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PubMed1995

Central processes in gustatory adaptation.

In two experiments the adapting stimuli at the periphery of the taste system were of a constant objective intensity but, using mixture suppression and spatial summation, their perceived intensity was varied. The results have shown that, in spite of the constancy in stimulus concentration, the adaptation degree changed with the perceived intensity of the stimulus. The adaptation to the compounds when in binary mixtures proved to be significantly less effective than the adaptation to the same equimolar compounds when unmixed. Similarly, the adaptation effects of solutions of a constant concentration, when applied to a small tongue area, were significantly smaller than when applied to a larger area. This adaptation dependence upon the taste sensation intensity suggests that in the gustatory adaptation, peripheral as well as central processes take part.

Attention↗

PubMed1995

Decline of taste sensitivity in protein deficient adult rats.

The influence of dietary protein levels on taste sensitivity was studied in adult rats. Low protein diets of 0.0, 2.5, or 5.0% purified egg protein (PEP) were fed to animals for 28 days. Two bottle choice preference tests between aqueous solutions of either 2, 9, 17, or 86 mM sodium chloride and deionized water were conducted in an ascending order on days 14, 16, 18, and 20. Urine samples were collected for zinc and creatinine analysis. Blood samples were also collected for measuring serum zinc and creatinine concentrations. Scanning electron microscopy was performed to observe rats' tongue epithelia. Protein free diet group showed significantly lower taste sensitivity and renal reabsorption rate than other protein containing diet groups, while serum zinc and creatinine concentrations, and creatinine clearance were not affected by dietary protein level. Degeneration of filiform papillae and imperforation of taste pore of fungiform papillae were observed in protein free diet group. This experiment implies at least 2.5% dietary protein is required to manifest normal taste function in the adult.

Age Factors↗

PubMed1994

Menstrual cycle and sex differences influence salt preference.

Previous studies demonstrate that some women have a greater preference for palatable high-sugar and high-fat foods premenstrually. Because salt may also be considered palatable, it was of interest to discover whether salt preference also varies. To determine whether there are differences in salt preference across the menstrual cycle, 49 women and 31 men rated popcorn sprayed with five different concentrations (0M, 1M, 2M, 3M, 3M+) of salt solution. Between-subjects comparisons of women revealed that those tested in separate weeks of their menstrual cycle had differing preferences for salt. Specifically, women in their luteal week preferred unsalted popcorn (0M) significantly less than women tested during their ovulatory or follicular weeks. Women in the menstrual week also tended to find the saltiest popcorn (3M+) much less palatable than women tested in their follicular, luteal, or ovulatory weeks. When men's and women's preference ratings of the same stimuli were compared, an overall sex difference was found. Men liked the mildly salty popcorn (2M) more than women. There were no significant differences in perceived saltiness ratings between men and women or among women tested in different weeks of their cycle.

Adolescent↗

PubMed1994

Flavor preferences conditioned by intragastric infusions of dilute polycose solutions.

Prior studies have obtained strong conditioned preferences (> 90%) for flavors paired with intragastric (IG) infusions of Polycose (hydrolyzed starch) over different flavors paired with IG water infusions. These experiments used concentrated Polycose solutions (16-32%; 0.6-1.2 kcal/ml) that contributed 50% or more of the animals' daily caloric intake. The present experiment sought to determine if calorically dilute solutions would also support preference conditioning. Adult female rats with gastric cannulas were trained with a cue solution (the CS+) paired with Polycose infusions. On alternate days a different cue solution (the CS-) was paired with IG water infusions. The CSs were unsweetened or saccharin-sweetened citric acid and sucrose octaacetate solutions that were available 22 h/day; chow was freely available. Separate groups were infused with Polycose at concentrations of 0.5%, 1%, 2%, and 4% (0.019-0.152 kcal/ml). The three higher concentrations conditioned flavor preferences of up to 89%. The infused Polycose represented only 1-14% of the animals' daily caloric intake and did not reliably reduce chow consumption. These findings demonstrate the sensitivity of the viscerosensory feedback system mediating flavor conditioning.

Animals↗

PubMed1994

Taste preference of Old World monkeys: I. A single-bottle preference test.

There have been relatively few published reports of the taste preferences of nonhuman primates due, in part, to the expense and relative difficulty associated with maintaining a large group of these animals. The present report describes a version of the single-bottle preference test that can be used effectively with small groups of macaque monkeys. Experiment 1 determined the optimal durations for the pretest water deprivation period, the test trial itself, and the posttest rehydration period. Experiment 2 used this procedure to examine intake of the four prototypical gustatory stimuli. The results showed that cynomolgus monkeys, like other species, accept solutions containing sucrose and isotomic saline and reject those containing quinine hydrochloride. Unlike most other species, however, these monkeys do not find moderate concentrations of hydrochloric acid aversive.

Animals↗

PubMed1994

Adaptation of sweeteners in water and in tannic acid solutions.

Repeated exposure to a tastant often leads to a decrease in magnitude of the perceived intensity; this phenomenon is termed adaptation. The purpose of this study was to determine the degree of adaptation of the sweet response for a variety of sweeteners in water and in the presence of two levels of tannic acid. Sweetness intensity ratings were given by a trained panel for 14 sweeteners: three sugars (fructose, glucose, sucrose), two polyhydric alcohols (mannitol, sorbitol), two terpenoid glycosides (rebaudioside-A, stevioside), two dipeptide derivatives (alitame, aspartame), one sulfamate (sodium cyclamate), one protein (thaumatin), two N-sulfonyl amides (acesulfame-K, sodium saccharin), and one dihydrochalcone (neohesperidin dihydrochalcone). Panelists were given four isointense concentrations of each sweetener by itself and in the presence of two concentrations of tannic acid. Each sweetener concentration was tasted and rated four consecutive times with a 30 s interval between each taste and a 2 min interval between each concentration. Within a taste session, a series of concentrations of a given sweetener was presented in ascending order of magnitude. Adaptation was calculated as the decrease in intensity from the first to the fourth sample. The greatest adaptation in water solutions was found for acesulfame-K, Na saccharin, rebaudioside-A, and stevioside. This was followed by the dipeptide sweeteners, alitame and aspartame. The least adaptation occurred with the sugars, polyhydric alcohols, and neohesperidin dihydrochalcone. Adaptation was greater in tannic acid solutions than in water for six sweeteners. Adaptation of sweet taste may result from the desensitization of sweetener receptors analogous to the homologous desensitization found in the beta adrenergic system.

Adult↗

PubMed1994

Amiloride reduces the aversiveness of acids in preference tests.

Experiments were conducted to determine the relative contribution of amiloride-sensitive pathways to the aversiveness of acid stimuli in preference tests performed on male Golden Syrian hamsters. In Experiment 1 hamsters were given a choice between water and test solutions in two-bottle preference tests lasting 4 days. The results showed that although citric acid at pH 3.0-5.0 was not aversive, at pH 1.4 or 2.0 citric acid was avoided by all animals, as indicated by both consummatory behavior and licking activity. Experiment 2 was conducted to determine whether amiloride could reduce the aversiveness of citric acid in preference tests. Citric acid at pH 2.4, an aversive solution, and citric acid at pH 3.8, which was not aversive, were tested either alone or in the presence of amiloride. Amiloride (30-300 microM), which when presented alone was neither preferred nor avoided, significantly reduced the aversiveness of citric acid at pH 2.4, similar to its effect on NaCl aversiveness. However, amiloride had no effect on intake of citric acid at pH 3.8, nor upon preference for saccharin. These results support those found in isolated hamster taste cells and from in situ taste bud recordings, which suggested that amiloride-sensitive pathways contribute to the transduction of acidic stimuli.

Amiloride↗

PubMed1994

Electrophysiological and behavioral studies of taste discrimination in the axolotl (Ambystoma mexicanum).

Electrophysiological and behavioral experiments were performed to determine whether the taste system of the aquatic salamander, axolotl, discriminates taste stimuli. Taste responses were recorded extracellularly from the glossopharyngeal nerve bundle. The behavioral responses of axolotls towards various concentrations of NaCl, KCl, citric acid, quinine-hydrochloride, and sucrose were quantified by measuring the ratio of rejection towards gel pellets, each containing either unitary stimuli or binary mixtures of these chemicals. Rejection ratios [rejection/(rejection+swallowing)] towards the unitary stimuli except sucrose increased with concentration, but were not a single function of the magnitude of neural response induced by the stimuli. Degree of rejection was different depending on the quality of taste stimuli, suggesting that information processing of taste quality occurs in axolotls. The potential of NaCl to induce positive feeding behavior (swallowing) was suggested by a reduction in the rejection ratio of quinine-tainted pellets when they were mixed with 100 mM NaCl. Differential behavioral responses to quinine and NaCl show that axolotls have the ability to discriminate the taste quality of these stimuli.

Ambystoma mexicanum↗

PubMed1994

Sweet taste in the calf: III. Behavioral responses to sweeteners.

The hedonic response to the sweeteners acesulfame-K, aspartame, fructose, galactose, glucose, glycine, lactose, maltose, Na-saccharine, sucrose, and xylitol was recorded in five groups of 4-16-week-old calves. The compounds were presented to the calves for 12 or 24 h in two-bottle preference tests with tap water as one choice. Glycine (10 mM and higher), sucrose (20 mM and higher), and fructose concentrations were most preferred. Sodium-saccharine was highly preferred at and above 4 mM concentration, fructose and lactose were preferred above 40 mM, galactose was preferred moderately, acesulfame-K and maltose were preferred inconsistently, and aspartame and xylitol were not preferred at any concentration. The change of preference during the tests was also studied. Three types of consumption changes were observed. 1) Increased preference of the tastant during consumption, seen during sucrose and, to lesser a extent, fructose consumption. 2) Initial high preference for the tastants, diminishing during the test period, observed with fructose, galactose, glucose, glycine, lactose, and maltose. 3) Initial large fluctuations in consumption from the two bottles, but no change in overall preference. This pattern was seen with xylitol and aspartame. This technique seems to offer a method to assess the long-term preference for a compound within one relatively short two-bottle preference session.

Age Factors↗

PubMed1994

Elevated sweet taste pleasantness ratings in bulimia nervosa.

Recent studies suggest that some patients with bulimia nervosa may experience elevated pleasantness responses to sweet taste. This study explored possible associations between symptoms patterns and pleasantness ratings for sucrose solutions in bulimic patients. Subjects included 15 women meeting DSM III-R criteria for narrowly defined bulimia nervosa (no history of other eating disorder); five patients with current bulimia nervosa and a past history of anorexia nervosa; and 20 healthy age-matched female controls. Subjects ate a standardized breakfast prior to the morning study visit. Sucrose-water solutions (0% to 40% sucrose) were rated for sweetness intensity and pleasantness. Patients with narrowly defined bulimia nervosa showed significantly higher pleasantness ratings for 40% sucrose solutions than controls and patients with a history of anorexia nervosa. Pleasantness ratings were not significantly correlated with frequency of binge eating or purging behaviors. These results extend previous evidence for altered sweet taste pleasantness responses in bulimia nervosa, and for differences in eating-related behaviors between patients with narrowly defined bulimia nervosa vs. those with past anorexia nervosa.

Adult↗

PubMed1994

Genetics of bitter perception in mice.

Inbred and congenic strains exhibited several patterns of relative sensitivity to bitter tastants in 48-h, two-bottle preference tests. With segregation analyses of descendents of crosses between contrasting strains, these patterns suggested at least three genetic loci influencing bitter perception. The extensively characterized Soa (sucrose octaacetate) locus underlies one pattern. Variation at this locus had pleiotropic effects on avoidance of other acetylated sugars, plus such structurally dissimilar bitter tastants as brucine, denatonium benzoate, and quinine sulfate. Unlike SOA, however, sensitivity to quinine sulfate was polygenically determined, and produced a second characteristic pattern. At least one, possibly several, additional unlinked loci contributed to quinine differences. Phenylthiocarbamide (PTC) aversion differences exemplified a third pattern. Segregation consistent with monogenic control of PTC aversion has been reported, and within segregating populations PTC aversion did not covary with SOA or quinine sulfate avoidance. Variants of the three major patterns may be useful for analysis of specific mechanisms. While both showed the SOA pattern, strychnine differences were markedly smaller than brucine (dimethoxystrychnine) differences. Likewise, a hop extract containing primarily iso-alpha acids (e.g., isohumulone) produced an SOA-like pattern, while an extract with nonisomerized alpha-acids (e.g., humulone) did not.

Animals↗

PubMed1994

Generation of inositol phosphates in bitter taste transduction.

It is probable that there is a diversity of mechanisms involved in the transduction of bitter taste. One of these mechanisms uses the second messengers, inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG). Partial membrane preparations from circumvallate and foliate taste regions of mice tongues responded to the addition of known bitter taste stimuli by increasing the amount of inositol phosphates produced after 30 s incubation. Addition of both the bitter stimulus, sucrose octaacetate and the G-protein stimulant, GTP gamma S, led to an enhanced production of inositol phosphates compared with either alone. Pretreatment of the tissue samples with pertussis toxin eliminated all response to sucrose octaacetate plus GTP gamma S, whereas pretreatment with cholera toxin was without effect. Western blots of solubilized tissue from circumvallate and foliate regions probed with antibodies to the alpha-subunit of several types of G-proteins revealed bands reactive to antibodies against G alpha i1-2 and G alpha o, with no apparent activity to antibodies against G alpha i3. Given the results from the immunoblots and those of the toxin experiments, it is proposed that the transduction of the bitter taste of sucrose octaacetate in mice involves a receptor-mediated activation of a Gi-type protein which activates a phospholipase C to produce the two second messengers, IP3 and DAG.

Animals↗

PubMed1994

Bitter taste in single chorda tympani taste fibers from chimpanzee.

We have found earlier that chimpanzee chorda tympani taste fibers fall into groups that conform with the human taste qualities. This study focuses on bitter taste and its relation to sweet taste. Eight fibers were classified as bitter fibers according to their responses to 31 stimuli. The stimuli included the bitter compounds quinine, denatonium benzoate and caffeine. The results indicate a clear dichotomy between the bitter and sweet fibers. Sweet fibers never responded to the bitter compounds. However, in addition to their responses to the above compounds, some of the bitter fibers were stimulated by other compounds. Most prominent were responses to NaCl-amiloride mixture, KCl and xylitol. In most cases the cause could be assumed to be a bitter taste in the compound. These results suggest that the bitter and sweet tastes are conveyed in specific and separate groups of nerve fibers in the chimpanzee. Because of the closeness between chimpanzee and human, this finding has implications on the question of taste coding in human and the concept of taste qualities.

Animals↗

PubMed1994

Representation of hedonics and quality of taste stimuli in the parabrachial nucleus of the rat.

The distribution of evoked expression of the proto-oncogene c-fos was immunohistochemically examined in the parabrachial nucleus (PBN) of water-deprived rats after free ingestion of palatable liquids, after intra-oral infusion of aversive taste solutions including various bitter substances, and after an intraperitoneal injection of LiCl. C-fos immunoreactive neurons (c-fos neurons) were densely packed in the external lateral subnucleus (els), external medial subnucleus (ems), dorsal lateral subnucleus (dls), central lateral subnucleus (cls), and the central medial subnucleus (cms) depending on the kind of stimulation. The rostral part of the els may be related to general visceral inputs; the caudal part of the els, negative hedonics or aversive behavior; the dls, positive hedonics or ingestive behaviour. Both the ems and the els may be related to taste information for bitter tasting compounds and HCl; the cls, for sucrose and saccharin; and the cms, for NaCl.

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↗

PubMed1994

Bitterness in wine.

Bitterness in wine is elicited primarily by flavonoid phenols, which are bitter and astringent, and by ethanol. Monomeric flavonoid phenols are primarily bitter but as the molecular weight increases upon polymerization, astringency increases more rapidly than bitterness. The chiral difference between the two wine flavan-3-ol monomers produces a significant difference in temporal perception of bitterness: (-)-epicatechin is significantly more bitter and had significantly longer duration of bitterness than (+)-catechin. Ethanol enhances bitterness intensity and duration, whereas varying wine pH has little or no effect on perceived bitterness. Whereas PROP status had no significant effect on temporal perception of bitterness or astringency, subjects with low salivary flow rates took longer to reach maximum bitterness and astringency intensity and reported longer persistence of both attributes than high-flow subjects.

Ethanol↗

PubMed1994

Chemoreception and perception of the bitterness of isohumulones.

Psychophysical experiments were conducted to determine whether isohumulones share a common receptor mechanism with other bitter compounds, and whether parotid saliva flow affects perception of their bitterness. Findings from a study of inter-individual differences in sensitivity to 23 sweet and/or bitter compounds among 25 subjects using the time-intensity (TI) method suggest that isohumulone and tetrahydroisohumulone may share a common receptor mechanism with other bitter compounds except those with the thiourea moiety. Isohumulone and tetrahydroisohumulone displayed a unique dome-shaped TI profile. The bitterness of the two compounds took longer to develop, but it lasted as long as for other bitter stimuli. In a study of the relation between perception of bitterness in beer and parotid saliva flow in 20 young adults, no significant difference was found among the mean saliva flows triggered by 0, 15 and 30 mg/L of isohumulones added to beer, and no significant correlation was found between saliva flow and maximum intensity or total duration of bitterness.

Adolescent↗

PubMed1994

Enhancement of salt intake by choline chloride.

The ingestion of salt (NaCl) in most societies far exceeds levels that are considered necessary and safe. To reduce salt intake, a rat model of salt taste acceptance was created to identify novel, more palatable salt substitutes/enhancers. To induce salt craving, male Sprague-Dawley rats were placed on a low-salt diet and injected weekly (SC) with either 100 mg/kg of deoxycorticosterone acetate (DOCA) or its vehicle, peanut oil. Following 16 h of fluid deprivation, intake was evaluated in a one-bottle acceptance procedure. The DOCA-injected animals consumed large volumes of salt-containing solutions (up to 120 ml in 2 h) and showed sensitivity to and specificity for the salt taste (generally lacking acceptance of dextrose, KCl, ammonium chloride, and water solutions). Using this model, choline chloride was identified as having salt taste-enhancing properties. Choline chloride (0.1-0.7%) significantly enhanced the intake of a dilute salt solution (0.1%). The relevance of the rat model was demonstrated in human taste trials; choline chloride enhanced the palatability of and preference for foods containing this compound. The results of the present experiments support the use of this animal model for evaluating compounds for salt-like taste qualities and suggest that choline chloride will be an effective salt taste enhancer in man.

Animals↗