Findings support idea that gut micro biome has a role
Doses of a human gut microbe helped to reverse behavioral problems in mice with autism-like symptoms, researchers report today in Cell. The treatment also reduced gastrointestinal problems in the animals that were similar to those that often accompany autism in humans.
The work builds on previous research by Paul Patterson, a neurobiologist
at the California Institute of Technology (Caltech) in Pasadena. In
2012, he and his team created mice with autism-like symptoms by
injecting a chemical that mimics viral infection into pregnant mice;
those animals then bore offspring that were less sociable and more anxious than wild-type animals.
The autistic mice also had 'leaky guts', in which the walls of the
intestine break down and allow substances to leak through. Several
studies have found that humans with autism are also more likely to have
gastrointestinal disorders, suggesting that the two problems may be linked.
To investigate what role the gut might play in the animals’ symptoms,
Patterson and his colleagues at Caltech took a census of the bacteria
living in the guts of the mice. They found that mice with symptoms of
autism had lower levels of a bacterium called Bacteroides fragilis that is normally present in the mouse gut. When the researchers fed B. fragilis to these mice, the animals began behaving more normally and their gastrointestinal symptoms improved.
Chemical imbalance
Next, the researchers tried to determine how the bacteria 'talk' to the
brain by examining the blood of autistic and wild-type mice for
chemicals that indicate how cells are working in the body. They found
that the blood of mice with autism symptoms had levels of a chemical
called 4-ethylphenylsulphate (4EPS) that were 46 times higher than that
of the control group. This substance is structurally similar to a
chemical called para-cresol that is elevated in people with autism.
When the researchers injected 4EPS into wild-type mice, they started
behaving like the untreated autistic mice — obsessively repeating some
behaviors and squeaking differently when greeting other mice. Study
co-author Elaine Hsiao, a neuroscientist at Caltech, says that although
it is still unclear whether 4EPS is made by B. fragilis, it does seem to be made by gut bacteria.
“It’s incredible that putting this one bacteria back can reverse all
these widespread changes,” says John Cryan, a pharmacologist at
University College Cork in Ireland. Although many anecdotal reports and
small studies have suggested that ‘probiotic’ bacteria, such as those
found in yoghurt, and antibiotics can help with the symptoms of autism,
Cryan says more research needs to be done. Because there are a number of
types of autism in humans, it will be important to look at how
different symptoms might be affected by different microbes. Another
question is whether the microbiomes of the mice — whose symptoms result
from maternal infection — differ from those of mice that are genetically
predisposed to autism-like symptoms, Cryan adds.
“I think there is now sufficient proof of concept where people can start
to look at probiotic bacteria to improve brain function in humans,”
says gastroenterologist Stephen Collins of McMaster University in
Ontario, Canada. The next step, he says, will be to determine more
precisely how different bacteria use the immune, metabolic and nervous
systems to influence the brain.
Source
via http://www.scientificamerican.com
This article is reproduced with permission from the magazine Nature. The article was first published on December 5, 2013.
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