Essay: Linking biocrobiomes to mental health,

As part of the human experience, we have natural reactions of anxiety, stress, and depression. Research towards these emotions should be centered around the brain, so it may be odd to focus on bacteria from the stomach, more specifically from the gut. But when we think about how we describe these emotions through language as “butterflies in your stomach” or getting a “gut feeling,” it’s no surprise that they are connected.

By now, gut bacteria affecting a person’s health isn’t something new. Humans have lived in a symbiotic relationship with these microbes as they influence digestion, metabolism, and allergies. But as of recent studies, these microbes my reach much further in our body: the human brain.

A group of researchers have been investigating how this microbiome can regulate how people feel and think. John Cryan, a researcher at the University College of Cork in Ireland, discovered this link through an experiment done on mice. By examining mice with and without gut bacteria, they discovered that mice without bacteria had a reduced fear response. Cryan also coined the term “psychobiotics” which refers to live organisms, that when ingested, produce benefits in patients with mental illnesses, such as PTSD or some types of anxiety disorders.

Fueled by the many rodent studies linking these biocrobiomes to mental health, UCLA biologist Emeran Mayer was the first to test this hypothesis in humans. They administered probiotic yogurt to a group of healthy women for four weeks. By using functional magnetic resonance imaging scans to assess the results, they found that the women had reduced brain responses to images with a negative connotation.

Though it is important to note that no firm conclusions can be drawn from these results as correlation does not necessarily mean causation, the results do still support the connection between gut bacteria and the brain leading to healthier humans. The question still remains: Does gut bacteria directly influence changes in the brain or do changes in the brain influence the type of bacteria that reside in the gut? Also, how do various lifestyle, dietary, and environmental factors influence brain-gut-microbiota interactions in humans?

Some interesting work on the topic has been done in the field of autism. It is known that three-quarters of people with autism also have some type of intestinal abnormalities, such as food allergies, digestive problems, or extra sensitivity to gluten. This understanding led researchers to examine the potential connections between gut microbes and autism. Sarkis Mazmanian, a microbiologist from CIT, inserted a species of gut bacteria Bacteroides fragilis into mice with symptoms that relate to that of autism. This treatment altered the makeup fo the animals microbiome and improved their behavior, showing less anxiousness, improved communication skills and less repetitive behavior. Researchers see this as a potential breakthrough in understanding how microbes from the gut contribute to autism and other neurological disorders. The results so far suggest that adjusting gut bacteria could be a viable treatment for the disease in some patients.

Not only this, but researchers have also found evidence that suggest gut bacteria can influence depression and anxiety. Stephen Collins, a gastroenterology researcher at McMaster University in Hamilton, Ontario, has found two strains of bacteria, lactobacillus and bifidobacterium, that reduce anxiety-like behavior in mice. Humans also carry these strains of bacteria in their guts. In a study, he collected gut bacteria from mice prone to anxious behavior, and then transplanted these microbes into another strain inclined to be calm. The results suggested that the calm mice gained tendencies of anxiety-like behavior.

Overall, these microbes seem to be major players in the gut-brain connection. It’s not yet clear how the microbiome alters the brain. Most researchers agree that microbes probably influence the brain via multiple mechanisms. Scientists have found that gut bacteria produce neurotransmitters such as serotonin, dopamine and GABA, all of which play a key role in mood. This relates to the many antidepressants that also increase levels of these hormones. Certain bacteria microbes also affect how people metabolize these compounds, effectively regulating the amount that circulates in the blood and brain. Gut bacteria may also generate other neuroactive chemicals, including one called butyrate, that have been linked to reduced anxiety and depression. Cryan and others have also shown that some microbes can activate the vagus nerve, the main line of communication between the gut and the brain. In addition, the microbiome is intertwined with the immune system, which itself influences mood and behavior.

As scientists learn more about how the gut-brain microbial network operates, Cryan thinks it could be hacked to treat psychiatric disorders. He states that the future of these bacteria types could be used a Prozac is used now.  And because these microbes have eons of experience modifying our brains, they are likely to be more precise and subtle than current pharmacological approaches, which could mean fewer side effects. These microbes will have a real effect on how we treat these disorders. This is a whole new way to modulate brain function.