Have you ever heard of the Chinese restaurant syndrome (headache, skin flushing, and sweating) often presumed to be associated with monosodium glutamate (MSG) added to food? MSG was found to give “meaty, umami or savory” taste and is regarded as the 5th sensory taste besides sweet, sour, bitter and salty. MSG as its acidic equivalent glutamic acid is abundantly present in foods as a building block of proteins. In the bound form, almost all proteins contain glutamic acid. It is classified by the FDA as safe food ingredient. MSG gives savory taste to foods such as ripe tomatoes and parmesan cheese. The MSG, savory taste receptors are present on the tongue and also in the gut. However, this simple molecule is used cleverly by the body as nerve messenger or neurotransmitter. The gut can tell the brain about arrival and presence of nutrients containing glutamic acid. The brain then makes decisions about food and related physiological functions such as appetite hunger and feeling full and more.
Route of Transmission of Message
It was accepted that the stomach and intestines use hormones to communicate with brain of being hungry or feeling full. Hormones which travel to the brain via blood take few minutes to transmit the message. Dr. Diego Bohórquez of Duke University has found a faster way the gut can transmit information to the brain in milliseconds. Certain cells in the gut called enteroendocrine cells act as synapses or neurotransmitter junctions. They are directly connected with neurons which transmit information to the brain. Dr. Bohorquez and colleagues used rabies virus to study how the message is transmitted to brain. Using mice, the scientists tracked how the virus travels through neurons to the brain. The virus travels through infected enteroendocrine (gut) cells through the neurons to the vagus nerve and finally to the brain.
Speed of Transmission
In order to find how fast the message is transmitted the scientists grew vagal neurons and enteroendocrine cells together in culture that formed synapses. The gut cells (enteroendocrine cells) when presented with sugar fired neurons to transmit signals to vagal neurons about presence of sugar in just 60 to 800 milliseconds.
These findings may have profound implications on ways to control diet, appetite, and feeling full and ways to control obesity in relation to food intake. The researchers plan to do further experiments to understand how this system transmits specific information about the nutrient and caloric content of food.