Identifying the Neural Link Between Gut Bacteria and Social Behavior in Mice

Very recommendable! Amazing stuff!

Perhaps this research will one day also lead to better treatments for excessively antisocial or violent humans!

"Research has shown that the communities of bacteria that live in a mouse's gut are essential for the animals to exhibit normal social behavior with other mice. Mice that have been bred to be germ-free, without a gut microbiome, display significant antisocial behaviors, such as avoiding a stranger mouse rather than interacting with it. ...
It had already been shown that, on a chemical level, germ-free mice have significantly higher levels of the hormone corticosterone (the analog of the so-called stress hormone, cortisol, in humans) than mice with healthy microbiomes. The team of researchers, led by former Mazmanian lab postdoctoral scholar Wei-Li Wu, aimed to identify the neurons that were both affected by corticosterone and played a role in social behaviors. ...
"There are a lot of neurons in the body that respond to corticosterone—called glucocorticoid receptor-positive neurons—and we wanted to know which cell populations and brain regions were then responsible for the altered social behaviors in germ-free mice?" ...
To address this, the team conducted fecal transplants from wild-type mice with normal gut microbiota into germ-free mice. These mice then showed decreased corticosterone levels and more normal social behavior. The team then systematically identified a species of bacteria that mediated this improvement, namely Enterococcus faecalis. Germ-free mice that were colonized with E. faecalis showed improved social behaviors and lowered corticosterone levels. The mechanisms through which E. faecalis is able to mediate this improvement will be the subject of future research. ...
This work strengthens the emerging appreciation of the profound effects of the gut-brain connection ..."

"... The gut microbiota contribute to social activity in mice, but the gut–brain connections that regulate this complex behaviour and its underlying neural basis are unclear. Here we show that the microbiome modulates neuronal activity in specific brain regions of male mice to regulate canonical stress responses and social behaviours. Social deviation in germ-free and antibiotic-treated mice is associated with elevated levels of the stress hormone corticosterone, which is primarily produced by activation of the hypothalamus–pituitary–adrenal (HPA) axis. Adrenalectomy, antagonism of glucocorticoid receptors, or pharmacological inhibition of corticosterone synthesis effectively corrects social deficits following microbiome depletion. Genetic ablation of glucocorticoid receptors in specific brain regions or chemogenetic inactivation of neurons in the paraventricular nucleus of the hypothalamus that produce corticotrophin-releasing hormone (CRH) reverse social impairments in antibiotic-treated mice. ..."

Identifying the Neural Link Between Gut Bacteria and Social Behavior in Mice | www.caltech.edu How the gut microbiome affects a specific set of neurons responsible for proper social function in mice. Could the germs that live inside of our bodies be affecting our ability to socialize and make friends? Research conducted in recent decades suggests that the answer—for mice—is yes.

Microbiota regulate social behaviour via stress response neurons in the brain (no public access)