The researchers found that manipulation of gut microbiota of mice shows a significant difference in learning in comparison with a mouse of the normal gut. Microbiota refers to a complex consortium of viruses, bacteria, fungi, and parasites. In mammals, they have found changes in microbiota composition to influence many physiologic processes such as development, metabolism, and immunity. Changes in the composition of microbiota can also modulate the behavior of the host—such as social activity, stress, and anxiety-related responses – that are linked to diverse neuropsychiatric disorders. However, one question remains enigmatic to the neuroscientist. How does the microbiota influence the neuronal activity and the behavior of the host?
They show that manipulation of the gut microbiota of adult mice results in significant deficits in fear extinction learning. First, the authors trained the mice to associate a sound with an electric shock. They first played a tone followed by giving an electric shock. The mouse developed fear when the tone was played. The researchers then performed an extinction task, in which they repeatedly played the tone without an electric shock. Then they observed the fearful behavior of the mice. In the study, they used two types of mice samples: Mice with normal gut microbiota and mice with an antibiotic-treated gut. The mice with normal microbiota stop developing fear after some time. This happens after the mice learned that no more electric shock was given even after they played a tone. However, when they observed the mice with antibiotic-treated gut, they found a contrasting behavior. The mice showed persistent fearful behavior for a long time. This shows that mice without gut microbiota are slower in learning.The researchers also found that four metabolites related to neuropsychiatric disorders are heavily down-regulated in antibiotic-treated mice. Single-nucleus RNA sequencing also revealed a significant alteration in gene expression in neuronal cells of the mice.
Takeaway from the research
The result shows that gut microbiota is important for learning.
The microbiota regulates neuronal function and fear extinction learning. Nature 574, 543–548 (2019)