Gut Bacteria and Brain Function

Gut Bacteria and Brain Function

• The microbiome may regulate how people think and feel.
• Gut bacteria's impact on health is increasingly recognized.
• Microbes in the gut influence digestion, allergies, and metabolism.
• Gut bacteria play a role in autism, anxiety, depression, and other disorders.
• There's growing interest in the connections between the microbiome and the brain.

Autism and Gut Microbiome

• About 75% of autistic people experience gastrointestinal abnormality.
• Gut microbes differ significantly between autistic and non-autistic people.
• Autistic individuals often have smaller quantities of Bacteroides fragilis.
• Mazmanian and colleagues fed B. fragilis to mice with autism symptoms, altering their microbiome and improving their behavior.
• 4-ethylphenylsulphate (4EPS), a chemical produced by gut bacteria, may be a link between gut bacteria and autism.
• Mice with autism symptoms have 40 times higher levels of 4EPS.
• Injecting animals with 4EPS induced autism-like symptoms.
• Adjusting gut bacteria could treat autism by turning off the "faucet" that produces 4EPS.

Anxiety, Depression and Gut Microbiome

• Lactobacillus and bifidobacterium strains reduce anxiety-like behavior in mice.
• Transplanting gut bacteria from anxious mice to calm mice made the latter anxious.
• Bifidobacterium or antidepressant Lexapro increased perseverance and reduced stress hormones in mice subjected to stressful situations.
• Lactobacillus produced similar results in another experiment.
• Collins transferred gut bacteria from anxious humans into "germ-free" mice, who then behaved anxiously.
• A prebiotic, galactooligosaccharide (GOS), affected stress levels in healthy volunteers.
• GOS fostered growth of Lactobacillus and Bifidobacteria.
• Mice with more of these microbes had increased levels of neurotransmitters that affect anxiety
• Subjects who ingested GOS had lower levels of cortisol, a key stress hormone.
• GOS group focused more on positive information and less on negative.

Modifying Brain Chemistry

• Yogurt eaters showed calmer reactions as compared to control group when viewing images of facial expressions.
• The bacteria in the yogurt changed the makeup of the subjects' gut microbes.
• The change led to the production of compounds that modified brain chemistry.
• Gut bacteria create neurotransmitters like serotonin, dopamine, and GABA.
• Certain organisms affect the rate at which compound in blood and the brain metabolize.
• Gut bacteria generate neuroactive chemicals like butyrate, linked to reduced anxiety and depression.
• Microbes activate the vagus nerve, which is the main line of communication between the gut and the brain.
• The microbiome is intertwined with the immune system.

Evolutionary Perspective

• Microbes may shape their hosts' behavior for their own ends.
• Modifying mood is a microbial survival strategy as "happy people tend to be more social."

Future use in Treatment

• Gut-brain microbial network can be hacked to treat psychiatric disorders.
• Microbes are more precise and subtle than current pharmacological approaches.
• Resulting in fewer side effects.