The Microbes in Our Gut: Architects of Our Brain
When was the last time something gave you a “stomachache”, or instead, you had “a good gut feeling”? Or is a new partner currently giving you “butterflies in the stomach”?
All these expressions indicate that common wisdom long suspected what science could later prove: The complex connection between our gut and our brain!
Many people view the gut solely as a digestive organ and often overlook its fascinating complexity and numerous other functions.
Our gut comprises approximately 100 million nerve cells, forming the so-called enteric nervous system. This functions almost independently of our brain, the central nervous system, and is merely modulated by it.
One of the most important communication pathways between the gut and the brain is the vagus nerve. Extending from the brain over a large part of the body, it plays a significant role in the bidirectional exchange of information between the gut and the brain. Surprisingly, only 10 % of all information traveling along the vagus nerve goes from the brain to the gut, while an impressive 90 % is sent in the opposite direction – from the gut to the brain. This fact alone hints at the profound impact our gut has on our brain. This has been confirmed by research.
The Forgotten Factor
For several decades, intensive research has focused on gut-brain communication. However, for many years, a crucial, even decisive factor was overlooked: our gut microbiome. However, this omission has been corrected, particularly in the last decade, through intensive research into our microbiota-gut-brain axis.
Given that trillions of our tiny cohabitants reside in our gut, compared to only about 100 million nerve cells, it’s no surprise that they have a big say. Not only in matters relating to our diet, such as what we crave, but also in relation to our mood. Moreover, the occurrence of diseases such as Parkinson’s Disease, Alzheimer’s Disease and Autism Spectrum Disorder also appears to be linked to the composition of our microbiome.
However, this raises a crucial question: since an average bacterium is only a few micrometers in size, how can the signals it transmits overcome the comparatively vast distance between the gut and the brain?
Communication Pathways: From the Gut to the Brain
Our gut microbes can communicate with our brain in three different ways:
- through our nervous system.
- through our immune system.
- through messengers in our blood.
Our gut bacteria can independently produce specific neurotransmitters, chemical messengers that transmit information between nerve cells. This enables them to interact directly with our nerves. Some of this information can be transmitted to the brain through the nerve pathways in our body, such as the vagus nerve.
Indirectly, our gut bacteria can also influence how many of these chemical messengers the body releases. For example, in model systems, it has been shown that our microbiome influences the production of the happiness hormone serotonin. Germ-free mice, meaning mice that had never come into contact with bacteria and thus were completely sterile, showed a lower level of happiness hormones compared to their normally colonized counterparts.
What Does This Mean for Us?
So what immediate, tangible effects does this communication between our gut microbes and our brain have on our health and well-being?
Although it seems likely, considering their capability to affect the production of the happiness hormone, it’s still surprising: our gut inhabitants have a say in our mood. For example, it has been shown that mice given a substance normally produced by gut bacteria exhibited less depressive behavior.
Moreover, in many neurodegenerative diseases, including Parkinson’s and Alzheimer’s Disease, a change in the gut microbiome has been observed. These findings are promising, suggesting that our microbiome plays a significant role in these diseases. However, it remains to be clarified whether these changes are the cause or the consequence of the disease. Despite this caution, the available data opens up a lot of room for the assumption that our microbiome plays a crucial role in these disease processes.
What Does the Future Hold?
The field of the microbiota-gut-brain axis is growing rapidly. Almost daily, new discoveries emerge, and it seems highly promising that our microbiome will increasingly become the target of therapies for various diseases in the coming years.
A healthy microbiome is therefore not just a “nice-to-have”; it can positively influence our sense of life and even our lifespan. In the coming years, much is likely to happen in this field, with new insights gained and the importance of our microbiome continuing to rise.
Therefore, it already makes sense today to actively care for the health of our microbiome to optimally support the body as a whole. (LS)
Morais LH, Schreiber HL 4th, Mazmanian SK. The gut microbiota-brain axis in behaviour and brain disorders. Nat Rev Microbiol. 2021 Apr;19(4):241-255. doi: 10.1038/s41579-020-00460-0.
Die Unentbehrlichen – Mikroben, des Körpers verborgene Helfer. – Thomas C.G. Bosh