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How the gut communicates with the brain

New research from Flinders University has discovered how specialised cells within the gut can communicate with both the brain and spinal cord, which up until now had remained a major mystery. The study, published in the American Journal of Physiology, reveals a breakthrough discovery regarding how enterochromaffin cells communicate with sensory nerve endings. “The gut–brain axis consists of bidirectional communication between the brain and the gut, which links emotional and cognitive centres of the brain with peripheral intestinal functions. Within the gut wall lie specialised cells called enterochromaffin [EC] cells that produce and release hormones and neurotransmitters in response to particular stimuli that are ingested when we eat,” said author Professor Nick Spencer. “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. 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.” The team made the discovery using a neuronal tracing technique developed in their lab, not used anywhere else in the world, allowing them to see the sensory nerve endings with clarity, for the first time, in the gut wall. The technique allowed the researchers to see that EC cells likely release substances by a process of diffusion, which then acts on the sensory nerves that communicate with the brain. No direct physical connection between the EC cells and sensory nerve endings were found, contrary to some suggestions.

How does COVID‐19 affect people’s ability to smell?

Olfactory dysfunction is a common symptom experienced by individuals with COVID‐19. In research published in The Laryngoscope, researchers searched the medical literature for studies reporting changes in olfactory structures detected through imaging tests of patients with COVID‐19. The prevalence of an olfactory cleft abnormality was nearly 16‐fold higher in patients with COVID‐19 and olfactory dysfunction (63%) compared with controls (4%). The olfactory clefts provide a crucial channel for airborne molecules to reach sensory olfactory neurons that connect to the brain to enable a person to perceive smells. “Before this study, most scientists thought that the loss of smell in COVID‐19 was mainly due to inflammation and damage to the olfactory nerves. Now, we have compiled evidence from medical imaging that COVID‐19 loss of smell is also due to swelling and blockage of the passages in the nose that conduct smells,” said senior author Neville Wei Yang Teo from Singapore General Hospital. “We think this is good news for patients who want to recover their sense of smell, since these blockages are expected to resolve with time, while nerve damage in comparison would likely be more difficult to recover from,” added co‐author Claire Jing‐Wen Tan, of the National University of Singapore. “These findings may not fully account for those who suffer from prolonged olfactory dysfunction, however, and further studies that evaluate patients in this group may provide more information.”