Abstract
It has been revealed that the brain mechanisms related to cognition of and adaptation to L-lysine (Lys) deficiency in rats involve the lateral hypothalamic area (LHA) and related nuclei controlling appetite and food preference, and that intake of particular nutrients shows plasticity in response to Lys in the diet. Similar plastic changes occur in the nucleus solitalis in response to gustatory and visceral information. This plasticity is induced by activin A activity in the brain. In addition, highly plastic changes in the LHA associated with auditory, olfactory and gustatory triggers are also observed. It has been demonstrated quantitatively that rats with Lys deficiency show a tendency to ingest Lys from among a variety of amino acids in solution, and display a preference for monosodium L-glutamate (MSG) solution while reducing their intake of sodium chloride, indicating normalization of protein nutrition status. With regard to other nutritional roles of free L-glutamate, it has been clarified that the vagal afferent fibers in the gastric branch respond specifically to glutamate alone, contributing to cognition of food intake and subsequent control of digestion, absorption and metabolism for efficient nutrient utilization in the body. Furthermore, this glutamate signaling from the stomach to the brain stimulates learning and memory function, as well as diet-induced thermogenesis, preventing the development of obesity.
