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PubMed1989

Alternative genetic models for the inheritance of the phenylthiocarbamide taste deficiency.

Pedigree segregation analysis was used to examine several one- and two-locus models of the inheritance of phenylthiocarbamide (PTC) taste deficiency that extend the traditional one-locus recessive model by the addition of either another allele or another locus, and in some cases predict two types of nontasters. These models allow nontaster by nontaster matings to produce taster offspring, consistent with our data and several previous studies which use the Harris and Kalmus [Annals of Eugenics 15:24-32, 1949] dilution method. The models fit our data set of 1,152 individuals from 120 families significantly better than the one-locus recessive model. The best fit was obtained with a two-locus model in which one locus controls PTC tasting and the other locus controls a more general taste ability. This model is consistent with research on the physiology of PTC tasting and with results from genetic linkage studies. Further study is suggested to evaluate better the accuracy of the proposed model.

Alleles↗

PubMed1976

A model for the stimulation of taste receptor cells by salt.

A taste cell mucosal surface is regarded as a planar region containing bound anionic sites and openings to ionic channels. It is assumed that the bulk aqueous properties of the exterior phase are not continuous with the surface but terminate at a plane near the surface. The region between the (Stern) plane and the membrane is regarded as having a lower dielectric constant than bulk water. This fact admits the possibility of ion pair formation between fixed sites and mobile cations. Mobile ion pairs entering the region may also bind to a fixed anionic site. Thus, it is assumed that mobile cations and ion pairs are potential determining species at the surface. Binding cations neutralizes surface charges, whereas binding mobile ion pairs does not. This competition accounts for the observed anion effect on stimulation of tast receptors by sodium salts. The potential profile is constructed by superimposing the phase boundary potentials with an ionic diffusion potential across the membrane. The model accounts for the anion effect on receptor potential, pH effects, the reversal of polarity when cells are treated with FeCl3, and the so-called "water reponse," depolarization of the taste cell upon dilution of the stimulant solution below a critical lower limit. The proposed model does not require both bound cationic and anionic receptors, and further suggests that limited access to a Stern-like region continuous with membrane channels may generally serve to control transport of ions.

Acetates↗

PubMed1976

Physicochemical studies of taste reception. III. Interpretation of the water response in taste reception.

The model membrane composed of a Millipore filter paper and the total lipids from bovine tongue epithelium or phosphatidylcholine from egg yolk simulated well the water response of a living taste cell, The water response observed with the model membrane adapted to various salt solutions was interpreted in terms of changes in electric potential at the membrane-solution interface, i.e. the water response was attributed to the e.m.f. change produced by diffusion of the electrolytes dissolved in (or adsorbed on) the membrane surface into the bulk solution. The water response of the frog tongue was also investigated by measuring the neural response of the glossopharyngeal nerve. The results obtained were consistent with the mechanism proposed in the present paper. The response of the frog to Ca2+ was examined under the condition where the water response was suppressed, and it was concluded that the water response of the frog is different from the response to Ca2+.

Animals↗

PubMed1987

Morphological evidence of innervation of taste buds of rat fungiform papillae after acute X-ray irradiation.

An acute dose of 2000 Roentgens (R) of x-ray was delivered to the head and neck area of Sprague-Dawley rats. Groups of rats were sacrificed at 0, 3, 7, 14, 21 and 30 days after x-ray irradiation. Both general nerve staining and localization of cholinergic nerves by special staining of fungiform papillae were performed. No apparent change in number and distribution of nerve fibres were observed light microscopically within the fungiform papillae containing normal, degenerating and regenerating taste buds. Similarly, cholinesterase activity was present in all control and experimental groups. These preliminary findings do not support the theory that taste bud degeneration is due to x-ray irradiation causing damage to related nerve fibres. A theoretical model of taste bud degeneration after acute x-ray irradiation is proposed.

Animals↗

PubMed1992

A review of sweet taste potentiation brought about by divalent oxygen and sulfur incorporation.

The plethora of high-potency sweetener research has allowed the construction of important structure-taste relationships. In light of new structure-taste relationships, it is instructive to review sweet taste potentiation brought about by divalent oxygen and sulfur incorporation. The taste of sulfur-containing organic compounds was reviewed in Japanese by Yasuo Ariyoshi in 1977. Several new representative examples of sweet taste potentiation and taste dichotomy (sweet and bitter) found within similar classes of oxygen- and sulfur-containing organic compound: amides, dipeptides, ureas, sulfamates, sulfonamides, oximes, sugars, dihydroisocoumarins, and others are reviewed. Special attention is given to the thioethers and thioureas in sulfamates, dipeptides, aryl ureas, and hybrid dipeptide ureas. The most notable contributions have arisen from the work of Nofre and Tinti at Université Claude Bernard in Lyons, France. A common trend emerges with certain sweeteners when a carbon atom is strategically replaced by sulfur or oxygen atoms. The net result is an increase in the sweetness two- to tenfold. With saccharins, the usual bitter, metallic taste is removed. Sweet taste receptor models that have been published are mainly based on the original Shallenberger and Acree model of the glucophores AH-B with contributions from Kier (AH-B-X). AH is a proton donor group, B is a proton acceptor group, and X is some hydrophobic group. All of the models have overlooked the contributions of divalent sulfur (often in place of oxygen) in bringing about sweetness potentiation. There is no precedence for localizing the energy-minimized structures of sulfur-containing sweeteners in a binding mode that includes sulfur. These sulfur potentiation loci are analyzed and illustrated in a computer-generated sweetener model to show the specific region in which sulfur is being "recognized" as a potentiating feature.

Humans↗

PubMed1979

Concept of neuron types in gustation in the rat.

1. In taste neurophysiology, from Pfaffmann's (49, 50) pioneering work until the present, the possibility of types of neurons corresponding in some sense with the "primary" taste qualities of Henning (33) has been entertained: recently types of gustatory neurons in peripheral nerves have been established according to which of the four classical stimuli is the "best stimulus." However, considerable variation occurs in the response profiles within neurons classified as belonging to the same type. The purpose of this research is to determine, using mathematical techniques where appropriate, if the within-type variation is spurious or, instead, indicates the absence of a typology of taste neurons. The data used were counts of the spike discharges of 50 individual taste neurons in the nucleus of the solitary tract of the rat, evoked by 32 diverse chemical stimuli. 2. Using as input the matrix of Pearson r correlation coefficients calculated for the responses of all pairings of neurons to all stimuli, multidimensional scaling analysis revealed a two-dimensional space in which no clear groupings of neurons occurred. 3. In a hierarchical cluster analysis of the neuron response profile similarities, no evidence of grouping was found, suggesting a more-or-less continuous variation among neurons. 4. When the organization of the 32 stimuli utilized was studied by the same techniques, no clear evidence for stimulus types was found, although the possibility of two stimulus types--"sweet" and "nonsweet"--was raised. 5. Construction of a joint neuron-stimulus space supported a spatial model of taste neuron-stimulus interaction, while analysis of the number and pattern of high correlations among neurons--even after allowance for attenuation due to measurement error--failed to support the notion of types of taste neurons with identical response profiles. 6. Aspects of the logical role of types of neurons in gustatory coding were discussed, and the results and methods of the present investigation were related to classification schemes for neurons in general. Suggestions for a formal taxonomy of neurons were given. 7. It should be emphasized that the present study and conclusions are of second-order, CNS neurons, whereas the studies advocating the presence of neurons types were of peripheral neurons. Taken together, the implication to be drawn from these studies is that if neural types do exist in peripheral taste nerves, the typology is lost at the first synapse and is thus unavailable to the CNS for coding purposes, at least in the rat.

Animals↗

PubMed1987

Sapid savvy in sucklings: the effect of quinine hydrochloride on intraoral negative pressure and intake by 11-13-day-old rat pups.

Three experiments describe the consummatory behavior of 11-13-day-old rat pups during and following experience with a model aversive taste, quinine hydrochloride. Pups were observed while away from the dam and while suckling. Results show that pups actively reject quinine adulterated solutions in both situations. They do so by spitting the solution from the mouth when away from the nipple and by leaving the nipple and/or decreasing their sucking effort when with the dam.

Animals↗

PubMed1991

Model for the dynamic responses of taste receptor cells to salty stimuli. I. Function of lipid bilayer membranes.

The dynamic response of the lipid bilayer membrane is studied theoretically using a microscopic model of the membrane. The time courses of membrane potential variations due to monovalent salt stimulation are calculated explicitly under various conditions. A set of equations describing the time evolution of membrane surface potential and diffusion potential is derived and solved numerically. It is shown that a rather simple membrane such as lipid bilayer has functions capable of reproducing the following properties of dynamic response observed in gustatory receptor potential. Initial transient depolarization does not occur under Ringer adaptation but does under water. It appears only for comparatively rapid flows of stimuli, the peak height of transient response is expressed by a power function of the flow rate, and the membrane potential gradually decreases after reaching its peak under long and strong stimulation. The dynamic responses in the present model arise from the differences between the time dependences in the surface potential phi s and the diffusion potential phi d across a membrane. Under salt stimulation phi d cannot immediately follow the variation in phi s because of the delay due to the charging up of membrane capacitance. It is suggested that lipid bilayer in the apical membrane is the most probable agency producing the initial phasic response to the stimulation.

Animals↗

PubMed1988

Ab initio molecular electrostatic potentials of perillartine analogues: implications for sweet-taste receptor recognition.

A model for the recognition of the perillartine analogues has been determined from a consideration of the molecular electrostatic potentials calculated at the ab initio 3-21G level for a select set of biologically active analogues. The model stresses the importance of two regions of negative electrostatic potential. One region, near the oxime moiety, does not vary in shape or value with substitution in the hydrocarbon domain. A second region in the hydrocarbon domain varies in depth, extension, orientation, and shape, depending on the nature of the substituent. The depth, relative position, and orientation of this latter region in the most potent systems (the 1,4-cyclohexadiene analogue and its p-methyl derivative) serve as the basis for the optimum recognition pattern of these analogues. The rank order of taste potencies is in general agreement with predictions based on this model. In addition, some conclusions are drawn concerning the receptor-analogue interaction as well as the electrostatic features of the receptor.

Cyclohexenes↗

PubMed1987

Taste and bulimia.

Binge-eating episodes in bulimia often involve sweet or fat-containing foods. Sensory perceptions and preferences for sweetness and fat content were examined in 16 normal-weight women with a diagnosis of DSM IIIR bulimia and in 16 normal-weight volunteer controls. Taste stimuli were 15 semi-liquid mixtures of dessert-type soft white cheese ("fromage blanc") containing 0, 3 or 7 grams of fat per 100 g, and sweetened with 1, 5, 10, 20, or 40% sucrose (wt./wt.). The subjects used 9-point category scales to rate the perceived sweetness and fat content of the stimuli, and assigned a pleasantness (hedonic) rating to each sample. Taste preferences were modelled using the Response Surface Method (RSM). Mean estimates of sweetness intensity and fat content were generally similar for bulimic patients and controls. In contrast, profiles of taste preference differed significantly between groups. Optimal stimulus sweetness was 15% sucrose wt./wt. for bulimic patients and only 9% for controls, while optimal fat levels were lower for bulimic patients relative to controls. The present data are consistent with previous reports that patients with eating disorders crave sweetness but show reduced sensory preferences for fat-containing foods.

Adult↗

PubMed1991

Gustatory neural coding in the monkey cortex: stimulus intensity.

1. We analyzed the activity of single neurons in gustatory cortex of alert cynomolgus monkeys in response to a range of stimulus intensities. Chemicals were deionized water, fruit juice, and several concentrations of the four prototypical taste stimuli: 10(-3)-1.0 M glucose, 10(-3)-1.0 M NaCl, 10(-4)-3 x 10(-2) M HCl, and 10(-5)-3 x 10(-3) M quinine HCl. 2. Taste-evoked responses could be recorded from a cortical gustatory area that measured 2.5 mm in its anteroposterior extent, 6.0 mm dorsoventrally, and 3.0 mm mediolaterally. Taste-responsive cells constituted 62 (3.7%) of the 1,661 neurons tested. Nongustatory cells gave responses associated with mouth movement (10.1%), somatosensory stimulation (2.2%), and approach or anticipation (0.9%). 3. Intensity-response functions were determined across 62 gustatory neurons. Neural thresholds for each stimulus quality conformed well to human psychophysical thresholds. Mean discharge rate was a direct function of stimulus concentration for glucose, NaCl, and quinine HCl. The most effective of the basic stimuli was glucose. 4. Power function exponents were calculated from the responses of neural subgroups most responsive to each basic stimulus. Those for glucose, NaCl, and quinine were within the range of psychophysically derived values. Thus the perceived intensity of each basic quality is presumably based on the activity of the appropriate neural subgroup rather than on the mean activity of all taste cells. 5. The mean breadth-of-tuning (entropy) coefficient for 62 gustatory neurons was 0.65 (range, 0.00-0.98). 6. There was no clear evidence of chemotopic organization in the gustatory cortex. 7. An analysis of taste quality indicated that sweet stimuli evoked patterns of activity that were clearly distinct from those of the nonsweet chemicals. Among the latter group, NaCl was differentiable from HCl and quinine HCl, whose patterns were closely related. 8. The response characteristics of cortical taste cells imply gustatory thresholds and intensity-response functions for the nonhuman primate that conform well to those reported in psychophysical studies of humans, reinforcing the value of this neural model for human taste intensity perception.

Action Potentials↗

PubMed1979

Salt taste adaptation: the psychophysical effects of adapting solutions and residual stimuli from prior tastings on the taste of sodium chloride.

The paper reviews how adaptation to sodium chloride, changing in concentration as a result of various experimental procedures, affects measurements of the sensitivity, intensity, and quality of the salt taste. The development of and evidence for the current model that the salt taste depends on an adaptation level (taste zero) determined by the sodium cation concentration is examined and found to be generally supported, despite great methodological complications. It would seem that lower adaptation levels elicit lower thresholds, higher intensity estimates, and altered quality descriptions with predictable effects on psychophysical measures.

Adaptation, Physiological↗

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↗

PubMed1989

The B6.SW bilineal congenic sucrose octaacetate (SOA)-taster mice.

SWR/J inbred mice (Tasters) reliably avoid, whereas C57BL/6J inbred mice (Nontasters) are indifferent to, sucrose octaacetate (SOA) at certain concentrations. From these strains we have developed a set of bilineal congenic Taster mice. Approximately 4000 mice, from 2 isogenic and 12 segregating generations, were tested in a program designed to evaluate genetic models for SOA tasting during development of congenic strains. The criterion phenotype was avoidance or nonavoidance in preference tests of the bitter tastant SOA at concentrations of 10(-4) and 10(-5) M. Across the 12 segregating generations, the results were consistent with Mendelian expectations for a single autosomal locus with complete dominance of the Taster phenotype. The breeding program produced 12 replicate B6.SW lines containing the taster allele on the B6-Nontaster genomic background. The congenic Taster mice may facilitate a functional analysis of the sense of taste.

Animals↗

PubMed1991

Specificity of mono- and divalent salt transduction mechanisms in frog gustation evidenced by cobalt chloride treatment.

1. Discrimination among stimuli with similar physical properties represents a formidable problem in sensory neurophysiology. The differential effect of cobalt chloride treatment on gustatory responses to monovalent and divalent salts may help to explain aspects of how the frog gustatory system encodes these stimuli. 2. Gustatory neural responses recorded from the glossopharyngeal nerve to divalent stimuli (CaCl2 and MgCl2) were inhibited by CoCl2 treatment, whereas monovalent responses (NaCl and KCl) were greatly augmented. Both effects were highly significant and completely reversible. 3. Intracellular recordings from the gustatory receptor cells, which synaptically initiate the impulses in the glossopharyngeal afferents, imply that these neural events are not a simple reflection of the receptor potential magnitude. Monovalent receptor potentials magnitudes (millivolts of depolarization) were enhanced by cobalt chloride, but receptor potentials to divalent stimuli were not inhibited. Rather they were either unaffected (MgCl2) or augmented (CaCl2). 4. Membrane resistance change during salt stimulation with cobalt chloride treatment followed the qualitative pattern observed with the neural response. Membrane resistance (in megohms) of the receptor cell was greater for divalent stimuli with cobalt treatment compared with divalent stimuli alone. Membrane resistance changes for monovalent stimuli were less with cobalt treatment compared with monovalent stimuli alone. These observations indicate that the glossopharyngeal neural response is not a simple reflection of the magnitude of the receptor potential but must be considered in conjunction with membrane resistance as an indicator of synaptic transmission. 5. These data were interpreted in terms of leading models of salt taste transduction, i.e., adsorption theories, phase boundary theories, and the direct penetration theories. Relevant mechanistic considerations for salt taste transduction in the frog include binding by divalents to membrane surface changes and amiloride-sensitive monovalent cation channels. It was concluded that the surface potential alone was not a critical variable in the mechanism of cobalt chloride alteration of salt responses.

Afferent Pathways↗

PubMed1986

[Contribution of stereochemistry to the study of the spatial organization of pharmacological receptors].

The important discovery by Pasteur of optical isomerism and the recent developments of stereochemistry showed that a complementarity exist between the geometry of molecules and their pharmacological receptors. The stereochemical bases and the principal configurational nomenclatures are briefly overviewed. The stereospecificity of the biological response and theories leading to an approach to stereochemical structures of main pharmacological receptors are developed. So, the biological activity of steroids is due to junctional modes of cycles and alpha or beta configurations of substituents. Acetylcholine has a skew conformation but it react by an anticlinal/anti-planar conformation with muscarinic receptor. To explain the difference in activity of adrenaline enantiomers, Easson and Stedman proposed a "three points" fixation to the adrenergic receptor. Dopaminergic receptor present a good degree of stereoselectivity: dopamine act by an anti-planar conformation in which the N-O distance is the same as in apomorphine (N-O10). The analgesic activity of morphinans is due to a cis junction of B and C cycles and to the stereoelectronic effect of the unshared lone pair on nitrogen. In the cyclamate sweeteners, some authors proposed for the sweet taste receptor a model with two points fixation (one acceptor and one donor) and two spatial barriers located at precise distances from this two sites. The stereoselectivity of molecules acting as substrates or inhibitors of enzymes is described. For example some oxazolidinone derivatives showed a selective inhibition toward monoamine oxidase A. Finally, the pharmacological activity falls often when molecules are administrated in racemic form. It seems that xenobiotics need to be dissymmetric for chiral recognition by biological systems.

Animals↗

PubMed1989

Lipid characterization and 14C-acetate metabolism in catfish taste epithelium.

The catfish, Ictalurus punctatus is an important model system for the study of the biochemical mechanisms of taste reception. A detailed lipid analysis of epithelial tissue from the taste organ (barbel) of the catfish has been performed. Polar lipids account for 62 +/- 1% of the total, neutrals for 38 +/- 1%. Phosphatidyl-cholines, serines and ethanolamines are the major constituents of the polar fraction. Plasmalogen concentration is high relative to that of non-neural tissues. [14C]-Acetate is incorporated into cell lipid fractions after incubation of barbel tissue at 37 degrees C for 60 min. Percentage amounts of most lipids change with time during this in vitro incubation. The phospholipids are the most metabolically active fractions. This work yields information for continuing reconstitution experiments and indicates that the taste epithelium of this important model system is a metabolically active tissue capable of supporting lipid turnover/synthesis.

Acetates↗

PubMed1988

Effects of magnetic fields from underwater electrical cutting on in vitro corrosion of dental amalgam.

Metallic taste has been reported from divers working with underwater electric welding and cutting. An in vitro model was designed to simulate the intraoral situation of the divers with respect to the magnetic field. Potentiostatic analyses were performed on amalgam samples exposed to AC and DC magnetic fields. Morphologic changes were analyzed using differential interference light microscopy and scanning electron microscopy. Chemical changes on the surface of the amalgam samples were analyzed with secondary ion mass spectrometry. Results demonstrated that dental amalgams exposed to a specific AC magnetic field underwent morphologic and chemical changes in the superficial amalgam layers.

Corrosion↗