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Putative mammalian taste receptors: a class of taste-specific GPCRs with distinct topographic selectivity.

Taste represents a major form of sensory input in the animal kingdom. In mammals, taste perception begins with the recognition of tastant molecules by unknown membrane receptors localized on the apical surface of receptor cells of the tongue and palate epithelium. We report the cloning and characterization of two novel seven-transmembrane domain proteins expressed in topographically distinct subpopulations of taste receptor cells and taste buds. These proteins are specifically localized to the taste pore and are members of a new group of G protein-coupled receptors distantly related to putative mammalian pheromone receptors. We propose that these genes encode taste receptors.

Animals↗

Taste disorders in acute stroke: a prospective observational study on taste disorders in 102 stroke patients.

BACKGROUND AND PURPOSE: The aim of the study was to assess whether and how frequently patients with acute first-ever stroke exhibit gustatory dysfunction. METHODS: We performed a 1-year prospective observational study. Gustatory function was assessed using the standardized "taste strips" test. In addition, we assessed olfactory function, swallowing, stroke location, comorbidities, and the patients' medication. RESULTS: A total of 102 consecutive patients were enrolled (45 female, 57 male; mean age, 63 years); 31 of them (30%) exhibited gustatory loss and 7 (6%) had lateralized impairment of taste function. Predictors of impaired taste function were male gender (P=0.003), high National Institutes of Health Stroke Scale (NIHSS) score at admission (P=0.009), coexisting swallowing dysfunction (P=0.026), and a stroke of partial anterior circulation subtype (PACS) (P=0.008). In particular, in hypogeusic patients the lesion was most frequently localized in the frontal lobe (P=0.009). Follow-up examinations in 14 patients indicated improvement of taste sensitivity. CONCLUSIONS: Taste disorders after stroke are frequent. A significant association was found for male gender, high NIHSS score, swallowing disorder, and PACS, particularly in the frontal lobe. Generally, taste disorders after stroke seem to have a good prognosis.

Adult↗

Biochemical studies of taste sensation. IX. Enhancement of L-[3H]glutamate binding to bovine taste papillae by 5'-ribonucleotides.

The interaction of the taste substance monosodium L-glutamate with taste receptors has been investigated. Binding of L-[3H]glutamate was measured to preparations of bovine circumvallate (taste) papillae (type I preparation) and to control tongue epithelial preparations (type II preparation) devoid of taste receptors. Binding is operationally defined using a membrane filtration assay. Substantially greater binding occurred to the type I preparation than to the type II preparation, and the binding to the type I preparation showed evidence of saturation. The apparent Kd of L-glutamate was estimated to be in the range of 20--30 mM. The unique taste effect of L-glutamate was considered to depend importantly on its demonstrated synergism in combination with certain 5'-ribonucleotides. A several-fold enhancement of binding of L-[3H]glutamate occurred in the presence of certain 5'-ribonucleotides. 5'-GMP, 5'-IMP and 5'-UMP each increased the binding of L-[3H]glutamate, while 5'-XMP, 5'-AMP and 5'-CMP did not. None of these nucleotides affected the lower level of binding to the type II preparation. Neither the free bases, adenine and guanine, their nucleosides nor their di- or triphosphonucleotides were effective in increasing L-[3H]glutamate binding to the type I preparation. The nucleotide specificity of the glutamate binding enhancement therefore shows a marked similarity with the nucleotide specificity in evoking the synergistic taste effect in humans.

Animals↗

Differences in health and taste attitudes and reported behaviour among Finnish, Dutch and British consumers: a cross-national validation of the Health and Taste Attitude Scales (HTAS).

The Health and Taste Attitude Scales (HTAS) developed by Roininen, Lähteenmäki and Tuorila in 1999 measure the importance of health and taste aspects of foods in the food choice process. These multi-item scales consist of sets of statements, ranging from "strongly disagree" to "strongly agree", which further divide into three Health (General health interest, Light product interest and Natural product interest) and three Taste (Craving for sweet foods, Using food as a reward and Pleasure) sub-scales. Finnish (N=467), Dutch (N=477), and British (N=361) respondents completed a questionnaire which contained four components: the HTAS, a separate "paper and pencil task" of choosing a food for a snack; pleasantness, healthiness and frequency of consumption of eight foods; and the Restraint Eating Scale of the Dutch Eating Behaviour Questionnaire (DEBQ). The latter three components were included in order to validate various aspects of the HTAS. The factor structure of HTAS was found to be equal in all three countries. However, there were some minor differences in factor loadings among countries, e.g. the Natural product interest and Pleasure sub-scale items had lower factor loadings in the UK than in Finland and The Netherlands. Finnish respondents had the most positive attitude towards light products. Dutch and British respondents scored higher on all Taste sub-scales than their Finnish counterparts. Respondents' health-related attitudes were good predictors of their "healthy food choices" in the snack task and self-reported consumption. Two of the Taste sub-scales (Craving for sweet foods and Using food as a reward) predicted well respondents' self-reported consumption of, for example, full-fat chocolate bars. All the Health and two of the Taste sub-scales proved to be useful tools for characterizing consumer attitudes within and between countries.

Adolescent↗

Lesions of the central nucleus of the amygdala. I: Effects on taste reactivity, taste aversion learning and sodium appetite.

Bilateral damage to the central nucleus of the amygdala (CeAX) in the rat blunts need-induced NaCl intake and abolishes daily need-free NaCl intake when measured with a two-bottle test. Such a deficit could be the result of impaired taste function. To assess the taste function of the CeAX rat various taste stimuli were introduced directly into the oral cavity and taste-elicited oral motor responses were measured. Oral motor responses elicited by 0.62 M and 0.13 M sodium chloride, 0.3 M sucrose and 0.01 M citric acid, were similar in control and CeAX rats. Additionally CeAX and control rats acquired a taste aversion for fructose or maltose when either was paired with LiCl. Finally, in CeAX rats, like in control rats, the pattern of oral motor responses to 0.5 M NaCl was dependent on internal state; sodium depletion dramatically altered taste-elicited oral motor behavior. These results suggest that, in the rat, the deficits in NaCl intake behavior that follow CeAX do not appear to be a result of dramatic changes in gustatory function.

Amygdala↗

Elucidating coding of taste qualities with the taste modifier miraculin in the common marmoset.

To investigate the relationships between the activity in different types of taste fibers and the gustatory behavior in marmosets, we used the taste modifier miraculin, which in humans adds a sweet taste quality to sour stimuli. In behavioral experiments, we measured marmosets' consumption of acids before and after tongue application of miraculin. In electrophysiological experiments responses of single taste fibers in chorda tympani and glossopharyngeal nerves were recorded before and after tongue application of miraculin. We found that after miraculin marmosets consumed acids more readily. Taste nerve recordings showed that after miraculin taste fibers which usually respond only to sweeteners, S fibers, became responsive to acids. These results further support our hypothesis that the activity in S fibers is translated into a hedonically positive behavioral response.

Animals↗

Identification of the taste enhancer alapyridaine in beef broth and evaluation of its sensory impact by taste reconstitution experiments.

An essential compound imparting the sweet taste to beef broth was investigated. Taste activity-guided fractionation of beef broth by ultrafiltration, gel permeation chromatography, and HPLC in combination with the recently developed comparative taste dilution analysis enabled the localization of a fraction possessing sweetness-enhancing activity upon degustation. Comparison of the chromatographic, spectroscopic, and sensory data with those of the synthetic reference compound led to the identification of the sweetness-enhancing N-(1-carboxyethyl)-6-(hydroxymethyl)pyridinium-3-ol inner salt, named alapyridaine, which was recently isolated from heated aqueous solutions of hexoses and l-alanine. After quantification of alapyridaine in beef broth, sensory analysis of synthetic beef taste recombinates spiked with synthetic alapyridaine in its "natural" concentration of 419 mug/L and comparison to the taste quality of a tastant recombinate lacking the alapyridaine revealed a significant increase in sweetness and umami character only when the alapyridaine was present in the recombinate. These data demonstrate for the first time that, in "natural" concentrations, the alapyridaine exhibited a pronounced effect on the overall taste quality of beef broth, in particular, on the sweet and umami character.

Alanine↗

Detection of changes in taste of japonica and indica brown and milled rice (Oryza sativa L.) during storage using physicochemical analyses and a taste sensing system.

Changes in the taste of japonica, hybrid, and indica brown and milled rice, stored for 10 months at low (5 degrees C, 65-70% relative humidity) and room temperatures were observed by physicochemical analyses and a novel method using a taste sensing system. During storage, some properties increased or decreased while others were fairly constant. The main taste components of cooked rice such as sweetness (sucrose) and umami tastes (glutamic acid and aspartic acid) were reduced during storage, whereas glucose and fructose increased. The increase of fat acidity and consequent decrease of the pH value of the cooking solution may contribute to the off-taste of cooked stored rice. A taste sensing system with 10 lipid membrane sensors was also used to classify new and old rice samples using principal component analysis. Fresh and room temperature stored japonica and indica rice could be clearly distinguished; however, it was not possible to differentiate the samples stored at low temperature.

Aspartic Acid↗

Thalamocortical relations in taste aversion learning: II. Involvement of the medial ventrobasal thalamic complex in taste aversion learning.

Previous neurobehavioral studies have implicated the gustatory thalamocortical relay as a functional substrate of conditioned taste aversion (CTA) learning. These experiments were conducted to examine the involvement of the gustatory thalamic nuclei in fundamental taste reactivity, gastrointestinal reactivity, and CTA learning. In Experiment 1, bilateral electrolytic lesions were produced in the medial ventrobasal thalamic complex (VBm), including the thalamic gustatory nuclei, in one group of rats. A separate group of rats received control lesion placements in the mediodorsal-periventricular (MD-PV) thalamic nuclei. Animals then received preference-aversion taste tests followed by CTA conditioning. At the conclusion of conditioning, lesions were produced in the anterior insular gustatory neocortex (AIGN) to evaluate whether or not the AIGN contributed to CTA learning in animals lacking VBm thalamus. Results of Experiment 1 indicated that control lesions did not disrupt taste reactivity, gastrointestinal reactivity, or CTA learning. Destruction of VBm thalamus attenuated taste reactivity to sucrose, citric acid, and quinine hydrochloride; however, such lesions did not impair normal taste reactivity to sodium chloride. Lesion placements in VBm thalamus also did not reliably impair gastrointestinal reactivity to ingested LiCl. Elimination of VBm thalamus markedly attenuated CTA learning. Results of neocortical lesion manipulations showed that the AIGN contributed to initial CTA learning in animals lacking MD-PV thalamus but that the AIGN did not mediate initial CTA learning in animals lacking VBm thalamus. Whether animals lacking VBm thalamus used olfactory cues associated with drinking solutions to acquire CTAs was evaluated in Experiment 2. Results of Experiment 2 demonstrated that animals lacking VBm thalamus and the olfactory bulbs could not acquire aversions to ingested LiCl following eight conditioning trials. These experiments demonstrate that destruction of VBm thalamus, including the gustatory thalamic nuclei, is sufficient to prevent CTA learning.

Afferent Pathways↗

Monosodium glutamate and sweet taste: generalization of conditioned taste aversion between glutamate and sweet stimuli in rats.

Even though monosodium glutamate (MSG) is a prototypical umami substance, previous studies reported that a conditioned taste aversion (CTA) to MSG, mixed with amiloride to block the taste of sodium, generalizes to sucrose. These findings suggest that the taste of glutamate mimics the taste of sucrose and raise the question of whether glutamate has a broadly tuned sweet taste component. To test this hypothesis, CTA experiments were conducted to test for generalization between MSG and several sweet stimuli: sucrose, glucose, maltose, saccharin and SC-45647. Strong bidirectional generalization was seen between MSG mixed with amiloride and sucrose, glucose, saccharin and SC-45647. Weak generalization was seen between MSG and maltose, and sucrose and maltose. None of the CTAs generalized to NMDA. These findings support the hypothesis that the taste of MSG has broadly tuned, sweet-like characteristics, possibly due to the convergence of afferent signals for MSG, natural sugars and artificial sweeteners.

Amiloride↗

Effect of concentration on taste-taste interactions in foods for elderly and young subjects.

An increase in concentration of one of the tastants in a 'real food' might affect not only the perception of the taste quality of that manipulated tastant but also the other perceivable taste qualities. The influence of concentration increase of sodium or potassium chloride in tomato soup, sucrose or aspartame in iced tea, acetic or citric acid in mayonnaise, caffeine or quinine HCl in chocolate drink, monosodium glutamate (MSG) or inosine 5'-monophosphate (IMP) in broth on the other perceivable taste qualities in these foods was studied in 21 young subjects (19-33 years) and 21 older subjects (60-75 years). The results showed that for each of these tastants, except for the two acids, increasing the concentration provoked significant positive or negative interaction effects on the perception of one or more other taste qualities of the product. Especially in the young, olfaction plays a larger role in the assessment of taste intensity than has been hitherto assumed. The elderly are less able to discriminate between the taste qualities in a product, whereas the young are more able to do so.

Acetic Acid↗

Mechanism of nonlinear responses of taste cells to mixed tastes.

Coupling between ionic flows through different kinds of channels affects essentially the responses of multisensitive taste cells to single- and mixed-taste stimuli. The mechanism of taste transduction is studied by using a realistic model of the multisensitive cells of the rat. The transduction pathways considered are amiloride-sensitive Na+ channels for NaCl and HCl and adenosine 3',5'-cyclic monophosphate-mediating K+ channels for sucrose. Contributions of paracellular pathways and taste-insensitive ionic channels are also studied. The calculated responses of various multisensitive cells induced by single stimuli of NaCl, HCl, or sucrose reproduce experimentally observed responses as well. The two main conclusions are as follows. 1) Whether the response of a cell to a binary mixture becomes synergetic or antagonistic can be estimated from the individual responses of the cell to each component of the mixture. 2) Whether the response is enhanced or suppressed by addition of a new taste to the original taste can be determined, for most receptive cells, from a viewpoint of linear superposition of the individual responses.

Animals↗

Sweet taste transduction in hamster: sweeteners and cyclic nucleotides depolarize taste cells by reducing a K+ current.

1. The gigaseal voltage-clamp technique was used to record responses of hamster taste receptor cells to synthetic sweeteners and cyclic nucleotides. Voltage-dependent currents and steady-state currents were monitored during bath exchanges of saccharin, two high-potency sweeteners, 8-chlorophenylthio-adenosine 3',5'-cyclic monophosphate (8cpt-cAMP), and dibutyryl-guanosine 3',5'-cyclic monophosphate (db-cGMP). 2. Of the 237 fungiform taste cells studied, only one in eight was sweet responsive. Outward currents, both voltage-dependent and resting, were reduced by all of the sweeteners tested in sweet-responsive taste cells, whereas these currents were unaffected by sweeteners in sweet-unresponsive taste cells. 3. In every sweet-responsive cell tested, 8cpt-cAMP and db-cGMP mimicked the response to the sweeteners, but neither nucleotide elicited responses in sweet-unresponsive cells. Thus there was a one-to-one correlation between sweet responsivity and cyclic nucleotide responsivity. 4. Sweet responses showed cross adaptation with cyclic nucleotide responses. This indicates that the same ion channel is modulated by sweeteners and cyclic nucleotides. 5. The sweetener- and cyclic nucleotide-blocked current had an apparent reversal potential of -50 mV, which was close to the potassium reversal potential in these experiments. In addition, there was no effect of sweeteners and cyclic nucleotides in the presence of the K+ channel blocker tetraethylammonium bromide (TEA). These data suggest that block of a resting, TEA-sensitive K+ current is the final common step leading to taste cell depolarization during sweet transduction. 6. These data, together with data from a previous study (Cummings et al. 1993), suggest that both synthetic sweeteners and sucrose utilize second-messenger pathways that block a resting K+ conductance to depolarize the taste cell membrane.

Animals↗

Jacalin and peanut agglutinin (PNA) bindings in the taste bud cells of the rat: new reliable markers for type IV cells of the rat taste buds.

Lectin histochemistry of Jacalin (Artocarpus integrifolia) and peanut agglutinin (PNA), specific lectins for galactosyl (beta-1, 3) N-acetylgalactosamine (galactosyl (beta-1, 3) GalNAc), was applied to the gustatory epithelium of the adult rat. In the ordinary lingual epithelium, Jacalin and PNA labeled the cell membrane from the basal to granular cell layer. They also bound membranes of rounded-cells at the basal portion of taste buds, but the number of PNA labeled cells was smaller than that of Jacalin labeled cells. There was no apparent difference in the binding patterns of Jacalin and PNA among the taste buds of the lingual papillae and those of the palatal epithelium. Occasionally, a few spindle-shaped cells were labeled with Jacalin, but not with PNA. Double labeling of Jacalin and alpha-gustducin, a specific marker for type II cells, revealed that Jacalin-labeled spindle-shaped taste cells were immunonegative for alpha-gustducin. Spindle-shaped cells expressing protein gene product 9.5 (PGP 9.5) immunoreactivity lacked Jacalin labeling. During the development of taste buds in circumvallate papillae, the binding pattern of Jacalin became almost identical from postnatal day 5. The present results indicate that rounded cells at the basal portion of the taste buds cells (type IV cells) bind to Jacalin and PNA, and these lectins are specific markers for type IV cells of the rat taste cells.

Animals↗

Mechanism of action of some bitter-tasting compounds on frog taste cells.

Effects of some bitter-tasting compounds on frog taste receptors were examined by recording glossopharyngeal nerve responses. The order of effectiveness of the compounds was quinine greater than brucine greater than formanilide greater than caffeine greater than urea. When the effects of quinine, brucine and caffeine on electrical responses in taste cells were examined, they all produced a depolarization associated with an increased input resistance. The action of the three compounds on taste receptors therefore, operates with a similar mechanism. The electrical responses in cells, produced by quinine, progressed slowly with time. Such effects with quinine are similar to those with procaine. After adaptation to quinine, the nerve responses to various chemical stimuli were gradually reduced in magnitude, while the electrical responses in taste cells during stimulation by chemicals became smaller. The mechanism of the effects of bitter stimuli are discussed in light of recent findings on the interaction of bitter stimuli with lipid monolayers and the extraction of lipid from bovine taste papillae by bitter stimuli.

Animals↗

Age-related olfactory and taste changes and interrelationships between taste and nutrition.

This article critically reviews the literature on age-related olfactory and taste changes and the interrelationships between nutrition and taste. Age-related taste alterations are controversial, but there is consensus on an olfactory decline with age. Much of the age-related chemoreceptive research has used inappropriate methodology, thus leaving many findings inconclusive. Changes in the taste system with age may be related to nutrient intake, which in turn can be influenced by taste. Literature on such interrelationships is limited. Vitamins A, thiamin, B-6, B-12, folacin, zinc, and copper are thought to influence taste function. Moreover, those nutrients are of concern in the aged. The use of appropriate methodology is critical not only for the sensory but also for the nutritional aspects, particularly for qualitative and quantitative assessments of nutrient intakes. This review considers the experimental deficiencies (small sample size, inappropriate age range, inadequate psychophysical and stimuli presentation procedures, and poor dietary intake assessment) of studies reported in the literature and suggests major needs for research.

Aging↗

Radiation-induced taste aversion: effects of radiation exposure level and the exposure-taste interval.

Radiation-induced taste aversion has been suggested to possibly play a role in the dietary difficulties observed in some radiotherapy patients. In rats, these aversions can still be formed even when the radiation exposure precedes the taste experience by several hours. This study was conducted to examine whether increasing the radiation exposure level could extend the range of the exposure-taste interval that would still support the formation of a taste aversion. Separate groups of rats received either a 100 or 300 R gamma-ray exposure followed 1, 3, 6, or 24 h later by a 10-min saccharin (0.1% w/v) presentation. A control group received a sham exposure followed 1 h later by a 10-min saccharin presentation. Twenty-four hours following the saccharin presentation all rats received a series of twelve 23-h two-bottle preference tests between saccharin and water. The results indicated that the duration of the exposure-taste interval plays an increasingly more important role in determining the initial extent of the aversion as the dose decreases. The course of recovery from taste aversion seems more affected by dose than by the temporal parameters of the conditioning trial.

Animals↗

Peptide interactions with taste receptors: overlap in taste receptor specificity.

Two hitherto unrelated areas of taste appear to provide an important insight into a class of taste receptor sites. A region of the sweet protein monellin is similar to a savory tasting beef octapeptide, and this peptide region could represent an overlap in the specificity of binding to a common peptide taste receptor site. Such an overlap in binding specificity explains the low but significant level of sweetness observed with savory tasting stimuli.

Amino Acid Sequence↗