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Amiloride reduces the taste intensity of Na+ and Li+ salts and sweeteners.

The diuretic amiloride, a potent inhibitor of sodium transport in a variety of epithelial systems, was applied to the human tongue. Application of amiloride reduced the taste intensity of sodium and lithium salts and of sweeteners ranging widely in chemical structure. The sweeteners included saccharides, glycosides, dipeptides, proteins, and amino acids. Amiloride did not affect perception of potassium or calcium salts, bitter and sour tastes, or amino acids without a sweet or salty component. These findings were supported by neurophysiological studies in rat, which showed that amiloride diminished the NaCl response relative to KCl. The results are consistent with the position that an amiloride-sensitive transport mechanism is involved in taste perception of sodium and lithium salts and of sweeteners.

Amiloride↗

The sweetness-inducing effect of miraculin; behavioural and neurophysiological experiments in the rhesus monkey Macaca mulatta.

1. The gustatory effects of miraculin, the sweetness-inducing protein from the miracle fruit Synsepalum dulcificum, was studied in the rhesus monkey, Macaca mulatta.2. The intake of five acids was recorded in two-bottle preference tests, one bottle containing acid and the other tap water, before and after miraculin treatment. All the acids tasted more pleasant after miraculin.3. The electrical activity of the chorda tympani nerve to stimulation of the tongue with a variety of sweeteners, acids, sodium chloride and quinine hydrochloride was recorded in anaesthetized animals.4. Pre-treatment of the tongue with 0.3-5 mg miraculin doubled the summated nerve response to the acids and diminished the response to sucrose by about 10%. The enhancement lasted for at least an hour and the diminution up to 20 min.5. After miraculin treatment the Spearman's rank correlation coefficient between the order of increased intake of acids and the order of enhancement of the summated nerve response was 0.99.6. A solution of 0.1 mg miraculin per ml. elicited a weak nerve response. No preference over water for this concentration of miraculin was recorded in the two-bottle tests.7. The activity of twenty-nine single taste fibres, selected for their responsiveness to sweetness or acids or both, was recorded after miraculin treatment. Effects were obtained in nine fibres which were similar but more pronounced than those observed in the summated recordings. Before miraculin, these fibres responded better and to a larger variety of sweeteners (81%) than the other fibres (40%). After miraculin, acids elicited on the average 2.3 times more activity than before, while the response to sweeteners was depressed. In twenty fibres no effect of miraculin was observed. These fibres responded to fewer of the sweeteners and were more stimulated by the non-sweet stimuli than the first group.8. The results suggest that miraculin acts on those structures in the taste cell membrane that are involved in perception of the sweet taste, making them sensitive to acids. The new quality of sweetness after miraculin treatment is signalled by taste fibres which normally respond to sweet substances but which, under the influence of miraculin, are responding to acids. It is likely that the quality of a taste stimulus is conveyed by the identity of the taste fibres.

Acids↗

Temperature modulates taste responsiveness and stimulates gustatory neurons in the rat geniculate ganglion.

In humans, temperature influences taste intensity and quality perception, and thermal stimulation itself may elicit taste sensations. However, peripheral coding mechanisms of taste have generally been examined independently of the influence of temperature. In anesthetized rats, we characterized the single-cell responses of geniculate ganglion neurons to 0.5 M sucrose, 0.1 M NaCl, 0.01 M citric acid, and 0.02 M quinine hydrochloride at a steady, baseline temperature (adapted) of 10, 25, and 40 degrees C; gradual cooling and warming (1 degrees C/s change in water temperature >5 s) from an adapted tongue temperature of 25 degrees C; gradual cooling from an adapted temperature of 40 degrees C; and gradual warming from an adapted temperature of 10 degrees C. Hierarchical cluster analysis of the taste responses at 25 degrees C divided 50 neurons into two major categories of narrowly tuned (Sucrose-specialists, NaCl-specialists) and broadly tuned (NaCl-generalists(I), NaCl- generalists(II), Acid-generalists, and QHCl-generalists) groups. NaCl specialists were excited by cooling from 25 to 10 degrees C and inhibited by warming from 10 to 25 degrees C. Acid-generalists were excited by cooling from 40 to 25 degrees C but not from 25 to 10 degrees C. In general, the taste responses of broadly tuned neurons decreased systematically to all stimuli with decreasing adapted temperatures. The response selectivity of Sucrose-specialists for sucrose and NaCl-specialists for NaCl was unaffected by adapted temperature. However, Sucrose-specialists were unresponsive to sucrose at 10 degrees C, whereas NaCl-specialists responded equally to NaCl at all adapted temperatures. In conclusion, we have shown that temperature modulates taste responsiveness and is itself a stimulus for activation in specific types of peripheral gustatory neurons.

Action Potentials↗

The riddle of L-glucose pentaacetate insulinotropic action (review).

The two anomers of L-glucose pentaacetate were recently found to stimulate insulin release. The insulinotropic action of these esters cannot be attributed to the catabolism in islet cells of their glucidic or acetic moieties. The present review deals with an alternative hypothesis. It is proposed that L-glucose pentaacetate itself directly interacts with a yet unidentified receptor leading to plasma membrane depolarization, induction of electrical activity and increase in the cytosolic concentration of ionized Ca2+. This process displays analogies with the identification of bitter compounds by taste buds. Thus, beta-L-glucose pentaacetate indeed displays a bitter, but no sweet, taste. Purified islet B-cells contain the alpha-gustducin G-protein involved in the perception of bitter taste by taste buds. The pentaacetate ester of beta-L-glucose decreases 86Rb outflow from prelabelled islets, provokes bioelectrical activity in islet B-cells and may induce oscillations of cytosolic Ca2+ in these insulin-producing cells. The effects of beta-L-glucose pentaacetate upon glucagon and somatostatin secretion by the isolated perfused pancreas are also compatible with the present hypothesis. It is proposed that the L-glucose pentaacetate anomers could be used as novel insulinotropic tools in the treatment of non-insulin-dependent diabetes mellitus.

Animals↗

Disorders of smell, taste, and food intake in a patient with a dorsomedial thalamic infarct.

BACKGROUND: We report that a lasting deficit in the hedonic character of olfactory and gustatory perception can be observed in bilateral dorsomedial and intralaminar thalamic lesions. CASE DESCRIPTION: A 68-year-old patient abruptly presented with vigilance disorders associated with a reduction of olfactory and gustatory perceptions. A severe drop in appetite for foods and a weight loss of 10 kg were observed, which were partially reversed with time. Two years later, the main persisting disorder was a change in the quality of perceptions: odors and taste were perceived either in a neutral way, their pleasant character having disappeared, or as unpleasant. However, identification was preserved. MRI showed that lesions principally involved the dorsomedial thalamic nuclei and the adjacent part of the intralaminar nuclei. CONCLUSIONS: This case suggests that the dorsomedial thalamus may play a role in the hedonic perception of food, thus affecting short-term regulation of food intake, and may possibly have a role in the long-term control of body weight.

Aged↗

Taste reactivity in high-alcohol-sensitive and low-alcohol-sensitive rats.

High, low, and control alcohol-sensitive (HAS, LAS, CAS, respectively) rats were tested for their perception of the taste of alcohol using the taste reactivity test. Reactivity tests with a single concentration of sucrose and quinine were also done. After initial taste reactivity, all rats were tested for alcohol consumption in a standard two-bottle test (water in the second bottle). Postconsumption taste reactivity tests completed the experiment. Results indicated that HAS, LAS, and CAS rats did not differ significantly in their taste reactivity response to a range of alcohol concentrations (5-40%), nor did they differ significantly in response to sucrose or quinine. Reactivity responses were similar for each group before and after the consumption tests. Despite the lack of line differences in taste reactivity, HAS and LAS rats consumed significantly less alcohol than the CAS rats during the two-bottle access tests. The present results are in contrast to research done with rats selectively bred for alcohol consumption (Alcohol Preferring and Nonpreferring rats, High Alcohol Drinking and Low Alcohol Drinking rats), which exhibit clear line differences in patterns of reactivity changes following alcohol access. The selection phenotype of alcohol sensitivity appears to be independent of rats' behavioral response to the taste of alcohol.

Alcohol Drinking↗

Age-associated increases in intensity discrimination for taste.

Impaired taste sensation in the aging person may affect the appreciation of food and beverages and compromise nutritional status. Changes in flavor perception may be due to altered ability to discriminate between intensities of suprathreshold taste stimuli. An interesting question is whether all taste qualities (sweet, salty, sour, bitter) show similar age-associated decline in intensity discrimination. Taste intensity discrimination has been shown to be significantly poorer in elderly than in young women for the bitter stimulus caffeine, but not for the sweet stimulus sucrose. The present experiment investigated effects of taste substance and age on taste intensity discrimination by assessing Weber ratios (WRs) for citric acid and sodium chloride (NaCl) in 60 people, half elderly, and half women. Results indicate a significant effect of age on WRs for citric acid and NaCl, suggesting the importance of suprathreshold intensity discrimination for taste perception in the elderly.

Adult↗

Functional expression of mammalian bitter taste receptors in Caenorhabditis elegans.

Bitter taste has evolved as a central warning signal against the ingestion of potentially toxic substances appearing in the environment. The molecular events in the perception of bitter taste start with the binding of specific water-soluble molecules to G protein-coupled receptors (GPCR) called T2Rs and expressed at the surface of taste receptor cells. The functional characterisation of T2R receptors is far from been completed due to the difficulty to functionally express them in heterologous systems. Taking advantage of the parallelisms between the Caenorhabditis elegans (C. elegans) and mammalian GPCR signalling pathways, we developed a C. elegans-based expression system to express functional human and rodent GPCRs of the T2R family. We generated transgenic worms expressing T2Rs in ASI chemosensory neurons and performed behavioural assays using a variety of bitter tastants. As a proof of the concept, we generated transgenic worms expressing human T2R4 or its mouse ortholog T2R8 receptors, which respond to two bitter tastants previously characterised as their functional ligands, 6-n-propyl-2-thiouracil and denatoniun. As expected, expression of human T2R4 or its mouse ortholog T2R8 in ASI neurons counteracted the water-soluble avoidance to 6-n-propyl-2-thiouracil and denatoniun observed in control wild-type worms. The expression in ASI neurons of human T2R16, the ligand of which, phenyl-beta-d-glucopyranoside, belong to a chemically different group of bitter tastants, also counteracted the water-soluble avoidance to this compound observed in wild-type worms. These results indicate that C. elegans is a suitable heterologous expression system to express functional T2Rs providing a tool to efficiently search for specific taste receptor ligands and to extend our understanding of the molecular basis of gustation.

Animals↗

[Variations in the taste function of smokers].

Cigarette smoke is linked to many pathologies and also affects a very important aspect of human physiology that is taste. In fact already in the past years, researchers have worked on this phenomenon and have come to the conclusion that smoke influences the perception of bitter taste. In our study we researched the detection and identification threshold in thirty smokers, for the citric acid, quinine, sodium chloride and saccharose, and it turned out that smokers suffer a raise in quinine identification and sodium chloride detection and identification threshold. On the basis of the results obtained with sodium chloride, a theory on hypertension etiopathogenesis is suggested.

Adult↗

Behavioral taste similarities and differences among monosodium L-glutamate and glutamate receptor agonists in C57BL mice.

Monosodium L-glutamate (MSG) and 5'-ribonucleotides elicit umami taste in humans and probably in some species of animals. Previous studies suggest that taste-mGluR4 and NMDA receptor may be involved in taste transduction for umami, but behavioral responses in rats do not support the involvement of NMDA receptor. In the present study, behavioral similarities and differences among MSG, mGluR4 agonist L(+)-2-amino-4-phosphonobutyrate (L-AP4), and NMDA receptor agonist N-methyl-D-aspartate (NMDA) were compared in C57BL mice by using a conditioned taste aversion paradigm. Mice conditioned to avoid either MSG or 10 mM L-AP4 appeared to avoid MSG, disodium 5'-inosinate (IMP), a mixture of MSG and IMP, and L-AP4, but not NMDA. Aversive conditioning to either sucrose or NMDA was generalized only to a mixture of MSG+IMP or NaCl. However, aversive conditioning to L-AP4 at 1 mM was generalized to NMDA and the umami substances. Lick rates for L-AP4 increased by mixing with (RS)-alpha-cycloprophy-4-phosphonophenylglycine (mGluR4 antagonist) when animals were conditioned to avoid MSG or L-AP4. Lick rates for NMDA also either decreased or increased by mixing with glycine (NMDA receptor coagonist) or D(-)-2-amino-5-phosphonopentanoic acid (NMDA receptor antagonist) when animals were conditioned to avoid L-AP4 or NMDA. In sucrose-conditioned mice. gurmarin (a sweet inhibiting peptide) suppressed the avoidance of sucrose and a mixture of MSG and IMP, but not L-AP4 and NMDA. The results suggest the possibility that to C 57BL mice MSG may taste similar to L-AP4 but different from NMDA, although both types of glutamate receptors as well as gurmarin-sensitive sweet receptor may be involved in perception of umami taste.

Animals↗

Repair of the lingual nerve after iatrogenic injury: a follow-up study of return of sensation and taste.

PURPOSE: To evaluate the return of sensation and taste after surgical repair of the lingual nerve in patients who had experienced lingual nerve sectioning. PATIENTS AND METHODS: Average follow-up was 3.7 years with a range of 1.1 to 4.6 yrs. The patients' assessment of tongue sensation and taste was registered. Clinical testing for sensibility included light touch, prick, sharp/dull discrimination, heat (45 degrees C), cold (0 degree C), anterior/posterior localization of touch, perception of direction of touch movement, and two-point discrimination. The sense of taste was tested with sweet (saccharose 5%), sour (citric acid 5%), salt (saline 5%), and bitter (chinin-hydrochloride 0.5%). RESULTS: Three patients rated their tongue sensation on the affected side as normal, another three scored subnormal, and one felt no sensibility. Likewise, four patients thought that their sense of taste was normal, two were undecided, and one felt no sense of taste on the affected side. The ability to differentiate the quality of taste on the operated side of the tongue was validated in four of 24 tests. Conversely, on the healthy side of the tongue, two of 24 tests proved negative for taste perception. CONCLUSION: There was a notable difference in the patients' assessment of normality of tongue sensation versus the result of neurological testing. Likewise, there was a remarkable difference between the patients' subjective impression of gustatory capability and their ability to diagnose the quality of taste on testing.

Adolescent↗

Effect of sensory perception of foods on appetite and food intake: a review of studies on humans.

OBJECTIVE: How much do the sensory properties of food influence the way people select their food and how much they eat? The objective of this paper is to review results from studies investigating the link between the sensory perception of food and human appetite regulation. CONTENT OF THE REVIEW: The influence of palatability on appetite and food intake in humans has been investigated in several studies. All reviewed studies have shown increased intake as palatability increased, whereas assessments of the effect of palatability using measures of subjective appetite sensations have shown diverging results, for example, subjects either feel more hungry and less full after a palatable meal compared to a less palatable meal, or they feel the opposite, or there is no difference. Whether palatability has an effect on appetite in the period following consumption of a test meal is unclear. Several studies have investigated which sensory properties of food are involved in sensory-specific satiety. Taste, smell, texture and appearance-specific satieties have been identified, whereas studies on the role of macronutrients and the energy content of the food in sensory-specific satiety have given equivocal results. Different studies have shown that macronutrients and energy content play a role in sensory-specific satiety or that macronutrients and energy content are not a factor in sensory-specific satiety. Sensory-specific satiety may have an important influence on the amount of food eaten. Studies have shown that increasing the food variety can increase food and energy intake and in the short to medium term alter energy balance. Further knowledge about the importance of flavour in appetite regulation is needed, for example, which flavour combinations improve satiety most, the possible connection between flavour intensity and satiety, the effect of persistence of chemesthetic sensation on palatability and satiety, and to what extent genetic variation in taste sensitivity and perception influences dietary habits and weight control.

Appetite↗

Expression of the sweet receptor protein, T1R3, in the human liver and pancreas.

The expression of T1R3, a taste receptor essential for the perception of sweetness and umami-taste, was examined by immunohistochemistry to determine whether and where it may be localized in the liver and pancreas. In the liver, both immunopositive and immunonegative reactions were detected; bile ducts and intercalated portions of the bile ductules were immunopositive to T1R3, while arterioles and venules were immunonegative in interlobular connective tissue. In the hepatic lobule, all other cells including liver cells (hepatocytes) and bile capillaries were immunonegative. In the pancreas, all endocrine portions of the pancreas were immunonegative to T1R3. Within the exocrine portions, immunopositive reactions were detected in excretory duct cells, intercalated cells, and centroacinar cells. In contrast, acinar cells were immunonegative, as were vessels, lymph capillaries, nerve fibers, and connective tissue cells in the exocrine portions. The restricted localization of T1R3 in the duct cells of the liver and pancreas in the present study may indicate that T1R3 is involved in monitoring changes in the makeup of bile and pancreatic juices in the hepatic and pancreatic duct systems.

Humans↗

Associations between taste genetics, oral sensation and alcohol intake.

Alcohol produces a range of oral sensations, some of which have been shown to vary with the perceived bitterness of 6-n-propylthiouracil (PROP), one marker for genetic variation in taste. Some studies report that offspring of alcoholics are most likely to be PROP nontasters [Physiol. Behav. 51 (1992) 1261; Physiol. Behav. 64 (1998) 147], yet others report the offspring as more responsive to sodium chloride (NaCl) and citric acid, which appears to contradict the taste genetic hypothesis. We predicted alcohol sensation and intake from measures of taste genetics (PROP bitterness and number of fungiform papilla), NaCl and citric acid intensity, and spatial taste pattern in 40 females and 43 males. Subjects used the general Labeled Magnitude Scale (gLMS) [Chem. Senses 18 (1993) 683; J. Food Qual. Pref. 14 (2002) 125] as an intensity and hedonic scale. Those who tasted PROP as most bitter or had highest numbers of fungiform papilla reported greatest oral burn from an alcohol probe; those who tasted least PROP bitterness consumed alcoholic beverages most frequently. Although higher NaCl and citric acid ratings associated with more frequent consumption of alcoholic beverages, the findings could be explained by lower intensity of tastants on the tongue tip (chorda tympani nerve) relative to whole mouth perception. In multiple regression analyses, PROP bitterness and the spatial pattern of taste perception were independent contributors to the prediction of alcohol intake. In summary, the results support that variation in oral sensation associates with alcohol intake. Those who taste PROP as least bitter and have low chorda tympani relative to whole mouth taste intensity appear to have fewest oral sensory hindrances to the consumption of alcoholic beverages.

Adult↗

[Disturbances of taste from oral disinfectants (author's transl)].

Oral disinfectants containing chlorhexidine or hexetidine are able to produce disturbances of taste, as demonstrated by Krarup's electrogustometric method and the gustometric method of Harris and Kalmus. Hypo- and dysgeusia are characterized by dissociated disturbances, the most prominent of which concerns the sweet perception. The bitter taste is least affected, whereas the effects on salty and acidic tastes range between that for sweet and bitter. Taste disturbances which include ageusia for 48 h were observed when the tongue was touched with a 20% solution of chlorhexidine. Not only the disinfectants themselves provoked dysgeusia but also other "taste improving" agents (particularly, the volatile oild). In addition to dysgeusia, the authors found disturbances of the mucous membrane sensitivity caused by the test substances.

Adult↗

Use of flavor-amplified foods to improve nutritional status in elderly patients.

Impairment of taste and smell perception can lead to decreased food intake in the elderly. The losses in chemosensory functioning can result from normal aging, disease state, drugs, and environmental pollutants. Experimental investigations are underway to develop practical taste enhancers. Clinical studies suggest that the addition of odors to foods to compensate for diminished chemosensory functioning is often helpful in increasing intake of nutrient-dense foods in older persons.

Aged↗

[Disorders of smell and taste. Standard and recent methods in diagnosis and therapy].

Compared to disorders of the ears and eyes, diseases of smell and taste seem to be far less outstanding: however, the unimpaired perception of odours and flavours comprises an important part of our well-being, as can be seen in the perfume industry or in drinking and eating habits. The ENT-specialist covers organic causes of these senses, as he has the tools to explore and treat in the depth of the nasal and oral cavities. The "Arbeitsgemeinchaft Olfaktologie/Gustologie der Deutschen Gesellschaft für Hals-Nasen-Ohrenheilkunde, Kopf- und Halschirurgie" therefore is in process of establishing a new set for a standardised smell and taste test, which is based in part on the sniffin'sticks, which were developed by Prof. Kobal, Erlangen. The examination procedure of nasal and oral chemosensory performance requires a high test-retest reliability and an efficiency comparable to internationally established measurements in order to render valid results in diagnostic and therapeutic procedures. The new test kit with the sniffin'sticks is presented in this paper, followed by an overview on some disorders of smell and taste perception and proposals for actual therapeutic procedures.

Ageusia↗

PROP taster status and oral fatty acid perception.

Recent studies with rat taste cells treated with polyunsaturated fatty acids suggest that fatty acids may play a role in dietary fat perception. In humans, sensitivity to the textural properties of fat is associated with the genetic ability to taste the bitter compound 6-N-2-propylthiouracil (PROP). However, it has not been shown that PROP tasters are more sensitive in discriminating fatty acids in a high-fat food. Our study with human subjects was designed to test the hypothesis that the ability to orally detect food-grade conjugated linoleic acid added to high-fat vanilla ice cream is associated with the ability to taste PROP. Eighty percent of the PROP tasters in this study, but only 17% of the PROP nontasters correctly discriminated the sample containing the added free fatty acid in a difference test versus unadulterated high-fat vanilla ice cream (Fisher's Exact Test, P=.05). Because most fatty foods contain minute amounts of free fatty acids, further studies with humans examining the contribution of fatty acids to fat perception seem warranted.

Journal Article↗