The intestines can determine the brain. Our cognition has been overturned again, right?

Recently, in a new study published in Science, a team of scientists from the Pasteur Institute in France and other institutions revealed the mysterious connection between the brain and intestinal bacteria. They found in a mouse model that hypothalamic neurons can directly detect changes in intestinal bacterial activity and regulate physiological processes such as appetite and body temperature based on these changes.

This is another article about the brain-gut axis. It is indeed "unclear mechanism, gut flora" (indecisive, quantum mechanics). Today I will talk to you about how gut microbes affect the human brain.

01. Gut flora and the gut-brain axis

Intestinal flora is related to humans. Intestinal microorganisms are a huge group in our human body. How big are these microorganisms? According to incomplete statistics, there are more than 1,000 kinds of intestinal microorganisms in the human body. They perform different functions and their number is even larger, reaching nearly 100 trillion. This number far exceeds the number of cells in the human body, not to mention hundreds of thousands of times the number of all human beings. Therefore, scientists call it the second genome of the human body.

It forms a perfect mutually beneficial system with our human body. They can not only help resist the invasion of foreign pathogens, but also secrete immunoglobulins to help the human body improve immunity; for example, they can regulate the human body's physiology by promoting the repair of damaged mucosa. In addition, intestinal microorganisms promote intestinal digestion and absorption and help degrade some sugars.

But is that all?

One of the most cutting-edge areas today: the gut-brain axis.

Of course, the brain-gut axis here is not the direct influence of the intestine on the brain as believed in some ancient books, but a concept in microbiology.

The gut-brain axis is simply defined as follows

The gut-brain axis refers to the bidirectional signaling and connection between the intestines and the brain, which is mainly related to intestinal microorganisms.

02. Cell-Gut-Brain Axis and Autism

Here, we first introduce the issue of the gut-brain axis by taking a study published in the top biology journal CELL as an example. The title of the study is "Human Gut Microbiota from Autism Spectrum Disorder Promote Behavioral Symptoms in Mice". I believe that many people have roughly guessed the research of this article after reading the title, that is, the intestinal microbiota of autistic patients can cause autism in mice.

Briefly introduce the author's research.

The authors first selected special germ-free mice as research materials, which can avoid the influence of the intestinal microorganisms of the mice to the greatest extent. At the same time, two groups of people with autism spectrum disorder (Autism spectrum disorder, ASD) and normal individuals (typically-developing, TD) were selected. However, instead of studying these people directly, their feces were taken because there are a lot of microorganisms in feces. Next, a formal study was carried out, and the feces of the two groups of patients were transplanted into the bodies of germ-free mice, and then the behavior of the mice was observed.

As expected, the feces of autistic patients and normal people showed significant differences in mice. The mice transplanted with autistic patients showed obvious symptoms similar to human autism, such as increased repetitive behaviors and reduced motor and communication abilities. Moreover, this behavior will be passed on to the next generation.

It can be said that this clearly confirms one point, that is, intestinal microorganisms have a direct impact on the brain.

The reason is that metabolites affect gene expression, such as GABA and glycine receptor agonists/inhibitors, which are related to autism.

03. Science-The brain-gut axis acts on nerves

If the above study introduces that the brain-gut axis affects some components of autism, then this article introduces that the intestinal flora affects neurons.

Let's first take a picture to introduce the process of the entire article

This diagram shows the regulation of metabolism by the gut-brain axis.

When the mice consumed food, the intestinal microbial flora began to expand, which then led to an increase in cell wall peptides. These components then reached the brain and targeted a portion of the transplanted hypothalamic neurons.

This part will reduce neuronal activity, thereby helping to regulate the mouse's satiety and body temperature.

Specifically, it is that simple. They found that the key factor of this regulation is called Nod2 (nucleotide oligomerization domain 2, which feels like playing Call of Duty).

The figure above shows the expression of Nod2 in the brain and intestine.

The Nod2 in the hypothalamus can be involved in regulating body weight and body temperature

04. Significance of the research

Since the brain can sense the condition of intestinal microorganisms, many people probably think of losing weight first.

Although there have been studies on fecal transplantation before, which is to find a thin person and transplant his intestinal flora into the stomach of a fat person, and then the person will lose weight.

But I guess many people will resist this.

This article proposes that brain nerves sense intestinal flora, which provides another idea, that is, regulating human metabolism by affecting intestinal flora. For example, intervention in intestinal flora can be done by using probiotics, adjusting the type of intestinal flora, and finally affecting the brain.

Of course, conversely, the intestinal flora can also be regulated through the brain, such as for some patients with gastrointestinal diseases.

It’s actually quite attractive, solving both mental illness and gastrointestinal problems together.

Of course, this is a very distant future.