Journal Articles

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    Peripherally Restricted Activation of Opioid Receptors Influences Anxiety-Related Behaviour and Alters Brain Gene Expression in a Sex-Specific Manner.
    (MDPI (Basel, Switzerland), 2024-12-07) Parkar N; Young W; Olson T; Hurst C; Janssen P; Spencer NJ; McNabb WC; Dalziel JE; Szumlinski KK; Shiina T
    Although effects of stress-induced anxiety on the gastrointestinal tract and enteric nervous system (ENS) are well studied, how ENS dysfunction impacts behaviour is not well understood. We investigated whether ENS modulation alters anxiety-related behaviour in rats. We used loperamide, a potent μ-opioid receptor agonist that does not cross the blood-brain barrier, to manipulate ENS function and assess changes in behaviour, gut and brain gene expression, and microbiota profile. Sprague Dawley (male/female) rats were acutely dosed with loperamide (subcutaneous) or control solution, and their behavioural phenotype was examined using open field and elevated plus maze tests. Gene expression in the proximal colon, prefrontal cortex, hippocampus, and amygdala was assessed by RNA-seq and caecal microbiota composition determined by shotgun metagenome sequencing. In female rats, loperamide treatment decreased distance moved and frequency of supported rearing, indicating decreased exploratory behaviour and increased anxiety, which was associated with altered hippocampal gene expression. Loperamide altered proximal colon gene expression and microbiome composition in both male and female rats. Our results demonstrate the importance of the ENS for communication between gut and brain for normo-anxious states in female rats and implicate corticotropin-releasing hormone and gamma-aminobutyric acid gene signalling pathways in the hippocampus. This study also sheds light on sexually dimorphic communication between the gut and the brain. Microbiome and colonic gene expression changes likely reflect localised effects of loperamide related to gut dysmotility. These results suggest possible ENS pharmacological targets to alter gut to brain signalling for modulating mood.
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    Characterisation of the Plasma and Faecal Metabolomes in Participants with Functional Gastrointestinal Disorders.
    (MDPI (Basel, Switzerland), 2024-12-16) Fraser K; James SC; Young W; Gearry RB; Heenan PE; Keenan JI; Talley NJ; McNabb WC; Roy NC; Fukui H
    There is evidence of perturbed microbial and host processes in the gastrointestinal tract of individuals with functional gastrointestinal disorders (FGID) compared to healthy controls. The faecal metabolome provides insight into the metabolic processes localised to the intestinal tract, while the plasma metabolome highlights the overall perturbances of host and/or microbial responses. This study profiled the faecal (n = 221) and plasma (n = 206) metabolomes of individuals with functional constipation (FC), constipation-predominant irritable bowel syndrome (IBS-C), functional diarrhoea (FD), diarrhoea-predominant IBS (IBS-D) and healthy controls (identified using the Rome Criteria IV) using multimodal LC-MS technologies. Discriminant analysis separated patients with the 'all constipation' group (FC and IBS-C) from the healthy control group and 'all diarrhoea' group (FD and IBS-D) from the healthy control group in both sample types. In plasma, almost all multimodal metabolite analyses separated the 'all constipation' or 'all diarrhoea' group from the healthy controls, and the IBS-C or IBS-D group from the healthy control group. Plasma phospholipids and metabolites linked to several amino acid and nucleoside pathways differed (p < 0.05) between healthy controls and IBS-C. In contrast, metabolites involved in bile acid and amino acid metabolism were the key differentiating classes in the plasma of subjects with IBS-D from healthy controls. Faecal lipids, particularly ceramides, diglycerides, and triglycerides, varied (p < 0.05) between healthy controls and the 'all constipation' group and between healthy controls and 'all diarrhoea' group. The faecal and plasma metabolomes showed perturbations between constipation, diarrhoea and healthy control groups that may reflect processes and mechanisms linked to FGIDs.
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    Slowed gastrointestinal transit is associated with an altered caecal microbiota in an aged rat model
    (Frontiers Media S.A., 2023-03-14) Parkar N; Dalziel JE; Spencer NJ; Janssen P; McNabb WC; Young W; Butcher J
    Gastrointestinal (GI) motility is largely dependent upon activity within the enteric nervous system (ENS) and is an important part of the digestive process. Dysfunction of the ENS can impair GI motility as is seen in the case of constipation where gut transit time is prolonged. Animal models mimicking symptoms of constipation have been developed by way of pharmacological manipulations. Studies have reported an association between altered GI motility and gut microbial population. Little is known about the changes in gut microbiota profile resulting specifically from pharmacologically induced slowed GI motility in rats. Moreover, the relationship between gut microbiota and altered intestinal motility is based on studies using faecal samples, which are easier to obtain but do not accurately reflect the intestinal microbiome. The aim of this study was to examine how delayed GI transit due to opioid receptor agonism in the ENS modifies caecal microbiota composition. Differences in caecal microbial composition of loperamide-treated or control male Sprague Dawley rats were determined by 16S rRNA gene amplicon sequencing. The results revealed that significant differences were observed at both genus and family level between treatment groups. Bacteroides were relatively abundant in the loperamide-induced slowed GI transit group, compared to controls. Richness and diversity of the bacterial communities was significantly lower in the loperamide-treated group compared to the control group. Understanding the link between specific microbial species and varying transit times is crucial to design interventions targeting the microbiome and to treat intestinal motility disorders.
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    Metabolome and microbiome profiling of a stress-sensitive rat model of gut-brain axis dysfunction
    (Springer Nature Limited, 2019-10-01) Bassett SA; Young W; Fraser K; Dalziel JE; Webster J; Ryan L; Fitzgerald P; Stanton C; Dinan TG; Cryan JF; Clarke G; Hyland N; Roy NC
    Stress negatively impacts gut and brain health. Individual differences in response to stress have been linked to genetic and environmental factors and more recently, a role for the gut microbiota in the regulation of stress-related changes has been demonstrated. However, the mechanisms by which these factors influence each other are poorly understood, and there are currently no established robust biomarkers of stress susceptibility. To determine the metabolic and microbial signatures underpinning physiological stress responses, we compared stress-sensitive Wistar Kyoto (WKY) rats to the normo-anxious Sprague Dawley (SD) strain. Here we report that acute stress-induced strain-specific changes in brain lipid metabolites were a prominent feature in WKY rats. The relative abundance of Lactococcus correlated with the relative proportions of many brain lipids. In contrast, plasma lipids were significantly elevated in response to stress in SD rats, but not in WKY rats. Supporting these findings, we found that the greatest difference between the SD and WKY microbiomes were the predicted relative abundance of microbial genes involved in lipid and energy metabolism. Our results provide potential insights for developing novel biomarkers of stress vulnerability, some of which appear genotype specific.
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    Nourishing the Infant Gut Microbiome to Support Immune Health: Protocol of SUN (Seeding Through Feeding) Randomized Controlled Trial.
    (JMIR Publications, 2024-09-02) Wall CR; Roy NC; Mullaney JA; McNabb WC; Gasser O; Fraser K; Altermann E; Young W; Cooney J; Lawrence R; Jiang Y; Galland BC; Fu X; Tonkie JN; Mahawar N; Lovell AL; Ma S
    Background: The introduction of complementary foods during the first year of life influences the diversity of the gut microbiome. How this diversity affects immune development and health is unclear. Objective: This study evaluates the effect of consuming kūmara or kūmara with added banana powder (resistant starch) compared to a reference control at 4 months post randomization on the prevalence of respiratory tract infections and the development of the gut microbiome. Methods: This study is a double-blind, randomized controlled trial of mothers and their 6-month-old infants (up to n=300) who have not yet started solids. Infants are randomized into one of 3 groups: control arm (C), standard kūmara intervention (K), and a kūmara intervention with added banana powder product (K+) to be consumed daily for 4 months until the infant is approximately 10 months old. Infants are matched for sex using stratified randomization. Data are collected at baseline (prior to commencing solid food) and at 2 and 4 months after commencing solid food (at around 8 and 10 months of age). Data and samples collected at each timepoint include weight and length, intervention adherence (months 2 and 4), illness and medication history, dietary intake (months 2 and 4), sleep (diary and actigraphy), maternal dietary intake, breast milk, feces (baseline and 4 months), and blood samples (baseline and 4 months). Results: The trial was approved by the Health and Disability Ethics Committee of the Ministry of Health, New Zealand (reference 20/NTA/9). Recruitment and data collection did not commence until January 2022 due to the COVID-19 pandemic. Data collection and analyses are expected to conclude in January 2024 and early 2025, respectively. Results are to be published in 2024 and 2025. Conclusions: The results of this study will help us understand how the introduction of a specific prebiotic complementary food affects the microbiota and relative abundances of the microbial species, the modulation of immune development, and infant health. It will contribute to the expanding body of research that aims to deepen our understanding of the connections between nutrition, gut microbiota, and early-life postnatal health. Trial Registration: Australian New Zealand Clinical Trials Registry ACTRN12620000026921; https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=378654 International Registered Report Identifier (IRRID): DERR1-10.2196/56772 JMIR Res Protoc 2024;13:e56772