Behavioral Effects of Microbiota
The human gut microbiota, the collection of bacteria that live in the human gut and help with digestion, regulating the immune system, and more, has a largely unknown impact on the human nervous system and human behavior. More research, however, is being carried out to shed light on the potential effects the microbiota can have on people’s behavior and brain function. Recently, a team of researchers at Cornell University published their findings from a study that explored how the microbiota affects psychological behavior in mice.
The researchers started their experiment by testing how the microbiota affects fear conditioning, a method used in psychology where an animal learns to associate an object or event with an unpleasant, adverse stimulant through repeated exposure. After fear conditioning, mice were tested on extinction learning, which is the gradual decline in fear conditioning. When an animal is not continuously exposed to the adverse stimulation presented in fear conditioning, their learned association will decrease. A control group, adult mice with no antibiotics, was compared to an experimental group, adult mice with antibiotics (ABX mice). Because the microbiota is a collection of bacteria, taking antibiotics reduces the diversity and amount of bacteria in the human body. While both the ABX and control group showed responses to fear conditioning, ABX mice showed a reduction in extinction learning. Researchers then confirmed results by using adult germ-free mice, which are specially raised mice that don’t have a microbiota altogether. Both ABX and germ-free mice showed reduced extinction learning, which meant that they were unable to decrease the fear conditioning they had been exposed to.
The researchers started their experiment by testing how the microbiota affects fear conditioning, a method used in psychology where an animal learns to associate an object or event with an unpleasant, adverse stimulant through repeated exposure. After fear conditioning, mice were tested on extinction learning, which is the gradual decline in fear conditioning. When an animal is not continuously exposed to the adverse stimulation presented in fear conditioning, their learned association will decrease. A control group, adult mice with no antibiotics, was compared to an experimental group, adult mice with antibiotics (ABX mice). Because the microbiota is a collection of bacteria, taking antibiotics reduces the diversity and amount of bacteria in the human body. While both the ABX and control group showed responses to fear conditioning, ABX mice showed a reduction in extinction learning. Researchers then confirmed results by using adult germ-free mice, which are specially raised mice that don’t have a microbiota altogether. Both ABX and germ-free mice showed reduced extinction learning, which meant that they were unable to decrease the fear conditioning they had been exposed to.
Researchers then tested various hypotheses on why microbiota may affect extinction learning. First, they explored the possibility that the microbiota affects the vagus nerve, a nerve that sends information between the intestine and the brain. To do this, researchers surgically cut the vagus nerve of a group of ABX mice and compared their extinction learning to a group of control ABX that did not have their vagus nerve cut. Both groups showed similar results, which led to the conclusion that the vagus nerve is not the cause of impaired extinction learning.
Their final hypothesis proved to be more promising. They theorized that microbiota may affect the levels of microglia, which are cells that help maintain healthy brain function. They found that ABX mice did show different levels of microglia compared to the control mice. Specifically, they found that extinction learning increased the formation of dendritic spine in control mice but not in ABX mice. This may be a potential explanation of the differences in extinction learning, as dendritic spines are important in maintaining normal brain cell function and are affected by microglia.
While a deficit in extinction learning was found in mice with lower microbiota, researchers also found that reintroducing a diverse microbiota had the potential of normalizing extinction learning. The researchers were only able to find normal rates of extinction learning when they introduced microbiota into germ-free mice before the mice weaned, or when the mice were still dependent on their mother’s milk. They also found that simply increasing one type of bacterium found in the microbiota was not enough to form normal extinction learning; a diverse collection of bacteria must be introduced.
This research has significant findings, as humans also have microbiota. Increasing research is showing that the microbiota influences behavior, and some research even hints at the possibility of a connection between the microbiota and some human diseases. This research sheds light on the necessity of maintaining a healthy, diverse microbiota, as our cognitive behaviors may be influenced by microbiota, as well.
Their final hypothesis proved to be more promising. They theorized that microbiota may affect the levels of microglia, which are cells that help maintain healthy brain function. They found that ABX mice did show different levels of microglia compared to the control mice. Specifically, they found that extinction learning increased the formation of dendritic spine in control mice but not in ABX mice. This may be a potential explanation of the differences in extinction learning, as dendritic spines are important in maintaining normal brain cell function and are affected by microglia.
While a deficit in extinction learning was found in mice with lower microbiota, researchers also found that reintroducing a diverse microbiota had the potential of normalizing extinction learning. The researchers were only able to find normal rates of extinction learning when they introduced microbiota into germ-free mice before the mice weaned, or when the mice were still dependent on their mother’s milk. They also found that simply increasing one type of bacterium found in the microbiota was not enough to form normal extinction learning; a diverse collection of bacteria must be introduced.
This research has significant findings, as humans also have microbiota. Increasing research is showing that the microbiota influences behavior, and some research even hints at the possibility of a connection between the microbiota and some human diseases. This research sheds light on the necessity of maintaining a healthy, diverse microbiota, as our cognitive behaviors may be influenced by microbiota, as well.
Featured Image Source: Microbiome by National Human Genome Research Institute is licensed by CC BY-NC 2.0
RELATED ARTICLES
Vertical Divider
|
Vertical Divider
|
Vertical Divider
|