Abstract
Compelling evidence is building for the involvement of the complex, bidirectional communication axis between the gastrointestinal tract and the brain in neuropsychiatric disorders such as depression. With depression projected to be the number one health concern by 2030 and its pathophysiology yet to be fully elucidated, a comprehensive understanding of the interactions between environmental factors, such as stress and diet, with the neurobiology of depression is needed. In this review, the latest research on the effects of stress on the bidirectional connections between the brain and the gut across the most widely used animal models of stress and depression is summarised, followed by comparisons of the diversity and composition of the gut microbiota across animal models of stress and depression with possible implications for the gut–brain axis and the impact of dietary changes on these. The composition of the gut microbiota was consistently altered across the animal models investigated, although differences between each of the studies and models existed. Chronic stressors appeared to have negative effects on both brain and gut health, while supplementation with prebiotics and/or probiotics show promise in alleviating depression pathophysiology.
Highlights
Depression is becoming increasingly prevalent as the world modernizes and is projected to be the number one health concern by 2030, which may be in part due to its close association with stress [1,2,3,4]
These findings indicate that the stress response, via the HPA axis, may have significant consequences for gut health in animal models of stress and depression, potentially impacting other pathways since stress affects multiple central and peripheral pathways including neuroplasticity, tryptophan metabolism and immune function [2,7]
Burokas et al [115] showed in their study that general increases in short chain fatty acids (SCFA) levels brought about by fructooligosaccharide and galactooligosaccharide supplementation were strongly correlated with positive changes in anhedonic, depressionlike and social behaviour
Summary
Depression is becoming increasingly prevalent as the world modernizes and is projected to be the number one health concern by 2030, which may be in part due to its close association with stress [1,2,3,4]. Compelling evidence is building for the involvement of the complex, bidirectional communication axis between the gastrointestinal tract and the central nervous system (CNS) which serves to mediate mood states, in turn affecting intestinal motility, secretion and immune function [8,9]. Acting as a brake on these sympathetic driven responses on gut function, the vagus nerve, which largely contributes to the parasympathetic nervous system, acts efferently to decrease intestinal inflammation and strengthen intestinal barrier function [11,12] These efferent fibres of the vagus nerve are inhibited by stress, allowing the sympathetic effects on the gut to continue unchecked [11,12]. This review will evaluate recent studies which used common animal models of stress and depression to investigate the effects of stress and diets on the brain-to-gut and gut-to-brain pathways
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