Gut Microbiota's Impact on Behavior and Health

Aug 13, 2024

Lecture Notes: The Influence of Gut Microbiota on Behavior and Health

Introduction

  • Debate on the existence of free will and control over our destiny.
  • Biological perspective: more than one entity influences our actions.
  • Half the cells in the body are non-human (bacteria, protozoa, fungi, etc.).
  • These microorganisms, known as microbiota, significantly impact various bodily functions and behavior.

Microbiota and Behavior

  • Microbiota are abundant in the gut.
  • Influence digestion, mood, energy, appetite, and even personality.

Research on Mice

  • Bubble Mice: Raised in sterile environments, lack natural microbiota.
    • Show reduced curiosity and learning ability.
    • Lack stress response to separation from mothers.
    • Normal behavior resumes when colonized with microbiota from birth.

Evidence in Humans

  • Gut bacteria from overweight twins cause weight gain in mice, while bacteria from thin twins do not.
  • Gut bacteria from depressed humans induce depression-like symptoms in mice.

Mechanisms of Influence

  1. Psychoactive Compounds:

    • Gut bacteria produce neurotransmitters.
    • Communicate with the brain via the vagus nerve.
    • 80% of vagus nerve signals are gut-to-brain.

  2. Circulatory System:

    • Transport psychoactive compounds to the brain.

  3. Immune Response:

    • Aggressive bacteria trigger immune response that can travel to the brain, causing inflammation and depression.

Treatments and Research

  • Vagus Nerve Stimulation (VNS):

    • Used for epilepsy, depression, ADHD, OCD, PTSD.
    • May mimic effects of gut bacteria on the vagus nerve.

  • Microbiota-based Treatments:

    • Changing gut bacteria composition or blocking their chemical actions.
    • Identifying 'good' and 'bad' bacteria for specific conditions.

Autism Spectrum Disorder

  • High levels of a bacterial molecule linked to anxiety and altered brain connectivity.
  • Axial Therapeutics: Clinical trial for a drug targeting this molecule.
  • Lactobacillus reuteri: Promotes social bonding in animal models.

ALS

  • Certain bacteria accelerate or slow down the disease.
  • Benefits attributed to a vitamin produced by good bacteria.

Parkinson's Disease

  • Misfolding of alpha-synuclein protein linked to gut bacteria.
  • Misfolded proteins may spread from gut to brain via vagus nerve.

Conclusion

  • Early days in research, but potential for new treatments is promising.
  • The concept of 'self' involves both human and microbial elements.
  • Encourages a broader understanding of influences on behavior.

Takeaway: The interplay between human cells and microbiota significantly influences behavior and health, offering new avenues for understanding and potentially treating various conditions.