Psychobiotics are Revolutionizing Psychiatry
Psychobiotics are microbes that lift your mood. Psychiatry needs them now.
What are psychobiotics? Despite their somewhat sinister-sounding name, psychobiotics are microbes that can lift your mood and decrease anxiety. The word was coined by psychiatrist and researcher Dr. Ted Dinan and colleague John Cryan, Chair of Anatomy and Neuroscience at University College Cork, in Ireland. These prolific investigators have pioneered research into the gut-brain axis, along with other scientists from fields as disparate as microbiology, immunology, psychiatry, endocrinology, gastroenterology, and neurology. Researching the gut-brain axis requires a surprising diversity of disciplines.
What is depression?
There are many reasons for people to feel depressed or anxious. Bereavement, for one, often leads people into depression. That is normal and expected, as long as it doesn’t linger too long.
There are many treatments for people with depression, including psychoactive drugs that attempt to rebalance the neurotransmitters used by brain cells to communicate with each other. These drugs tend to target dopamine and serotonin centers of the brain, because these areas of the brain seem to be involved in happiness and motivation. There is also cognitive behavioral therapy, which has had a great track record for many people.
But there is a growing appreciation for the damage that can result from a “leaky gut”, a phenomenon that allows toxins and bacteria to enter the bloodstream. Once that happens, the heart diligently pumps these pathogens to every organ in the body, including the brain.
There is a barricade, called the blood-brain barrier, that keeps pathogens out of the brain, but we now have evidence that this barrier can be breached, creating a “leaky brain” analogous to the leaky gut. In extreme cases, this leads to brain inflammation that can deeply disturb the affected person, causing anxiety, confusion, hallucinations, and sharp personality changes.
But inflammation can also lead to garden-variety depression and anxiety. It is not a small problem. The comorbidity of depression and gut disease can be as high as 75%. It looks similar to “ordinary” depression, but the cause lies in the gut, not the brain. This is the gut-brain axis, which initially popped out of the first germ-free mouse experiments by Nobuyuki Sudo in 2004.
Germ-free mice changed everything
Sudo found that mice born and raised with no bacteria behaved differently than normally germy mice. It was a stunningly simple, but powerful, observation.
At that time, we were just beginning to realize that gut bacteria were, for the most part, beneficial to us. That was a huge break from the "kill all germs" philosophy. But just what those microbes were doing in our gut was a big mystery. Germ-free mice presented a golden opportunity to investigate.
When Sudo realized that germ-free mice had a different reaction to stress, it was confounding. How in the world could bacteria affect behavior? Sudo then introduced normal gut bacteria to the mice and discovered something else: he could fix their stress response, but only if he inoculated them before they were three weeks old – the equivalent of a human teenager. After that, the window of opportunity slammed shut.
Since then, researchers have shown that this is not just happenstance or a mere association. The relationship is causal. An astounding series of experiments have shown that you can transmit depression by transferring microbes. Most of these studies use fecal transfers, and some have gone from humans to mice, thus demonstrating cross-species causality. In general, feces from depressed animals will make the recipient depressed as well. From a psychiatric point of view, that is truly revolutionary.
The idea that our exalted human brains are affected by tiny gut microbes is humbling and sobering. But it also means that we can improve our brains by addressing our gut, which represents a marvelous opportunity. Stay tuned for next week when I’ll discuss some of the mechanics of the gut-brain axis and how you can leverage it for better cognition, memory, and mood.