Bacteria in mouse gut affect development and behaviour

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1 February 2011

Bacteria in mouse gut affect development and behaviour

The teeming trillions of bacteria in the digestive tracts of mice have been

shown to affect the animals' brain development and behaviour.

Mice bred in sterile environments without these " gut flora " were seen to be more

adventurous and less anxious than mice with normal gut flora.

The research adds weight to the idea that gut bacteria are a critical part of

the overall development of mammals.

The study is published in Proceedings of the National Academy of Sciences.

Gut flora were once thought to be harmless residents of the guts of mammals, and

in time it became clear that they not only aid in digestion but also protect

against the arrival of more harmful invaders.

But research in recent years has shown an increasingly complex picture in which

the bugs play significant roles in several critical bodily systems, having

already been implicated in obesity, asthma, and liver function.

" Germ-free " mice, born without the bugs and protected from their arrival, have

shown a number of effects distinct from mice born in the normal way.

" We know that animals in 'germ-free' conditions can reproduce, they have a

longer lifespan, and they seem to live perfectly OK, provided you don't expose

them to stress or damage, " said Sven Pettersson, the Karolinska Institute

microbiologist who, along with neuroscientist Rochellys Heijtz, led the

research.

" The moment you do that they're much more fragile - that means there are certain

aspects of life which seem to be taking place in the absence of microorganisms,

but there are clearly aspects connected to the presence of them, " he told BBC

News.

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“Start Quote

The microorganisms were there long before us - so all aspects of life would

have to involve an adaptation to them”

End Quote Professor Sven Pettersson Karolinska Institute

Professor Petterson and his colleagues bred a number of mice under normal and

germ-free conditions. In stantardised tests of activity, the germ-free mice

explored more of an " open-field activity box " , rearing up on their hind legs

more often, and showed less of the signs associated with anxiety.

In studies of the animals' brains, they showed higher levels of a number of

hormones, and even differences in the expression of over 170 genes.

The result does not paint a clear picture of whether the development of the

germ-free mice is specifically " better " or " worse " for the animals, Professor

Pettersson explained, but is a " very, very interesting " first demonstration that

the bugs can have such profound effects even within the brain.

It follows a long line of studies that suggest the bugs are far more involved in

mammalian function than just in their digestion.

" Twenty years ago you wouldn't have expected this, but there's been a dramatic

change in the view of what microorganisms like bacteria can do to host

physiology, " he said.

" If you look at it from the perspective that life has existed for hundreds of

millions of years, and man has been around for maybe just a fraction of this,

that means the microorganisms were there long before us - so all aspects of life

would have to involve an adaptation to them. "

How the bacteria effect these long-range changes in development and behaviour

remains a mystery, so the group is aiming to first identify which bacterial

species are implicated.