When we eat food that's been contaminated by potentially harmful bacteria, vomiting is a key way the body expels the toxins. To get a closer look at the process from go to throw, a team of researchers tracked a similar process in mice, from their gut to their brain.
Strangely, mice don't actually vomit, perhaps because compared to their body size their esophagus is too long and muscle strength is too weak.
They do retch, however, which is a good enough sign for examining the biological signals behind food poisoning.
"The neural mechanism of retching is similar to that of vomiting," says neurobiologist Peng Cao, from the National Institute of Biological Sciences in Beijing.
"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."
After giving mice a sample of the bacterial toxin Staphylococcal Enterotoxin A (SEA) – which is produced by Staphylococcus aureus and also leads to foodborne illness in humans – the researchers observed unusually wide mouth-opening actions in the animals, as well as contractions of the diaphragm and abdominal muscles (something we also see in dogs when they're vomiting).
Through a process of fluorescent labeling, it was shown that SEA in the intestine activated the release of the neurotransmitter serotonin. This serotonin then kicks off a chemical process that sends a message along the vagus nerves – the main connectors between the gut and the brain – to specific cells known as Tac1+DVC neurons in the brainstem.
When these Tac1+DVC neurons were artificially deactivated by the researchers, the retching lessened. The same happened with nausea induced by doxorubicin, a common chemotherapy drug: when the Tac1+DVC neurons were switched off or serotonin production was stopped, the mice retched much less compared with a control group.
"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 Cao.
Intestinal tissues made up of so-called enterochromaffin cells are responsible for releasing serotonin in the gut, the researchers found, and future studies could look at how toxins interact with these cells in particular to trigger the process of vomiting.
The detailed map resulting from the study could have could potentially teach us more about both food poisoning and chemotherapy. The results would suggest that the body produces similar defensive responses to both, although further studies on humans would be required to determine the relevance of the results to our own biology.
Ultimately, the research might lead the way to better anti-nausea medications for people who are undergoing courses of chemotherapy, allowing the prescribed drugs to fight cancer with fewer of the uncomfortable side effects.
"In addition to foodborne germs, humans encounter a lot of pathogens, and our body is equipped with similar mechanisms to expel these toxic substances," says Cao.
"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."
The research has been published in Cell.