Research is clear: a healthy microbiome is essential for overall health and well-being ^1–4. Under healthy conditions, the gut microbiome plays a vital role in vitamin synthesis, the immune system, protection against pathogens, and influencing the brain  ^1,2,5–13. This communication with the brain happens via the gut-brain axis, which has recently been thought to be a significant contributor to regulating normal brain functions and a possible risk factor for neuropathological conditions ^14,15.

What is the gut-brain axis?

The gut-brain axis is a complex bidirectional communication pathway enabling the brain (nervous system) and the gastrointestinal tract (gut microbiome) to communicate and is assumed to involve many different pathways, including immune, neural, endocrine, and metabolic pathways ^2,16–25.

It may be more correct to call the connection between the brain and the gut the microbiota-gut-brain axis, as increasing scientific evidence has shown that gut microbiota are essential not only for gut health but also for the development and maintenance of brain function ^17,18. This more recent appreciation for the role of gut microbiota in the gut-brain axis comes from the discovery that different microbial composition is associated with alterations in behaviour and cognition ^16,26. Therefore, the microbiota-gut-brain axis can be defined as a bidirectional communication system enabling gut microbes to communicate with the brain and the brain with the gut, which can modulate our brain and behaviour. ^{14,16–18,22}

^{Figure from Moloney et al., 2013: The microbiota-gut-brain axis}

How does the gut communicate with the brain (and vice versa)?

Microbiota-gut-brain communication is complex and has not yet been wholly defined ¹⁸. We know that there are multiple connections between the gut and brain, which help explain the widespread effects of the gut microbiome. This axis involves different pathways, such as: ^{2,14,16–18,27–29,29–32}

• The autonomic and enteric nervous system
• Vagus, sympathetic and spinal nerves
• The endocrine system
• The hypothalamic-pituitary-adrenal axis (HPA)
• The immune system
• Neural and hormonal pathways (include cytokines, hormones, short-chain fatty acids (SCFAs), cytokines, and neuromodulators and neuropeptides as signalling molecules)
• Microbiota metabolites and by-products

Two areas to highlight are the immune system and neurotransmitters:

1.  The immune systems: the gut microbiome has been suggested to influence the immune system through by-products of the gut microbiota, such as neurotransmitters, essential vitamins, amino acids, and short-chain fatty acids, which can modulate the immune system pathways, which can influence behaviour, memory, learning, and neurodegenerative disorders. ^2,23,33–42.

2. Neurotransmitters: The gut microbiome can produce neurotransmitters, a ground-breaking finding in the world of gut-brain communication that helps explain the gut's influence on the brain. ^2,42–44. This production means that the gut can, directly and indirectly, contribute to the communication between the gut and the brain ². The gut microbiota regulates key neurotransmitters such as g-aminobutyric acid (GABA), noradrenaline, serotonin, dopamine, glutamate, glutamine, neurotrophic factors and acetylcholine by altering levels of precursor molecules via short-chain fatty acids and synthesizing and releasing neurotransmitters ^{2,14,18,45–49}. Surprisingly, 90% of our bodies' serotonin, which is required for mood, behaviour, sleep, and several other functions, is produced in the gut ^{2,14,42,50,51}.

Overall, the mechanisms of communication in the microbiota-gut-brain axis are complex and not fully elucidated but generally thought to include neural, endocrine, immune, and metabolic pathways ^18,52,53.

At Novel Biome, we're passionate about the importance of the gut microbiome and the transformative potential of Fecal Microbiota Transplantation (FMT) treatment to restore health. As an FMT contract manufacturer, we leverage our years of experience in FMT to manufacture high-quality FMT products utilizing our highly-screened donors and stringent manufacturing standards. If you are interested in learning more about our FMT products and manufacturing capabilities, please contact us HERE or to register as a clinical partner to order FMT products, click HERE.

References: 1. Belkaid, Y. & Hand, T. W. 2014, 2. Rutsch, A. et al. 2020, 3. Vatanen, T. et al. 2016, 4. Wilson, B. C. et al. 2019, 5. Choi, H. H. & Cho, Y.-S. 2016, 6. Chung, H. et al. 2012, 7.Hansen, N. & Sams, A. 2018, 8. Hooper, L. V. et al. 2012, 9. LeBlanc, J. G. et al. 2017, 10. Rautava, S. & Walker, W. A. 2007, 11. Sassone-Corsi, M. & Raffatellu, M. 2015, 12. Sommer, F. & Bäckhed, F. 2013, 13. Stecher, B. & Hardt, W.D. 2011, 14. Deidda, G. & Biazzo, M. 2021, 15. Ma, B. et al. 2019, 16. Chen, X. et al. 2013, 17. Cryan, J. F. et al. 2019, 18. Dinan, T. G. & Cryan, J. F. 2017, 19. Ding, X. et al. 2020, 20. Jendraszak, M. et al. 2021, 21. Liu, Z. et al. 2021, 22. Rhee, S. H. et al. 2009, 23. Skonieczna-Żydecka, K. et al. 2018, 24. Sudo, N. et al. 2004, 25. Wan, Y. et al. 2021, 26. Stilling, R. M. et al. 2014, 27. Blacher, E. et al. 2019, 28. Burberry, A. et al. 2020, 29. Cataldi, S. et al. 2022, 30. Clarke, S. F. et al. 2014, 31. Cryan, J. F. & O’Mahony, S. M. 2011, 32. Duvallet, C. et al. 2017, 33. Baj, A. et al. 2019, 34. Dalile, B. et al. 2019, 35. Engelhardt, B. et al. 2016, 36. Jenkins, T. et al. 2016, 37. Kennedy, P. J. et a. 2017, 38. Kipnis, J. 2016, 39. Mertens, K. L. et al. 2017, 40. Mittal, R. et al. 2017, 41. O’Keefe, S. J. D. 2016, 42. Yano, J. M. et al. 2015, 43. Komatsuzaki, Y. et al. 2005, 44. Pokusaeva, K. et al. 2017, 45. Desbonnet, L. et al. 2010, 46. Frost, G. et al. 2014, 47. Liu, R. et al. 2017, 48. Lyte, M. 2013, 49. Strandwitz, P. et al. 2019, 50. Desbonnet, L. et al. 2014, 51. Gershon, M. D. 2013, 52. El Aidy, S. et al. 2015, 53. Grenham, S. et al. 2011.