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Effects of intragastric infusion of inosine monophosphate and L: -glutamate on vagal gastric afferent activity and subsequent autonomic reflexes.

Kitamura A, Sato W, Uneyama H, Torii K, Niijima A - J Physiol Sci (2010)

Bottom Line: To test the three selected taste groups, rats were infused with inosine monophosphate (IMP) and L: -glutamate (GLU) for umami, with glucose and sucrose for sweet, and with sodium chloride (NaCl) for salty.Infusions of glucose, sucrose and NaCl solutions, conversely, had no significant effects on VGA activity.These results suggest that umami substances in the stomach send information through the VGA to the brain and play a role in the reflex regulation of visceral functions.

View Article: PubMed Central - PubMed

Affiliation: Physiology and Nutrition Group, Institute of Life Sciences, Ajinomoto Co., Inc., 1-1 Suzuki-cho, Kawasaki-ku, Kawasaki, 210-8681, Japan.

ABSTRACT
In this study we investigated the effects of intragastric infusion of palatable basic taste substances (umami, sweet, and salty) on the activity of the vagal gastric afferent nerve (VGA), the vagal celiac efferent nerve (VCE), and the splanchnic adrenal efferent nerve (SAE) in anesthetized rats. To test the three selected taste groups, rats were infused with inosine monophosphate (IMP) and L: -glutamate (GLU) for umami, with glucose and sucrose for sweet, and with sodium chloride (NaCl) for salty. Infusions of IMP and GLU solutions significantly increased VGA activity and induced the autonomic reflex, which activated VCE and SAE; these reflexes were abolished after sectioning of the VGA. Infusions of glucose, sucrose and NaCl solutions, conversely, had no significant effects on VGA activity. These results suggest that umami substances in the stomach send information through the VGA to the brain and play a role in the reflex regulation of visceral functions.

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Effects of intragastric infusion of IMP on the afferent discharge rate of a vagal gastric nerve (VGA) filament. a Example of intragastric infusion of 30 mM IMP on VGA activity. Actual wave recording at each point was displayed before (left) and after 30 min of (right) intragastric infusion of IMP (Top). Representative recording of gastric afferent discharge displayed as a sequential rate histogram after intragastric infusion of IMP (Bottom). Arrowheads indicate the points at which the IMP solution was infused. The vertical bar indicates 100 impulses/5 s. The horizontal bar indicates 30 min. b The time course of changes in VGA activity from 5 different rats in which 30 mM IMP was administrated. *p < 0.05, **p < 0.01, one-way repeated ANOVA with the post-hoc Dunnett’s method. Vertical bars indicate ±SEM. c Dose-dependent effects of luminal IMP on the afferent discharge rate of VGA activity. Each IMP solution (1, 3, 10, and 30 mM) was introduced into the rat stomach, and the mean change in discharge rate above baseline at 30 min was plotted. Columns and vertical bars represent mean ± SEM from 5 different rats
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Fig1: Effects of intragastric infusion of IMP on the afferent discharge rate of a vagal gastric nerve (VGA) filament. a Example of intragastric infusion of 30 mM IMP on VGA activity. Actual wave recording at each point was displayed before (left) and after 30 min of (right) intragastric infusion of IMP (Top). Representative recording of gastric afferent discharge displayed as a sequential rate histogram after intragastric infusion of IMP (Bottom). Arrowheads indicate the points at which the IMP solution was infused. The vertical bar indicates 100 impulses/5 s. The horizontal bar indicates 30 min. b The time course of changes in VGA activity from 5 different rats in which 30 mM IMP was administrated. *p < 0.05, **p < 0.01, one-way repeated ANOVA with the post-hoc Dunnett’s method. Vertical bars indicate ±SEM. c Dose-dependent effects of luminal IMP on the afferent discharge rate of VGA activity. Each IMP solution (1, 3, 10, and 30 mM) was introduced into the rat stomach, and the mean change in discharge rate above baseline at 30 min was plotted. Columns and vertical bars represent mean ± SEM from 5 different rats

Mentions: To examine the effects of IMP on VGA activity, we used intragastric infusions of the IMP solution and recorded VGA activity. After infusion with the 30 mM IMP solution, a long-lasting increase in afferent activity was observed (Fig. 1a). The time course response to IMP on VGA activity is summarized in Fig. 1b. The discharge rate before and 10, 20, and 30 min after infusion was 64.5 ± 1.3, 77.5 ± 2.6*, 76.8 ± 4.5*, and 86.5 ± 3.9** impulses/5 s, respectively (n = 5, *p < 0.05, **p < 0.01 compared with the value of the pre-IMP infusion, one-way repeated ANOVA with post-hoc Dunnett’s method). These data show that the effect of 30 mM IMP on VGA activity is highest 30 min after intragastric infusion. Thus, we determined that nerve activity was evaluated 30 min after administration of the taste substances. The concentration-dependent response to IMP on VGA activity is summarized in Fig. 1c. The change in discharge rate for the 1, 3, 10, and 30 mM IMP infusions was 0.0 ± 2.7, 14.3 ± 3.4*, 18.0 ± 5.3*, and 22.0 ± 3.8** impulses/5 s, respectively (n = 5, *p < 0.05, **p < 0.01 compared with the value of the pre-IMP infusion, paired t test). This shows that afferent discharge rates above baseline were dose-dependently increased 30 min after each dose of the IMP application (3, 10, and 30 mM); however, intragastric infusion of 1 mM IMP had no significant effect on the discharge rates. Therefore, the threshold concentration for IMP had to be below 3 mM.Fig. 1


Effects of intragastric infusion of inosine monophosphate and L: -glutamate on vagal gastric afferent activity and subsequent autonomic reflexes.

Kitamura A, Sato W, Uneyama H, Torii K, Niijima A - J Physiol Sci (2010)

Effects of intragastric infusion of IMP on the afferent discharge rate of a vagal gastric nerve (VGA) filament. a Example of intragastric infusion of 30 mM IMP on VGA activity. Actual wave recording at each point was displayed before (left) and after 30 min of (right) intragastric infusion of IMP (Top). Representative recording of gastric afferent discharge displayed as a sequential rate histogram after intragastric infusion of IMP (Bottom). Arrowheads indicate the points at which the IMP solution was infused. The vertical bar indicates 100 impulses/5 s. The horizontal bar indicates 30 min. b The time course of changes in VGA activity from 5 different rats in which 30 mM IMP was administrated. *p < 0.05, **p < 0.01, one-way repeated ANOVA with the post-hoc Dunnett’s method. Vertical bars indicate ±SEM. c Dose-dependent effects of luminal IMP on the afferent discharge rate of VGA activity. Each IMP solution (1, 3, 10, and 30 mM) was introduced into the rat stomach, and the mean change in discharge rate above baseline at 30 min was plotted. Columns and vertical bars represent mean ± SEM from 5 different rats
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Related In: Results  -  Collection

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Fig1: Effects of intragastric infusion of IMP on the afferent discharge rate of a vagal gastric nerve (VGA) filament. a Example of intragastric infusion of 30 mM IMP on VGA activity. Actual wave recording at each point was displayed before (left) and after 30 min of (right) intragastric infusion of IMP (Top). Representative recording of gastric afferent discharge displayed as a sequential rate histogram after intragastric infusion of IMP (Bottom). Arrowheads indicate the points at which the IMP solution was infused. The vertical bar indicates 100 impulses/5 s. The horizontal bar indicates 30 min. b The time course of changes in VGA activity from 5 different rats in which 30 mM IMP was administrated. *p < 0.05, **p < 0.01, one-way repeated ANOVA with the post-hoc Dunnett’s method. Vertical bars indicate ±SEM. c Dose-dependent effects of luminal IMP on the afferent discharge rate of VGA activity. Each IMP solution (1, 3, 10, and 30 mM) was introduced into the rat stomach, and the mean change in discharge rate above baseline at 30 min was plotted. Columns and vertical bars represent mean ± SEM from 5 different rats
Mentions: To examine the effects of IMP on VGA activity, we used intragastric infusions of the IMP solution and recorded VGA activity. After infusion with the 30 mM IMP solution, a long-lasting increase in afferent activity was observed (Fig. 1a). The time course response to IMP on VGA activity is summarized in Fig. 1b. The discharge rate before and 10, 20, and 30 min after infusion was 64.5 ± 1.3, 77.5 ± 2.6*, 76.8 ± 4.5*, and 86.5 ± 3.9** impulses/5 s, respectively (n = 5, *p < 0.05, **p < 0.01 compared with the value of the pre-IMP infusion, one-way repeated ANOVA with post-hoc Dunnett’s method). These data show that the effect of 30 mM IMP on VGA activity is highest 30 min after intragastric infusion. Thus, we determined that nerve activity was evaluated 30 min after administration of the taste substances. The concentration-dependent response to IMP on VGA activity is summarized in Fig. 1c. The change in discharge rate for the 1, 3, 10, and 30 mM IMP infusions was 0.0 ± 2.7, 14.3 ± 3.4*, 18.0 ± 5.3*, and 22.0 ± 3.8** impulses/5 s, respectively (n = 5, *p < 0.05, **p < 0.01 compared with the value of the pre-IMP infusion, paired t test). This shows that afferent discharge rates above baseline were dose-dependently increased 30 min after each dose of the IMP application (3, 10, and 30 mM); however, intragastric infusion of 1 mM IMP had no significant effect on the discharge rates. Therefore, the threshold concentration for IMP had to be below 3 mM.Fig. 1

Bottom Line: To test the three selected taste groups, rats were infused with inosine monophosphate (IMP) and L: -glutamate (GLU) for umami, with glucose and sucrose for sweet, and with sodium chloride (NaCl) for salty.Infusions of glucose, sucrose and NaCl solutions, conversely, had no significant effects on VGA activity.These results suggest that umami substances in the stomach send information through the VGA to the brain and play a role in the reflex regulation of visceral functions.

View Article: PubMed Central - PubMed

Affiliation: Physiology and Nutrition Group, Institute of Life Sciences, Ajinomoto Co., Inc., 1-1 Suzuki-cho, Kawasaki-ku, Kawasaki, 210-8681, Japan.

ABSTRACT
In this study we investigated the effects of intragastric infusion of palatable basic taste substances (umami, sweet, and salty) on the activity of the vagal gastric afferent nerve (VGA), the vagal celiac efferent nerve (VCE), and the splanchnic adrenal efferent nerve (SAE) in anesthetized rats. To test the three selected taste groups, rats were infused with inosine monophosphate (IMP) and L: -glutamate (GLU) for umami, with glucose and sucrose for sweet, and with sodium chloride (NaCl) for salty. Infusions of IMP and GLU solutions significantly increased VGA activity and induced the autonomic reflex, which activated VCE and SAE; these reflexes were abolished after sectioning of the VGA. Infusions of glucose, sucrose and NaCl solutions, conversely, had no significant effects on VGA activity. These results suggest that umami substances in the stomach send information through the VGA to the brain and play a role in the reflex regulation of visceral functions.

Show MeSH
Related in: MedlinePlus