How does the signal to vomit arrive?

Anyone who has eaten something that did not agree with them remembers the discomfort that heralds bad times to come. The bacteria release toxins that start the body’s process of rapidly evacuating stomach contents. It’s a kind of protective mechanism—getting rid of invaders en masse is likely to be helpful in the long run, even if it’s unpleasant in the short run. But it remained a mystery how the brain receives the alarm signal and then sends another to tell the stomach to start the process.

Food poisoning is not the only reason to understand this particular neural pathway. Finding out how to counteract it could be helpful for people who develop nausea caused by chemotherapy drugs and other drugs. Patients often feel such a dislike for food that maintaining their weight becomes a huge battle.

In a new study, researchers report that both bacteria and chemotherapy drugs appear to trigger the same molecular pathways in the gut. The findings, which were based on experiments with mice, showed that a bacterial toxin and a chemotherapy drug activate a cascade of similar neural messages that cause discomfort. The choice of mice for the study was unusual. It turns out that mice cannot vomit. But mouse biology in general is much better understood, with much better tools available to scientists.

Cao Peng, a professor at Tsinghua University in Beijing, and his colleagues gave mice a bacterial toxin and found that the rodents began to open their mouths strangely after treatment. Further tests showed that their abdominal muscles moved much like human stomachs do when they are about to vomit. Indeed, the scientists believe that the mice had started to vomit. A chemotherapy drug made the mice behave in a similar way.

The scientists traced the effect to certain neurons in the brain that released neurotransmitters when the drug or toxin reached the intestine. Following those messages, they discovered cells in the small intestine that reacted to the presence of these harmful substances. A central player in the path to nausea and vomiting was an immune system molecule called interleukin 33, or IL33. Preventing the mice from producing IL33 significantly reduced their symptoms.

It is possible that drugs that interfere with IL33 or other participants in this pathway could help alleviate the suffering of people undergoing chemotherapy, Cao said. This study is a first step to potentially improve the quality of life of chemotherapy patients, if the results hold up in humans.

By: VERONIQUE GREENWOOD