Scientists have known for years that there’s a “second brain” of autonomous neurons in your long, winding human digestive tract—but that’s about where their knowledge of the so-called abdominal brain ends.
Now, research published in 2020 shows that scientists have catalogued 12 different kinds of neurons in the enteric nervous system (ENS) of mice. This “fundamental knowledge” unlocks a huge number of paths to new experiments and findings.
The gut brain greatly affects on how you body works. Your digestive system has a daily job to do as part of your metabolism, but it’s also subject to fluctuations in functionality, and otherwise related to your emotions.
More: Getting the Inside Dope on Ketamine’s Mysterious Ability to Rapidly Relieve Depression
Digestive symptoms and anxiety can be comorbid, and your gut is heavily affected by stress. So scientists believe having a better understanding of what happens in your ENS could lead to better medicines and treatments for a variety of conditions, as well as improved knowledge of the connection between the ENS and central nervous system.
The research appears in Nature Neuroscience. In a related commentary, scientist Julia Ganz explains what the researchers found and why it’s so important:
“Using single-cell RNA-sequencing to profile the developing and juvenile ENS, the authors discovered a conceptually new model of neuronal diversification in the ENS and establish a new molecular taxonomy of enteric neurons based on a plethora of molecular markers.”
Neuronal diversification happens in, well, all the organisms that have neurons. Similar to stem cells, neurons develop first as more generic “blanks” and then into functional specialties. The human brain has types like sensory and motor neurons, each of which has subtypes. There are so many subtypes, in fact, that scientists aren’t sure how to even fully catalog them yet.
More: Here’s How Long Alcohol-Induced Brain Damage Persists After Drinking
Neurons of the same superficial type are different in the brain versus the brain stem—let alone in the digestive tract. So researchers had to start at the very beginning and trace how these neurons develop. They tracked RNA, which determines how DNA is expressed in the cells made by your body, to follow how neurons formed both before and after birth. Some specialties emerge in utero, and some split and form afterward.
To find this new information, the scientists developed a finer way to separate and identify cells. Ganz explains:
“Using extensive co-staining with established markers, they were able to relate the twelve neuron classes to previously discovered molecular characteristics of functional enteric neuron types, thus classifying the ENCs into excitatory and inhibitory motor neurons, interneurons, and intrinsic primary afferent neurons.”
With a sharper protocol and new information, the researchers were able to confirm and expand on the existing body of ENS neuron knowledge. And now they can work on finding out what each of the 12 ENS neuron types is responsible for, they say.
By isolating different kinds and “switching” them on or off using genetic information, scientists can try to identify what’s missing from the function of the mouse ENS. And studying these genes could lead to new treatments that use stem cells or RNA to control the expression of harmful genes.
The Mind-Gut Connection is something that people have intuitively known for a long time but science has only I would say in the last few years gotten a grasp and acceptance of this concept. It essentially means that your brain has intimate connections with the gut and another entity in our gut, the second brain, which is about 100 million nerve cells that are sandwiched in between the layers of the gut.
And they can do a lot of things on their own in terms of regulating our digestive processes. But there’s a very intimate conversation between that little brain, the second brain in the gut and our main brain. They use the same neurotransmitters. They’re connected by nerve pathways. And so we have really an integrated system from our brain to the little brain in the gut and it goes in both directions.
The little brain, or the second brain, in the gut you’re not able to see it because as I said it’s spread out through the entire length of the gut from your esophagus to the end of your large intestine, several layers of nerve cells interconnected. And what they do is even if you – and you can do this in animal experiments if you completely disconnect this little brain in the gut from your main brain this little brain can completely take care of all the digestive processes, the contractions, peristaltic reflex, regulation of blood flow in the intestine.
And it has many sensors so it knows exactly what’s going on inside the gut, what goes on in the wall of the gut, any distention, any chemicals. All of this is being picked up by these sensory nerves, fed into the interior nervous system, the second brain. And then the second brain generates these stereotypic responses. So when you vomit, when you have diarrhea, when you have normal digestion, all of this is encoded in programs in your second brain.
What the second brain can’t do it cannot generate any conscious perceptions or gut feelings. That really is the only ability that allows us to do this and perceive all the stuff that goes on inside of us is really the big brain and the specific areas and circuits within the brain that process information that comes up from the gut. Still most of that information is not really consciously perceived. So 95 percent of all this massive amount of information coming from the gut is processed, integrated with other inputs that the brain gets from the outside, from smell, visual stimuli.
And only a very small portion is then actually made conscious. So when you feel good after a meal or when you ate the wrong thing and you’re nauseated those are the few occasions where actually we realize and become aware of our gut feelings. Even though a lot of other stuff is going on in this brain-gut access all the time.
When we talk about the connection between depression and the gut there’s some very intriguing observations both clinically but also now more recently scientifically that make it highly plausible that there is an integrate connection between serotonin in the gut, serotonin in our food, depression and gut function.
By: Caroline Delbert
Caroline Delbert is a writer, book editor, researcher, and avid reader. She’s also an enthusiast of just about everything.
The enteric nervous system (ENS) or intrinsic nervous system is one of the main divisions of the autonomic nervous system (ANS) and consists of a mesh-like system of neurons that governs the function of the gastrointestinal tract. It is capable of acting independently of the sympathetic and parasympathetic nervous systems, although it may be influenced by them. The ENS is also called the second brain. It is derived from neural crest cells.
The enteric nervous system is capable of operating independently of the brain and spinal cord,but does rely on innervation from the autonomic nervous system via the vagus nerve and prevertebral ganglia in healthy subjects. However, studies have shown that the system is operable with a severed vagus nerve.
The neurons of the enteric nervous system control the motor functions of the system, in addition to the secretion of gastrointestinal enzymes. These neurons communicate through many neurotransmitters similar to the CNS, including acetylcholine, dopamine, and serotonin. The large presence of serotonin and dopamine in the gut are key areas of research for neurogastroenterologists.