A team of researchers from the California Institute of Technology (Caltech) has recently discovered a connection between levels of gut microbes and levels of serotonin in mice. In addition to providing a means of communication between neurons in the brain, serotonin has other roles in the human body, especially in the gastrointestinal tract (GIT) (1).
This is the gastrointestinal tract, a prominent site for serotonin production in the human body.
Source: Wikimedia Commons
It is not surprising, then, that the GIT produces approximately 90 percent of all serotonin (2). Enterochromaffin (EC) cells of the GIT are directly involved in making this serotonin, deemed peripheral serotonin. According to the team of Caltech scientists, however, the EC cells are not acting alone but are aided immensely by gut microbes (2). Jessica Yano – one of the researchers on the team – summarizes their discovery by saying, “our work demonstrates that microbes normally present in the gut stimulate host intestinal cells to produce serotonin” (2).
The microbes here are not indicative of abnormality: they are naturally occurring bacteria in the gut. The research team found that EC cells exposed to standard levels of these bacteria generated roughly 60 percent more serotonin than “germ-free” cells (2). Furthermore, when bacteria were reintroduced to the germ-free cells, they quickly began to produce more serotonin, thus suggesting the bacteria play an integral role.
Upon establishing this new correlation, the Caltech scientists sought to determine if certain types of microbes were particularly influential. They were able to narrow the field to 20 specific species that produced significantly higher amounts of serotonin when coexisting in EC cells of previously germ-free mice. These species contained particular metabolites – substances produced by metabolism– that caused this extra potency. The bacteria also influenced activities such as clotting, which occurs in the presence of serotonin (2).
This research is significant on many levels. First, it examines the sparsely researched area of microbe-host interactions (2). Second, as Sarkis K. Mazmanian (another researcher on the study) states, it explores the “role gut microbes play in shaping the nervous system…an exciting frontier in the biological sciences” (2).
Hopefully, this newfound information will be used to prevent diseases like those mentioned previously and to understand the developing brain. However, the scientists believe that additional research is necessary. They also acknowledge that exceedingly high quantities of serotonin in the body may be harmful (2). It is clear, however, that the information gathered from this study is the first step towards a deeper understanding of microbes, serotonin, and the complex interactions that govern certain biological functions.
Sources:
1. McIntosh, J. (2015, February 12). “What is serotonin? What does serotonin do?” Medical News Today. Retrieved from
http://www.medicalnewstoday.com/articles/232248.php.
2. California Institute of Technology. (2015, April 9). Microbes help produce serotonin in gut. ScienceDaily. Retrieved April 11, 2015 from www.sciencedaily.com/releases/2015/04/150409143045.htm