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Researchers at University College Cork in Ireland transplanted gut microbes from people with social anxiety disorder into ordinary mice. After the procedure, the rodents stayed healthy but began to show signs of social anxiety. The team says this work points to the gut as a potential place to start treating the disorder.
Social anxiety, or social phobia, is a condition marked by persistent fear and distress in social situations or interactions with other people.
How the Study Was Conducted
For the experiment reported by the Daily Mail, researchers collected gut microbiome samples from volunteers who agreed to participate. The samples came from six people diagnosed with social anxiety disorder and six people without the condition.
Before the study, all participants confirmed that they were not taking psychiatric medications or dietary supplements that could affect their gut microbiota.
The team prepared 72 mice for the study. For a week, they fed the mice a cocktail of four antibiotics to deplete their resident microbiota, aiming to work with effectively ‘clean’ intestines.
Over three days, the scientists transferred gut microbes from the human participants to the mice through a feeding tube to help the new microbiome take hold. Ultimately, 36 mice received transplants from people with social anxiety, while 36 received transplants from participants without the disorder.
Ten days after the experiment began, the mice underwent a series of tests that measured sociability, general anxiety, gut function, depression-like behavior, and social fear. In most of those tests, both groups performed the same.
But in the social fear test, the mice that received transplants from people with social phobia performed significantly worse. Those rodents displayed behaviors resembling social anxiety disorder; the scientists described it as a ‘mouse version of social anxiety.’
What the Researchers Discovered
The team also found that the animals showing signs of social phobia had lower levels of the hormone corticosterone. That hormone helps regulate energy, immune responses, and stress reactions. Immune markers indicated the mice experienced immune system disruptions after receiving microbes from people with social phobia.
The researchers suggested that inflammatory molecules might travel from the gut to the brain. In addition to the new anxiety-like behavior, the mice’s brains showed specific changes. In the nucleus accumbens, a region involved in reward processing, oxytocin levels dropped; oxytocin is often called the ‘love hormone’ and supports parent-child bonding as well as romantic and social relationships.
In the amygdala and prefrontal cortex of the mice that received microbes from people with social anxiety, the team observed reduced expression of genes linked to oxytocin. Those brain areas help govern fear processing and personality-related behaviors.
The researchers concluded that altering the microbiome produced significant behavioral changes in the mice.
The results led the team to suggest the microbiota-gut-brain axis could be an ideal target for developing new treatments to relieve social phobia symptoms in humans.
This work adds to a growing body of studies showing a complex relationship between the gut and the brain and supports the idea that treating anxiety, depression, autism, and other mental disorders may involve targeting the gut. The study did not test specific treatments, but it opens the door to developing them.
The study’s results were published in the Proceedings of the National Academy of Sciences.
