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Not all brain cells are found in the brain. Scientists have now identified neurons in the abdomen that appear to control certain aspects of digestion. NPR's Jon Hamilton reports.
JON HAMILTON, BYLINE: When the brain senses danger like a predator, it activates the sympathetic nervous system. This network of neurons, which runs all around the body, is what puts us in survival mode. Yuki Oka, a researcher at Caltech, says these neurons tell your heart to beat faster, your pupils to dilate and your adrenal glands to go into overdrive.
YUKI OKA: Your adrenaline goes up and your glucose level in the blood is, like, really high because you need to fight or flight.
HAMILTON: But it's not all go, go, go. The sympathetic nervous system also hits the brakes on functions that are less urgent, like digestion and moving food through the gut. But how does the system get the right message to each internal organ? Oka's team had a hunch.
OKA: Our model or idea is that maybe sympathetic system might have, like, different types of neurons, just like in a brain.
HAMILTON: In the brain, certain types of neurons have specific jobs. Sensory neurons, for example, carry information coming from the eyes and ears. Oka's team thought the same approach might be used by neurons in the body. So his team began studying mice, focusing on clusters of abdominal neurons known as ganglia.
OKA: We looked at one of those big ganglia that controls the lower gut function, like intestine, spleen, stomach, pretty much, like, a digestive-related function.
HAMILTON: Oka's team used cutting-edge genetic techniques to characterize the neurons in that cluster, and he says they found two distinct types of cells with distinctly different jobs.
OKA: It turned out that digestive-related function are controlled by one major cell type. And then another class of neuron that is in involved in gut motility.
HAMILTON: When the team stimulated one type of neuron, the animal's liver would produce less bile - a digestive fluid that breaks down fat. When the team stimulated the other type of neuron, the animal's gut would move food more slowly. Each type of neuron had a specialized function, just like in the brain. The finding appears in the journal Nature. And Frank Duca of the University of Arizona says it shows how specialized neurons in the body can act like an extension of the brain.
FRANK DUCA: The gut can relay signals to the brain about a status of a meal or inflammation at the level of the gut, and then the brain can generate a response back to the gut on how to react to that situation.
HAMILTON: This two-way interaction is all part of the peripheral nervous system, which includes all the neurons found outside the brain and spinal cord. Duca says it makes sense that at least some of these neurons are organized in a way that gives them fine control of the gut, as well as other internal organs like the heart, lungs and liver.
DUCA: You have multiple components performing a wide variety of functions, either with the brain's help or sometimes even without the brain's input.
HAMILTON: The heart, for example, contains an internal network of neurons that can regulate electrical and mechanical activity even when the organ has been removed from the body. Duca says fully understanding the peripheral nervous system could lead to new treatments for everything from high blood pressure to irritable bowel syndrome.
DUCA: There's the potential now that future drugs could target only specific subsets of those neurons to activate just one function and not have all the functions be activated.
HAMILTON: Which would mean drugs with fewer side effects, all thanks to brain cells that are not found in the brain.
Jon Hamilton, NPR News. Transcript provided by NPR, Copyright NPR.
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