A Synergistic Relationship in the Gut

How Serotonin and Fluoxetine Affect Microbiota Residing in the Gut

A study led by UCLA biologists hints that serotonin and drugs that target serotonin, such as antidepressants, can have a major effect on the gut's microbiota—the 100 trillion or so bacteria and other microbes that live in the human body's intestines. It is, though, a finding from an animal study and so a long way from the last word on the subject.

An estimated 90% of the body's serotonin is produced in the gut, where it influences gut immunity.

The researchers identified a specific gut bacterium that can detect and transport serotonin into bacterial cells. When mice were given fluoxetine, the activce ingredient in Prozac, the biologists found it reduced the transport of serotonin into their cells. This bacterium, about which little is known, is called Turicibacter sanguinis

In an earlier study, the researchers had found that in mice, a specific mixture of bacteria, consisting mainly of T sanguinis and Clostridia, produces molecules that signal to gut cells to increase production of serotonin. When researchers raised mice without the bacteria, more than 50% of their gut serotonin was missing. The researchers then added the bacteria mixture of mainly Turicibacter and Clostridia, and their serotonin increased to a normal level.

In this new study, published in Nature Microbiology, the researchers added serotonin to the drinking water of some mice and raised others with a mutation that increased the levels of serotonin in their guts. After studying the microbiota, the researchers discovered that Turicibacter and Clostridia increased significantly when there was more serotonin in the gut.

If these bacteria increase in the presence of serotonin, perhaps they have some cellular machinery to detect serotonin, the researchers speculated. And, indeed, they found a protein in multiple species of Turicibacter that has some structural similarity to a protein that transports serotonin in mammals.

The team found that exposing T sanguinis to serotonin or fluoxetine influenced how well the bacterium could thrive in the gastrointestinal tract. In the presence of serotonin, the bacterium grew to high levels in mice, but when exposed to fluoxetine, the bacterium grew to only low levels in mice.

The team's research on Turicibacter aligns with a growing number of studies reporting that anti-depressants can alter the gut microbiota. "For the future," says senior author Elaine Hsiao, "we want to learn whether microbial interactions with antidepressants have consequences for health and disease."

Source: ScienceDaily.com, Sept. 6