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Taste synergism between monosodium glutamate and disodium 5'-guanylate.

The examples of "synergism" reported in the taste literature fit the common definition of the term but may merely reflect normal additivity in the taste system. That is, the perceived intensities of these "synergistic" mixtures exceed the sums of the perceived intensities of the unmixed taste components (addition of perceived intensities), but do not exceed the perceived intensities predicted by adding along the expandng psychophysical functions which describe the unmixed taste components (stimulus addition). True synergism requires that the perceived intensity of a mixture be greater than that predicted by both types of additivity. Subjects used magnitude estimation to judge the perceived intensity of unmixed monosodium glutamate and disodium 5'-guanylate and mixtures of these two taste substances. The mixtures showed synergism according to both crtieria. The robustness of this phenomenon is striking; for all subjects the taste mixtures showed true synergism. True synergism in taste is an extremely rare phenomenon.

Adult↗

The suppression of sucrose intake by cholecystokinin is scaled according to the magnitude of the orosensory control over feeding.

The intestinal hormone cholecystokinin (CCK) has been shown to play a role in the termination of food intake, however its behavioral mechanism of action remains to be determined. Recent work from this laboratory suggested that the suppression of intake with CCK is dependent upon the specific orosensory characteristics of the substance being consumed and that the hormone may suppress intake by altering the behavior maintaining characteristics of orosensory stimuli. The present study further investigated this suggestion by determining whether changes in the orosensory characteristics of food after the magnitude of the suppressive effect of CCK. Specifically, the magnitude of the CCK effect on the intake of sucrose solutions of various concentrations was determined on non-deprived rats. The results of this work indicate that the suppressive effect of synthetic CCK (CCK-8) cannot be overridden by increases in sucrose concentration. In contrast, it was found that over a range of sucrose concentrations, the magnitude of the CCK effect increased with solution concentration. Because sucrose concentration predicts both caloric density and the magnitude of orosensory control (as measured by grams consumed), it appears that CCK may act on this control to regulate meal size in proportion to the caloric density of the food.

Animals↗

Effects of temperature on the perceived sweetness of sucrose.

The sweetness of sucrose depends on the temperature as well as the concentration of a solution. The main effect is that relatively low concentrations gain sweetness as temperature increases. This effect diminishes with progressively higher concentration and finally becomes negligible at about 0.5 M. At this concentration the various functions that relate perceived sweetness to concentration for various temperatures converge. The mechanism of the taste-temperature interaction is speculative, but the interaction is large enough to be of practical interest in the perception of common foods and beverages as well as a variable to be strictly controlled in taste experiments. An examination of method of tasting showed that swallowing stimuli did not substantially increase perceived sweetness.

Female↗

Responsiveness of dog thalamic neurons to taste stimulation of various tongue regions.

Receptive fields of single thalamic taste neurons in dogs were studied by examining responses to stimuli representing the four basic taste qualities applied to five different regions on the tongue surface. Twenty single thalamic units responded to taste stimulation of the tongue ipsilateral to the recording site were classified into three types according to characteristics of their receptive fields. In 11 out of 20 units, the location and the size of the receptive field and the most sensitive region in the receptive field did not vary among their effective taste stimuli (type A units). In 5 units, the location and the size of the receptive field varied with taste stimulus, although the most sensitive region was common to the stimuli (type B units). In the remaining 4 units, the most sensitive region varied with taste stimulus (type C units).

Afferent Pathways↗

Paradoxical adaptation to taste mixtures.

Quinine, sucrose, quinine-sucrose mixtures, and water were employed both as preadapting rinses and as stimuli in a factorial experiment. Human subjects judged the perceived taste intensity of the 16 stimulus-rinse pairs, which were flowed over the dorsal anterior tongue surface. Previously documented effects of adaptation, mixture suppression, and release from suppression were observed. Following adaptation to quinine-sucrose mixtures, presentation of equimolar unmixed quinine or equimolar unmixed sucrose resulted in a reliable residual bitter or sweet taste, respectively, which was significantly greater than the taste following self-adaptation of the unmixed solutions. The residual taste following mixture adaptation suggests a peripheral mechanism underlying suppression between bitter and sweet tastes in a mixture.

Adaptation, Psychological↗

Sensory-specific and motivation-specific satiety for the sight and taste of food and water in man.

In normal weight humans it was shown first that the sight of food is pleasant when hungry, and that the pleasantness of the sight of a food which has been eaten to satiety decreases more than the pleasantness of the sight of foods which have not been eaten. Thus the specificity of satiety extends to the visual modality, and this may be an important factor in influencing which foods are selected for ingestion. Second, it was shown that the pleasantness of both the sight and taste of food are modulated in a motivation-specific manner, in that in hungry and thirsty humans the pleasantness of the sight and taste of food but not water is decreased by eating to satiety, and the pleasantness of the sight and taste of water but not food is decreased by drinking water to satiety. Third, it was shown that sensory-specific decreases in the pleasantness of the taste of a particular food produced by its ingestion are associated with only minor changes in the intensity of its taste, which do not account for the changes in pleasantness as shown by an analysis of covariance and by the relation between pleasantness and intensity, so that it is unlikely that sensory adaptation is an important part of the mechanism of sensory-specific satiety.

Adult↗

Relative singularity/mixedness judgements for selected taste stimuli.

Quinine hydrochloride, fructose, citric acid, NaCl, monosodium glutamate, KCl, and mixtures of two, three and four solutes were rated and ranked along a continuum from "single" to "mixed" tasting. Quinine was judged most singular, with fructose and citric acid forming a second most singular group. Other stimuli were intermediate while the mixtures were judged most mixed, the mixedness increasing with mixture complexity. When NaCl and fructose were judged with their binary mixtures in the same manner, the degree of mixedness of the mixtures varied with the proportions of the components.

Adolescent↗

Neural and behavioral responses to taste stimuli in the mouse.

Neural responses to lingual stimulations with varying kinds of chemicals were recorded from the chorda tympani nerve of the ddy mouse and preferences for NaCl, sucrose and Na saccharin were measured using the two bottle-choice technique. Sucrose, Na saccharin, HCl, and quinine produced large neural responses compared with that for NaCl. Divalent salts also elicited larger responses than NaCl response. The effectiveness of cations was in the order of Sr greater than Mg = Ca greater than Li not equal to Na not equal to NH4 greater than K. Neural response magnitudes for Na salts with varying anions decrease with the relative hydrated size of anions. Mice highly preferred sucrose and Na saccharin but showed a poor preference for NaCl. Similarity in the gustatory responses between mice and hamsters as well as macaque monkeys, and difference between mice and rats are pointed out.

Animals↗

Effects of oral chemical irritation on taste.

Oral irritation was induced by rinses with capsicum oleoresin and with piperine, constituents of red and black pepper, respectively. The perceived intensities of two concentrations of each of four tastants representing the four classical taste qualities were evaluated after rinsing with these irritants. Comparing taste intensity after rinses with capsicum and after control rinses with emulsifying agents or water, there were significant decrements in taste intensity of citric acid and quinine, and on one concentration of sucrose, but no effect on salt. The effects of piperine were more broad, with significant decrements in perceived intensity relative to emulsion controls for all substances.

Adult↗

Taste effectiveness of some D- and L-amino acids in mice.

To measure the hedonic effectiveness of some D-amino acids two-bottle preference tests were carried out on ddy mice, and subsequently conditioned taste aversion (CTA) experiments were performed to determine to what degree hedonic responses to D- and L-amino acids are related to sweet taste in mice. Mice showed preferences for D-Trp, D-His, and D-Leu over certain concentration ranges, but were behaviorally neutral to D-Ser and D-Val up to 0.1 M. The preference magnitudes for D-amino acids increased with increasing molecular weight (MW) or the bulk of the side chain. CTA experiments using 0.2 M sucrose as a conditioning stimulus and 4 D- and 6 L-amino acids as test stimuli indicated that generalization of sucrose taste became stronger with increasing MW of D-amino acids and decreasing MW of L-amino acids. There was a highly significant positive correlation between the degree of generalization of sucrose taste and the preference magnitude for D- and L-amino acids. The results indicate that preferences for D- and L-amino acids in mice result from sweet taste produced by these chemicals. Comparison of the results with the human psychophysical data reveal similarity between humans and ddy mice in taste sensitivity to amino acids.

Amino Acids↗

The effect of cooling on the perception of carbohydrate and intensive sweeteners.

The effect of cooling on the perceived intensity of sweetness was measured for four different compounds: glucose, fructose, aspartame and saccharin. Perceived sweetness was rated in a sip and spit paradigm when the taste solution, the tongue, or both were either held at 36 degrees C or cooled to 20 degrees C. It was discovered that for glucose and fructose perceived sweetness was significantly reduced by cooling, and that cooling the tongue reduced sweetness more than did cooling the solution. The perceived sweetness of aspartame was also lessened by cooling, but in that case the temperature of the tongue and the temperature of the solution had similar effects on sweetness. In contrast to the other compounds, the sweetness of saccharin was not affected by temperature. These results (when combined with data previously reported for sucrose) raise the possibility that as a group, carbohydrate sweeteners are affected similarly by temperature, whereas thermal effects on intensive sweeteners may be less predictable. The data thereby provide indirect support for the hypothesis that the sweet taste is mediated by more than one type of gustatory receptor.

Adult↗

Suprathreshold sour taste intensity and pleasantness perception with age.

Magnitude estimates for perceived intensity and pleasantness of suprathreshold concentrations of citric acid in solution and drink were examined in 180 healthy, free-living subjects divided into three groups: young (20-29 years), old (70-79 years) and very old (80-99 years). Psychophysical functions showed significant age effects. For both aqueous and food systems, the old gave higher intensity estimates to high acid concentrations and lower intensity estimates to low acid levels compared to the young and very old whose estimates were comparable. Sex had a significant effect on the intensity estimates with the women giving low acid levels lower estimates and high acid levels higher estimates than the men. All subjects gave low acid levels in solution lower intensity estimates than comparable drinks while at high concentrations, higher intensity estimates were given to solutions than drinks. Trend analysis of pleasantness estimates indicated significant age group differences. For both systems, the breakpoint, the acid level assigned the highest pleasantness estimate was lower for the young than for the elderly.

Adult↗

Acid and NaCl self-adaptation with micro-drop stimulation of fungiform papillae.

A small drop of either citric acid, HCl, or NaCl, judged to be approximately equal in magnitude, was applied to two papillae for a fixed duration (15 sec). The stimulus was then reapplied to the same papillae and judged for magnitude of sensation ("self-adaptation" design). NaCl was about 50% less intense after 15 sec of prior exposure whereas citric acid showed no significant decline and HCl showed either no decline or a significant increase in magnitude. When citric acid was tested with a longer exposure time (55 sec), significant decline in citric acid magnitude occurred for all subjects. These outcomes are discussed with regard to the problem of cutaneous irritation caused by certain stimuli and the difficulty of extracting cutaneous sensations from the sensory experience of strong concentrations of acids and salts.

Adult↗

No influence of adrenalectomy on measures of taste sensitivity in the rat.

The influence of adrenalectomy on the taste sensitivity and responsivity of Long-Evans rats to sodium chloride and sucrose tastants presented separately and in mixtures was examined using high precision gustometry, computer-controlled go/no-go operant procedures, and nonparametric signal detection measures. Relative to baseline levels, adrenalectomized rats' plasma corticosterone levels decreased by 328% while sodium chloride and water consumption increased by 548% and 165%, respectively. The same measures remained unchanged in sham-operated animals. Taste sensitivity and responsivity to sodium chloride and sucrose did not differ between adrenalectomized and sham-operated animals and discrimination performance remained the same between the groups as well. The present results support and extend previous findings that adrenalectomy and the resultant corticosteroid deficiency does not influence taste sensitivity or responsivity in the rat.

Adrenal Cortex↗

Dietary sodium deprivation does not alter taste sensitivity in the rat.

The influence of 33 days of combined dietary sodium and water deprivation on the taste sensitivity and responsivity of the rat to a wide range of NaCl solutions and discrimination tasks was examined using double-blind procedures, high-precision gustometry, and an automated operant go/no-go task. Sodium concentration in urine and saliva but not plasma decreased significantly only in the sodium-deficient rats. The same measures remained unchanged in control animals. Nonparametric measures of taste sensitivity and responsivity to NaCl did not differ between sodium-deficient and control animals and performance on taste discrimination, reversal learning, and lick-rate tasks remained the same between the groups as well. The present results support and extend previous findings that dietary-induced sodium deficiency increases NaCl and water consumption, but alters neither the sodium-deficient rat's taste sensitivity and responsivity nor performance on simple and complex tasks in which tastants serve as cues for discriminative responding.

Animals↗

Temporal gustatory and salivary responses to capsaicin upon repeated stimulation.

Repeated oral stimulation with solutions of 2 ppm capsaicin increased time to maximum intensity, but yielded a decrease in sequential mouth-burn intensity due to a rising minimum irritation rating between stimuli. Two response patterns were observed: for 18 subjects mouth-burn increased, while 14 subjects showed depression upon repeated stimulation. Because of across-subject variability, there was little correlation between parotid salivary response and perceived sensory responses. Capsaicin-stimulated salivary flow was significantly higher than flow stimulated by distilled water in 9 high-flow subjects, but not in 14 low-flow subjects. Oral adaptation to capsaicin may attenuate parotid salivary response, although eaters and noneaters of chili peppers did not differ significantly in their perception of mouth-burn or in salivary flow.

Capsaicin↗

Temporal effectiveness of mouth-rinsing on capsaicin mouth-burn.

Oral rinsing with different solutions significantly reduced mouth-burn of capsaicin solutions in both eaters and noneaters of chili peppers. Cold solutions (5 degrees C) were more effective in reduction of mouth-burn than solutions at 20 degrees C. Sucrose solutions (10%) at 20 degrees C and whole milk at 5 degrees C were equally effective while 5% ethanol was no more effective in mouth-burn reduction than water at 20 degrees C. Reduction of mouth-burn by sucrose was not dose dependent. Noneaters of chili peppers experienced a slightly greater reduction of mouth-burn from sucrose solutions than eaters. Oral rinsing with sweetened milk containing 0 and 10% fat, of varying globule size, resulted in similar degree of mouth-burn reduction. The first (control) sample was rated higher in intensity than subsequent ones, suggesting desensitization, which appears to be due to the interaction of stimulation of chemo-, mechano-, thermo- and gustatory receptors.

Adult↗

A new gustometer for psychophysical taste testing in the rat.

This paper provides a detailed description of a gustometer designed and constructed in our laboratory for psychophysical taste testing in rats. The gustometer features: a) 12 stimulus channels, b) the ability to deliver a specified volume of a taste stimulus per lick (e.g., 5 microliters), c) the accurate measurement of immediate licking responses, d) an automatic drinking spout cleaning mechanism for use between taste trials, and e) complete computer control and analysis. Complete plans and electronic schematics are included. In addition, results from contamination tests are presented verifying the reliability of the stimulus delivery system. The usefulness and versatility of this apparatus in a variety of behavioral tasks is discussed.

Animals↗