Feeling Sick to Your Stomach? It's All in Your Head!

September 29, 2000 Cold and flu season is approaching and it's possible that you may catch a "bug" or two. New research suggests that the "sick-to-your-stomach" feeling you get when you are ill may have its origins in the brain stem. When foreign substances, such as bacteria and viruses enter your body, your immune system gears up to fight these invaders and to ward off infection. One chemical released by the immune system is called tumor necrosis factor (TNF). Studies have shown that small injections of TNF into the brain stem can slow the movement of food in the digestive system. This interruption of digestive processes may cause the feeling of nausea when you are sick. New research in the Department of Neuroscience at Ohio State University shows that TNF can activate neurons in the part of the brain stem called the nucleus of the solitary tract (NST). The NST is involved in controlling different parts of digestion. Investigators used a glass electrode with three different barrels to inject small amounts of TNF into the NST of rats. After recording from NST neurons in the vicinity where the TNF was injected, the researchers found that TNF caused an increase in the firing rate of the NST neurons. Many of these same NST neurons are known to be responsive to stretching of the stomach. These experiments are an example of how the immune system communicates directly with the nervous system and indirectly with the digestive system. This work also demonstrates how the interaction between the immune system, nervous system and digestive system may give rise to the feelings of nausea. Now you know what's making you feel sick...too bad it won't cure your cold!

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