New Therapeutic Strategy for Amino Acid Medicine: Effects of Dietary Glutamate on Gut and Brain Function

Abstract

Abstract. The gustatory and visceral stimulation from food regulates digestion and nutrient utilization, and free glutamate (Glu) release from food is responsible for the umami taste perception that increases food palatability. The results of recent studies reveal a variety of physiological roles for Glu. For example, luminal applications of Glu into the mouth, stomach, and intestine increase the afferent nerve activities of the glossopharyngeal nerve, the gastric branch of the vagus nerve, and the celiac branch of the vagus nerve, respectively. Additionally, luminal Glu evokes efferent nerve activation of each branch of the abdominal vagus nerve. The intragastric administration of Glu activates several brain areas (e.g., insular cortex, limbic system, and hypothalamus) and has been shown to induce flavor-preference learning in rats. Functional magnetic resonance imaging of rats has shown that the intragastric administration of Glu activates the nucleus tractus solitarius, amygdala, and lateral hypothalamus. In addition, Glu may increase flavor preference as a result of its postingestive effect. Considering these results, we propose that dietary Glu functions as a signal for the regulation of the gastrointestinal tract via the gut-brain axis and contributes to the maintenance of a healthy life.

The Neuro-endocrinological Role of Microbial Glutamate and GABA Signaling

“…The ECs of the gut mucosa are the predominant site for the synthesis and storage of 5-HT in humans (Gershon and Tack, 2007). The release of 5-HT occurs in response to chemical stimuli, e.g., the presence of nutrients (e.g., glutamate, glucose), or food-related/bacterial toxins in the intestinal lumen (Mayer, 2011; Kitamura et al, 2012). However, 5-HT produced by gut microbiota could possibly contribute to the overall 5-HT pool in the gut.…”

“…Multiple Glu receptor types (including ionotropic, types 1 and 4 metabotropic receptors and heterodimeric, TAS1R1 + TAS1R3, L -Glu taste receptors) have been detected in GI epithelial cells and/or enteric neurons in the stomach, small intestine and colon (Kondoh et al, 2009; San Gabriel et al, 2009; Kitamura et al, 2012). More in detail, mGlu 4 receptors have been detected in the mucosa of both the gastric antrum and duodenum (Akiba et al, 2009), while both mGlu 4 and mGlu 7 receptors have been identified in the colon epithelium (Chang et al, 2005; Julio-Pieper et al, 2010).…”

“…These data strongly suggest a role of ECs in the mediation of luminal Glu sensing. This luminal Glu sensing mechanism stimulates different areas in the CNS, including the cerebral cortex, basal ganglia, limbic system, and hypothalamus (for a comprehensive review, refer to Kondoh et al, 2009), and induces flavor preference in rats (Kitamura et al, 2012). …”

The redox interplay between nitrite and nitric oxide: From the gut to the brain

“…For instance, there is an operative amino acid sensing system within the gastric mucosa that recognizes dietary glutamate [89]. Albeit being the major excitatory neurotransmitter in the central nervous system, this amino acid also modulates important gut functions such as secretion, motility and metabolism [90] via mechanisms that include the generation of • NO and serotonin [91]. Given the high steady state concentrations of • NO achieved in the gastric lumen and mucosa upon nitrite reduction, glutamate-dependent pathways in the gastrointestinal tract are likely to be modulated by dietary nitrate.…”

Bioactive components and the effect of aqueous leaf extract of Maesobotrya barteri (Baill.) Hutch. (Euphorbiaceae) on haematological profile in paracetamol-induced Wistar rats

“…The World Health Organization (WHO) estimates that 4 billion people, 80% of the world population presently used herbal medicine for some aspects of primary health care. As nutraceuticals or functional foods, plants possess some health promoting and or disease preventing property beyond the basic nutritional function of supplying nutrients (Kitamura et al, 2012). Studies have shown that consumption of many different wild plants as food provides nutritional benefits (Cook et al, 2000.…”