Have you ever wondered what gives you the feeling of being full after eating big meals over the holidays? We have long known that when we eat big meals, the cells lining of our stomach and intestines releases hormones into the bloodstream that signals the brain that we are full and hence, we should stop eating. The researchers at the Duke University have now revealed that they have mapped out another system which is a cell to cell connection between the gut and the nervous system which could be a more direct signal than the release of hormones in the blood.
The study that was published recently in the Journal of Clinical Investigation, said that the new system could be instrumental in changing the researchers' understanding of how we sense being full and how that sensation could be affected by gastric bypass surgery. It is also hoped that this will shed light on a potential new mechanism that gives foodborne viruses' access to the brain.
Diego BohÃ³rquez, an assistant professor of medicine at Duke and who is a part of this study as a Postdoctoral researcher in the lab of Dr. Rodger Liddle, a professor of gastroenterology said, that the study reveals that there is likely a real biology of gut feelings. When the food comes in contact with the wall of the gut, a signal is sent to the brain in real-time about what is going on in the gut.
In some previous research several years ago, Liddle's team had developed methods to visualize a kind of cell that is found scattered throughout the lining of the mouse gut and which is remarkably similar to a neuron. It was seen that even though the cells have a normal shape on the gut’s surface, it has a long arm on the underside. BohÃ³rquez said since, the cell had an arm; it was likely that the cell had more functions than just release hormones.
These cells are dubbed as neuropods and their special arms are nurtured by support cells called glia that work with neurons. It leads to the assumption that these cells could be a part of a neuronal circuit. In the recent study, the researchers studied the contacts of the neuropods in greater detail. It is found that they came close to individual nerve fibers, but not blood vessels, in the small and large intestine. It was also discovered that about 60% of neuropods contacted sensory neurons, supporting the idea that they could be involved in gut sensation.
In order to solidify their assumption, the researchers went a step further to show that the neuropods and neurons not only contacted each other, but also they connect. In a dish, single sensory neurons isolated from the brain were kept along with a neuropods. It was seen that it reached out to contact a neuropod that was, on a cellular scale, about half a football field away. That was a significant finding said BohÃ³rquez. It reveals that that these cells know how to get closer to neurons. However, the mechanism is not completely clear.
Neuropods, much like neurons follow the same machinery for sending and receiving signals. The researchers tried infecting the colons of mice with a disabled version of the rabies virus, which is known to move through the body by infecting neurons initially. A week after introducing the virus, it was found that only the cells with neuropods became infected.
Dr. Liddle said that it provided a pathway where rabies can go from the lumen of the gut to the nervous system. So, it implies that one might be able to get rabies by eating rabies. It is possible that this pathway could be used by other viruses to infect the nervous system. This study mainly concentrated on connections between neuropods and neurons closest to the intestine. The team is now working to trace the whole path from the gut to brain.