Here is how your brain reacts when you vomit food

Vomiting is probably one of the most unpredictable things that can happen anytime to anyone. You may have seen many people vomiting on Earth but do you know people even throw up in space? In August 1961, Soviet astronaut Gherman Titov became the first person to vomit in space, and interestingly his body demanded him to puke right before he was about to become the second human to ever orbit Earth.

Although scientists define vomiting just as a natural way of eliminating toxic or undigestible material from our gut, a new study highlight that there is much more to it. Recently, a team of researchers from China’s National Institute of Biological Sciences (NIBS) mapped the brain of mice during the time the mice felt the urge to vomit.

The researchers claim that by understanding what happens inside the brain during vomiting, they could further develop improved anti-nausea medications for cancer patients who have to go through chemotherapy.

By controlling neurons, you can control vomiting

Unlike humans, mice have long food and air pipes compared to their body size. Plus, their body muscles are too weak to withstand the stress resulting from puking, and therefore mice (and other rodents) can never vomit. However, they do feel the urge to vomit, so they barf or retch.

“The neural mechanism of retching is similar to that of vomiting. In this experiment, we successfully build a paradigm for studying toxin-induced retching in mice, with which we can look into the defensive responses from the brain to toxins at the molecular and cellular levels,” one of the authors and assistant investigator at NIBS, Peng Cao wrote.

During their study, the researchers observed two groups of mice. The researchers tried to induce retching in members of the first group by exposing them to staphylococcal enterotoxin A (SEA), a bacterial toxin that leads to several gut-related problems in humans, such as enteritis, bowel disease, and diarrhea. Mice in the second group were subjected to saline water.

The body of SEA-exposed mice reacted in a way a dog’s body responds when it vomits. Their body muscles and diaphragm underwent simultaneous contractions and they opened mouths much wider than the mice that had saline water. The researchers also noticed the activation and release of several neurotransmitters.

They observed that during retching, the mice’s brains ordered the release of serotonin from the enterochromaffin cells in the intestine. Within the intestine, there are neural receptors that send signals directly to the brain. The released serotonin also interacts with the brain receptors and this interaction leads to the activation of Tac1+DVC (dorsal vagal complex) neurons located in the dorsal vagal region of the mice brain.

Interestingly, when the researchers inactivated the Tac1+DVC neurons, the retching behavior was reduced in the mice.

Why does it matter to cancer patients?

They realized that when a cancer patient is subjected to chemotherapy, his body’s defense mechanism also leads to behaviors like vomiting and nausea. These unwanted side effects make the life of cancer patients more uncomfortable. Cao and his team thought that maybe by inactivating the Tac1+DVC neurons, they could also reduce nausea that develops as a result of chemotherapy.

In order to prove this theory, they exposed mice to a chemotherapy drug called doxorubicin, and as expected this experiment made the mice retch. The researchers then deactivated the Tac+DVC neurons and it worked! They noticed that after the deactivation of the neurons, the retching behavior got reduced to a large extent.

These findings also shed light on why and how some already available anti-nausea drugs work effectively by blocking the serotonin receptors. “With this study, we can now better understand the molecular and cellular mechanisms of nausea and vomiting, which will help us develop better medications.”

The study is published in the journal Cell.