Suzana Herculano-Houzel

Brazilian discovers direct connection between gut and brain

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You know that story that the role of the nerves in the stomach during a meal is just to inform the brain of the arrival of food and satisfy hunger? It’s just been buried by a Brazilian neuroscientist, one who was featured in this column recently with a beautiful piece of work, very difficult to do, about a region of the brain that, when stimulated by a laser, makes mice attack wind-up toys. It’s the stuff of science fiction, funded by the US government, which has shown that there is a part of the amygdala in the brain that triggers lethal violent attacks, essential for those who need to hunt in order to survive.

Ivan de Araujo is back with another equally complicated and elegant piece of work, this time attacking the gut-brain connection, the one that has been the talk of the town since it became fashionable to study the microbiome: the “good” bacteria that inhabit our guts. The fact that they change our metabolism and even affect our state of mind is common knowledge. The question remains: how?

Using modified dyes or viruses, injected sometimes into the stomach, sometimes into the nodose ganglion of the vagus nerve, sometimes into different parts of the brain of mice with submillimeter precision to make the infected cells sensitive to a blue laser, Ivan’s team was able to control which cells activated on demand, and trace their connections between body and brain. The pieces, fitted together like a well-assembled jigsaw puzzle, revealed the whole: the vagus nerve monitors the stomach and intestines and, via the nucleus of the solitary tract (the name is reminiscent of poetry), causes the substantia nigra to release dopamine directly into the striatum.

If the names of the structures don’t sound familiar, the result is certainly: pleasure. No satiety. Stimulation of the stomach gives pleasure, directly to the brain.

With a degree in philosophy and mathematics from the University of Brasilia, a post-graduate degree in Scotland and a stint at Duke University in the USA, Ivan de Araujo had been doing well in the USA for some time, at Yale University, where he began studying the circuits between the brain and the body. He did so well that other universities wanted the honor of hosting his research, and now his new home is the Mount Sinai School of Medicine in New York, where he is a Full Professor. Because that’s how it is in countries that take research seriously: scientists are fought over with competitive bids, like soccer players by sports clubs, and their colleagues cheer them on when their work is recognized.

Originally published in Folha de São Paulo in September 2018.

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