Microbiota-Gut & Brain Axis Overview

Microbiota-Gut & Brain Axis

• The gut microbiota plays a significant role in human health, influencing various aspects including immune function, gastrointestinal health, and even brain function.
• Studies show a bidirectional interaction between the gut and brain, often referred to as the gut-brain axis.
• Variations and changes in gut microbial composition can affect normal physiology and contribute to diseases ranging from inflammation to obesity.
• Gut microbiota communicates with the central nervous system (CNS) through neural, endocrine, and immune pathways, directly influencing brain function and behavior.
• The research on the gut-brain axis has identified microbes associated with different neurological diseases, such as depression, anxiety, Alzheimer's, Parkinson's disease, and Autism Spectrum Disorder.
• Dysbiosis, an imbalance in the gut microbiota, is linked to various neurological and mental health conditions.
• Factors such as stress, diet, and infections can alter gut microbiota composition, impacting the gut-brain axis.
• Studies involving germ-free animals, antibiotic treatments, and probiotics suggest the impact of gut microbiota on brain health.
• The gut can affect the brain through various mechanisms such as the production of neurotransmitters, metabolites, and immunological signaling.
• The gut-brain axis influences mood, cognitive functions, and pain perception.
• The bidirectional nature of the gut-brain axis implies that both the gut and brain can influence each other.
• The gut microbiota can affect neurogenesis and the production of various hormones and neurochemicals in the brain.

Anatomical Locations of Bacteria & Yeast

• Bacteria and yeast are found in various parts of the human body as indigenous microbiota.
• Each location has a specific type of bacteria and yeast present in varying amounts.
• The table shows the presence, or less common presence, of certain species in specific locations.

Opportunistic Pathogens & Microbiota

• Immunosuppressed individuals or those with co-morbidities can experience the transfer of gut microbiota to sterile locations (opportunistic).
• This can lead to diseases caused by these opportunistic gut members.
• In a sick milieu, where the balance of the microbiota in the gut is negatively impacted, it can result in the domination of opportunistic microorganisms, causing negative consequences like disease formation.

Bacteria Phyla & Genera

• Firmicutes (60-80%) is a dominant phylum encompassing crucial genera like Ruminococcus, Clostridium, and Lactobacillus, in the human gut microbiome.
• Bacteroidetes (20-30%), another major phylum, includes species like Enterococcus, Bacteroides, Prevotella, and Xylanibacter.
• Actinobacteria (less than 10%) and Proteobacteria (less than 1%) are represented by other genera. 

Stomach, Duodenum and Colon Microbiota

• Different parts of the gut have distinct microbiota compositions, influenced by factors like pH, oxygen levels, and the presence of chemicals (like bile).
• Stomach's sparse bacterial load (low diversity) with high pH, and oxygenated nature.
• Duodenum has elevated bacterial load (moderate diversity).
• Colon exhibits the highest bacterial load and high diversity, mostly Firmicutes and Bacteroidetes.

Diseases of the Gut & Non-Mucosal Diseases

• Several diseases affect the gastrointestinal tract: Malabsorption syndrome, Malignant conditions (Colorectal cancer), Inflammatory Bowel Disease (IBD), Irritable Bowel Syndrome (IBS), Diarrhea, and Clostridium difficile infection, also known as CDI.
• Non-mucosal diseases can also be linked to gut health, including obesity and metabolic syndrome, liver cancer, complications of liver cirrhosis, allergic conditions, autoimmune disorders, neurologic disorders, and diseases like diabetes and chronic fatigue. 

Microbiota and Neurological Functions

• The gut microbiota affects mood, cognitive functions, and behavior.
• The gut microbiota can act on neurological functions via a two-way communication system.
• The gut microbiome affects neurologic functions via the brain-gut-axis.

Dysbiosis-CNS and Effects

• Dysbiosis disrupts the gut health, causing a cascade of effects in the central nervous system.
• This leads to alterations in behavior, cognition, emotion, and nociception.
• Dysbiosis and inflammatory responses could impact CNS function.
• Physiological levels of inflammatory mediators influence gut microbiota balance impacting CNS functionality.

Microbiome and Gut-Brain Axis

• It involves the interaction between the gut microbiota and brain.
• A bidirectional relationship where the gut influences the brain, and vice versa.
• The gut microbiome influences the production of neurochemicals and can affect mood, cognition, and behavior.

Mind-altering Microorganisms

• Gut microbiota influence brain functions and behavior with varied mechanisms including neural, endocrine, and immune pathways.
• Gut microbiota plays a role in anxiety, mood, cognition and pain, and probiotics can positively affect the gut-brain axis.
• The gut microbiota can regulate anxiety, mood, cognition, and pain.

Approach to Studying Microbiota Effects on CNS

• Using germ-free studies examines the effect of removing the gut microbiome.
• Infection studies observe the effects of bacterial infections.
• Studies using Probiotics look at the effect of beneficial bacteria.
• Antibiotic studies monitor the impacts of antibiotic treatments.
• Fecal transplantation studies analyze the impact of fecal microbiota from one subject to another.

Micrbrota's Impact on CNS

• Variations in microbial composition impact inflammatory responses and influence the brain-gut axis.
• The vagus nerve is a key component conveying signals about the gut.
• Tryptophan metabolism, bile acids, and short-chain fatty acids (SCFAs) have neuroactive effects and influence the brain-gut axis.

Gut Microbiota and Neurological Diseases

• Gut Dysbiosis can be linked to diseases like multiple sclerosis (MS), Parkinson's disease, Alzheimer's disease, and autism spectrum disorder.
• Both the gut and brain are involved in the pathogenesis of various neurological diseases.

Gut Microbiota and Inflammation

• The gut microbiota can affect inflammatory status, impacting neuropsychiatric illnesses.
• Changes in microbial composition induce changes in inflammatory responses.
• Some microorganisms exacerbate inflammatory conditions, leading to intestinal permeability problems.

Mechanism of Microbiota Effects on CNS

• Microorganisms such as Lactobacilli and Bifidobacterium produce GABA, norepinephrine, and acetylcholine in the gastrointestinal tract.
• These compounds influence neurotransmission and affect neural functions.
• The direct interaction between gut bacteria and the nervous system involves cytokines, neurotransmitters (serotonin), and microbial metabolites.
• Inflammation and the altered gut microbiome influence the gut-brain axis contributing to neurological conditions.

Gut Microbiota and the Gut-Brain Axis

• The interplay between the gut and brain is bidirectional, meaning that the gut microbiota can influence the brain and vice versa.
• The gut microbiota plays a crucial role in normal physiology and plays a significant role in the pathogenesis of diseases like anxiety, depression, and Parkinson’s Disease.
• Changes in gut microbiota composition, and intestinal inflammation, can trigger changes in brain function and behavior.