The urge to vomit after eating contaminated food is the body’s natural defensive response to get rid of bacterial toxins. However, the process of how our brain initiates this biological reaction upon detecting the germs remains elusive. For the first time, researchers mapped out the detailed neural pathway of the defensive responses from the gut to the brain in mice. The study, presented November 1 in the journal Cell, could help scientists develop better anti-nausea medications for cancer patients who undergo chemotherapy.
Many foodborne bacteria produce toxins in the host after being ingested. The brain, after sensing their presence, will initiate a series of biological responses, including vomit and nausea, to get rid of the substances and develop an aversion toward foods that taste or look the same.
“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,” says Peng Cao, the paper’s corresponding author at the National Institute of Biological Sciences in Beijing. Rodents cannot vomit, likely because of their long esophagus and weaker muscle strength compared to their body size. As a result, scientists have been studying vomit in other animals like dogs and cats, but these animals are not comprehensively studied and thus failed to reveal the mechanism of nausea and vomiting.
Cao and his team noticed that while mice don’t vomit, they retch — meaning they also experience the urge to vomit without throwing up. The team found that after receiving Staphylococcal enterotoxin A (SEA), which is a common bacterial toxin produced by Staphylococcus aureus that also leads to foodborne illnesses in humans, mice developed episodes of unusual mouth opening. Mice that received SEA opened their mouths at angles wider than those observed in the control group, where mice received saline water. Moreover, during these episodes, the diaphragm and abdominal muscles of the SEA-treated mice contract simultaneously, a pattern seen in dogs when they are vomiting. During normal breathing, animals’ diaphragm and abdominal muscles contract alternatively.
“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 says.