Social stress: how does it affect microbiota and community hierarchies?

It is well known that our brain and our entrails influence each other – although many of the ways they are interconnected remain mysterious. A new study explores how conflict-related stress affects intestinal bacteria, asking: is there a difference between how “winners” and “losers” are affected? The main mechanism of competition between intestinal bacterial species is the subtraction of nutrient substrates and the production of “personalized” antibiotics (lantionine), which act as killer against the “next” species. Research has shown that stress exposure can affect heart health and intestinal health. In fact, studies have even found that mood disorders are often associated with gastrointestinal disorders, among other physical symptoms.

But different aspects of the brain-intestine relationship remain unclear. For example, if the stress we are exposed to comes from social conflicts, our final position as it emerges from that situation (“winners” or “losers”) to what extent does this influence our microbiota? Scientists at Georgia State University in Atlanta decided to investigate this problem by observing the physiological changes that occur in hamsters when they faced stressful situations. These animals lend themselves very well to researching biological responses to social stress. This is because, put together, they compete to establish hierarchies, dividing into dominant and subordinate animals. Dr. Kim Huhman and colleagues worked with adult male hamsters and observed how stressful social situations altered their intestinal microbiota. They predicted that the hamster “losers” could be the most affected by the conflict with other animals, but their study revealed some surprises.

The results of this project have been published in the journal Behavioral Brain Research. Dr. Huhman and the team analyzed the intestinal bacteria of hamsters at the beginning of the study, before the animals were allowed to meet, both in the end, after they had competed to establish a hierarchy in their newly assembled group. The researchers compared these samples with those taken from a group of control hamsters, who already knew each other and therefore did not have to deal with social stress. They found that even a single exposure to social stress causes a change in the intestinal microbiota, similar to what is observed following other, much more severe physical stressors, and this change increases after repeated exposures.

Because “subordinates” show much more stress hormone release than “dominant”, the team initially hypothesized that microbial changes would be more pronounced in the animals they lost compared to the animals they won. However, the researchers were surprised; comparing the samples of microbiota taken by the dominant with those coming from their subordinate counterparts, the differences they were looking for were not there. Both the “winners” and the “losers” had a much less diversified intestinal microbiota. In fact, the only noteworthy variation was found in the types of bacteria the hamsters’ gut now housed. Interestingly, social stress, regardless of who won, led to similar general changes in the microbiota, although the particular bacteria affected were somewhat different between dominant and subordinate.

Another series of samples, taken from animals before they were exposed to social stress, brought a different kind of surprise to the researchers. In fact, it emerged that the original differences in individual populations of intestinal bacteria of hamsters could, in fact, predict those that would be successful in their struggle for domination and that they would probably lose the “competition“. It is an intriguing discovery that there were some bacteria that seemed to predict if an animal would become a winner or a loser. These results suggest that two-way communication occurs, with stress having an impact on the microbiota and, on the other hand, with some specific bacteria that in turn influence the stress response.

So much for “intestine wars”…..

  • edited by Dr. Gianfrancesco Cormaci, PhD, specialist in Clinical Biochemistry.

Scientific references

Partrick KA et al. Huhman KL. Behav Brain Res. 2018; 345:39-48.

Tsilimigras MCB, et al. Psychosom Med. 2018 Mar. 

Kim N, Yun M et al. J Microbiol. 2018 Mar;56(3):172-182.

Zha Y, Eiler A et al. Microbiome. 2018 Feb 6;6(1):28. 

Informazioni su Dott. Gianfrancesco Cormaci 2484 Articoli
- Laurea in Medicina e Chirurgia nel 1998 (MD Degree in 1998) - Specialista in Biochimica Clinica nel 2002 (Clinical Biochemistry specialty in 2002) - Dottorato in Neurobiologia nel 2006 (Neurobiology PhD in 2006) - Ha soggiornato negli Stati Uniti, Baltimora (MD) come ricercatore alle dipendenze del National Institute on Drug Abuse (NIDA/NIH) e poi alla Johns Hopkins University, dal 2004 al 2008. - Dal 2009 si occupa di Medicina personalizzata. - Detentore di un brevetto sulla preparazione di prodotti gluten-free a partire da regolare farina di frumento immunologicamente neutralizzata (owner of a patent concerning the production of bakery gluten-free products, starting from regular wheat flour). - Responsabile del reparto Ricerca e Sviluppo per la società CoFood s.r.l. (leader of the R&D for the partnership CoFood s.r.l.) - Autore di un libro riguardante la salute e l'alimentazione, con approfondimenti su come questa condizioni tutti i sistemi corporei. - Autore di articoli su informazione medica, salute e benessere sui siti web salutesicilia.com e medicomunicare.it