Gut–brain axis: how the microbiome influences anxiety and depression

Within the first few days of life, humans are colonized by commensal intestinal microbiota. Here, we review recent findings showing that microbiota are important in normal healthy brain function. We also discuss the relation between stress and microbiota, and how alterations in microbiota influence stress-related behaviors. New studies show that bacteria, including commensal, probiotic, and pathogenic bacteria, in the gastrointestinal (GI) tract can activate neural pathways and central nervous system (CNS) signaling systems. Ongoing and future animal and clinical studies aimed at understanding the microbiota–gut–brain axis may provide novel approaches for prevention and treatment of mental illness, including anxiety and depression. Within the first few days of life, humans are colonized by commensal intestinal microbiota. Here, we review recent findings showing that microbiota are important in normal healthy brain function. We also discuss the relation between stress and microbiota, and how alterations in microbiota influence stress-related behaviors. New studies show that bacteria, including commensal, probiotic, and pathogenic bacteria, in the gastrointestinal (GI) tract can activate neural pathways and central nervous system (CNS) signaling systems. Ongoing and future animal and clinical studies aimed at understanding the microbiota–gut–brain axis may provide novel approaches for prevention and treatment of mental illness, including anxiety and depression. naturally occurring bacterial colonization of infants (human) or pups (rodents) begins at birth and continues through postnatal life. Experimentally, mice lacking microbiota (GF mice) can be colonized by removal from the gnotobiotic rearing conditions, followed by exposure to microbiota (often exposure to mouse feces); these mice are referred to as ‘conventionalized’ mice. several bacteria phyla are represented in the intestinal microbiome, including Firmicutes, Bacteroides, Proteobacteria, Actinobacteria, Fusobacteria, and Verrucomicrobia. Recent metagenomic population studies have attempted to classify different profiles of bacterial phyla across groups of humans that are referred to as ‘enterotypes’. the human intestine is home to nearly 100 trillion microbes. The relation between these microbes and their host begins at birth and continues throughout life as a mutually beneficial relation. These naturally occurring, ever-present microbes are referred to as commensal intestinal microbiota or commensals. refers to the collection of microbes and their genetic material in a particular site, for example the human GI tract. live microorganisms that are administered as dietary supplements or as food products, such as yogurt. Experimentally, several probiotic bacteria have been tested for health benefits, including Lactobacillus sp. (Firmicutes) and Bifidobacterium sp. (Actinobacteria), which are both gram-positive anaerobic bacteria.