Monosodium Glutamate Solution Research Articles

The transgenerational study of insulin action in female offspring adult Wistar rats

Materials and methods Twelve newborn female Wistar rats were used, and half of them submitted to saline solution administration (control) and the other half were administrated monosodium glutamate solution, 4.0 mg/Kg body weight (obese) in neonatal period. At adult age (90 days of life) these female rats were mated with health male rats and the female offspring were used, divided into two groups: control (CONT, n=28) and obese (OB, n=15), according to its previous dam group. In all adult age (from 3rd to 7th months) the rats were monthly evaluate the Lee Index, water and food intake, 12h-fasting glycemia, oral glucose tolerance test (OGTT) and insulin test tolerance (ITT). In addition, from OGTT Results it was estimated the area under the glycemic curve (AUC). All data were statistically analyzed with 5% significance.

Effect of maternal obesity on insulin action in male adult offspring rats

Materials and methods twelve newborn female Wistar rats were used, and half of them submitted to saline solution administration (control) and the other half were administrated monosodium glutamate solution, 4.0 mg/Kg body weight (obese) in neonatal period. At adult age (90 days of life) these female rats were mated with health male rats and the male offspring were used, divided into two groups: control (CONT, n=29) and obese (OB, n=19), according to its previous dam group. In all adult age (from 3rd to 7th months) the rats were monthly evaluate the Lee Index, water and food intake, 12h-fasting glycemia, oral glucose tolerance test (OGTT) and insulin test tolerance (ITT). In addition, from OGTT Results it was estimated the area under the glycemic curve (AUC). All data were statistically analyzed with 5% significance.

Optimization of a sensory evaluation protocol for measuring the umami taste

Umami substances linger in mouth for a long time, making it difficult to achieve an accurate sensory measurement. The objective was to establish a reproducible protocol to accurately measure the intensity of umami taste. Two-alternative-forced choice (2-AFC), ranking, and rating methods were compared for discrimination ability of umami taste intensities of monosodium glutamate solutions. Monadic rating and rank-rating methods were compared for accuracy in measurement of umami intensities since neither 2-AFC nor ranking method generates numerical intensity values. Mouth rinsing protocol efficiencies were investigated for 7 palate cleansing methods during umami intensity evaluation. 2-AFC was the most powerful method, followed by ranking and rating methods, for discrimination of different umami samples. Monadic rating and rank-rating methods both showed similar error rates but monadic rating was slightly more accurate than rank-rating. Crackers, a toothbrush, and water at 45oC were more effective palate cleansers than carrots and water at 18oC.

Brain amino acid sensing.

The 20 different amino acids, in blood as well as in the brain, are strictly maintained at the same levels throughout the day, regardless of food intake. Gastric vagal afferents only respond to free glutamate and sugars, providing recognition of food intake and initiating digestion. Metabolic control of amino acid homeostasis and diet-induced thermogenesis is triggered by this glutamate signalling in the stomach through the gut-brain axis. Rats chronically fed high-sugar and high-fat diets do not develop obesity when a 1% (w/v) monosodium glutamate (MSG) solution is available in a choice paradigm. Deficiency of the essential amino acid lysine (Lys) induced a plasticity in rats in response to Lys. This result shows how the body is able to identify deficient nutrients to maintain homeostasis. This plastic effect is induced by activin A activity in the brain, particularly in certain neurons in the lateral hypothalamic area (LHA) which is the centre for amino acid homeostasis and appetite. These neurons respond to glutamate signalling in the oral cavity by which umami taste is perceived. They play a quantitative role in regulating ingestion of deficient nutrients, thereby leading to a healthier life. After recovery from malnutrition, rats prefer MSG solutions, which serve as biomarkers for protein nutrition.

Development of an umami taste sensitivity test and its clinical use.

There is a close relationship between perception of umami, which has become recognized as the fifth taste, and the human physical condition. We have developed a clinical test for umami taste sensitivity using a filter paper disc with a range of six monosodium glutamate (MSG) concentrations. We recruited 28 patients with taste disorders (45–78 years) and 184 controls with no taste disorders (102 young [18–25 years] and 82 older [65–89 years] participants). Filter paper discs (5 mm dia.) were soaked in aqueous MSG solutions (1, 5, 10, 50, 100 and 200 mM), then placed on three oral sites innervated by different taste nerves. The lowest concentration participants correctly identified was defined as the recognition threshold (RT) for MSG. This test showed good reproducibility for inter- and intra-observer variability. We concluded that: (1) The RT of healthy controls differed at measurement sites innervated by different taste nerves; that is, the RT of the anterior tongue was higher than that of either the posterior tongue or the soft palate in both young and older individuals. (2) No significant difference in RT was found between young adults and older individuals at any measurement site. (3) The RT of patients with taste disorders was higher before treatment than that of the healthy controls at any measurement site. (4) The RT after treatment in these patients improved to the same level as that of the healthy controls. (5) The cutoff values of RT, showing the highest diagnostic accuracy (true positives + true negatives), were 200 mM MSG for AT and 50 mM MSG for PT and SP. The diagnostic accuracy at these cutoff values was 0.92, 0.87 and 0.86 for AT, PT and SP, respectively. Consequently, this umami taste sensitivity test is useful for discriminating between normal and abnormal umami taste sensations.

Effects of food flavour enhancer (Monosodium Glutamate and Maggi Poulet) supplementation on glucose tolerance in <i>Sprague Dawley</i> rat

This study was designed to evaluate the effects of purified monosodium glutamate and ‘Maggi Poulet’, on body weight gain, lipid profile, hepatic lipid peroxidation and glucose tolerance in rats. Thirty five young male Sprague Dawley rats were divided into five groups and fed by oral route as follow: group I (distilled water), group II (monosodium glutamate solution), group III (‘Maggi Poulet’solution), group IV (monosodium glutamate solution. and high fat solution) and group V (‘Maggi Poulet’ solution and high fat solution). During the experimental period, fasting glycemia was taken and an oral glucose tolerance test has been performed at the end . Blood samples were then collected in all groups and serum cholesterol and triglyceride were assayed. Animals were killed after and abdominal adipose tissue, liver and heart were excised and weighed. Liver samples were also used to estimate hepatic malondialdehyde level in rats. The results proved that the dietary feeding did not affect the body gain and lipid profile in experimental groups. The hepatic lipid peroxidation has also increased in all experimental groups and at the same time, rats in group II, group IV and group V present a two-hour plasma glucose level signifantly higher. However, purified monosodium glutamate and ‘Maggi Poulet’ at the dose of 1500 mg/kg. b. wt. have not impaired fasting glycemia in Sprague Dawley rat. All changes observed in the glycemia of rats in experimental groups do not allow to qualify them to be glucose intolerant, nevertheless monosodium glutamate consumption in association or not with high fat is hepatotoxic and may contribute to the emergence of prediabetes in human being. © 2013 International Formulae Group. All rights reserved. Keywords : Malondialdehyde, lipid profile, glucose homeostasis, prediabetes.

Metabolic profile and genotoxicity in obese rats exposed to cigarette smoke

Experimental studies have shown that exposure to cigarette smoke has negative effects on lipid metabolism and oxidative stress status. Cigarette smoke exposure in nonpregnant and pregnant rats causes significant genotoxicity (DNA damage). However, no previous studies have directly evaluated the effects of obesity or the association between obesity and cigarette smoke exposure on genotoxicity. Therefore, the aim of the present investigation was to evaluate DNA damage levels, oxidative stress status and lipid profiles in obese Wistar rats exposed to cigarette smoke. Female rats subcutaneously (s.c.) received a monosodium glutamate solution or vehicle (control) during the neonatal period to induce obesity. The rats were randomly distributed into three experimental groups: control, obese exposed to filtered air, and obese exposed to tobacco cigarette smoke. After a 2-month exposure period, the rats were anesthetized and killed to obtain blood samples for genotoxicity, lipid profile, and oxidative stress status analyses. The obese rats exposed to tobacco cigarette smoke presented higher DNA damage, triglycerides, total cholesterol, free fatty acids, VLDL-c, HDL-c, and LDL-c levels compared to control and obese rats exposed to filtered air. Both obese groups showed reduced SOD activity. These results showed that cigarette smoke enhanced the effects of obesity. In conclusion, the association between obesity and cigarette smoke exposure exacerbated the genotoxicity, negatively impacted the biochemical profile and antioxidant defenses and caused early glucose intolerance. Thus, the changes caused by cigarette smoke exposure can trigger the earlier onset of metabolic disorders associated with obesity, such as diabetes and metabolic syndrome.

Long-Term Ingestion of Monosodium L-Glutamate Did Not Induce Obesity, Dyslipidemia or Insulin Resistance: A Two-Generation Study in Mice

The use of monosodium glutamate (MSG) as a flavor enhancer spans more than 100 y and there are many studies indicating the safety of general use of MSG. Recently, however, Collison et al. (2010) reported a two-generation study with a low dose of MSG that caused abdominal obesity, insulin resistance and dyslipidemia in mice. Due to public health concerns over metabolic syndrome, their report merits careful analysis. The present study attempted to repeat the Collison et al. findings. Groups of male or female C57BL/6J mice were fed a control diet or one supplemented with high-fructose corn syrup (HFCS) at a level of 20%. Drinking water control was provided or treatment groups were given 0.064% MSG solution (w/v). Diets and MSG administration continued throughout mating and during gestation and lactation periods. To further investigate the effects of ingestion of MSG, the offspring were continued on the same dosing conditions until they reached 32 wk of age. MSG administration in mice fed a normal or a HFCS diet throughout gestation and for 32 wk after birth, did not affect growth, girth size, abdominal fat weight or body composition. This study reports that MSG did not trigger insulin resistance, dyslipidemia or hepatic steatosis, regardless of the diet, not reproducing the results of the above-mentioned study (Collison et al., 2010).

Flavor preferences conditioned by postingestive effect of sucrose and porcine digestive peptides in postweaning pigs1

Pigs can learn to prefer a flavor if it has been previously associated to positive consequences. The aim of this experiment was to study flavor preferences conditioned by the postingestive effect of nutrients in pigs. In total, 240 weanling piglets were allocated in 24 pens (10 piglets/pen) and distributed to 2 groups of animals (12 pens per group). Pigs in Group 1 (G1) were trained during 8 d with one flavor [positive conditioned stimulus (CS+)] into a protein solution [4% porcine digestible peptides (PDP)] on odd days and another flavor [negative conditioned stimulus (CS-)] into 100 mM of monosodium glutamate (MSG) solution on even days (5-L bottle for 24 h). In the second group of pigs [Group 2 (G2)], CS+ was mixed into a 4% sucrose solution in odd days and CS- into 1% sucrose + 0.08% saccharine on even days. Therefore, treatments were defined as CS+, the flavor associated with PDP or sucrose, on odd days, which were assumed to have a higher postingestive effect than MSG or saccharine + sucrose, the ingredients associated to CS-. Concentration of ingredients in the solutions were chosen to ensure that hedonic attraction for PDP and MSG solutions and for sucrose and saccharine + sucrose were similar (checked in previous double-choice studies). The amount of solution offered during training period was prepared to be totally consumed each day to equalize flavors intake. Flavors (0.0375% anise or garlic) were counterbalanced across replicates to act as CS+ or CS-. Double-choice test between flavors dissolved in water (CS+ and CS-) were performed by selecting 2 pigs/pen on days 1, 6, and 8 after the training period. Solution intake was measured after 30 min. Piglets showed higher intakes for CS+ than CS- in G2 [212 vs. 76 mL and 168 vs. 86 mL (P < 0.05) and 195 vs. 78 mL (P = 0.15)] on days 1, 6, and 8, respectively. Differences between CS+ and CS- consumption were observed in G1 on day 8 (231 vs. 130 mL; P < 0.05). In conclusion, weanling pigs can acquire flavor preferences through associative learning between a flavor and postingestive effects of some nutrients.

MSG intake and preference in mice are influenced by prior testing experience

Monosodium glutamate (MSG), the prototypical umami substance, is used as a flavor enhancer in many foods, but when presented alone is often only weakly attractive. Yet with experience mice will develop strong preferences for MSG solution over water. The present experiments explored the conditions that change indifference to preference for MSG. C57BL/6J mice were given a series of 2-day two-bottle tests with water vs. an ascending series of MSG concentrations (0.1–450mM) to assess preference and intake. Naive mice were indifferent to all concentrations, but following forced one-bottle exposure to 300mM MSG they preferred most concentrations and consumed more MSG. Exposure to 100mM MSG also increased subsequent MSG preference but not intake. Experience with other nutritive solutions (8% sucrose, 8% Polycose, 8% casein hydrolysate, and isocaloric 3.5% soybean oil emulsion) also enhanced subsequent MSG preference and intake. Polycose and sucrose experience were almost as effective as MSG experience. However, not all sapid solutions were effective; 0.8% sucralose and 10mM MSG exposure did not alter subsequent MSG preference. The generality of the preexposure effect was tested by offering an ascending series (0.1–100mM) of inosine monophosphate (IMP), another umami substance; initial indifference was converted to preference after forced exposure to 300mM MSG. Together these results suggest that a combination of oral and post-oral effects may be responsible for the experience effect, with MSG itself the most potent stimulus. A final experiment revealed that MSG preference in naïve mice is enhanced by presenting the MSG and water drinking spouts far apart rather than side by side. Thus the preferences for umami solutions in mice are subject to influence from prior tastant experience as well spout position, which should be taken into account when studying acceptance of taste solutions in mice.

Effects of oral monosodium glutamate in mouse models of asthma

The available evidence from numerous clinical studies has failed to demonstrate a clear and consistent relationship between monosodium glutamate (MSG) and asthma. The objective of this study was to investigate the effects of MSG on bronchial inflammation by measuring cytological, histological and functional changes in an ovalbumin-induced asthma mouse model. BALB/c mice with experimentally induced asthma were fed a diet containing 0.5% or 5% MSG the week before the first ovalbumin injection and for the subsequent 3-week period. MSG feeding did not affect pulmonary eosinophil infiltration, production of Th2 cytokines, circulating IgE concentrations or airway hyperresponsiveness (induced by methacholine). Histological observations did not reveal pulmonary inflammation, including secondary changes, in the asthmatic mice. An oral gavage challenge with an MSG solution (0.5% or 5%, w/w) did not exert any acute effects on lung inflammation or airway hyperresponsiveness in the asthmatic mice. The results of this study suggest that MSG is not involved in the development of asthma or in acute asthmatic responses, and they support previous observations from well-designed clinical studies.

A natação minimiza o retardo no crescimento somático e ósseo de ratos?

A formação óssea é regulada por fatores hormonais e modificada por estímulos extrínsecos, como a prática de exercícios. Avaliou-se o efeito da natação sobre o crescimento somático e ósseo de ratas submetidas a dois modelos experimentais a fim de reproduzir déficit hormonal. Utilizou-se 28 ratas Wistar neonatas fêmeas separadas em: grupo Glutamato Monossódico (GluM, n = 14; solução de GM 4.0mg/g, dias alternados, primeiros 14 dias de vida) e grupo Salina (Sal, n = 14; solução salina). Peso corpóreo e mensurações murinométricas (eixos laterolateral, anteroposterior do crânio - LLC/APC - e comprimento da cauda - CC) foram avaliados do primeiro ao 30º dia de vida. Aos 60 dias, o Grupo GluM foi ovariectomizado (GluMO) e o sal apenas passou pelo estresse cirúrgico. Então, metade dos animais de cada grupo iniciou o programa de natação (12 semanas, cinco dias/semanas, 60 min/sessão) resultando nos seguintes grupos experimentais: Salina Sedentário (Salsed, n = 7), Salina Natação (Salnat, n = 7), Glutamato Ovariectomia Sedentário (GluMOsed, n = 7) e Glutamato Ovariectomia Natação (GluMOnat, n = 7). Ao final do experimento o fêmur direito foi pesado e seu comprimento avaliado. Nos 30 dias iniciais, GluM reduziu o peso corpóreo e os eixos LLC, APC e CC comparado ao grupo SAL. Aos 60 dias, o peso corpóreo do GLuM permaneceu menor comparado ao SAL e ao final foi similar entre os grupos SALsed e SALnat e, GLuMOsed e GluMOnat. Porém, houve redução no peso do GlutMOsed comparado ao SALsed. A natação favoreceu o peso do fêmur no SAL e não o alterou entre os GluMOsed e GluMOnat, entretanto, houve aumento no grupo SALsed comparado ao GluMOsed. No comprimento, o SALnat foi similar ao SALsed e o mesmo ocorreu entre GluMOnat e GluMOsed. Porém, SALsed apresentou comprimento maior que GluMOsed. A natação não foi capaz de reverter, em animais adultos jovens, os efeitos provocados por situações de desequilíbrio corpóreo induzidas precocemente no tecido ósseo.

Closed‐Loop Control of Reactive Crystallization PART II: Polymorphism Control ofL‐Glutamic Acid by Sonocrystallization and Seeding

AbstractThe impact of different nucleation methods with controlled supersaturation on the polymorphism ofL‐glutamic acid crystals was studied in a 50 dm3semi‐batch crystallizer, in which 1.5 M H2SO4was fed into a 1.5 M monosodium glutamate solution. Supersaturation was controlled by a feedback loop based on measured ATR‐FTIR spectra and on a thermodynamic model developed in house.Ultrasound‐initiated nucleation produced pure α‐polymorph (over 99.5 wt %) in the end product crystals at 1 mol/dm3supersaturation. Seeded crystallization also produced almost pure α‐polymorph crystals (over 93 wt %), whereas spontaneous nucleation produced a polymorph mixture (from 30–70 wt %) under the same operating conditions. This indicates that supersaturation‐controlled sonocrystallization can be used to control polymorphism in crystals. The novelty herein is the simplicity of the method directing the generation of a desired polymorph.

Monosodium glutamate neonatal treatment as a seizure and excitotoxic model

Monosodium glutamate (MSG) subcutaneously administrated to neonatal rats induces several neurochemical alterations in the brain, which have been associated with an excitotoxic process triggered by an over activation of glutamate receptors; however there are few systematic studies about initial changes in intracerebroventricular (ICV) Glu levels produced by MSG in the brain. Thus, to characterize these changes, rat pups were injected with a MSG solution at 1, 3, 5 and 7 postnatal days (PD), and ICV Glu levels and hippocampal total content of related amino acids (Asp, Glu, Gln, Gly, Tau, Ala and GABA) were estimated before, immediately and after each injection. Behavioral and EEG responses were also monitored after MSG administrations. Significant rise in ICV Glu levels were found, mainly in response to the first and second injection. Moreover, the total content of all amino acids evaluated also increased during the first hour after the first MSG administration but only Glu and GABA remained elevated after 24 h. These biochemical modifications were accompanied with behavioral alterations characterized by: screeching, tail stiffness, head nodding, emprosthotonic flexion episodes and generalized tonic–clonic convulsions, which were associated with electroencephalographic pattern alterations. Altered behavior found in animals treated with MSG suggests an initial seizure situation. Although four MSG administrations were used, the most relevant findings were observed after the first and second administrations at PD1 and PD3, suggesting that only two MSG injections could be sufficient to resemble a seizure and/or excitotoxic model.

Saltiness Enhancement by the Characteristic Flavor of Dried Bonito Stock

There is a pressing need for the development of ways of preparing palatable salt-reduced foods to reduce the salt intake of the Japanese population. The salt-reducing effect of the characteristic flavors other than umami of dried bonito stock, which is widely used in everyday Japanese food, was examined by sensory evaluation. In the 1st sensory evaluation, the effect was evaluated in a model solution. The saltiness of 0.80% NaCl solution was equivalent to that of 0.12% monosodium glutamate (MSG) solution containing 0.81% NaCl and dried bonito stock containing 0.68% NaCl. Saltiness enhancement could not be found when MSG solution was used, but was found with 6% dried bonito stock. The 2nd evaluation examined whether the effect was valid for 2 everyday Japanese foods--traditional Japanese clear soup (sumashi-jiru) and steamed egg custard (tamagodoufu). Although enhancement of saltiness by dried bonito stock could not be clearly demonstrated in the soup, a change in NaCl concentration within 15% did not affect the palatability of the soup. However, dried bonito stock not only enhanced the saltiness but also improved the palatability of steamed egg custard. These findings are expected to be useful for improving the palatability of salt-reduced food.

Mercaptoacetate inhibition of fatty acid β-oxidation attenuates the oral acceptance of fat in BALB/c mice

We investigated the effect of beta-oxidation inhibition on the fat ingestive behavior of BALB/c mice. Intraperitoneal administration to mice of mercaptoacetate, an inhibitor of fatty acid oxidation, significantly suppressed intake of corn oil but not intake of sucrose solution or laboratory chow. To further examine the effect of mercaptoacetate on the acceptability of corn oil in the oral cavity, we examined short-term licking behavior. Mercaptoacetate significantly and specifically decreased the number of licks of corn oil within a 60-s period but did not affect those of a sucrose solution, a monosodium glutamate solution, or mineral oil. In contrast, the administration of 2-deoxyglucose, an inhibitor of glucose metabolism, did not affect the intake or short-term licking counts of any of the tasted solutions. These findings suggest that fat metabolism is involved in the mechanism underlying the oral acceptance of fat as an energy source.

Molecular and Sensory Characterization of γ-Glutamyl Peptides as Key Contributors to the Kokumi Taste of Edible Beans (Phaseolus vulgaris L.)

Addition of a nearly tasteless aqueous extract isolated from beans (Phaseolus vulgaris L.) to a model chicken broth enhanced its mouthfulness and complexity and induced a much more long-lasting savory taste sensation on the tongue. Gel permeation chromatography and hydrophilic interaction liquid chromatography/comparative taste dilution analysis (HILIC/cTDA), followed by LC-MS/MS and 1D/2D-NMR experiments, led to the identification of gamma-L-glutamyl-L-leucine, gamma-L-glutamyl-L-valine, and gamma-L-glutamyl-L-cysteinyl-beta-alanine as key molecules inducing this taste-modifying effect. Sensory analysis of aqueous solutions of these peptides showed threshold concentrations between 3.3 and 9.4 mmol/L for an unspecific, slightly astringent sensation. More interestingly, when added to a savory matrix such as sodium chloride and monosodium glutamate solutions or chicken broth, the detection thresholds of these gamma-glutamyl peptides decreased significantly and remarkably enhanced mouthfulness, complexity, and long-lastingness of the savory taste were observed; for example, the threshold of gamma-glutamyl-cysteinyl-beta-alanine decreased by a factor of 32 in a binary mixture of glutamic acid and sodium chloride. As tasteless molecules inducing mouthfulness, thickness, and increasing continuity of savory foods were coined about 10 years ago as "kokumi" flavor compounds, the peptides identified in raw as well as thermally treated beans have to be considered as kokumi compounds.

Precipitation of L‐Glutamic Acid: Determination of Nucleation Kinetics

AbstractThis work presents a new procedure to determine the nucleation kinetics during the reactive precipitation of an organic substance. The new method has been applied to the pH‐shift precipitation of L‐glutamic acid upon mixing of an aqueous monosodium glutamate solution with hydrochloric acid. The induction time has been measured precisely in a stirred batch reactor by the combination of two in‐situ measurement techniques, namely ATR‐FTIR spectroscopy (attenuated total reflection Fourier Transform technique) and Focused Beam Reflectance Measurement (FBRM). It is shown that ATR‐FTIR is a suitable tool to measure the concentrations of the different L‐glutamic acid ions, and can be used to determine the starting time of the process when the desired supersaturation is established in the reactor. The onset of particle formation is detected through FBRM. The precipitated polymorph is identified using in‐situ Raman spectroscopy and Particle Vision &amp; Measurement (PVM). Finally, the induction time is used together with the independently measured growth kinetics to determine the nucleation rate.

Monosodium glutamate and sweet taste: discrimination between the tastes of sweet stimuli and glutamate in rats.

Generalization of a conditioned taste aversion (CTA) is based on similarities in taste qualities shared by the aversive substance and another taste substance. CTA experiments with rats have found that an aversion to a variety of sweet stimuli will cross-generalize with monosodium glutamate (MSG) when amiloride, a sodium channel blocker, is added to all solutions to reduce the taste of sodium. These findings suggest that the glutamate anion elicits a sweet taste sensation in rats. CTA experiments, however, generally do not indicate whether two substances have different taste qualities. In this study, discrimination methods in which rats focused on perceptual differences were used to determine if they could distinguish between the tastes of MSG and four sweet substances. As expected, rats readily discriminated between two natural sugars (sucrose, glucose) and two artificial sweeteners (saccharin, SC45647). Rats also easily discriminated between MSG and glucose, saccharin and, to a lesser extent, SC45647 when the taste of the sodium ion of MSG was reduced by the addition of amiloride to all solutions, or the addition of amiloride to all solutions and NaCl to each sweet stimulus to match the concentration of Na+ in the MSG solutions. In contrast, reducing the cue function of the Na+ ion significantly decreased their ability to discriminate between sucrose and MSG. These results suggest that the sweet qualities of glutamate taste is not as dominate a component of glutamate taste as CTA experiments suggest and these qualities are most closely related to the taste qualities of sucrose. The findings of this study, in conjunction with other research, suggest that sweet and umami afferent signaling may converge through a taste receptor with a high affinity for glutamate and sucrose or a downstream transduction mechanism. These data also suggest that rats do not necessarily perceive the tastes of these sweet stimuli as similar and that these sweet stimuli are detected by multiple sweet receptors.

Behavioral evidence for a role of alpha-gustducin in glutamate taste.

The taste perception of monosodium glutamate (MSG) is termed 'umami'. Two putative taste receptors for glutamate have been identified, a truncated form of mGluR4 (taste-mGluR4) and the presumed heterodimer T1R1 + T1R3. Both receptors respond to glutamate when expressed in heterologous cells, but the G protein involved is not known. Galpha-Gustducin mediates the transduction of several bitter and sweet compounds; however, its role in umami has not been determined. We used standard two-bottle preference tests on alpha-gustducin knockout (KO) and wildtype (WT) mice to compare preferences for ascending concentrations of MSG and MSG + 5'-inosine monophosphate (IMP). A Latin Square was used to assign the order of tastants presented to each mouse. Statistical comparisons between KO and WT mice revealed that whereas WT mice preferred solutions of MSG and MSG + IMP over water, KO mice showed little preference for these stimuli. Denatonium and sucrose served as control stimuli and, as shown previously, WT mice prefered sucrose and avoided denatonium significantly more than did KO mice. Naïve mice were also tested, and while prior exposure to taste stimuli influenced the magnitude of the preferences, experience did not change the overall pattern of intake. These data suggest that alpha-gustducin plays a role in glutamate taste.