Mental health, behavior and mood are all controlled by your brain, right? Not necessarily, research is reveling that your mental health is very much dependent on the microbes in your gut. Your gut lining is embedded with the enteric nervous system (ENS), working both independently of and in conjunction with your brain. Your ENS contains 500 million neurons which is constantly sending information to your brain and gut microbes make neuroactive compounds that also act on the brain. Learn how these gut microorganisms effect behavior and brain function below.
Germ-Free Mice Show the Importance of a Microbiome
So-called germ-free mice, which have no microbiome to speak of, have altered behavior and brain function. In a study by John Cryan from the University College Cork in Ireland, mice without microbes in their intestines are unable to recognize other mice around them.
He believes that microbes may communicate with the brain and help us be social, which in turn allows the microbes to spread to others.3 In addition, mice lacking gut bacteria have been found to engage in “high-risk behavior,” and this altered behavior was accompanied by neurochemical changes in the mouse brain.4
When examining the animals’ brains, the researchers discovered a number of genetic alterations in the germ-free mice. According to The Guardian:5
“Brain-derived neurotrophic factor (BDNF) was significantly up-regulated, and the 5HT1A serotonin receptor sub-type down-regulated, in the dentate gyrus of the hippocampus.
The gene encoding the NR2B subunit of the NMDA receptor was also down-regulated in the amygdala. All three genes have previously been implicated in emotion and anxiety-like behaviors.
BDNF is a growth factor that is essential for proper brain development, and a recent study showed that deleting the BDNF receptor TrkB alters the way in which newborn neurons integrate into hippocampal circuitry and increases anxiety-like behaviors in mice.
Serotonin receptors, which are distributed widely throughout the brain, are well known to be involved in mood, and compounds that activate the 5HT1A subtype also produce anxiety-like behaviors.“
Further, researchers have discovered that the absence or presence of gut microorganisms during infancy permanently alters gene expression. Through gene profiling, they were able to discern that absence of gut bacteria altered genes and signaling pathways involved in learning, memory, and motor control.
This suggests that gut bacteria are closely tied to early brain development and subsequent behavior.
These behavioral changes could be reversed as long as the mice were exposed to normal microorganisms early in life. But once the germ-free mice had reached adulthood, colonizing them with bacteria did not influence their behavior.6
Psychobiotics: A New Treatment for Mental Health
Cryan believes beneficial microbes could one day be used to treat mental health problems in humans. He dubbed the compounds “psychobiotics.” He told Scientific American:7
“That dietary treatments could be used as either adjunct or sole therapy for mood disorders is not beyond the realm of possibility.”
Interesting research led by microbiologist Premsyl Bercik and gastroenterologist Stephen Collins also found that when the intestines of germ-free mice were colonized with bacteria from other mice, they took on aspects of the donor’s personality.8
Other research shows that women who had high prolonged fevers during pregnancy are more likely to have children with autism.
The finding held up in mice, too, and the MIA (maternal immune activation) mice were also found to have leaky intestines and abnormal microbiomes – a common occurrence in children with autism as well.9
Of particular importance, when the MIA mice were treated with a microbe called bacteroides fragilis, their gut permeability was corrected and many of their behavioral symptoms went away. According to the researchers:10
“…these findings support a gut-microbiome-brain connection in a mouse model of ASD [autism spectrum disorder] and identify a potential probiotic therapy for GI and particular behavioral symptoms in human neurodevelopmental disorders.”