The mouse taste cell response to five sugar stimuli

Intracellular recordings of mouse taste cell responses were made using glass microelectrodes filled with procion yellow dye solution. Only responses recorded from taste buds with fluorescent cells, as observed in subsequent histological preparations, were used in this study. The mouse taste cell depolarizes when stimulated with sucrose and is accompanied by either a resistance increase or no change. On the other hand, a NaCl stimulus produces a depolarization, hyperpolarization or null response and is accompanied by either a membrane resistance decrease or no change. Four sugars other than sucrose (maltose, fructose, glucose and lactose) produced the depolarization or null responses and were accompanied by an increase or no change in membrane resistance. From the above observations, it is suggested that each taste cell produces its own characteristic response profiles and membrane resistance changes for the five sugars and NaCl tested.     

Attention and the detectability of weak taste stimuli

Subjects detected weak solutions of sucrose or citric acid under conditions in which attention was directed toward one of the tastants or the other. Detection thresholds were measured using an adaptive, forced-choice procedure, with a three-down one-up rule, which computer simulations suggest should be more reliable than the popular two-down one-up rule. The thresholds were modestly but systematically lower for attended tastants than for unattended ones. Similar results have been reported in other sense modalities, including vision (greater sensitivity to stimuli presented to attended versus unattended spatial locations) and hearing (greater sensitivity to stimuli presented at attended versus unattended sound frequencies). Taken together, the findings are consistent with a general hypothesis regarding attention in sensory systems: gains or losses in detectability occur when a central attentional mechanism (or, conceivably, a preattentive mechanism) selectively and preferentially monitors signals arising from particular subsets of peripheral neural inputs.      

Studies on after-taste of various taste stimuli in humans

This series of experiments was performed in order to evaluatethe physiological characteristics and patterns of after-tasteof various taste substances. The durations of after-taste followingmonosodium glutamate (MSG), inosine-5'-monophosphate (IMP) andguanosine-5'-monophosphate (GMP) (umami substances) were longerthan those for sucrose, NaCl, tartaric acid and quinine-HCIat concentrations corresponding to the recognition threshold.The periods of after-taste of solutions of MSG and IMP, andMSG and GMP, were longer than those for the single componentsolutions. Most subjects recognized sucrose as sweet, NaCl assalty, tartaric acid as sour and quinine-HCI as bitter, bothin terms of immediate taste and after-taste. According to thepatterns of after-taste for umami substances, the subjects weredivided into three groups. In group A, umami (appealing, savorytaste in Japanese cuisine) was the main quality of the after-tastesensation; in group B, an indefinite, equivocal taste was thecharacteristic quality of the aftertaste; and no differencewas reported in group C between the immediate taste and after-taste.These results suggest that the characteristics of after-tastefor MSG, IMP and GMP are different from those of the four basictastes.     

Effects of various taste stimuli on heart rate in humans

Relationships between taste stimuli and heart rate were evaluated in 29 healthy university students. The test solutions were sucrose, NaCl, citric acid, quinine-HCl and monosodium glutamate (MSG). Heart rate increased by 7.1-13.6% for all the taste stimuli after use as compared with pre-stimuli values. The maximum increases in heart rate came approximately 25 s after the taste stimuli. After the increases, heart rate returned to pre-stimuli levels after between 80 and 100 s. Heart rate reached its maximum with citric acid. Recovery from the heart-rate increase was more delayed for quinine-HCl and MSG than for the other stimuli. Except for sucrose, increases in heart rate and the hedonic scale values of the taste solutions showed significant negative correlation. These findings show that the taste stimuli solutions increased the heart rate and that the increase differed with the concentration and taste solution used.     

Iontophoretic application of bitter taste stimuli in hamsters

Recent electrophysiological studies on the iontophoretic applicationof taste stimuli by weak electric currents using rodents andfrogs have produced stimuli which appear to mimic the actionof salty, sour and sweet solutions. However, there has beenno report of an ionic stimulus which might serve as a bitteriontophoretic probe. Many common bitter stimuli are either uncharged(e.g. quinine, urea) or have mixed quality sensations (e.g.the bitter salts KCl, MgCl₂) and therefore are unsuitable. Thisreport investigates the use of four organic anions, all of whichare bitter to humans, which may serve as potential bitter stimulifor iontophoretic application to the tongue of the hamster whilerecording electrophysiologically from its chorda tympani nerve.These anions are m-nitrobenzene sulfonate (NBSA), picrate, cholateand m-nitrobenzoate (NBA). The electrophysiological responsesto cathodal polarization via these four anions plus saccharin,an effective cathodal stimulus in the hamster, form the sameefficacy series as chemical (i.e. normal sapid) presentationsof sodium salts of these anions, i.e. saccharin > NBSA >picrate > NBA > cholate. Behavioral evidence suggeststhat NBSA is sweet to hamsters while the latter three anions,picrate, NBA and cholate, are bitter. Electrophyiological observations,based on magnitude of response, appear to support these behavioralfindings. It was concluded that picrate, NBA and cholate mayserve as useful bitter stimulus probes for ionto-phoretic applicationin the hamster.     

Effect of amiloride on bulk flow and iontophoretic taste stimuli in the hamster

Summary This investigation 1) demonstrates the effect of amiloride on various taste responses in the hamster, and 2) tests the hypothesis that its action on iontophoretic application of taste stimuli parallels its action on bulk flow delivery. Amiloride has not previously been tested in the hamster nor has its effect on iontophoretic stimuli (socalled electric taste), which is thought to behave similarly to bulk flow stimuli, been examined. Amiloride treatment (4 min of 0.0001M) of the hamster's tongue effectively inhibited chorda tympani responses to NaCl and LiCl solutions. Bulk flow (0.1M) and iontophoretic (+7 A through 0.001M) presentations of NaCl and LiCl, which had unequal response magnitudes pre-treatment, were inhibited to the same residual response magnitude post-treatment. Recovery then proceeded along two distinct curves asymptotically returning to pre-treatment response levels. These curves could be adequately described by a simple exponential relationship. KCl responses were unaffected when presented via bulk flow techniques but significantly reduced when presented iontophoretically. HCl responses via either method were only slightly diminished. No decrement in response level was observed for the sweet stimuli sucrose (0.5M) or saccharin (–9 A through 0.001M Na-saccharin) nor for potassium picrate, a bitter stimulus, (0.01M or –10 A through 0.001M). Amiloride treatment of the hamster tongue was as specific in its action for sodium and lithium as reported in other species, and with the exception of KCl the action of amiloride on iontophoretic stimulation paralleled its action on bulk flow stimulation.     

Multiple sensitivity of single taste cells of the frog tongue to four basic taste stimuli

The electrical response of the taste cells of the frog fungiform papillae to four fundamental taste solutions (NaCl, acetic acid, quinine-HCl and sucrose) was studied by using the intracellular recording technique. The average value of resting membrane potential was 22.5 mV, inside negative. Each of the four taste solutions applied to the tongue produced a slow depolarizing potential, the receptor potential, on which no spike potential was superimposed. The amplitude of the receptor potentials increased linearly as a function of the logarithm of the concentration of the stimulus. Amplitudes of depolarizations to a given taste stimulation varied from one cell to another even within a single taste bud. Most of the cells responded to more than two of the four basic taste solutions. Sensitivity patterns in terms of the number of effective solutions and the relative effectiveness of different kinds of solutions were variable among cells. Statistical analysis suggests that at the receptor membranes of the taste cells, the sensitivities for the four basic stimuli are independent and random.     

Facial electromyography: responses of children to odor and taste stimuli

The study investigated the potential for facial electromyography (EMG) to be used as a clinical tool for measuring the responses of children to pleasant and unpleasant smell and taste stimuli. Responses in the zygomaticus major and levator labii muscles to 4 odorants and 4 tastants were recorded from 34 children aged 6-9 years. The results indicated that EMG activities in the 2 muscles discriminated between pleasant and unpleasant stimuli within each modality in a manner that indicated that the children perceived the hedonic qualities of the stimuli in a manner similar to that reported for adults. Importantly, there was unanimous agreement across the children as regards the differential nature of the activities exhibited. These outcomes together with the results of earlier facial expression studies suggest that facial EMG may provide an objective procedure that could be suitable for the clinical assessment of taste and smell function in newborns and young infants.     

Apical K+ channels in Necturus taste cells. Modulation by intracellular factors and taste stimuli

The apically restricted, voltage-dependent K+ conductance of Necturus taste receptor cells was studied using cell-attached, inside-out and outside-out configurations of the patch-clamp recording technique. Patches from the apical membrane typically contained many channels with unitary conductances ranging from 30 to 175 pS in symmetrical K+ solutions. Channel density was so high that unitary currents could be resolved only at negative voltages; at positive voltages patch recordings resembled whole-cell recordings. These multi-channel patches had a small but significant resting conductance that was strongly activated by depolarization. Patch current was highly K+ selective, with a PK/PNa ratio of 28. Patches containing single K+ channels were obtained by allowing the apical membrane to redistribute into the basolateral membrane with time. Two types of K+ channels were observed in isolation. Ca(2+)-dependent channels of large conductance (135-175 pS) were activated in cell-attached patches by strong depolarization, with a half-activation voltage of approximately -10 mV. An ATP-blocked K+ channel of 100 pS was activated in cell-attached patches by weak depolarization, with a half-activation voltage of approximately -47 mV. All apical K+ channels were blocked by the sour taste stimulus citric acid directly applied to outside-out and perfused cell-attached patches. The bitter stimulus quinine also blocked all channels when applied directly by altering channel gating to reduce the open probability. When quinine was applied extracellularly only to the membrane outside the patch pipette and also to inside-out patches, it produced a flickery block. Thus, sour and bitter taste stimuli appear to block the same apical K+ channels via different mechanisms to produce depolarizing receptor potentials.     

The influence of emotionally significant visual stimuli on cortical evoked potentials

Electrophysiological correlates of the perception of emotional stimuli were studied by means of recording the visual evoked potentials (EP) in 20 derivations (Fz, Cz, Pz, Oz, Fp _1/2,F _3/4,F _7/8,C _3/4,P _3/4,T _3/4,T _5/6, andO _1/2) during the emotional test performance. The performance of a special task by subjects was assessed positively or negatively (by administering emotionally positive or negative stimuli, respectively). Factor analysis revealed seven factors, which described the EP component structure. Analysis of variance demonstrated the influence of the emotional stimuli sign on the factorsP ₁₀₀,P ₁₄₀,N ₁₆₀,P ₂₂₀,P ₃₄₀, and “slow wave.” Hemispheric difference in reactions to the stimuli of a different emotional sign were recorded. During presentation of the positive and negative assessments, the amplitudes of the factorsP ₁₀₀,P ₃₄₀, and “slow wave” were maximally different in the left hemisphere, while the factorsN ₁₆₀ andP ₂₂₀ were maximally different in the right hemisphere.     

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

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

Effects of pharmacologic reductions in salivary flow on judgments of suprathreshold taste stimuli

The effects of short term salivary flow reductions on suprathresholdjudgments of taste intensity were measured using both a seriesof taste solutions and a comparable series of tastants driedon a filter paper base. Decreases in salivary flow were producedby the oral administration of either Elavil^®, Benadryl^®or atropine. The pharmacologic agents produced a 25 –82% reduction in salivary flow during the period that tastetesting occurred but no measurable effects on perceived tasteintensity were found. The exponents of power functions describingmolar concentration and perceived intensity were unchanged aswas the spread in perceived intensity between aqueous and drystimuli. Significant relationships between individual differencesin salivary flow and suprathreshold taste parameters also failedto emerge.     

Genetic variation in taste and its influence on food selection

Abstract Taste perception plays a key role in determining individual food preferences and dietary habits. Individual differences in bitter, sweet, umami, sour, or salty taste perception may influence dietary habits, affecting nutritional status and nutrition-related chronic disease risk. In addition to these traditional taste modalities there is growing evidence that "fat taste" may represent a sixth modality. Several taste receptors have been identified within taste cell membranes on the surface of the tongue, and they include the T2R family of bitter taste receptors, the T1R receptors associated with sweet and umami taste perception, the ion channels PKD1L3 and PKD2L1 linked to sour taste, and the integral membrane protein CD36, which is a putative "fat taste" receptor. Additionally, epithelial sodium channels and a vanilloid receptor, TRPV1, may account for salty taste perception. Common polymorphisms in genes involved in taste perception may account for some of the interindividual differences in food preferences and dietary habits within and between populations. This variability could affect food choices and dietary habits, which may influence nutritional and health status and the risk of chronic disease. This review will summarize the present state of knowledge of the genetic variation in taste, and how such variation might influence food intake behaviors.     

The K+-H+ exchanger, nigericin, modulates taste cell pH and chorda tympani taste nerve responses to acidic stimuli

The relationship between acidic pH, taste cell pH(i), and chorda tympani (CT) nerve responses was investigated before and after incorporating the K(+)-H(+) exchanger, nigericin, in the apical membrane of taste cells. CT responses were recorded in anesthetized rats in vivo, and changes in pH(i) were monitored in polarized fungiform taste cells in vitro. Under control conditions, stimulating the tongue with 0.15 M potassium phosphate (KP) or 0.15 M sodium phosphate (NaP) buffers of pHs between 8.0 and 4.6, KP or NaP buffers did not elicit a CT response. Post-nigericin (500 × 10(-6) M), KP buffers, but not NaP buffers, induced CT responses at pHs ≤ 6.6. The effect of nigericin was reversed by the topical lingual application of carbonyl cyanide 3-chloro-phenylhydrazone, a protonophore. Post-nigericin (150 × 10(-6) M), KP buffers induced a greater decrease in taste cell pH(i) relative to NaP buffers and to NaP and KP buffers under control conditions. A decrease in pH(i) to about 6.9 induced by KP buffers was sufficient to elicit a CT response. The results suggest that facilitating apical H(+) entry via nigericin decreases taste cell pH(i) and demonstrates directly a strong correlation between pH(i) and the magnitude of the CT response.