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PubMed2003

Preexposure to the stimulus elements, but not training to detect them, retards human odour-taste learning.

Odours are judged to smell sweeter following simultaneous oral pairings with the tastant sucrose and sourer after parings with the tastant citric acid. This effect may result from human participants perceiving and encoding a unitary odour-taste percept. This study examined two factors thought likely to disrupt such encoding; (a) preexposure to the mixture elements and (b) training to spot the elements of taste-odour mixtures. Half of the participants were trained to identify tastes and smells and half received no training. All participants were preexposed to two odours (A, B) and two tastes (X, Y), followed by pairings of these stimuli (AX, BY) and then by pairings between two non-preexposed odours and the same tastes (CX, DY). This process was then repeated on a second session. Odour-taste learning was retarded following preexposure, but was unaffected by training. These findings suggest; (1) that odour-taste mixtures may be cognitively impenetrable and (2) that preexposure leads to encoding of A and B, which are then resistant to interference when further pairings are presented (i.e. AX, BY).

Journal Article↗
PubMed1996

Vallate, foliate and fungiform human papillae gustatory cells. An immunocytochemical and ultrastructural study.

We studied the classifications, topographic distribution and cellular lines of taste bud components in vallate, foliate and fungiform papillae of young, mature and old men with light microscopy, SEM, and TEM. By identifying ultrastructural and immunocytochemical characteristics, three distinct sensorial cells were identified, along with a few basal cells: dark type I cells, light type II cells and light type III cells. These cells extend from the epithelial basal lamina to the gustatory canal, where their apical cytoplasm sends long microvillous expansions. Excluding those of the fungiform papillae-which never go beyond the lower third of the gustatory canal, and are always void of dense substance-the microvillous expansions continue to the external border of the taste pore. Dark type I cells are rich in free ribosomes, tubular RER and large dense granules. Light type II cells with scarce ribosomes and RER, do not have enough peculiar ultrastructural characteristics to be considered effector or phagocyte elements. Light type III cells are characterizes by dense core vesicles whose peculiar ultrastructural characteristics in the foliate and vallate papillae, should be considered a consequence of different functional phases. After comparative evaluation the authors hypothesized on the functional value of some ultrastructural aspects and on the dense core vesicles which are immunoreactive to 5-HT. They observed that all gustatory cells are involved in taste transduction based on behaviours caused by microvilli in the gustatory canal and gustatory cell relationships with nerve endings. Moreover the authors noted that age does not seem to influence taste perception.

Adult↗
PubMed1999

Confusing tastes and smells: how odours can influence the perception of sweet and sour tastes.

This study investigated the relationship between perception of an odour when smelled and the taste of a solution to which the odour is added as a flavorant. In Experiment 1 (E1) sweetness, sourness, liking and intensity ratings were obtained for 20 odours. Taste ratings were then obtained for sucrose solutions to which the odours had been added as flavorants. Certain odours were found to enhance tasted sweetness while others suppressed it. The degree to which an odour smelled sweet was the best predictor of the taste ratings. These findings were extended in Experiment 2 (E2), which included a second tastant, citric acid, and employed four odours from E1. The most sweet smelling odour, caramel, was found to suppress the sourness of citric acid and, as in E1, to enhance the sweetness of sucrose. Again, odours with low sweetness suppressed the sweetness of tasted sucrose. The study demonstrated that the effects of odours on taste perception are not limited to sweetness enhancement and apply to sour as well as sweet tastes. The overall pattern of results is consistent with an explanation of the taste properties of odours in terms of prior flavour-taste associations.

Adult↗
PubMed1997

Analysis and comparison of partial sequences of clones from a taste-bud-enriched cDNA library.

Differential patterns of cellular development and function are determined, at least in part, by the specific gene expression of particular cells. Thus, determination of differential patterns of gene expression between tissues is likely to help elucidate molecular details of tissue-specific processes. Our hypothesis was that cells of the circumvallate papilla involved in taste perception would express genes that are not expressed in the surrounding epithelium and that determination of the nature of these genes could be helpful in our understanding of the molecular details of taste. Using partial sequencing of clones derived from rat circumvallate papillae, we have begun to characterize genes that could be important in taste. We prepared a cDNA library of whole circumvallate papillae and, by means of a novel subtraction procedure, enriched taste-specific clones. Characterization of the libraries showed that subtraction resulted in good enrichment of taste-specific clones. Here we report the partial sequencing and analysis of 410 cDNA clones from the taste-bud-enriched cDNA library. Approximately 25% of the genes were identified on the basis of their high homology to known transcripts. These included the developmentally important molecules Pax-1, esp1, Notch 1, and Notch 3 that may play roles in the continuous turnover of taste receptor cells. A further 20% of the genes had no significant homology to known DNA sequences and were identified as taste-specific by Southern blot analysis.

Animals↗
PubMed1992

Early developmental change in bitter taste responses in human infants.

Human newborns (birth-6 days) and older infants (14-180 days) were allowed to ingest both urea (0.12-0.24 M) in a mildly sweet diluent and the diluent alone, and multiple measures of responsivity were obtained (relative intake, sucking behavior, and hedonic ratings based on facial expressions and body movements). For newborns, there was no indication of rejection of urea relative to the diluent in measures of intake or sucking behavior; rather, their responses were predominantly controlled by the order of presentation of the two tastes. In contrast, older infants tended to reject all concentrations of urea according to these measures. Hedonic ratings provided an indication of limited rejection of the bitter taste by newborns, but older infants were still found to respond more consistently. These data suggest there is an early developmental change in bitter taste perception.

Facial Expression↗
PubMed1999

Neural coding of gustatory information.

The nervous system encodes information relating chemical stimuli to taste perception, beginning with transduction mechanisms at the receptor and ending in the representation of stimulus attributes by the activity of neurons in the brain. Recent studies have rekindled the long-standing debate about whether taste information is coded by the pattern of activity across afferent neurons or by specifically tuned 'labeled lines'. Taste neurons are broadly tuned to stimuli representing different qualities and are also responsive to stimulus intensity and often to touch and temperature. Their responsiveness is also modulated by a number of physiological factors. In addition to representing stimulus quality and intensity, activity in taste neurons must code information about the hedonic value of gustatory stimuli. These considerations suggest that individual gustatory neurons contribute to the coding of more than one stimulus parameter, making the response of any one cell meaningful only in the context of the activity of its neighbors.

Acids↗
PubMed1986

Clinical applications and mechanism of intravenous taste tests.

It is well known that there are two ways to measure human blood circulation time: the arm-to-lung and the arm-to-tongue method. The decholin (20% dehydrocholic acid) test is usually used to measure the arm-to-tongue circulation time. In this study, this procedure was used to examine taste function. Findings on the clinical application of this intravenous taste test using decholin and a study on the mechanism of venous taste perception are reported here. The following method was used: Five ml of 20% decholin were injected into the right cubital vein over a 10-sec period and the latent time, the duration, the quality of the taste sensation and the region of the tongue where the taste appeared were noted. The results were as follows: 1) In dysgeusic subjects, the latent period was longer, and the duration of the taste sensation was shorter than in normal subjects (p is less than 0.01, p is less than 0.05). 2) Some of the dysgeusic subjects perceived the taste as other than bitter; their prognosis of taste dysfunction tended to be worse than that of other subjects. 3) Some of the dysgeusic subjects perceived the taste in regions of the tongue other than the bilateral edges or over the entire tongue; their prognosis of taste dysfunction tended to be worse than that of other subjects. 3) Some of the dysgeusic subjects perceived the taste in regions of the tongue other than bilateral edges or over the entire tongue; their prognosis tended to be worse than that of other subjects. In addition, photofluorograms of the tongue were taken to clarify the mechanism of intravenous taste; the time needed for fluorescence to appear in the fungiform papillae and their diffusion form in the papillae were observed and investigated.

Adolescent↗
PubMed1992

Gustatory neural coding in the monkey cortex: L-amino acids.

1. Single-neuron activity in the primary gustatory cortex of the alert cynomolgus monkey (Macaca fascicularis) was analyzed in response to a range of taste stimuli. Tastants included the four prototypical stimuli (glucose, NaCl, HCl, and quinine), fruit juice, and 12 amino acids selected for their chemical characteristics, nutritional significance, and biological importance, as well as for the availability of human psychophysical data on their perceived qualities. 2. Taste-evoked responses could be recorded from a cortical area that measured 3.5 mm in its anteroposterior extent, 2.0 mm mediolaterally, and 6.0 mm dorsoventrally. Gustatory cells constituted 4.8% of the 1,129 neurons tested. Nongustatory cells gave responses associated with mouth movements (11.1%), somatosensory stimulation (3.8%), approach or anticipation of the taste stimulus (2.2%), and tongue extension (0.4%). 3. The most effective taste stimuli were those with qualities that humans describe as salty or sweet: NaCl, monosodium glutamate, glucose, proline, glycine, and fruit juice. The least effective tastants were those rated bitter or insipid: tyrosine, tryptophan, phenylalanine, and leucine. Accordingly, 79% of the gustatory neurons responded best to glucose (46%) or NaCl (33%) among the basic stimuli; only 19% responded best to quinine (13%) or HCl (6%). One cell (2%) responded exclusively to fruit juice. 4. Cortical gustatory neurons showed a moderate breadth of sensitivity, with a mean breadth of tuning coefficient of 0.71 across 54 cells. There was no evidence of chemotopic organization in the taste cortex. 5. The taste quality of each stimulus was inferred from the relative similarity of the profiles they evoked. The clearest distinction among stimuli was between those that humans characterize as sweet versus those with other qualities. Several amino acids that have dominant sweet (glycine and proline), salty (arginine and monosodium glutamate), sour (tryptophan), or bitter (phenylalanine) components to humans evoked activity profiles that were associated with those of the appropriate prototypical stimuli. Others (cysteine and lysine) were not closely related to any single prototype. 6. Conclusions based on the responses of cortical cells in the monkey are in close agreement with those that derive from human psychophysical studies of L-amino acids, reinforcing the value of this neural model for human taste perception.

Amino Acids↗
PubMed1986

[Differential taste sensitivity of Pygmy and non-Pygmy populations of the dense forest, Sudanese and Eskimos, in relation to their biochemical environment].

Significant differences of taste thresholds for different sugars, salt, organic acids, and bitter products, observed in human populations in contrasted environments, are related to potential variations of traditional diet. In this respect, biochemical composition of the environment would be the major selective pressure for taste perception.

Adult↗
PubMed1993

Latent learning about calcium and sodium.

We used the latent-learning paradigm to examine whether replete rats can recognize sodium and calcium and whether they use that knowledge to guide consumption when subsequently mineral deprived. Rats fed a nutritionally complete diet received four pairs of 17-h training trials. During one trial of each pair, the rats drank grape- or cherry-flavored water; during the other, they drank the other flavor mixed with 100 mM CaCl2 (experiment 1), 750 mM NaCl (experiment 2), or 584 mM (20% wt/vol) sucrose (experiment 3). The rats were then fed nutritionally complete, calcium-deficient, or sodium-deficient diet for 3 wk and were given a two-bottle preference test between the two flavors. Relative to rats fed complete diet, calcium-deprived rats had elevated preferences for calcium- and sodium-paired flavors but not sucrose-paired flavors. Sodium-deprived rats had elevated preferences only for sodium-paired flavors. These results provide evidence for the existence of innate calcium and sodium appetites in calcium-deprived rats. They indicate that these distinct appetites are centrally generated behaviors and are not simply due to peripheral alterations in taste perception.

Animals↗
PubMed1980

Malrecognition of taste in uremia.

Impaired cognitive functions were reported in uremia. The purpose of this study was to quantify the functional state of taste in various stages of chronic renal failure. Taste sensitivity was assessed by asking the subjects to identify test solutions of sucrose ('sweet'), NaCl ('salty'), citric acid ('sour'), quinine ('bitter') and water presented randomly in five concentrations. The number of recognition errors was statistically analyzed as a measure of taste acuity. Four groups of subjects were examined: 20 nondialyzed uremic patients, 23 patients on regular hemodialysis, 20 patients suffering from chronic diseases with normal renal functions and 22 healthy volunteers. Non dialyzed and dialyzed uremic patients younger than 55 years had a significant impairment of recognition in all taste modalities when compared to both control groups. This was less obvious in patients older than 55 years. No differences in taste recognition were found between dialyzed and nondialyzed uremics of all ages. In the younger age group, however, there was imrpovement in the recognition of 'sour' and 'bitter' when tested before and immediately after the dialysis session. As zinc deficiency was excluded in all of the uremic patients we conclude that the impaired taste perception is another subtle facet of the uremic neuropathy.

Adult↗
PubMed1987

[Blood levels of corticosterone, aldosterone, angiotensin and ACTH in rats after deafferentation of the tongue].

The influence of tongue deafferentation on the plasma level of sodium homeostasis-controlling hormones has been studied. Using radioimmunoassay, high corticosterone and aldosterone plasma levels were discovered in rats with tongue deafferentation, as compared to sham-operated controls. ACTH and angiotensin I plasma concentrations in deafferentated rats were the same as in sham-operated rats. The role of emotional factors of taste perception in sodium homeostasis control is being discussed.

Adrenocorticotropic Hormone↗
PubMed1982

Flavor enhances the antidipsogenic effect of naloxone.

Naloxone suppressed ingestion of tap water following a 15 hour deprivation at doses of 20, 10 and 5 mg/kg. Addition of saccharine (0.2%), saline (0.8%), sucrose (2%) and HCl (0.1 M) to tap water resulted in an increased sensitivity to naloxone-induced suppression of water intake following the 15 hour deprivation. The volume of quinine solution (0.1%) consumed was not altered by administration of naloxone. We suggest that naloxone suppresses drinking behavior due to alterations in taste perception.

Animals↗
PubMed1993

Gustatory neural coding in the monkey cortex: the quality of sweetness.

1. We analyzed the activity of single neurons in gustatory cortex of alert cynomolgus monkeys in response to the four basic taste stimuli and to a range of chemicals, all of which are predominantly sweet to humans. 2. We recorded taste-evoked responses from a cortical area that measured 4.0 mm in its anteroposterior extent, 5.6 mm dorsoventrally and 2.2 mm mediolaterally. Taste-responsive neurons constituted 4.7% of the 3,066 neurons tested in the course of 66 recording tracks. Nongustatory cells included those responsive to mouth movement (34.1%), tongue touch (1.9%), stimulus approach (0.7%), and tongue extension (0.5%). The functions of 58.2% of the cells we isolated could not be determined. 3. The mean breadth of tuning of these cortical taste neurons was a moderate 0.59 (range 0.00-0.93). 4. There was no evidence that taste cells with similar functional attributes were clustered in the cortex, i.e., there was no apparent topographic organization of taste qualities. 5. A taste space was generated from the correlations among patterns of neural activity evoked by the stimulus array. Within the space, NaCl was most isolated from other stimuli; the profiles elicited by HCl, quinine HCl, and water were all moderately intercorrelated and were clearly distinct from the cluster of sweet stimuli. 6. The 19 sweet chemicals formed a coherent cluster centered on the simple carbohydrates (glucose, fructose, sucrose, maltose) and sorbitol. Nearest this core were calcium cyclamate, aspartame, and cran-raspberry juice. In the next concentric ring were acesulfame potassium, xylose, xylitol, sorbose, polycose, and myoinositol. Increasingly distant from the sugars were sodium saccharin, stevioside, neohesperidin DHC, L-tryptophan and monellin. 7. We compared these results with those of a human psychophysical study of sweet stimuli. Using the position of glucose as a reference, we measured the distances to all other stimuli that were common to the two studies (n = 15). The correlation between the human psychophysical data and those derived from evoked activity in the macaque cortex was +0.82. 8. The high correlation between human psychophysical and macaque electrophysiological data implies that the subtle distinctions among stimuli that are predominantly sweet are quite similar for these two species and reinforces the value of this neural model for human taste perception.

Action Potentials↗
PubMed2026

Dietary soybean or seaweed (Kappaphycus sp.) modulates taste-related gene (tas1r1 and tas1r2.2) expression in Nile tilapia (Oreochromis niloticus).

Taste perception plays a central role in fish feeding behaviour by influencing feed recognition, intake, and nutrient sensing. As aquaculture increasingly adopts plant-based ingredients to replace fishmeal, understanding how these diets affect gustatory mechanisms is critical. This study evaluated TAS-family taste receptor genes in Nile tilapia (Oreochromis niloticus) fed nutritionally formulated diets containing fishmeal (TFM), soybean meal (TSB), red seaweed (Kappaphycus sp., TSW), alongside a natural meal (TNM) reference. Fish were reared for 62 days under controlled conditions, after which growth performance was evaluated, and tongue transcriptomes were analysed using RNA sequencing to identify diet-associated gene expression changes. Candidate TAS1R and TAS2R receptors were identified through conserved domain screening and phylogenetic validation, and differential expression analysis was performed using DESeq2. Growth performance did not differ significantly among diets, although the soybean group showed the highest weight gain. Under the conditions of this study, most taste-related genes remained transcriptionally stable across formulated diets, indicating limited responsiveness of the gustatory system to ingredient substitution. Transcriptional differences were mainly observed in comparisons involving the TNM (TSB vs TNM and TSW vs TNM), where tas1r1 was upregulated, suggesting altered amino acid sensing relative to the non-formulated diet. Among formulated diets, tas1r2.2 was upregulated in the TSW vs TFM comparison, indicating potential modulation of carbohydrate-related taste pathways associated with seaweed inclusion. No reliable TAS2R transcripts were detected, likely due to low expression or tissue-specific distribution. Overall, taste receptor expression in Nile tilapia appears resilient to dietary variation, with selective modulation of TAS1R genes providing molecular insight into chemosensory adaptation to sustainable feed ingredients.

Animals↗
PubMed2000

Taste sensitivity to sodium chloride and sucrose in a group of adolescent children in Northern Nigeria.

In a sub-population of Nigerian children in the southern rain forest of Edo State, we recently observed widespread relative insensitivity to the taste of sodium chloride (NaCl-salt). This prompted the present study, in which we measured taste recognition threshold to NaCl (30, 60, 120, 180 mM) and sucrose (15, 50, 100, 150 mM) in a group of fifth-and sixth-grade pupils in the northeastern semi-Sahel part of Nigeria, in order to observe the extent to which the findings cited above would apply to similar groups of Nigerians with different ethnic backgrounds in other parts of the country. Three hundred twenty-eight pupils (149 boys, 179 girls) from 9 to 18 years of age were involved. Five subjects were taste-blind to the highest concentration (180 mM) of NaCl. In addition, 44.5% of the study population did not taste NaCl until a concentration of 60 mm or higher was used. This distribution was influenced neither by gender (x2 = 2.75, df = 3, P = .43) nor age (r = .029, P = .60). In addition, only 33% of the population recognized sucrose sweetness at a sucrose concentration of 15 mm or lower. The remaining two-thirds of the population had sucrose threshold values of 50 mm or higher and neither gender (x2 = 3.09, df = 3, P = .379) nor age (r = .046, P = .41) influenced these findings. These results substantiate our earlier observations that relative taste insensitivity to salt (NaCl) may be common in Nigerian children. When compared to our earlier data, these results indicate that taste insensitivity to NaCl and sucrose may be more common in children in the northern parts of the country, thus suggesting that geographic location and ethnicity may be important variables in taste perception of NaCl and sucrose in adolescent Nigerians.

Child↗
PubMed1999

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↗
PubMed1994

Perceptual interactions in mixtures containing bitter tasting substances.

Mixtures of Quinine HCl and NaCl elicit heterogeneous taste percepts. Each such percept consists of a bitter and a salt sensation. Using functional measurement in combination with a two-stimulus procedures, it was found that the NaCl suppresses the QHCl bitterness and that QHCl has almost no suppressive effect on NaCl saltiness. In addition, it was shown that the total intensity of the mixture percept is almost identical to the sum of the intensities of the bitterness and saltiness sensations-within-the-percept. As was found in earlier experiments with mixtures of other tastants, central sensory integration within a heterogeneous percept seems to be a fairly simple additive process.

Adult↗