Researchers have discovered a neuron circuit that directly connects the gut to the brain stem, shedding light on how the digestive system quickly communicates with the brain. While it was already known that the gut can communicate by releasing hormones into the bloodstream, sending messages about hunger over roughly 10 minutes, the new study reveals a much more direct and rapid connection. The neural circuit takes only seconds or less to send a signal to the brain, according to Science.
The new findings show that the brain has a way of picking up signals from the gut more similarly to how it receives signals from senses like sight and smell, according to ScienceDaily.com. For the many issues that have been linked to problems in the gut, including a range of conditions from obesity to arthritis to autism, the discovery may signal a new path toward treatments.
Enteroendocrine cells, which line the gut and produce hormones that aid digestion and control hunger, can also communicate with the central nervous system using hormonal messages. While scientists have suspected, since a key 2010 discovery, that they also may use electrical signals to rapidly communicate with the brain like neurons, they have only now discovered that the enteroendocrine vagal neurons are communicating directly with vagal neurons.
Researchers added green fluorescence to a rabies virus, and tracked the signals between the intestines and brains of mice, observing that the virus labeled the vagus nerve before reaching the brain stem. Next, in a petri dish, they found that cells formed direct synaptic connections with the vagal neurons, sending glutamate, a neurotransmitter crucial to the senses of taste and smell. The vagal neurons received the signals within 100 milliseconds, considerably faster than hormones are able to reach the brain through the bloodstream, according to Duke University neuroscientist Diego Bohórquez, the senior author of the new paper, who also conducted the 2010 research.
The time it takes for the slower, hormonal mode of communication may explain why appetite suppressants that target hormones are often ineffective, Bohórquez says. Next, he says researchers will need to determine if the more rapid signals are conveying information about the nutritional value derived from food.
“Scientists talk about appetite in terms of minutes to hours. Here we are talking about seconds,” says Bohórquez. “That has profound implications for our understanding of appetite.”
Real-time communication between the brain and the digestive system is likely advantageous in reacting to toxins and poisons, but scientists believe there me other benefits as well.
“We think these findings are going to be the biological basis of a new sense,” according to Bohórquez. “One that serves as the entry point for how the brain knows when the stomach is full of food and calories. It brings legitimacy to idea of the ‘gut feeling’ as a sixth sense.”