previous findings obtained in males and underline the importance of gender-specific studies and controlling for menstrual cycle to further elucidate the mechanism of ATD-induced changes within intrinsic thought processes.
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