Brain activation by the umami taste substance monosodium L-glutamate via gustatory and visceral signaling pathways, and its physiological significance due to homeostasis after a meal

Monosodium l-glutamate (MSG) elicits a unique taste sensation termed umami and is widely used as a flavor enhancer in various cuisines. In addition, recent studies have suggested the existence of receptors for l-glutamate (Glu) and transduction molecules in the gut mucosa as well as in the oral cavity. The gastric afferent vagal nerve responds specifically to luminal stimulation by Glu in the stomach and regulates autonomic reflexes. The intragastric infusion of MSG also activates several brain areas (insular cortex, limbic system, and hypothalamus) and is able to induce flavor-preference learning in rats. These results suggest that Glu signaling via the gustatory and visceral pathways plays an important role in digestion, absorption, metabolism, and other physiological functions by activating the brain.