Biological Significance of Glutamate Signaling during Digestion of Food through the Gut-Brain Axis

Abstract

Monosodium L-glutamate (MSG) elicits a unique taste termed umami and is widely used as a flavor enhancer in various cuisines. In addition, recent studies suggest the existence of sensors for L-glutamate (Glu) and transduction molecules in the gut mucosa as well as in the oral cavity. The vagal gastric afferent responds specifically to the luminal stimulation of Glu in the stomach and regulates the autonomic reflexes. The intragastric infusion of Glu 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 umami signaling via gustatory and visceral pathways plays an important role in the processes of digestion, absorption, metabolism, and other physiological functions via activation of the brain.

Effects of chronic dietary exposure to monosodium glutamate on feeding behavior, adiposity, gastrointestinal motility, and cardiovascular function in healthy adult rats

“…Ingested MSG stimulates the umami taste receptors on the tongue, leading to depolarization, calcium‐induced transmitter release and activation of taste nerve fibers, and also the glutamate sensors in the stomach and intestine, locally activating the functions of the digestive tract …”

Monosodium glutamate delivered in a protein-rich soup improves subsequent energy compensation

“…Indeed, it may be that the characteristics of MSG are more strongly associated with protein than are the sensory characteristics of thickness and creaminess previously identified and thus act as a more reliable cue for protein-based satiety. Alternatively, this improved compensation of protein in the MSG+ condition could be related to post-ingestive stimulation of gut glutamate sensors ( 15 , 42 ) which have been related to enhanced satiety in animals ( 43 – 45 ) .…”

Nutrient and the Mind-Body Axis, in Relation to Omega-3 Fatty Acids and Amino Acids

“…Effect of glutamate on brain function: Gustatory and anticipatory cephalic stimuli during a meal yield nutritional information and aid efficient food digestion (Uneyama et al, 2008;McCabe and Rolls, 2007;Young and Ajami, 2000;Tomporowski, 2003;Koopmans, 2011;Uematsu et al, 2009;2010;Kitamura et al, 2011). There is evidence that mammals, including humans, can detect the amount of dietary protein and its quality via cephalic relay to initiate proper digestion in the upper gastrointestinal tract.…”

“…Further evidence showed that abdominal vagal afferents, which were innervated into the stomach and intestine sending information to the brain, were activated by luminal glutamate (Uneyama et al, 2008;McCabe and Rolls, 2007). There is existence of a glutamate signaling system, metabotrophic glutamate receptors in the gastrointestinal tract (Uneyama et al, 2008;McCabe and Rolls, 2007;Kitamura et al, 2011). Luminal glutamate in the stomach and intestine provides the efferent reflection of the abdominal vagus, supporting the modulation of exocrine and endocrine excretion during digestion.…”

“…These results strongly indicate that glutamate has regulatory effects on the food digestive processes through the gut nutrientsensing system. Glutamate plays physiological and nutritional roles and initiates digestion in the stomach as well as anticipating subsequent processes in the small intestine and the liver (Uematsu et al, 2009;2010;Kitamura et al, 2011). The physiological significance of dietary free glutamate in the regulation of gut function, focusing on the visceral sensation from the stomach appears to be very interesting.…”