People who suffer from anxiety may take antidepressants or another medicine to treat their brain.

But a new study suggests gut bacteria actually plays a major role in anxious feelings.

A team of scientists discovered that certain gene regulators in the brain - called microRNAs - play a key roll in anxiety-type illness and behaviour and are affected by bacteria levels in the gut.

This study, done by the University of Cork, is one in a growing body of data on gut bacteria and physical and mental health.

Pharmaceutical and wellness companies have noticed, and have been marketing probiotics said to improve general physical and mental health for years already, as we reported in January of 2014.

It's unclear, though, if the gut is influencing the brain and its development, or if the brain is influencing the gut.

A team of scientists discovered that certain gene regulators in the brain - called microRNAs - play a key roll in anxiety-type illness and behaviour and are affected by bacteria levels in the gut (stock image)

THE GUT-BRAIN CONNECTION This study is one in a growing body of data on gut bacteria and physical and mental health. Pharmaceutical and wellness companies have noticed, and have been marketing probiotics said to improve general physical and mental health for years already, as we reported in January of 2014. It's unclear, though, if the gut is influencing the brain and its development, or if the brain is influencing the gut. Researchers warn that it is hard to draw conclusions at this point, as this is still a young field of research and most of the large-scale studies are ongoing. Other research has tried to establish a connection between 'microbial communities,' or microbiotic profiles and geography. But a 2016 Brown University study found that that there was no consistent profile once a wide sample was taken, and the prevalence of Bacteroides over Prevotella or visa versa was probably determined more by diet, lifestyle and health than it was by location. The study reexamined the division of Western and non-Western gut bacteria profiles, but its conclusions suggested that digestive flora are determined by nurture than by nature. Advertisement

Researchers found that the microRNAs (miRNAs) changed in the brains of microbe-free mice who were reared in a germ-free bubble.

Those mice displayed abnormal anxiety, deficits in sociability and cognition, and depressive-like behaviours.

Gut microbes appear to influence miRNAs in two specific parts of the brain - the amygdala, which is commonly associated with experiencing emotions, and the prefrontal cortex, which plays a role in personality development.

'This is important because these miRNAs may affect physiological processes that are fundamental to the functioning of the central nervous system and in brain regions, such as the amygdala and prefrontal cortex, which are heavily implicated in anxiety and depression' Dr Gerard Clarke, one of the study's corresponding authors, explained.

miRNAs are a short sequence of nucleotides - which are the building blocks of DNA and RNA - that control how genes are expressed.

When they don't function properly, it's thought miRNAs contribute significantly to stress-related psychiatric disorders, neurodegenerative diseases and neurodevelopmental abnormalities.

So changes in how certain genes are expressed in the brain are caused by miRNAs and can be linked to anxiety-like behaviors.

'It may be possible to modulate miRNAs in the brain for the treatment of psychiatric disorders but research in this area has faced several challenges, for example, finding safe and biologically stable compounds that are able to cross the blood-brain barrier and then act at the desired location in the brain,' Dr Clarke said.

'Our study suggests that some of the hurdles that stand in the way of exploiting the therapeutic potential of miRNAs could be cleared by instead targeting the gut microbiome.'

The gut microbiome refers to the population of bacteria and other microbes in the intestine that is unique to each person.

The team of scientists looked at the interplay of gut bacteria and the miRNA level in the amygdala and prefrontal cortex of a group of 12 mice.

Specifically they looked at 103 miRNAs in the amygdala and 31 in the prefrontal cortex in one group raised with no gut bacteria, who were reared in a kind of 'bubble.' Their levels of miRNAs were compared against a group of mice brought up conventionally.

The researchers used next-generation-sequencing to analyse which miRNAs were present in the prefrontal cortex and amygdala in each group of mice.

They found that depleting the microbiota of adult mice with antibiotics in both groups impacted the miRNAs in the same way, which suggests that even if there is healthy bacteria present throughout an individual's life changes during adulthood can cause anxiety-like behaviours.

Alternatively, they also found that adding gut bacteria later in life normalised some of those pre-examined changes.

The findings suggest that a healthy balance of gut bacteria is necessary for appropriate regulation of miRNAS, which

Previous research has demonstrated that some manipulation of the balance of bacteria in the gut can impact anxiety-like behaviors, but this study is the first that links that balance to miRNAs in the amygdala and prefrontal cortex.

The authors note that the exact mechanism by which the gut microbiota is able to influence the miRNAs in the brain remains unclear.

Further research into the possible connection between gut bacteria, miRNAs and anxiety-like behaviors is needed before the findings can be translated to a clinical setting.

Dr Clarke said: 'This is early stage research but the possibility of achieving the desired impact on miRNAs in specific brain regions by targeting the gut microbiota -- for example by using psychobiotics -- is an appealing prospect.'