BEIJING, China — A cure for chronic nausea could be on the horizon thanks to a discovery in the brain. Scientists have mapped the neural networks behind vomiting for the first time, offering hope of combating morning sickness and the painful side-effects of cancer drugs.
“With this study, we can now better understand the molecular and cellular mechanisms of nausea and vomiting, which will help us develop better medications,” says Peng Cao, the paper’s corresponding author at the National Institute of Biological Sciences in Beijing, in a media release.
Feeling overwhelmed by the sensation that you’re going to throw up is one of the most miserably debilitating experiences. Some people live with it for days, weeks, or even months. It’s the body’s natural defensive response, which gets rid of bacterial toxins.
The Chinese team tracked this defense to the dorsal vagal complex (DVC) in the central nervous system. It opens the door to better anti-nausea medications. Many foodborne bacteria produce toxins after people ingest them. Vomiting begins after the host’s brain senses their presence.
“But details on how the signals are transmitted from the gut to the brain were unclear, because scientists couldn’t study the process on mice,” Cao adds.
Chronic nausea is common, with as many as one in eight people suffering from it on a regular basis. Causes range from chemotherapy to persistent stomach conditions such as chronic indigestion. However, it can also be a long-term effect of winter viruses and, more surprisingly, can be a result of anxiety and depression.
Nausea and vomiting linked to serotonin
Rodents cannot vomit due to a long gullet and weak muscle strength relative to their body, but they do retch — meaning they experience the urge to vomit without actually throwing up.
In tests, unusual episodes developed after lab mice ingested SEA (Staphylococcal enterotoxin A), a common food poisoning bug in humans. They opened their mouths at angles wider than those observed in a control group consuming saline water.
The diaphragm and abdominal muscles also contracted simultaneously; a pattern seen in vomiting dogs. During normal breathing, they contract alternately.
“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,” Cao continues.
The researchers found the toxin in the intestine activates the release of serotonin, a type of neurotransmitter, by cells on the lining of the intestines. The chemical binds to the receptors on the vagal sensory neurons, which transmits the signals along the vagus nerves from the gut to the DVC in the brainstem. Inactivating them led mice to retch less than their infected peers.
How do anti-nausea drugs work?
The team confirmed the results after injections of doxorubicin, a common chemotherapy drug. Current anti-nausea medications such as Granisetron work by blocking serotonin. The study, published in Cell, sheds fresh light on why the drug works.
Dr. Cao now wants to explore how toxins act on intestinal cells. Preliminary research shows they don’t sense their presence directly. The process likely involves complex immune responses of damaged cells in the intestine.
“In addition to foodborne germs, humans encounter a lot of pathogens, and our body is equipped with similar mechanisms to expel these toxic substances. For example, coughing is our body’s attempt to remove the coronavirus. It’s a new and exciting field of research about how the brain senses the existence of pathogens and initiates responses to get rid of them,” Cao concludes, adding that future studies may reveal better targets for drugs, including anti-nausea medications.
South West News Service writer Mark Waghorn contributed to this report.