The connection between the brain and the gut goes both ways. Psychobiotics in the gut can soothe your brain, but the brain can also affect your microbes. In a new study from the University of Nottingham, rats raised in isolation showed differences in their gut bacteria as well as changes in anxiety and brain development. The study suggests that life in solitary is no picnic. Early stress can produce lasting changes in gut microbes, leading to abnormal brain and immune function. This in turn can produce abnormal behavior and may play a key role in the development of psychiatric illness.
We’ve known for a hundred years that the brain can control important aspects of the stomach. In 1822, a fellow named Alexis St. Martin was shot in the stomach and was treated by Dr. William Beaumont, who didn’t expect his patient to live. Against the odds, St. Martin survived, but his body formed a fistula, or a hole, from his stomach to his side. It was pretty much gross and had to be bandaged up to keep stomach acids from squirting out, but Dr. Beaumont was delighted. It gave him an unprecedented living laboratory for studying human digestion.
Seizing the opportunity, Dr. Beaumont took St. Martin on as a servant and semi-willing guinea pig. The doctor extracted stomach juices through the fistula and had them analyzed. He tied string around different foods, dipping them into the stomach of the amazingly tolerant St. Martin and then retracting them over time to monitor the digestion process. This catch-and-release strategy illuminated many new details of digestion.
St. Martin, on the other hand, was not always thrilled with these fishing expeditions and sometimes complained. During a particularly acrimonious examination, Dr. Beaumont found significant changes in the acidity of St. Martin’s stomach juices. Beaumont had discovered something completely unexpected: emotions could directly affect the chemistry of the stomach.
This is not an atypical science story. Science advances when we get new tools, like microscopes and telescopes, that allow us to see things that are normally hidden. Alexis St. Martin’s fistula was just such a scope, providing one of the first windows into a living stomach, and making Alexis the true hero of this story.
Schizophrenia, like many mental problems, is poorly understood. We know that nerves in the brain use chemicals called neurotransmitters to talk to each other, and psychiatrists have made a great deal of progress by tweaking these neurotransmitters. Selective serotonin-reuptake inhibitors (SSRIs) have vastly improved the lives of many people suffering from depression by increasing brain levels of the neurotransmitter serotonin. Nevertheless, everyone understands that the brain is complex, with many different neurotransmitters involved in many different parts of the brain. Just “topping off” some of these chemicals may be too simplistic. Schizophrenia, in particular, doesn’t always respond to such straightforward treatments.
A recent case study has shown that, remarkably, a bone-marrow transplant can throw schizophrenia into remission. How in the world is your bone marrow involved with your brain? The answer leads to a new understanding of mental health that is just starting to gain traction: inflammation seems to be behind many cases of mental illness. Inflammation is dealt with by the immune system, and much of that system starts in the bone marrow. How your particular immune system reacts to inflammation was determined when you were just a toddler. Disease, breast feeding and antibiotic treatments all affect how your immune system works. If you were lucky, you got a hardy immune system. If not, you may be stuck with a hinky immune system for the rest of your life — unless you get a bone-marrow transplant.
Inflammation research is leading to a new treatments for everything from depression and anxiety to many kinds of psychosis. The treatments of the future will likely be addressing inflammation — from the gut microbiota to the body’s defense system — rather than merely topping off your neurotransmitters. With depression now being labeled the number one cause of disability in the world, that future can’t come too soon.
Multiple sclerosis (MS) is an autoimmune disease with an uncertain cause. However, recent research has linked it to gut microbes. We know that the Western diet, full of processed “foods” and remarkably high in sugar, is associated with many diseases, and we may soon be able to add MS to that list.
What is it about the Western diet that is so unhealthy? It appears to be the impact of those manufactured foods on the microbes that live in the gut, the microbiota. In particular, it seems that a species of helpful bacteria, Prevotella histicola, is being steadily exterminated by the Western diet. That is largely due to the diet’s lack of prebiotics, the fiber that feeds microbes in the colon.
Using a mouse model of MS, researchers found that by feeding the mice P. histicola, they could reduce the symptoms. Apparently P. histicola is able to chill out the immune system and prevent it from attacking the mouse’s own cells. If this work translates into humans, it will be a welcome development, as current treatments can have unpleasant side effects.
Because it affects the brain and because depression is common among MS sufferers, P. histicola acts here as a psychobiotic.