Researchers Uncover Mechanism For Communication Between Brain and Gut

Researchers in Australia have discovered new details about how the gastrointestinal tract communicates with the brain, and say the findings could have significant relevance for human health and disease.

The gut is often called the second brain because it is the only organ with its own nervous system. However, understanding of how the gut and brain communicate has been limited by a lack of techniques to identify the precise spatial relationship between extrinsic nerve endings and their proximity to specific cell types that line the inner surface of the gastrointestinal tract. 

“The gut-brain axis consists of bidirectional communication between the brain and the gut, which links emotional and cognitive centers of the brain with peripheral intestinal functions,” says study author Professor Nick Spencer from the Flinders University College of Medicine and Public Health. “Recent advances in research have described the importance of gut microbiota in influencing these pathways but we had yet to uncover how the communication was working.”

Using an in vivo anterograde tracing technique previously developed in the Flinders laboratory, the team was able to selectively label single spinal afferent axons and their nerve endings in mouse colonic mucosa. This method enabled visualization of the sensory nerve endings in the gut wall with clarity that was previously unattainable. “This has not been possible, until now, because there were so many other types of nerves also present in the gut – it’s like finding a needle in a haystack,” Spencer says.

The work, published recently in the American Journal of Physiology, reveals a breakthrough discovery about how enterochromaffin (EC) cells release hormones and neurotransmitters in response to stimuli that are ingested when we eat.

“These EC cells release the vast majority of serotonin into the body, so our study has uncovered a major clue into how the food we eat stimulates the release of serotonin, which then acts on the nerves to communicate with the brain,” Spencer says. “There is a direct connection between serotonin levels in our body and depression and how we feel. So, understanding how the gut EC cells communicate with the brain is of major importance.” No direct physical connection between the EC cells and sensory nerve endings were found, however, contrary to some suggestions.