抄録
Postingestive consequences (nutrition, satiation, etc.), as well as oro-nasal sensory stimuli (taste, smell, and texture), are the key factors that determine preference and appetite for foods and fluids. Recent studies have demonstrated expression of taste receptors and their taste transduction elements in the gastrointestinal (GI) epithelium, suggesting an existence of chemical sensing systems both in the oral cavity and GI tract. Oral stimulation with monosodium L-glutamate (MSG), a representative umami-taste substance, elicits neuronal activation along with ascending gustatory pathways (dorsal "taste" and ventral "hedonic" pathways). For example, some neurons in the lateral hypothalamic area (LHA), a feeding center, respond to MSG during ingestion in rats. In addition to taste-related responses, we have demonstrated spatio-temporal activation of rat forebrain regions, including the cortex, hypothalamus, basal ganglia, and limbic system following intragastric delivery of taste substances (glucose, MSG, NaCl) by using functional magnetic resonance imaging (fMRI). Subdiaphragmatic total vagotomy (TVX) substantially eliminated brain activation induced by intragastric administration with MSG and NaCl. Consumption of MSG solution was greatly reduced by TVX. These results suggest that taste substances can activate higher brain centers via neural signaling pathway (gustatory and vagus nerves), which is involved in regulation of preference and appetite for foods and fluids. [J Physiol Sci. 2008;58 Suppl:S28]