Monosodium Glutamate and Sweet  Taste: Generalization of Conditioned Taste Aversion between Glutamate  and Sweet Stimuli in Rats

Heyer, Beth R.; Taylor-Burds, Carol; Tran, Lavinia; Delay, Eugene R.

doi:10.1093/chemse/bjg056

Cited by 63 publications

(48 citation statements)

References 33 publications

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“…These findings together with our observation that OLETF rats responded more to MSG, sucrose as well as alanine, but not salts (sodium or nonsodium moieties, a taste category for mineral intake), indicate that the augmented ingestive response to MSG is likely to be the result rather of the generalization to sweet (a taste category for energy intake). This notion is further supported by a recent study in rat showing that conditioned aversions to MSG cross generalize to sucrose and other sweeteners (33). This cross generalization may also explain our observation and reinforce our conclusion that taste preference in OLETF was indeed altered in ways specific to mechanisms that code for sweet.…”

Section: Summary Of Results With Relevance To Modelsupporting

confidence: 91%

Altered taste sensitivity in obese, prediabetic OLETF rats lacking CCK-1 receptors

Hajnal¹,

Covașă²,

Bello³

2005

American Journal of Physiology-Regulatory, Integrative and Comp

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-Otsuka Long-Evans Tokushima fatty (OLETF) rats lack the CCK-1 receptor, are hyperphagic, progressively become obese, and develop type-2 diabetes. We recently demonstrated an increased preference for both real and sham feeding of sucrose in this strain, suggesting altered orosensory sensitivity. To investigate taste functions, we used an automated gustometer with 10-s access to different concentrations of various sapid stimuli. Tests were repeated at 10 and 18 wk of age to assess the early and advanced stages of prediabetes, respectively. Compared with age-matched, nonmutant controls, the OLETF rats showed higher avidity for sucrose at both ages. This difference increased as a function of age and tastant concentration. An exaggerated response also occurred for saccharin, alanine, and fructose, but not for Polycose. Similarly, OLETF rats consumed monosodiumglutamate more at the lower concentrations compared with controls, an effect that age also accentuated. In contrast, there was no statistical strain or age differences in responses to NaCl, MgCl2, citric acid, quinine-HCl, and the trigeminal stimulus capsaicin. These findings demonstrate that compared with controls, OLETF rats differ in their gustatory functions with an overall augmented sensitivity for sweet that progresses during prediabetes. This effect explains their overconsumption of sweet solutions and may contribute to the overall hyperphagia and obesity in this strain.overeating; dietary obesity; insulin resistance; sweet receptors; hedonic coding OBESITY IS A GLOBAL PANDEMIC that continues to accelerate and increases the risk of multiple medical conditions, such as noninsulin-dependent diabetes mellitus (NIDDM), hypertension, and coronary heart disease (34). Although the etiology of obesity is complex, overconsumption induced by the high palatability of the modern diet, in general, and individual differences in responsivity to palatability, in particular, may contribute to obesity (34,74,87). Meal size is controlled by orosensory stimulatory and postingestive inhibitory feedback (71). Thus increased appetite and overeating can be the result of either an enhanced responsiveness to orosensory stimulatory properties of a meal, a decreased sensitivity to postingestive inhibitory signals, or both. Importantly, the signaling systems that underlie appetite control appear to operate independently from the energy homeostatic regulation resulting in sustained overeating and body weight gain in some individuals and also in animal models of obesity.Despite the controversy about the particular contribution of different nutrients to the epidemic of obesity, there is agreement that an increased palatability of foods that taste sweet and contain fats, plays a critical role by increasing the overall calorie intake (40, 56). As with humans, high carbohydrate and high fat foods are strongly preferred by rats (59). Postingestive factors play an important role in this preference (63, 84), but rats also sham feed sugar and fat solutions (i.e., fatty acids and triglycerides...

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Section: Summary Of Results With Relevance To Modelsupporting

confidence: 91%

Altered taste sensitivity in obese, prediabetic OLETF rats lacking CCK-1 receptors

Hajnal¹,

Covașă²,

Bello³

2005

American Journal of Physiology-Regulatory, Integrative and Comp

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“…Our finding that all four primate species tested clearly preferred sucrose over equimolar concentrations of MSG and thus were clearly able to discriminate between these tastants is not trivial considering that rats have been shown to crossgeneralize between the tastes of monosodium glutamate and sucrose in conditioned taste aversion tests (Heyer et al, 2003) suggesting that MSG, in addition to activating glutamate receptors, may also activate sweet receptors in the apical membrane of taste cells. This supposition is supported by electrophysiological studies in nonhuman primates that reported umami compounds to stimulate sweet-best (and also salt-best) fibers in addition to specialized fibers exclusively responsive to MSG and ribonucleotides (Hellekant and Ninomiya,'91).…”

Section: Discussionmentioning

confidence: 78%

“…Additionally, we assessed relative preferences for MSG when tested against equimolar concentrations of sucrose and sodium chloride, respectively, in order to try the discriminability of these tastants, particularly as rats have been shown to cross-generalize betwen the tastes of MSG and sucrose in conditioned taste aversion tests (Heyer et al, 2003).…”

Section: Introductionmentioning

confidence: 99%

Gustatory responsiveness to monosodium glutamate and sodium chloride in four species of nonhuman primates

Laska¹,

Salazar

2004

J. Exp. Zool.

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The taste responsiveness of six squirrel monkeys, five pigtail macaques, four olive baboons and four spider monkeys to monsodium glutamate (MSG) and to sodium chloride was assessed in two-bottle preference tests of brief duration (2 min). When given the choice between tap water and defined concentrations of the two tastants dissolved in tap water, the animals were found to significantly discriminate concentrations of MSG as low as 2 mM (spider monkeys and olive baboons), 50 mM (pigtail macaques) and 300 mM (squirrel monkeys) from the solvent. With sodium chloride, taste preference thresholds were found to be 1 mM (spider monkeys), 20 mM (pigtail macaques), 50 mM (olive baboons), and 200 mM (squirrel monkeys), respectively. Across-species comparisons of the degree of preference for MSG and sodium chloride displayed by the four primate species showed the same order of spider monkeys>olive baboons>pigtail macaques>squirrel monkeys. When presented with equimolar concentrations of different tastants, all four species preferred sucrose as well as a mixture of sucrose and sodium chloride over MSG, and--at least at one concentration--they preferred MSG over sodium chloride. The results support the assertion that the taste responsiveness of the four primate species to MSG and sodium chloride might reflect an evolutionary adaptation to their respective dietary habits.

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“…#CS suppression ratio for each LiCl-injected group that was significantly lower than its corresponding control group. dium glutamate as similar but discriminable (Chaudhari et al, 1996;Stapleton et al, 1999;Heyer et al, 2003Heyer et al, , 2004.…”

Section: Discussionmentioning

confidence: 96%

Behavioral Discrimination between Sucrose and Other Natural Sweeteners in Mice: Implications for the Neural Coding of T1R Ligands

Dotson

Spector²

2007

J. Neurosci.

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In taste bud cells, two different T1R heteromeric taste receptors mediate signal transduction of sugars (the canonical "sweet" taste receptor, T1R2 ϩ T1R3) and L-amino acids (the T1R1 ϩ T1R3 receptor). The T1R1 ϩ T1R3 receptor is thought to mediate what is considered the fifth basic taste quality "umami." However, a subset of L-amino acids is "sweet tasting" to humans and appears to possess a "sucrose-like" taste quality to nonhuman mammals. This suggests, to varying degrees, that all of these compounds activate a single neural channel that leads to the perception of sweetness.The experiments detailed here were designed to test the ability of mice to distinguish between sucrose and various others sugars and L-amino acids in operant taste discrimination tasks. Mice had at least some difficulty discriminating sucrose from L-serine, L-threonine, maltose, fructose, and glucose. For example, when concentration effects are taken into consideration, mice discriminated poorly, if at all, sucrose from glucose or fructose and, to a lesser extent maltose, suggesting that sugars generate a unitary perceptual quality. However, mice were able to reliably discriminate sucrose from L-serine and L-threonine. Data gathered using a conditioned taste aversion assay also suggest that, although qualitatively similar to the taste of sucrose, L-serine and L-threonine generate distinctive percepts.In conclusion, it appears that some signals from taste receptor proteins binding with sugars and some L-amino acids converge somewhere along the gustatory neuraxis. However, the results of these experiments also imply that sweet-tasting L-amino acids may possess qualitative taste characteristics that are distinguishable from the prototypical sweetener sucrose.

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Monosodium Glutamate and Sweet Taste: Generalization of Conditioned Taste Aversion between Glutamate and Sweet Stimuli in Rats

Cited by 63 publications

References 33 publications

Altered taste sensitivity in obese, prediabetic OLETF rats lacking CCK-1 receptors

Altered taste sensitivity in obese, prediabetic OLETF rats lacking CCK-1 receptors

Gustatory responsiveness to monosodium glutamate and sodium chloride in four species of nonhuman primates

Behavioral Discrimination between Sucrose and Other Natural Sweeteners in Mice: Implications for the Neural Coding of T1R Ligands

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