While some people may enjoy the prospect of a New Year’s party, for others socializing can cause feelings of fear, anxiety and distress. Now researchers say microbes in the gut may play a role in causing social anxiety disorder, opening up new possibilities for therapy.
Scientists previously found the gut microbiome – the collection of bacteria and other organisms that live in the digestive system – different for people who have social anxiety disorder (SAD). compared to healthy individuals, while a growing body of research has revealed that microbes in the gut can affect the brain – and vice versa.
Now researchers have found that when microbes from the guts of people with SAD are transplanted into mice, the animals have a heightened response to social fear.
The findings build on previous work showing similar results for conditions ranging from depression on irritable bowel syndrome.
Prof John Cryan, a co-author of the research from University College Cork, said that while it was known that genetics, the environment and other factors could also play a role in disorders including SAD, the new work highlighted the importance of emphasizes our gut flora. .
“The bottom line is that we need to look at our microbes, especially through development and even into adulthood, to keep the social brain working properly,” he said.
Writing in the Proceedings of the National Academy of SciencesCryan and colleagues report how they took fecal samples from six healthy people and six people with SAD, with DNA analyzes confirming that the gut microbiome differed significantly between the two groups.
The team transferred each sample to six lab mice, giving a total of 72 creatures, all of which had previously been given antibiotics to kill their natural gut microbes.
The mice were then presented with a series of tests to examine various aspects of their behavior. To investigate social fear, the team gave the mice small electric shocks when they approached a new mouse, and then observed how the animals behaved around new mice when the shocks were no longer applied.
The results revealed that the mice that received gut microbes from people with SAD had different levels of three bacterial species in their feces than those that received gut microbes from healthy people.
The team adds that while behavior of the mice did not differ for most of the experiments investigating anxiety and social behavior, they did behave differently after the social fear experiment. While mice with gut microbes from healthy people quickly regained their curiosity for strangers in the following days, those with microbes from people with SAD continued to be afraid to approach other mice.
“They never fully recovered to be able to be social again,” Cryan said.
Further analysis suggested that levels of certain hormones and aspects of the immune system also differed between the mice.
“Both oxytocin, a key hormone involved in bonding, and the immune system have previously been involved in social behavior, so it was good to see that changes in these occurred in animals that received the SAD microbiota,” Cryan said .
The team says the results suggest that the gut microbiome may play a causal role in heightened social fear responses in social anxiety disorder, while the study also offers new avenues when it comes to developing therapeutics for people with SAD.
Cryan said this could include diets designed to alter the microbiome.
“Increasing the amount of fiber and fermented foods in the diet can have beneficial effects,” he said. “And that’s something we’re very interested in exploring, moving forward.”
