Brief Rationale of the Symposium

Nutrient sensing in the gut plays an important roles both in the regulation of gastrointestinal processes and in the control of food intake. Both cephalic and visceral inputs contribute to controlling preferences and amounts of food intake. The vagus nerve carries information on visceral input concerning the content of ingested foods and subsequent output for controlling gut functions such as digestion, absorption, and motility. There is accumulating evidence to support that dietary proteins and amino acids are detected throughout the entire extent of the gastrointestinal tract. A first detection process for amino acid involves specialized cells present in the entire gastro-intestinal tract which carry amino acid receptors on their luminal membranes. These cells would initiate a signalling process resulting in the release of gut hormones by enteroendocrine cells present in the epithelia of the gastrointestinal tract. Another important detection process could involve epithelial absorptive cells that have the ability to sense variations in luminal amino acid concentrations via changes in their cellular metabolism. Recently, the expression of a glutamate receptor has been demonstrated in the rat stomach; and the gastric vagal afferent fibers respond specifically to umami substances, i.e., monosodium glutamate and 5’-ribonucleotides, through the release of nitric oxide and serotonin. This symposium will provide recent evidences obtained from basic animal studies to intensive human studies containing significant roles of dietary glutamate in monitoring and controlling of food intake via taste and vagus nerves. The psychological and physiological mechanisms of liking/wanting and satiety with the impacts of protein, amino acids, and savory tastes will be discussed.