Conditioned flavor preference learning by intragastric administration of l-glutamate in rats

Uematsu, Akira; Tsurugizawa, Tomokazu; Kondoh, Takashi; Torii, Kunio

doi:10.1016/j.neulet.2008.12.054

Cited by 48 publications

(53 citation statements)

References 21 publications

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“…Behavioral studies have also shown that ingested Glu, glucose, and corn oil emulsions have positive postingestive effects on the flavor preferences in rats (3,38,39). In rodents and humans, the preference for the flavor of an ingested solution can be increased by repeatedly pairing the solution with ingestion or the intragastric administration of a nutrient solution.…”

Section: Brain Activation By Gut Nutrient Stimulationmentioning

confidence: 99%

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

et al. 2012

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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.

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Section: Brain Activation By Gut Nutrient Stimulationmentioning

confidence: 99%

“…Moreover, Glu acts as a reinforcer after ingestion via vagal afferent activation in the GI tract. For example, we recently observed that an intragastric administration of Glu induced conditioned flavor preference in rats (3,4).…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2012

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“…Behavioral studies have shown that ingested L-glutamate, glucose, and corn oil emulsion have positive postingestive effects with regard to CFP in rats. 5,7,9) Based on the results of functional brain imaging and CFP studies, the brain regions commonly activated in response to the intragastric infusion of positive postingestive nutrients include the anterior cingulate cortex, insular cortex, amygdala, caudate-putamen, hippocampus, and the lateral hypothalamus. 11,12) Thus, these regions should be related to CFP.…”

Section: Functional Imaging Of the Postingestive Neural Response To Nmentioning

confidence: 99%

“…3) On the other hand, L-glutamate, a representative amino acid, induces preferable impression after ingestion via afferent vagal activation in the gut. Recently, we observed that an intragastric load of L-glutamate induced conditioned flavor preference in rats, 4,5) which did not include the activation of the dopaminergic pathway. 6) This finding is unlike those observed for glucose, sucrose, and lipids, as carbohydrate and lipid intake induce dopamine secretion in the nucleus accumbens.…”

Section: Introductionmentioning

confidence: 98%

Physiological Roles of Glutamate Signaling in Gut and Brain Function

Tsurugizawa

Torii

2010

Biological & Pharmaceutical Bulletin

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Some ingested nutrients have postingestive effects that modulate food intake and improve mood subconsciously. Here, we provide an overview of the positive postingestive effects of such nutrients, primarily L-glutamate, sugar, and lipids, with respect to behavior and brain function. We also discuss the mechanisms of brain activation resulting from signaling through the gut-brain axis. Recent studies have shown that rats prefer solutions paired with intragastric nutrients that have positive postingestive effects. Using functional magnetic resonance imaging (fMRI), we previously evaluated neural activation in response to ingested glucose, L-glutamate, and corn oil emulsion in rats and found that distinct forebrain regions were activated by these nutrients. Most of the areas activated by intragastric administration of L-glutamate were eliminated by abdominal vagotomy. On the other hand, the areas activated by intragastric administration of glucose were not affected by vagotomy. A behavioral study showed similar results for L-glutamate and glucose. These results indicate that brain activation in response to ingested nutrients occurs through distinct internal signals from the gut to the brain. Distinct regional and temporal activation in the brain determines the variety of postingestive behaviors and physiological responses.

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“…However, the influence of postingestive effects produced by umami substances on this paradigm have not been addressed. In a recent report (53), rats implanted with chronic intragastric cannulae were trained (conditioned) to drink either an orange or grape-flavored solution (conditioned stimulus; CS+) paired with intragastric infusions of a test solution (MSG, NaCl, or glucose at 60 mM) or a second flavored solution (CS-) paired with intragastric infusion of water. After this conditioning phase, the MSG group showed significantly higher intake and preference for the CS+ over the CS-solution during two-bottle preference tests.…”

Section: Luminal Glutamate and Positive Reinforcementmentioning

confidence: 99%

Physiological Significance of Glutamate Signaling in Gut-Brain Communication

Kondoh

Mallick

Torii

2009

Bioscience Microflora

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L-Glutamate is involved in the perception of umami taste, intermediary metabolism, and excitatory neurotransmission. In addition, recent studies have uncovered a variety of physiological roles for dietary glutamate, as evidenced by the fact that intragastric glutamate infusions induce flavor preference learning in rats. Moreover, glutamate increases digestive juice secretion and gastric emptying of protein-rich meals. Glutamate levels in blood and brain remain stable all day long even after the food intake since most of glutamate absorbed is oxidized in the mucosa of the small intestine as a primary energy source. Chronic ad libitum ingestion of glutamate solution contributes to reducing weight gain, fat deposition, and plasma leptin levels in comparison to ingestion of water. Glutamate receptors and their cellular transduction molecules have recently been identified in gut epithelial cells. Stimulation of gut glutamate receptors enhances the apical expression of glutamate transporters and also triggers the release of nitric oxide. Nitric oxide in its turn induces gut serotonin release, which increases vagal afferent inputs to different brain regions. Notably, three brain areas, i.e., the medial preoptic area, the dorsomedial nucleus of the hypothalamus, and the habenular nucleus are activated by intragastric glutamate infusions. Total subdiaphragmatic vagotomy abolishes this response. Consistent with the above, vagotomy specifically reduces the overall intake of glutamate. Taken together, these findings contribute to the growing body of evidence indicating that glutamate signaling via dedicated taste and gut receptors influences multiple physiological functions including gut secretion, motility, digestion, absorption, metabolism and energy homeostasis.

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Conditioned flavor preference learning by intragastric administration of l-glutamate in rats

Cited by 48 publications

References 21 publications

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

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

Physiological Roles of Glutamate Signaling in Gut and Brain Function

Physiological Significance of Glutamate Signaling in Gut-Brain Communication

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