New findings on the connections between gut microbiota and the brain

May 30, 2016

Intestinal bacteria that can boost bravery or trigger multiple sclerosis: An increasing body of research results confirms the importance of the "gut-brain axis" for neurology and indicates that the triggers for a number of neurological diseases may be located in the digestive tract.

"The gut microbiome can influence the central nervous system, the development of nerve cells and the immune system. A better understanding of its effect could revolutionize our therapy options," noted Dr Patricia Lepage from the Institut National de la Recherche Agronomique in Jouy-en-Josas, France, at the Second Congress of the European Academy of Neurology (EAN) in Copenhagen.

Gut microbiota influences behaviour

The gut microbiome is the aggregate of human gut microorganisms with all its bacteria, archaea, viruses and fungi. For a long time, it seemed far-fetched to think that the microbiome could also be responsible for processes outside the . Yet the scientific community keeps uncovering further amazing details. Recent studies on laboratory animals which grow up without any microorganisms (germ-free) show for example that microorganisms in the gut are even capable of influencing behaviour. Dr Lepage: "Intestinal microbes can verifiably produce neuromediators that have an effect on the brain. Germ free mice showed less anxiety than their conspecifics whose gut was populated with commensal microbiota. However, there is only scant evidence thus far on how this process works in the human brain."

It has been proven in the meantime that the gut and the brain communicate with each other via several routes including the vagus nerve, the immune system, the enteric nervous system or by way of microbial metabolic processes. For instance, convert carbohydrates into short chain fatty acids, e.g. in butyric acid. This strengthens the connections between the cells and reinforces the blood-brain barrier, which serves as a cellular wall to protect the brain from infections and inflammations.

Gut microbiome regulates brain processes

For the neuroscientist Prof John F. Cryan (APC Microbiome Institute, University College Cork, Ireland), there is no question that the gut microbiome regulates fundamental brain processes important for the development of neurological diseases: "We studied the brains of germ free mice. In one region, the prefrontal cortex, we found increased myelination compared with animals kept under normal conditions. This may have direct implications for myelin-related disorders. Microbiome-dependent processes have also been shown to include adult hippocampal neurogenesis and microglia activation, i.e. the activation of brain and marrow cells similar to immune cells."

Experimental models on the origin of autoimmunity suggest that the microbiome plays an important role in this context, too. This insight opens up a new approach for finding the cause of multiple sclerosis (MS). MS is an autoimmune disease that results from a combination of genetic and environmental factors. Dr Gurumoorthy Krishnamoorthy from the Max Plank Institute for Neurobiology in Martinsried, Germany: "Apparently, the bacteria that can trigger are not disease-causing bacteria but rather useful bacteria needed for digestion." A study with genetically modified mice showed that animals featuring normal intestinal microbiota and subject to no external influences developed inflammation in the brain. By contrast, mice kept in a germ-free environment remained healthy. As Dr Krishnamoorthy explained, the immune system of the mice with normal intestinal microbiota is activated in two phases: First, T-cells become active and multiply in the lymphatic vessels of the intestinal tract. Together
with surface proteins in the myelin sheath, they then stimulate B-cells to form disease-causing antibodies. Dr Krishnamoorthy: "Both trigger inflammatory reactions in the brain, which destroy the myelin sheath in phases – very similar to the way MS unfolds in human beings." This process suggests that it is not disorders in the nervous system but rather a change in the immune system that leads to MS. Researchers assume that in human beings can likewise cause the to overreact to the if a corresponding genetic predisposition exists. It is still unclear, however, which bacteria are involved in the development of MS.

Gut microbiome

The microbiome consists of up to 1,000 different types of bacteria and of about 100 trillion cells. As such it has ten times as many cells and 150 times as many genes as the human genome. The microbiome co-evolves with its human host in a symbiotic relationship. The development of the as a finely tuned ecosystem depends on a number of factors: whether and which microorganisms a person absorbs from his/her mother's birth canal at the time of birth; whether a person is subject to antibodies; what food a person eats; infections; stress and genetic predisposition. Elderly individuals who are in poor health often have a lower diversity of microorganisms in their microbiome or inflammation-promoting manifestations.

Explore further: Mouse study finds link between gut bacteria and neurogenesis

Related Stories

Mouse study finds link between gut bacteria and neurogenesis

May 19, 2016
Antibiotics strong enough to kill off gut bacteria can also stop the growth of new brain cells in the hippocampus, a section of the brain associated with memory, reports a study in mice published May 19 in Cell Reports. Researchers ...

Gut microbiome of mother found to impact immunity of mice pups

March 18, 2016
(Medical Xpress)—A team of researchers from Switzerland and Germany has found that the gut microbiome of a pregnant mouse can have an impact on the development of the immune system in the pups she delivers. In their paper ...

Children with and without multiple sclerosis have differences in gut bacteria

May 16, 2016
In a recent study, children with multiple sclerosis had differences in the abundance of specific gut bacteria than children without the disease. Certain types of bacteria were either more or less abundant in children with ...

You are what you eat: How gut bacteria affect brain health

January 22, 2015
The hundred trillion bacteria living in an adult human—mostly in the intestines, making up the gut microbiome—have a significant impact on behavior and brain health. The many ways gut bacteria can impact normal brain ...

Transfer of gut bacteria affects brain function and nerve fiber insulation

April 20, 2016
Specific combinations of gut bacteria produce substances that affect myelin content and cause social avoidance behaviors in mice, according to a study conducted at the Icahn School of Medicine at Mount Sinai and published ...

High-fat diet alters behavior and produces signs of brain inflammation

March 26, 2015
Can the consumption of fatty foods change your behavior and your brain?

Recommended for you

Touching helps build the sexual brain

September 21, 2017
Hormones or sexual experience? Which of these is crucial for the onset of puberty? It seems that when rats are touched on their genitals, their brain changes and puberty accelerates. In a new study publishing September 21 ...

Gene immunotherapy protects against multiple sclerosis in mice

September 21, 2017
A potent and long-lasting gene immunotherapy approach prevents and reverses symptoms of multiple sclerosis in mice, according to a study published September 21st in the journal Molecular Therapy. Multiple sclerosis is an ...

Neuron types in brain are defined by gene activity shaping their communication patterns

September 21, 2017
In a major step forward in research, scientists at Cold Spring Harbor Laboratory (CSHL) today publish in Cell a discovery about the molecular-genetic basis of neuronal cell types. Neurons are the basic building blocks that ...

Your neurons register familiar faces, whether you notice them or not

September 21, 2017
When people see an image of a person they recognize—the famous tennis player Roger Federer or actress Halle Berry, for instance—particular cells light up in the brain. Now, researchers reporting in Current Biology on ...

Highly precise wiring in the cerebral cortex

September 21, 2017
Our brains house extremely complex neuronal circuits whose detailed structures are still largely unknown. This is especially true for the cerebral cortex of mammals, where, among other things, vision, thoughts or spatial ...

Faulty cell signaling derails cerebral cortex development, could it lead to autism?

September 20, 2017
As the embryonic brain develops, an incredibly complex cascade of cellular events occur, starting with progenitors - the originating cells that generate neurons and spur proper cortex development. If this cascade malfunctions ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet May 31, 2016
There is no profit for pharmaceutical companies in this line of research, so expect progress to be slow. And don't expect your doctor to be talking about it anytime soon. But there is plenty of practical info out in Internet-land. You just have to find it.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.