What you think is going on in your head may be caused in part by what’s happening in your gut.
A growing body of research shows the gut affects bodily functions far beyond digestion. Studies have shown intriguing links from the gut’s health to bone formation, learning and memory and even conditions including Parkinson’s disease. Recent research found disruptions to the stomach or intestinal bacteria can prompt depression and anxiety—at least in lab rats.
Better understanding the communication between the gut and the brain could help reveal the causes of and treatments for a range of ailments, and provide diagnostic clues for doctors.
The gut—considered as a single digestive organ that includes the esophagus, stomach and intestines—has its own nervous system that allows it to operate independently from the brain.
This enteric nervous system is known among researchers as the “gut brain.” It controls organs including the pancreas and gall bladder via nerve connections. Hormones and neurotransmitters generated in the gut interact with organs such as the lungs and heart.
Like the brain and spinal cord, the gut is filled with nerve cells. The small intestine alone has 100 million neurons, roughly equal to the amount found in the spinal cord, says Michael Gershon, a professor at Columbia University.
The vagus nerve, which stretches down from the brainstem, is the main conduit between the brain and gut. But the gut doesn’t just take orders from the brain.
“The brain is a CEO that doesn’t like to micromanage,” says Dr. Gershon. The brain receives much more information from the gut than it sends down, he adds.
Many people with psychiatric and brain conditions also report gastrointestinal issues. New research indicates problems in the gut may cause problems in the brain, just as a mental ailment, such as anxiety, can upset the stomach.
Stanford’s Dr. Pasricha and colleagues examined this question in the lab by irritating the stomachs of newborn rats. By the time the animals were eight to 10 weeks old, the physical disturbance had healed, but these animals displayed more depressed and anxious behaviors, such as giving up more quickly in a swimming task, than rats whose stomachs weren’t irritated.
Compared to controls, the rats also showed increased sensitivity to stress and produced more of a stress hormone, in a study published in May in a Public Library of Science journal, PLoS One.
Other work, such as that of researchers from McMaster University in Hamilton, Ontario, demonstrated that bacteria in the gut—known as gut flora—play a role in how the body responds to stress. The exact mechanism is unknown, but certain bacteria are thought to facilitate important interactions between the gut and the brain.
Electrically stimulating the vagus nerve has been shown to reduce the symptoms of epilepsy and depression. (One treatment approved by the Food and Drug Administration, made by Cyberonics Inc., is already on the market.)
Exactly why such stimulation works isn’t known, experts say, but a similar procedure has been shown in animal studies to help improve learning and memory.
Earlier this month, researchers made a small step toward understanding a gastrointestinal ailment that typically affects children with autism.
In a study of 23 autistic children and nine typically developing kids, a bacterium unique to the intestines of those with autism called Sutterella was discovered.
The results, published online in the journal mBio by researchers at Columbia’s school of public health, need to be studied further, but suggest Sutterella may be important in understanding the link between autism and digestive ailments, the authors wrote.
Dr. Gershon, professor of pathology and cell biology at Columbia, has been studying how the gut controls its behavior and that of other organs by investigating the neurotransmitter serotonin.
Low serotonin levels in the brain are known to affect mood and sleep. Several common antidepressants work by raising levels of serotonin in the brain.
Yet about 95% of the serotonin in the body is made in the gut, not in the brain, says Dr. Gershon. Serotonin and other neurotransmitters produced by gut neurons help the digestive track push food through the gut.
Work by Dr. Gershon and others has shown that serotonin is necessary for the repair of cells in the liver and lungs, and plays a role in normal heart development and bone-mass accumulation.
Studying the neurons in the gut also may also help shed light on Parkinson’s disease. Some of the damage the disease causes to brain neurons that make the neurotransmitter dopamine also occur in the gut neurons, researchers say.
Researchers are now studying whether gut neurons, which can be sampled through a routine colonoscopy, may help clinicians diagnose and track the disease without invasive brain biopsies, says Pascal Derkinderen, a professor of neurology at Inserm, France’s national institute of health.
It is well known that there are relationships between gastrointestinal (GI) disorders such as irritable bowel syndrome anddisorders including anxiety disorders. Another aspect of these relationships was highlighted recently in an article in the Proceedings of the National Academy of Sciences (PNAS) that demonstrated that bacteria in the gut are likely to affect the and may influence psychiatric symptoms including anxiety and .
This study investigated the effects of a strain of Lactobacillus on mouse models of behaviors that correlate with human conditions such as anxiety and depression. Lactobacillus is a “good” type of bacteria that lives normally in our GI system. These bacteria, or similar bacteria, are found in certain foods, including yogurt. Mice who received chronic feedings of these good bacteria exhibited behaviors in various testing procedures that correlate with fewer symptoms of anxiety and depression in humans.
The GI system interacts with the brain via several mechanisms. One mechanism involves the vagus nerve. The vagus nerve plays a number of critical roles including conveying information from various body regions to the brain and vice versa. This nerve and its brain connections have become increasingly important in psychiatry and are targets for a novel form of treatment called “vagus nerve stimulation” (VNS), which may be helpful for patients with depression who have not responded to other treatment approaches. In VNS, a form of electrical pacemaker is used to activate the nerve. VNS is also used to treat patients with treatment-resistant epilepsy.
GABA (gamma amino butyric acid) is the major fast inhibitory neurotransmitter in the brain and is involved in many aspects of brain function. The GABA system in specific brain regions can be involved in the regulation of anxiety andand is the primary target for benzodiazepine-type anti-anxiety medications such as Valium (diazepam), Xanax (alprazolam), and Ativan (lorazepam).
The PNAS study found changes in the GABA system of several brain regions in the mice fed the good bacteria. In addition, when the vagus nerve was cut in these animals, the anti-anxiety andeffects of the GI bacteria were eliminated. The influence of the gut bacteria on the brain’s GABA system was also eliminated. These results indicate that something related to good bacteria in the GI system influences the vagus nerve and that the vagus nerve then interacts with the GABA system and changes behavior.
In our opinion, it is likely that other neurotransmitter systems, possibly including the serotonin system, are influenced by various GI bacteria.
The take home message from this study is that our GI system can influence our brain and our behaviors. In turn, our brain influences our gut. The strong possibility that the foods we eat influence how we feel and how we act via effects on the GI system opens up new avenues of research that may lead to creative ways to treat people who suffer from various psychiatric disorders.
This type of research gives new meaning to the phrase “gut feeling.”
June 9, 2011
You may be surprised to hear that you have a second brain. It is your enteric nervous system, which is found in the attractive environs of your gut.
It’s totally understandable if this doesn’t sound particularly brain-like to you. But that’s because you haven’t yet heard that within your alimentary canal (beginning at the esophagus, and ending at, well, at the end) reside the same types of neurotransmitters and neurons that dwell in the brain and spinal cord of your central nervous system.
So said the health.harvard.edu website, which also assured us that the enteric nervous system uses its neurotransmitters and neurons to communicate with the central nervous system on a regular basis.
In fact, according to scientificamerican.com, the enteric nervous system is the proud owner of more neurons than you’ll find in the spinal cord or in the peripheral nervous system. And something like 90 percent of fibers in the vagus nerve are busy carrying messages from the GI tract to the brain.
This information was most unexpected. But perhaps it should not be that surprising when you consider the fact that 95 percent of your serotonin is “down there”.
This serotonin that is milling about in the neighborhood of the enteric nervous system appears to contribute to some types of diseases.
The February 7, 2010 Nature Medicine study indicated that the gut is involved with bone mass and the risk of osteoporosis. Autism may be partly explained by action of serotonin in the gut. Irritable bowel syndrome (IBS) brings suffering to over two million Americans and uses an excess of serotonin to do it.
Sciencedaily.com reported in an August 6, 2009 article that a quarter of adults in the U.S. are challenged by an assortment of GI disorders, from mild unpleasant symptoms to crippling pain and gastric distress that necessitates time off from work, and bowing out of family and social life.
Irritable bowel syndrome may hamper 10 percent of the nation, as estimated in a Eurekalert! public release from August 19, 2010.
As odd as it may sound, this very physical malady has often been considered to be psychosomatic. Apparently that is about to change.
The IBS segment of the population will feel vindicated to learn that research from the Technische Universitaet Muenchen seems to have found a cause for all the agony.
Tiny inflammations in the gut’s mucosa set the enteric nervous system on its ear. Mediators from mast cells and enterochromaffin cells have a direct and profound effect on the bowel’s nerve cells.
Consequently the gut’s mucosa releases too much histamine, protease and serotonin for comfort. The mucosa’s conversation with the enteric nervous system takes a turn for the worst.
Hopefully future research will uncover more about the enteric nervous system and lead to treatments to relieve the pain that is hatched by our second brain.
Adult Gut Can Generate New Neurons
Fix My Gut
Think Twice: How the Gut’s “Second Brain” Influences Mood and Well-Being
Proof that a gut-wrenching complaint — irritable bowel syndrome — is not in your head
Stress and the sensitive gut