All of us experience anxiety at one point or another; whether down to a job interview or a first date, that nervous feeling in the gut often takes hold. Interestingly, a new study suggests that when it comes to anxiety, the gut could play a key role. Share on Pinterest Researchers have shed further light on the link between gut bacteria and anxiety. Researchers found that the absence of gut bacteria in mice altered the expression of microRNAs (miRNAs) in regions of the brain that play a role in anxiety and depression. Study co-author Dr. Gerard Clarke, of the APC Microbiome Institute at University College Cork in the Republic of Ireland, and colleagues recently reported their findings in the journal Microbiome. This is not the first study to suggest a link between gut bacteria and anxiety. A study reported by Medical News Today in 2015, for example, found that stress in early life may alter gut bacteria in a way that may increase the risk of anxiety in later life. But what are the mechanisms that underly the possible link between gut bacteria and anxiety? The new study from Dr. Clarke and team helps to shed light.

Gut bacteria and miRNAs To reach their findings, the researchers analyzed groups of mice that had three different gut bacteria conditions: Germ-free mice, which had no gut bacteria due to being bred in an environment free of microorganisms

Ex germ-free mice, which had been colonized with gut bacteria in later life

Mice with normal gut bacteria, which had been bred in their usual conditions The team notes that mice bred in germ-free conditions are more likely to develop symptoms of anxiety, depression, problems with sociability, and cognitive dysfunctions. As part of the study, the team looked at how the absence of gut bacteria affected miRNAs in the rodents’ brains. miRNAs are tiny RNA molecules that regulate gene expression. Specifically, the researchers sought to pinpoint which miRNAs were present in the amygdala and prefrontal cortex of the mice in each gut bacteria condition. Compared with the conventional mice, the researchers found that the germ-free mice showed differences in 103 miRNAs in the amygdala – which is the brain region involved in emotional processing – and 31 changes in miRNAs in the prefrontal cortex – which is the brain region involved in behavior, planning, and impulse control, among other functions. Importantly, when the researchers introduced bacteria to the guts of the germ-free mice in later life, some of the differences in miRNAs within the amygdala and the prefrontal cortex disappeared. As such, the team speculates that a healthy gut microbiome is required for normal miRNA regulation. “Gut microbes seem to influence miRNAs in the amygdala and the prefrontal cortex,” says Dr. Clarke. “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.”