Why do they say the gut is the second brain? – 04/19/2023 – Fundamental Science

Aristotle held that the heart was the organ responsible for consciousness, sensation, and movement, and that the brain was a kind of “radiator” that served only to cool the heart. After 2,500 years, this hypothesis can be immediately refuted by studies in the area of ​​neuroscience: it is the brain that, through the complexity of its wrinkles, folds and cell types, coordinates cognitive and “automatic” functions, such as heartbeats. and the breath. A reversal without size in relation to what the Greek philosopher postulated. As Karl Popper, one of the greatest philosophers of science, said, “Science produces falsifiable theories, which are valid as long as they are not refuted.”

Today, if you ask anyone (including neuroscientists) what the “boss” of our body is, the answer will most likely be: the brain. But is he really in charge? New studies have questioned its hegemony as a control organ and what has been gaining strength is a region almost as mysterious as the brain: the intestine. The gut has been called “our second brain”, and indeed there are an abundance of nerve cells living in our guts. Gut neurons maintain a direct contact with the brain, which can have an impact on our behavior.

The reader should now have understood what I’m getting at. That’s right: the brain and gut can work together dictating our thoughts and actions. So it is possible to say that the intestine interferes with the functioning of the brain and vice versa, and currently there is even an area of ​​research focused only on the so-called intestine-brain axis. A brief search of the largest biomedical research database (PubMed) with the term “gut-brain” in English (gut-brain axis) shows that in 2022 alone, more than 1,400 scientific articles on the subject were produced worldwide.

But this brain-intestine axis story has the potential to get even more interesting: there is scientific evidence that intestinal bacteria command the intestinal and central nervous systems. What seems to be more extravagant than Aristotle’s initial idea has been confirmed, as studies show that the intestinal microbiota is capable of modulating our behavior. The human intestine is colonized by no less than an astonishing 100 trillion living microorganisms, the vast majority of which are bacteria.

These diverse bacteria communicate with each other and with our body, forming an unlikely and complex ecosystem. All this bacterial diversity is translated into thousands of substances – the so-called metabolites – produced by these single-celled organisms, which may have physiological functions and sometimes may even interfere with the functioning of the brain. That’s exactly what the reader is thinking: in the human body there are other living organisms that, fed by our diet, are able to, on the sly, control us. Intestinal bacteria perhaps act as the hidden individual who, by means of strings, manipulates puppets or puppets — us, in this case.

These studies are being confirmed day after day (some examples here and here), and with them a revolution in the treatment of mental disorders is expected. One of the biggest challenges in neuropharmacology is to obtain drugs that can cross the biological barriers that protect the brain and act inside, interfering with synapses and resolving dysfunctions.

Imagine if we could deliver drugs in the gut to bacteria that modulate the brain over long distances or even send metabolites there to the central nervous system. That would be, or will be, a revolution in the study and development of new drugs to treat brain pathologies. Who knew that we, the ultra-powerful humans, could be being silently manipulated by these microscopic single-celled organisms. The concept of free will needs to be updated: after all, it seems that we do what they, the bacteria, say.

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Eduardo Zimmer is a biochemist and professor at the Department of Pharmacology at the Federal University of Rio Grande do Sul.

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