Monopotassium Glutamate Research Articles

Gustatory modulation of the responses of trigeminal subnucleus caudalis neurons to noxious stimulation of the tongue in rats

Certain tastants inhibit oral irritation by capsaicin, whereas anesthesia of the chorda tympani (CT) enhances oral capsaicin burn. We tested the hypothesis that tastants activate the CT to suppress responses of trigeminal subnucleus caudalis (Vc) neurons to noxious oral stimuli. In anesthetized rats, we recorded Vc unit responses to noxious electrical, chemical (pentanoic acid, 200μm) and thermal (55°C) stimulation of the tongue. Electrically evoked responses were significantly reduced by a tastant mix and individually applied NaCl, monosodium glutamate (MSG), and monopotassium glutamate. Sucrose, citric acid, quinine and water (control) had no effect. Pentanoic acid-evoked responses were similarly attenuated by NaCl and MSG, but not by other tastants. Responses to noxious heat were not affected by any tastant. Transection and/or anesthesia of the CT bilaterally affected neither Vc neuronal responses to electrical or pentanoic acid stimulation, nor the depressant effect of NaCl and MSG on electrically evoked responses. Calcium imaging showed that neither NaCl nor MSG directly excited any trigeminal ganglion cells or affected their responses to pentanoic acid. GABA also had no effect, arguing against peripheral effects of GABA, NaCl or MSG on lingual nocicepive nerve endings. The data also rule out a central mechanism, as the effects of NaCl and MSG were intact following CT transection. We speculate that the effect is mediated peripherally by the release from taste receptor cells (type III) of some mediator(s) other than GABA to indirectly inhibit trigeminal nociceptors. The results also indicate that the CT does not exert a tonic inhibitory effect on nociceptive Vc neurons.

Speed and accuracy of taste identification and palatability: impact of learning, reward expectancy, and consummatory licking

Despite decades of study, it remains a matter of controversy as to whether in rats taste identification is a rapid process that occurs in about 250-600 ms (one to three licks) or a slow process that evolves over seconds. To address this issue, we trained rats to perform a taste-cued two-response discrimination task (2-RDT). It was found that, after learning, regardless of intensity, the delivery of 10 μl of a tastant (e.g., NaCl or monopotassium glutamate, MPG) was sufficient to identify its taste with maximal accuracy within 400 ms. However, despite overtraining, rats rarely stopped licking in one lick. Thus, a one-drop lick reaction task was developed in which subjects had to rapidly stop licking after release of a stop signal (tastants including water) to obtain rewards. The faster they stopped licking, the greater the reward. Rats did not stop licking after receiving either hedonically positive or negative stop signals, and thus failed to maximize rewards even when reinforced with even larger rewards. In fact, the higher the sucrose concentration given as a stop signal, the greater the number of consummatory licks elicited. However, with a stop signal of 2 mM quinine HCl, they stopped licking in ~370 ms, a time faster than that for sucrose or water, thus showing that in this rapid period, quinine HCl evoked an unpalatable response. Indeed, only when rats licked an empty sipper tube would they usually elicit a single lick to obtain a reward (operant licking). In summary, these data indicate that within 400 ms, taste identification and palatability, must either occur simultaneously or with marked overlap.

Evaluation of genotoxic effects of five flavour enhancers (glutamates) on the root meristem cells of Allium cepa

The effects of different treatments with flavour enhancers monosodium glutamate, monopotassium glutamate, calcium diglutamate, monoammonium glutamate, and magnesium diglutamate on the cytology, DNA content, and interphase nuclear volume (INV) of A. cepa were investigated. Three concentrations of these additives - 20, 40, and 60ppm - were applied for 6, 12, and 24h. All the concentrations of these chemicals showed an inhibitory effect on cell division in root tips of A. cepa and caused a decrease in mitotic index values. Additionally, all the treatments changed the frequency of mitotic phases when compared with the control groups. These compounds increased chromosome abnormalities, among them are micronuclei, c-mitosis, anaphase bridges, stickiness, binucleus, laggards, and breaks. The nuclear DNA content and INV decreased when compared with control groups.

Sweet-bitter and umami-bitter taste interactions in single parabrachial neurons in C57BL/6J mice

We investigated sweet-bitter and umami-bitter mixture taste interactions by presenting sucrose or umami stimuli mixed with quinine hydrochloride (QHCl) while recording single-unit activity of neurons in the parabrachial nucleus (PbN) of urethane-anesthetized C57BL/6J mice. A total of 70 taste-responsive neurons were classified according to which stimulus evoked the greatest net response (36 sucrose-best, 19 NaCl-best, 6 citric acid-best, and 9 QHCl-best). Although no neurons responded best to monopotassium glutamate (MPG) or inosine 5'-monophosphate (IMP), the combination of these two stimuli evoked a synergistic response (i.e., response > 120% of the sum of the component responses) in all sucrose-best and some NaCl-best neurons (n = 43). Adding QHCl to sucrose or MPG + IMP resulted in suppression of the response (responses to mixture < responses to the more effective component) in 41 of 43 synergistic neurons. Neurons showing QHCl suppression were classified into two types: an "MS1" type (n = 27) with suppressed responses both to sucrose and MPG + IMP and an "MS2" type (n = 14) that showed suppressed responses only to sucrose. No neuron displayed suppressed responses to MPG or IMP alone. The suppression ratio (1 - mixture response/sucrose or MPG + IMP response) of sucrose and MPG + IMP in MS1 neurons had a weak positive correlation (r = 0.36). The pattern of reconstructed recording sites of neuron types suggested chemotopic organization in the PbN. Although a peripheral basis for QHCl suppression has been demonstrated, our results suggest that convergence in the PbN plays a role in shaping responses to taste mixtures.

Umami taste in mice uses multiple receptors and transduction pathways

The distinctive umami taste elicited by l-glutamate and some other amino acids is thought to be initiated by G-protein-coupled receptors. Proposed umami receptors include heteromers of taste receptor type 1, members 1 and 3 (T1R1+T1R3), and metabotropic glutamate receptors 1 and 4 (mGluR1 and mGluR4). Multiple lines of evidence support the involvement of T1R1+T1R3 in umami responses of mice. Although several studies suggest the involvement of receptors other than T1R1+T1R3 in umami, the identity of those receptors remains unclear. Here, we examined taste responsiveness of umami-sensitive chorda tympani nerve fibres from wild-type mice and mice genetically lacking T1R3 or its downstream transduction molecule, the ion channel TRPM5. Our results indicate that single umami-sensitive fibres in wild-type mice fall into two major groups: sucrose-best (S-type) and monopotassium glutamate (MPG)-best (M-type). Each fibre type has two subtypes; one shows synergism between MPG and inosine monophosphate (S1, M1) and the other shows no synergism (S2, M2). In both T1R3 and TRPM5 null mice, S1-type fibres were absent, whereas S2-, M1- and M2-types remained. Lingual application of mGluR antagonists selectively suppressed MPG responses of M1- and M2-type fibres. These data suggest the existence of multiple receptors and transduction pathways for umami responses in mice. Information initiated from T1R3-containing receptors may be mediated by a transduction pathway including TRPM5 and conveyed by sweet-best fibres, whereas umami information from mGluRs may be mediated by TRPM5-independent pathway(s) and conveyed by glutamate-best fibres.

Gustatory neural responses to umami stimuli in the parabrachial nucleus of C57BL/6J mice

Umami is considered to be the fifth basic taste quality and is elicited by glutamate. The mouse is an ideal rodent model for the study of this taste quality because of evidence that suggests that this species, like humans, may sense umami-tasting compounds as unique from other basic taste qualities. We performed single-unit recording of taste responses in the parabrachial nucleus (PbN) of anesthetized C57BL/6J mice to investigate the central representation of umami taste. A total of 52 taste-responsive neurons (22 sucrose-best, 19 NaCl-best, 5 citric acid-best, and 6 quinine-best) were recorded from stimulation period with a large panel of basic and umami-tasting stimuli. No neuron responded best to monopotassium glutamate (MPG) or inosine 5'-monophosphate (IMP), suggesting convergence of input in the central nervous system. Synergism induced by an MPG-IMP mixture was observed in all sucrose-best and some NaCl-best neurons that possessed strong sensitivity to sucrose. In more than half of sucrose-best neurons, the MPG-IMP mixture evoked stronger responses than those elicited by their best stimulus. Furthermore, hierarchical cluster analysis and multidimensional analysis indicated close similarity between sucrose and the MPG-IMP mixture. These results strongly suggest the mixture tastes sweet to mice, a conclusion consistent with previous findings that show bidirectional generalization of conditioned taste aversion between sucrose and umami mixtures, and suppression of taste responses to both sucrose and mixtures by the antisweet polypeptide gurmarin in the chorda tympani nerve. The distribution pattern of reconstructed recording sites of specific neuron types suggested chemotopic organization in the PbN.

Taste Preference and Nerve Response to 5'-Inosine Monophosphate Are Enhanced by Glutathione in Mice

Previous human sensory evaluation studies have shown that glutathione (GSH) enhances deliciousness, accompanied by thickness, mouthfulness, and continuity feeling, which is known as "kokumi" in Japanese, in an umami solution containing monosodium glutamate and 5'-inosine monophosphate (IMP). We conducted behavioral and electrophysiological experiments to explore possible interactions of taste effectiveness between GSH and umami substances in mice. The 2-bottle preference test revealed that the mice preferred GSH at concentrations ranging from 1 to 10 mM. When GSH was added to IMP or a mixture of IMP and monopotassium glutamate (MPG), the mice showed increased preference for these solutions over the individual IMP or the binary mixture of IMP and MPG in both short-term and long-term tests. The addition of GSH to MPG, however, did not increase preference. Neural responses of the chorda tympani and glossopharyngeal nerves to the mixture of IMP and GSH showed synergism, whereas synergism was not observed in the mixture of MPG and GSH in either taste nerve. Another behavioral study with the use of the conditioned taste aversion paradigm showed that aversions to MPG generalized moderately to GSH, but aversions to GSH did not generalize to MPG. The present study suggests that GSH enhances preference for umami solutions containing 5'-ribonucleotide rather than glutamate. On the basis of these results, we discuss possible receptors involved for the action of GSH.

Perceptual variation in umami taste and polymorphisms in TAS1R taste receptor genes

BackgroundThe TAS1R1 and TAS1R3 G protein–coupled receptors are believed to function in combination as a heteromeric glutamate taste receptor in humans. ObjectiveWe hypothesized that variations in the umami perception of glutamate would correlate with variations in the sequence of these 2 genes, if they contribute directly to umami taste. DesignIn this study, we first characterized the general sensitivity to glutamate in a sample population of 242 subjects. We performed these experiments by sequencing the coding regions of the genomic TAS1R1 and TAS1R3 genes in a separate set of 87 individuals who were tested repeatedly with monopotassium glutamate (MPG) solutions. Last, we tested the role of the candidate umami taste receptor hTAS1R1-hTAS1R3 in a functional expression assay. ResultsA subset of subjects displays extremes of sensitivity, and a battery of different psychophysical tests validated this observation. Statistical analysis showed that the rare T allele of single nucleotide polymorphism (SNP) R757C in TAS1R3 led to a doubling of umami ratings of 25 mmol MPG/L. Other suggestive SNPs of TAS1R3 include the A allele of A5T and the A allele of R247H, which both resulted in an approximate doubling of umami ratings of 200 mmol MPG/L. We confirmed the potential role of the human TAS1R1-TAS1R3 heteromer receptor in umami taste by recording responses, specifically to l-glutamate and inosine 5′-monophosphate (IMP) mixtures in a heterologous expression assay in HEK (human embryonic kidney) T cells. ConclusionsThere is a reliable and valid variation in human umami taste of l-glutamate. Variations in perception of umami taste correlated with variations in the human TAS1R3 gene. The putative human taste receptor TAS1R1-TAS1R3 responds specifically to l-glutamate mixed with the ribonucleotide IMP. Thus, this receptor likely contributes to human umami taste perception.

Response properties of the pharyngeal branch of the glossopharyngeal nerve for umami taste in mice and rats

Many studies have reported the mechanism underlying umami taste. However, there are no investigations of responses to umami stimuli taste originating from chemoreceptors in the pharyngeal region. The pharyngeal branch of the glossopharyngeal nerve (GPN-ph) innervating the pharynx has unique responses to taste stimulation that differs from responses of the chorda tympani nerve and lingual branch of the glossopharyngeal nerve. Water evokes robust response, but NaCl solutions at physiological concentrations do not elicit responses. The present study was designed to examine umami taste (chemosensory) responses in the GPN-ph. Response characteristics to umami taste were compared between mice and rats. In mice, stimulation with compounds eliciting umami taste (0.1 M monosodium l-glutamate (MSG), 0.01 M inosine monophosphate (IMP) and the mixture of 0.1 M MSG + 0.01 M IMP) evoked higher responses than application of distilled water (DW). However, synergistic response of a mixture of 0.1 M MSG + 0.01 M IMP was not observed. In rats, there is no significant difference between the responses to umami taste (0.1 M MSG, 0.01 M IMP and the mixture of 0.1 M MSG + 0.01 M IMP) and DW. Monopotassium glutamate (MPG) was used in rats to examine the contribution of the sodium component of MSG on the response. Stimulation with 0.1 M MPG evoked a higher response when compared with responses to DW. The present results suggest that umami taste compounds are effective stimuli of the chemoreceptors in the pharynx of both mice and rats.

Glutamate Neurotoxicity in Culture Depends on the Presence of Glutamine: Implications for the Role of Glial Cells in Normal and Pathological Brain Development

Glutamate toxicity was studied in neuronal (SC9), glial (WC5), and neuroblastoma-glioma hybrid cell lines. In all three cell types, glutamate had a dual effect, depending on the concentration of glutamine in the culture medium. An expected dose-dependent cytotoxicity of the amino acid was observed when cells were cultured in medium containing the standard glutamine concentration (1-4 mM), but when the culture's glutamine content was decreased to 0.15-0.5 mM, glutamate had an apparent opposite, growth-promoting effect. The specificity of glutamate effect was indicated by the following: (a) it was stereospecific, with the L and not the D isomer being active; (b) monosodium aspartate was inactive in the presence of either high or low glutamine; and (c) monosodium glutamate and monopotassium glutamate had a similar dual effect. Furthermore, the glutamate receptor antagonist gamma-glutamylglycine blocked the amino acid cytotoxicity in a dose-dependent fashion. As glial cells are a major source of glutamine in the brain, neuronal-glial co-cultures were used to analyze the possible role of glial cells in glutamate neurotoxicity. It was found that SC9 cells were more sensitive to glutamate when co-cultured with WC5 cells. Continuous depolarization of the SC9 cells with KCl decreased cell number, but glutamate had no additive neurotoxic effect when added with KCl. We suggest that glutamine, glial cells, and neuronal activation play roles in modulating glutamate neurotoxicity, in developing as well as aged brains. It is tempting to speculate also that alterations in the glutamate/glutamine ratio under pathological conditions may take part in the etiology of some neurodegenerative diseases.

Taste effectiveness of glutamate compounds with different cations in rat.

A role of a cation of glutamate compounds for their taste has not been well elucidated yet. In this experiment, the difference of taste quality of glutamate compounds which have a different cation was compared to reveal the role of cations in the glutamate compounds on their characteristics of taste. Monosodium L-glutamate (MSG), monopotassium glutamate (MPG) and monocalcium glutamate (MCG) were used. The preference test in rats revealed that the rate of drinking volume per day was not statistically different among MSG, MPG and MCG. In the next experiment, the conditioned taste aversion test was performed in rats, and rats were conditioned to hate to drink MSG, MPG and MCG respectively by pairing the intraperitoneal injection of LiCl. In the MSG conditioned animals, the drinking rate of MSG decreased, and that of MPG significantly increased, but that of MCG did not change. In the MPG conditioned animals, drinking rate of MPG was strongly depressed, but that of MCG tended to increase, and that of MSG did not change at all. In the MCG conditioned animals, the drinking rate of MCG decreased, but MSG and MPG did not change. The chorda tympani responses to 0.1 M MSG applied to the tongue surface was larger than those to 0.1 M MCG, and the responses to 0.1 M MPG were the smallest out of these three glutamate compounds. The nerve responses of the glossopharyngeal nerve to MSG, MCG and MPG were very similar to each other.(ABSTRACT TRUNCATED AT 250 WORDS)

Water Binding Capacity of 22 L‐Amino Acids from Water Activity 0.33 to 0.95

ABSTRACTThe water sorption isotherms of 22 L‐amino acids were determined from a water activity of 0.331–0.946. In addition, water sorption isotherms of monosodium glutamate, monopotassium glutamate, monosodium aspartate, monopotassium aspartate, and hemimagnesium aspartate were determined over the same aw ranges. Proline and γ‐aminobutyric acid had a greater capacity to bind water than the other free amino acids examined. The water binding capacity of glutamate and aspartate as the monosodium, monopotassium or the hemimagnesium salts was greatly enhanced. These data may be useful in screening amino acids as potential humectants and in understanding the mechanism by which bacteria cope with reduced

Amino Acid Composition and Flavor of Fresh Market Tomatoes as Influenced by Fruit Ripeness When Harvested1

Abstract Four amino acids (glutamic, γ-aminobutyric, glutamine, and aspartic) make up about 80% of the total free amino acids in fruits of tomato (Lycopersicon esculentum Mill., cv. Cal Ace). Fruits harvested at the table-ripe stage contained more alanine and less glutamic acid than those picked green or at the breaker (incipient red color) stage and ripened at 20°C to table-ripe. The higher glutamic acid concentrations in fruit picked at the breaker or earlier stages were paralled to higher scores for “off-flavor,” as described by a taste panel, relative to fruits picked table-ripe. However, when monopotassium glutamate (60, 120, or 180 mg/l00g) was added to diced table-ripe fruits, the panelists were not able to detect flavor differences due to increased glutamic acid concn. Differences in amino acid composition associated with fruit ripeness when picked do not appear to be directly related to flavor differences.