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now know that our brains and guts influence each other — although many of the
ways in which they are interlinked remain mysterious. A new study explores how
stress related to conflict impacts gut bacteria, asking: is there a difference
between how "winners" vs. "losers" are affected?
In a new study, scientists look at social competitiveness to understand how stress changes the gut microbiota.
Research
has shown that exposure to stress can affect our
bodies in myriad ways, and that this can impact everything from the health of
our hearts to that of our guts.
In
fact, studies have even discovered that mood disorders are often linked
with gastrointestinal discomfort, among other physical symptoms.
But
several aspects of the brain-gut relationship remain unclear. For instance, if
the stress we are exposed to comes from social conflict, does our final
position — as "winners" or "losers" — as we emerge from
that situation determine to what degree our microbiome is affected?
Scientists
from Georgia State University in Atlanta set out to investigate this problem by
looking at physiological changes occurring in Syrian hamsters when they had to
deal with stressful situations.
These
animals — apart from being a source of joy as adorable pets — lend themselves
very well to research about biological responses to social stress. This is
because, when placed together, they compete to establish hierarchies, splitting
into dominant ("winning") and subordinate ("losing")
animals.
Dr.
Kim Huhman and colleagues worked with adult male hamsters and looked at how
such stressful social situations would alter their gut microbiota. They
predicted that hamster "losers" might be the most affected by
conflict with the other animals — but their study revealed some surprises.
The results of this project were published in the
journal Behavioural Brain
Research.
The question of 'winners' vs. 'losers'
Dr.
Huhman and team analyzed the gut bacteria of the hamsters both at the beginning
of the study, before the animals had been allowed to meet, and at 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 that were already familiar with each other and so did not have to deal
with any social stress.
"We found that even a single exposure to social
stress causes a change in the gut microbiota, similar to what is seen following
other, much more severe physical stressors, and this change gets bigger
following repeated exposures," explains Dr. Huhman.
She
adds, "Because 'losers' show much more stress hormone release than do
'winners,' we initially hypothesized that the microbial changes would be more
pronounced in animals that lost than in animals that won."
However,
the researchers were in for a surprise; when comparing the samples of gut
bacteria taken from "winners" to those sourced from their subordinate
counterparts, the differences that they were looking for were not there.
Both
"winners" and "losers" had much less diverse gut
microbiota. In fact, the only notable variation was found in the kinds of
bacteria that the hamsters' guts now housed.
"Interestingly,"
says Dr. Huhman, "we found that social stress, regardless of who won, led
to similar overall changes in the microbiota, although the particular bacteria
that were impacted were somewhat different in winners and losers."
"It might be that the impact of social stress was
somewhat greater for the subordinate animals, but we can't say that
strongly."
Dr. Kim Huhman
Another
set of samples — those taken from the animals before they had been exposed to
social stress — brought a different kind of surprise to the researchers.
They
discovered that the original differences in the hamsters' individual
populations of gut bacteria could, in fact, predict which ones were likely to
succeed in their struggle for dominance and which were likely to lose the
"competition."
"It's an intriguing finding that there were
some bacteria that seemed to predict whether an animal would become a winner or
a loser," Dr. Huhman explains.
"These
findings," says co-author Dr. Benoit Chassaing, "suggest that
bi-directional communication is occurring, with stress impacting the
microbiota, and on the other hand, with some specific bacteria in turn impacting
the response to stress."
Future
studies, the researchers say, should aim to investigate the potential of a
mutual impact of gut bacteria and the response to stress caused by social
conflict.
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