Why Does Nobody Talk About The Neurons In Our Gut? It Is Even Sometimes Called The Second Brain

This question was originally posted on Quora.com and was answered by Ayon Nandi, Researcher @ JHU; specialized in neuroreceptor imaging



The specific field you are looking for is “neurogastroenterology,” or the study of the brain, the gut, the neurons in the gut and their interactions as pertaining to gastrointestinal disease.

This scientific name may not be as punchy as “the second brain” or “the brain in your gut,” but the research in this field has expanded quite dramatically in the last few decades[1]. Much of the research seems to still be in the basic science phase, but there do seem to be some clinical applications coming out, although I am not sure if any have made their way to the clinic.

This means that in the lay science press, there may not be much mention because much of the research possibly isn’t at the point where it can be distilled into a easily accessible article.

However, with a little help from google and knowing the right keywords, you will find mentions of this research going back to the 90s[2]. and you know this is an official field of medicine as there is a society[3] and a journal[4],

Recently, a collaborative research effort was funded at the Center for Integrative Medicine at Johns Hopkins, and is focused on bringing together basic and clinical scientists to study “Food, Body and Mind”[5]

Some of the interesting findings from this area of research include (see footnotes for specific links and footnote 1 for a review):

1. There are at least as many neurons in the gut as the spinal cord.
2. 90% of the serotonin[6] and 50% of the dopamine[7] produced by the body, is produced in the gut.
3. The neurons that innervate the gut are collectively called “the enteric nervous system” and is just a huge mass of nerve cells that control the muscle contractions that allow your intestinal system to digest and abosrb food.
4. There is some evidence of cross-talk between enteric neurons, gut microflora, gut motility and emotions/mood. Relevant to treating disease, some researchers have postulated that disorders like irritable bowel syndrome (IBS) may affect the gut-brain interaction, and lead to problems with motility, mood and anxiety.[8]
   1. These findings are perhaps the newest and most controversial and are still being parsed by basic science researchers. Even more interestingly, the cross-talk might actually be two-way[9] [10] , there’s evidence that mood disorders affect motility in the gut as well.

This question was also answered by Ben Callif, M.S. Neuroscience & CRISPR, Marquette University (2017)

Ah yes, the gut-brain. Definitely a very interesting topic.

What I find particularly fascinating about the population of neurons in the gut is that it isn’t the second brain at all… In fact, stomach-associated brains were very likely the first kinds of brains that existed in evolutionary history. What we think of as “the brain” is really more of an offshoot of the gut-brain. So in a way, our “head-brain” is the second brain! We can see this in much simpler animals (well, simpler from a human perspective) that don’t have a distinct head (like starfish and jellyfish). Instead, they have a diffuse network of neurons that surrounds their mouths and stomachs. In the end, a brain is really a fancy tool that lets us know what, when, and where we should eat and reproduce.

This is somewhat off-topic, but that line of thought explains the unique and ancient role of serotonin as a modulator of 1) salience (what’s important), 2) circadian rhythms (timing for metabolism), and 3) social communication (how we can effectively make babies). Granted, that’s all a massive simplification of an extremely complex and amazing system of neural organization… but it’ll have to do for the brevity of this answer

Anyways, to answer your question more directly—nobody talks about it because it’s a relatively new area of research. More scientists and laypeople are gaining interest, but the translation from experts to the general population takes a long time, as with all things in science.

Personally, I think the biggest hurdle in making the topic interesting is that the whole idea becomes very complicated and scary when you consider the role of the microbiome in gut-brain function. Nobody wants to think that their behaviors, thoughts, and feelings are dictated by bacteria.

Footnotes

[1] Fundamentals of Neurogastroenterology: Basic Science

[2] Neurogastroenterologists Combine Old And New Research Approaches

[3] American Neurogastroenterology and Motility Society

[4] Journal of Neurogastroenterology and Motility

[5] Food, Body, Mind - Johns Hopkins Center for Innovative Medicine

[6] A Dialogue between the Immune System and Brain, Spoken in the Language of Serotonin

[7] Substantial Production of Dopamine in the Human Gastrointestinal Tract

[8] Irritable bowel syndrome: A microbiome-gut-brain axis disorder?

[9] Modulatory Effects of Gut Microbiota on the Central Nervous System: How Gut Could Play a Role in Neuropsychiatric Health and Diseases

[10] 1094 - Chronic Administration of Rifaximin Attenuates Pain as Well as Anxiety-Like Behaviors in a Mouse Model of Irritable Bowel Syndrome (IBS)

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