Gut-Brain Axis Overview and Microbiota Roles

Gut-Brain Axis Overview

• The gut microbiota plays a crucial role in influencing brain function and behavior.
• The gut microbiome communicates with the central nervous system (CNS) through various pathways, including neural, endocrine, and immune pathways.
• Variations in gut microbiota composition can impact mood, cognition, anxiety, and pain.
• This bidirectional communication is referred to as the microbiota-gut-brain axis.

Microbiota Composition in Different Regions

• Stomach: Sparse bacterial load, low diversity, Firmicutes and Actinobacteria predominate.
• Duodenum: Increased bacterial load, low diversity, Firmicutes and Proteobacteria predominate.
• Colon: High bacterial load, high diversity, Firmicutes and Bacteroidetes predominate.

Major Bacterial Phyla and Genera

• Firmicutes (60-80%): Ruminococcus, Clostridium, Lactobacillus
• Bacteroidetes (20-30%): Enterococcus, Bacteroides, Prevotella, Xylanibacter
• Actinobacteria (< 10%): Bifidobacterium
• Proteobacteria (< 1%): Escherichia, Enterobacteriaceae

Diseases Associated with Gut Dysbiosis

• Neurological: Multiple sclerosis (MS), Parkinson's disease, Alzheimer's disease, glioma, Autism Spectrum Disorder (ASD)
• Gastrointestinal: Malabsorption syndrome, inflammatory bowel disease (IBD), irritable bowel syndrome (IBS), diarrheal diseases, Clostridium difficile infection (CDI).

Dysbiosis and the CNS

• Gut dysbiosis can lead to alterations in brain behavior, cognition, emotion, and nociception.
• Dysbiosis can result in an altered inflammatory response in the gut, impacting the gut microbiome and the CNS.
• Gut dysbiosis can also trigger and exacerbate neurological diseases by altering the gut's immune system and microbiome composition

Gut Microbiota and Neurological Effects

• Inflammasome signaling (IL-1, 6, 18) influences neurological function
• Microbiota influences brain function through neurotransmitters, metabolites, and immune system interactions.
• Short-chain fatty acids (SCFAs) are produced by gut microbiota and have neuroactive effects on the CNS.
• Probiotic strains like Lactobacillus and Bifidobacterium can influence brain function and behavior.

Mechanisms of Gut Microbiota Effects on the CNS

• Gut microbiota impacts the brain and behavior by modulating several different neurotransmitters (e.g., Serotonin, dopamine, acetylcholine).
• Gut microbiota can alter the activity of the stress response axis in the hypothalamus-pituitary-adrenal (HPA) axis, affecting a range of bodily functions.
• Direct and indirect interactions between the gut and brain impact neuroinflammation.

Stress and Gut Microbiota

• Chronic stress can alter gut microbiota composition, increasing inflammation and permeability.
• Increased levels of Bacteroides, Clostridium species, Coprococcus, Pseudobutyrivibrio, and Dorea spp. can associate with inflammation and neurological symptoms.

Gut Microbiota and Probiotics

• Gut microbiota plays a role in the development of neurological diseases through interactions with the nervous system, immune system, and the metabolic pathways.
• Probiotics can modify nervous system development possibly through the gut microbiota-gut-brain axis.