Effect of umami taste stimulations on vagal efferent activity in the rat

Effects of umami taste stimulation with monosodium glutamate (MSG) on the efferent discharges in the pancreatic, gastric and hepatic branch of the vagus nerve were observed in the anesthetized rat, in comparison with those of sweet and salty taste stimulation. Umami taste stimulation with 2.8% MSG solution caused an enhancement of vagal activities in pancreatic, gastric and hepatic branches. Sweet taste stimulation with 5% glucose or 10% sucrose increased efferent activity of hepatic and pancreatic branches and inhibited in gastric branch of the vagus nerve. Salty taste stimulation with 5% NaCl resulted in an increase in vagal gastric nerve activity and a decrease in that of vagal pancreatic and hepatic nerve; however, weak salty taste stimulation with 0.9% NaCl solution caused no remarkable change in efferent activity. It was assumed that umami taste stimulation, strong salty taste stimulation and sweet taste stimulation revealed different patterns of vagal responses which play some role on different anticipatory changes in hepatic, pancreatic and gastric functions following ingestion of food with different taste.