How Stress Changes How a Body Functions

Psychological stress can produce many changes in the functioning of organs. Such stress-related changes in the intestines were examined in this study performed on laboratory mice. It is known that intestines of all animals, including humans, contain a large number of microorganisms living in a symbiotic relationship. The types and number of microbes in intestines are normally relatively stable. This study found that a few species of microbes are suppressed more than others after stress exposure. It also showed that microbial suppression is related to production of chemicals that cause inflammation like IL-6. The study throws light on a complex relationship between microbes, host physiology and stress-related changes.

The human body consists of its own cells as well as millions of microbes living inside the body. These microbes have a symbiotic relationship with the body. For example, synthesis of vitamins K and B complex is aided by intestinal microbes. Microbes residing in the gut are also important for the immune system. Gut microbes have a relatively stable population but diet and antibiotics can alter the composition of microbial colonies. Psychological stress also induces migration of bacteria and production of cytokines, the chemicals related to inflammation and immune response. This study tested the reaction between stress, intestinal microbial population and immune activity.

* Laboratory mice were divided into an experimental and a control group.
* Experimental mice were exposed to an aggressive mouse kept in the same cage for two hours each day. This mouse often attacked the experimental mice and induced social disruption stress in them.
* Mice from both groups were sacrificed after six experiments. The contents of the part of the intestine called the cecum were collected and immediately frozen. Later, these contents were subjected to DNA sequencing to identify the type of microbes and their percentage in the population.
* The effects of antibiotics were studied by feeding a few of the mice an antibiotic cocktail containing four drugs.

* Compared to the control group, there was a significant reduction in microbial diversity and richness in the intestines of mice exposed to stress.
* This difference was more evident in mice sacrificed immediately after their last exposure to stress. The difference between the two groups vanished when experimental mice, sacrificed 15 hours after the last exposure to stress, were compared with control mice sacrificed at the same time.
* Compared to the control group, exposure to stress resulted in a significant increase in IL-6, a body chemical that causes inflamation.
* This increase in cytokines was evident for mice sacrificed immediately after the last exposure to stress as well as mice sacrificed 15 hours after the last exposure to stress.

Next steps/Shortcomings
The study showed that stress affects the microbial population in the gut and this in turn produces immune response. Elevated levels of antibodies against gut microbes have been found in certain psychological diseases like mood disorder and irritable bowel syndrome. Further research might explain the possible link between microbes and certain psychiatric conditions.

This study demonstrated that exposure to stress leads to a rise in markers of inflammation like cytokine IL-6 in the blood of mice. The reduction of the normal microbial population of the gut of these mice by use of antibiotics reduced the level of cytokines. The study also found a reduction in the percentage of Lactobacilli, a type of microbe which suppresses inflammation, and an increase in the percentage of clostridia, another microbe which increases inflammatory response, after exposure to stress. The inflammatory response and translocation of microbes like clostridia, from gut to other organs after stress, could be an important factor affecting human immunity in health and disease.

For More Information:
Exposure to a Social Stressor Alters the Structure of the Intestinal Microbiota: Implications for Stressor-Induced Immunomodulation
Publication Journal: Brain, Behavior, and Immunity, October 2010
Michael T Bailey; Scot E Dowd; Ohio State University, Columbus, Ohio and Research and Testing Laboratory and Medical Biofilm Research Institute, Lubbock, Texas

*FYI Living Lab Reports Are Summaries of the Original Research.

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