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PubMed1988

Differential facial responses to four basic tastes in newborns.

The distinctiveness and recognizability of taste-elicited facial expressions in newborns were examined in 2 studies. Sucrose, sodium chloride, citric acid, and quinine hydrochloride solutions were presented to 12 infants at 2 hours of age. In Study 1, the anatomically based Facial Action Coding System adapted for infants (Baby FACS) was used to obtain detailed, objective descriptions of the infants' videotaped facial responses to each solution. Facial responses to sucrose were characterized primarily by facial relaxation and sucking. The responses to salty, sour, and bitter solutions shared the same hedonically negative upper- and midface components but differed in the accompanying lower-face actions: lip pursing in response to sour and mouth gaping in response to bitter. There was no distinctive facial expression for sodium chloride. These findings demonstrate that newborns differentiate sour and bitter from each other and from salt, as well as discriminating sweet versus nonsweet tastes. In Study 2, untrained adults viewing videotapes of the infants' facial reactions made forced-choice judgments identifying the stimuli presented and rated the hedonic tone of the infants' responses. While the judges accurately identified the newborns' responses to sucrose, there were systematic errors in their judgments of the 3 nonsweet stimuli. The judges' hedonic ratings, on the other hand, clearly differentiated between the infants' responses to the bitter stimulus and the other 3 tastes. The findings are discussed in terms of the possible functional origins and communicative value of taste-elicited facial expressions in infants.

Discrimination Learning↗
PubMed2005

A new set of amino acid descriptors and its application in peptide QSARs.

In this work, a new set of amino acid descriptors, i.e., VHSE (principal components score Vectors of Hydrophobic, Steric, and Electronic properties), is derived from principal components analysis (PCA) on independent families of 18 hydrophobic properties, 17 steric properties, and 15 electronic properties, respectively, which are included in total 50 physicochemical variables of 20 coded amino acids. Using the stepwise multiple regression (SMR) method combined with partial least squares (PLS), the VHSE scales are then applied to QSAR studies of bitter-tasting dipeptides (BTD), angiotensin-converting enzyme (ACE) inhibitors, and bradykinin-potentiating pentapeptides (BPP). To validate the predictive power of resulting models, external validation are also performed. A comparison of the results to those obtained with z scores and other two-dimensional (2D) or three-dimensional(3D) descriptors shows that the VHSE scales are comparable for parameterizing the structural variability of the peptide series.

Amino Acid Sequence↗
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↗
PubMed2001

Bitter substances suppress afferent responses to an appetitive mixture: evidence for peripheral integration of chemosensory stimuli.

The processes that lead from detection of chemicals, transduction, and coding with the appropriate message to initiate ingestion of a palatable meal or to reject a potentially noxious substance are poorly understood in vertebrates owing to the complex organization of the taste system. As a first step in elucidating the cellular basis of the behavioral differences elicited by appetitive stimuli and bitter compounds, we recorded from the afferent nerves conveying peripheral chemosensory information to the CNS in the head of the leech, Hirudo medicinalis. Superfusion of the chemosensory region of the lip of Hirudo with a mixture of NaCl (150 mM) and arginine (1 mM), an appetitive solution that elicits ingestion, increased the neuronal activity in the afferent cephalic nerves, for example (Zhang X, Wilson RJ, Li Y, Kleinhaus AL. 2000. Chemical and thermal stimuli have short-lived effects on the Retzius cell in the medicinal leech. J Neurobiol 43:304-311.). In the present paper we show that superfusing the lip with quinine or denatonium reduced the basal neural activity in the afferents. Furthermore, these bitter substances in the appetitive solution counteracted the increased activity the appetitive solution evoked in the cephalic nerves. Thus, the neural activity evoked by the application of appetitive and aversive stimuli to the chemosensory area of the lip paralleled the opposite behavioral responses to the same chemicals. The results suggest that individual leech taste cells possess receptors for both types of stimuli. Therefore, the leech may be a good model system in which to study peripheral taste events in cells that may possess multiple receptors and transduction mechanisms that interact to integrate information.

Action Potentials↗
PubMed1995

Gustatory neural coding in the monkey cortex: acid stimuli.

1. We sought to define the gustatory neural code for acidic stimuli. Therefore we analyzed the responses of 44 single neurons in the insular cortex of four alert cynomolgus macaques in response to the oral application of four basic taste stimuli (glucose, NaCl, HCl, and quinine HCl) and fruit juice, and to a series of 20 additional acids. 2. Neurons responsive to gustatory stimulation were encountered within a volume of 38.2 mm3 (3.5 mm anteroposterior x 2.1 mm mediolateral x 5.2 mm dorsoventral). Taste cells constituted 81 (5.2%) of the 1,552 neurons whose sensitivities were tested. Of these, the activity of 44 was followed through at least one complete application of the stimulus series, and those responses compose the data of this study. Nongustatory cells included those responsive to mouth movements (36.3%), tactile stimulation within the mouth (2.1%), visual approach of the taste stimulus (1.4%), and extension of the tongue (0.1%). The functions of the remaining 54.8% were not determined. 3. The mean spontaneous discharge rate of these cortical taste cells was 3.0 spikes/s (range 0.0-14.4 spikes/s). The mean breadth of tuning coefficient was a moderate 0.72 (range 0.26-0.98). Most evoked activity was excitatory, although inhibition was a prominent response option for four (9%) taste cells. 4. There was no evidence that taste cells with similar functional characteristics were clustered within the cortex, i.e., there was no apparent topographic organization of taste quality. 5. Thirty-four of the 44 cells were divisible into three functional types on the basis of their response profiles to the four basic stimuli used here.(ABSTRACT TRUNCATED AT 250 WORDS)

Acids↗
PubMed1998

The taste of sodium.

Sodium is crucial to physiological function. The responsibility for detecting it is assumed by the taste system, which devotes perhaps one quarter of its resources to the task. Sodium is transduced by passage into a subset of receptor cells, whose activity is relayed to the brain through a discrete gustatory channel. Responses in hindbrain, thalamus, and gustatory cortex identify the quality and concentration of sodium on the tongue. Coding of reinforcement may begin with the pons and ventral forebrain, particularly the lateral and medial hypothalamic nuclei. When body stores are sufficient, behavioral preference for sodium is mild, encompassing low concentrations and marked by weak avidity. This languid response disappears during sodium shortages. Avidity increases, and hypertonic concentrations are most preferred. This behavioral change may result from altered responsiveness in sodium-specific neurons that offer the sodium signal access to mechanisms of reinforcement. Thus, the taste system detects and recognizes sodium, and accords it a reward value commensurate with the needs of the animal.

Animals↗
PubMed2003

Oxidative remodeling of chromoplast carotenoids: identification of the carotenoid dioxygenase CsCCD and CsZCD genes involved in Crocus secondary metabolite biogenesis.

The accumulation of three major carotenoid derivatives-crocetin glycosides, picrocrocin, and safranal-is in large part responsible for the color, bitter taste, and aroma of saffron, which is obtained from the dried styles of Crocus. We have identified and functionally characterized the Crocus zeaxanthin 7,8(7',8')-cleavage dioxygenase gene (CsZCD), which codes for a chromoplast enzyme that initiates the biogenesis of these derivatives. The Crocus carotenoid 9,10(9',10')-cleavage dioxygenase gene (CsCCD) also has been cloned, and the comparison of substrate specificities between these two enzymes has shown that the CsCCD enzyme acts on a broader range of precursors. CsZCD expression is restricted to the style branch tissues and is enhanced under dehydration stress, whereas CsCCD is expressed constitutively in flower and leaf tissues irrespective of dehydration stress. Electron microscopy revealed that the accumulation of saffron metabolites is accompanied by the differentiation of amyloplasts and chromoplasts and by interactions between chromoplasts and the vacuole. Our data suggest that a stepwise sequence exists that involves the oxidative cleavage of zeaxanthin in chromoplasts followed by the sequestration of modified water-soluble derivatives into the central vacuole.

Amino Acid Sequence↗
PubMed2002

Gustatory processing is dynamic and distributed.

The process of gustatory coding consists of neural responses that provide information about the quantity and quality of food, its generalized sensation, its hedonic value, and whether it should be swallowed. Many of the models presently used to analyze gustatory signals are static in that they use the average neural firing rate as a measure of activity and are unimodal in the sense they are thought to only involve chemosensory information. We have recently elaborated upon a dynamic model of gustatory coding that involves interactions between neurons in single as well as in spatially separate, gustatory and somatosensory regions. We propose that the specifics of gustatory responses grow not only out of information ascending from taste receptor cells, but also from the cycling of information around a massively interconnected system.

Action Potentials↗
PubMed2005

[New 3D amino acid structure descriptors and its application to the polypeptide QSAR].

AIM: To establish a new amino acid structure descriptor that can be applied to polypeptide QSAR studies. METHODS: The new amino acid structure descriptor c-scales were derived from a principal components analysis of 167 amino acid structure descriptor indexes by theoretic calculation. The c1,c2,c3-scales were related to 3D structural features of amino acid such as steric, electronic and conformation properties etc. G/PLS regression method was used to find out the relationship between the c-scales and the biological activity and developed QSAR models of the polypeptides. RESULTS: Using the established method, we developed accordingly QSAR models of Bitter tasting dipeptide, ACE inhibitors and bradykinin-potentiating pentapeptides and their r2 and XV-r2 were more than 0.70. CONCLUSION: The c-scales can quantitatively describe the 3D structural features of any coded and non-coded amino acid and can be used to establish a QSAR model of good predictability.

Amino Acid Sequence↗
PubMed1996

Monogeusia for fructose, glucose, sucrose, and maltose.

We investigated the ability of subjects to discriminate sugars with a whole-mouth forced-choice paradigm, in which a standard solution was compared with a test solution of varied concentration. Discrimination probabilities were U-shaped functions of test concentration: for 6 subjects and pairwise combinations of fructose, glucose, and sucrose, discriminability always declined to chance over a narrow range of test concentrations. At concentrations < or = 100 mM, maltose was indiscriminable from fructose but discriminable at higher concentrations for 4 subjects. By analogy with the monochromacy of night vision, whereby any two lights are indiscriminable when their relative intensities are suitably adjusted, we call the gustatory indiscriminability of these sugars monogeusia. The simplest account of monogeusia is that all information about the indiscriminable sugars is represented by a single neural signal that varies only in magnitude. The discriminability of maltose from the other sugars at higher concentrations is consistent with the hypothesis that maltose also activates a second gustatory code.

Adult↗
PubMed1999

Altered taste responses in adult NST after neonatal chorda tympani denervation.

Anatomic and behavioral changes have been observed in the taste system after peripheral deafferentation, but their physiological consequences remain unknown. Interestingly, a recent behavioral study suggested that peripheral denervation could induce central plasticity. After neonatal chorda tympani (CT) transection, adult rats demonstrated a marked preference for a normally avoided salt, NH(4)Cl. In the present study, taste responses were recorded from the nucleus of the solitary tract (NST) in similarly CT-denervated rats to investigate a physiological basis for this behavioral phenomenon. We hypothesized that alterations in functional connectivity of remaining afferent nerves might underlie the behavioral change. Specifically, if NST neurons formerly activated by sodium-selective CT fibers were instead driven by more broadly tuned glossopharyngeal (GL) afferents, neural coding of salt responses would be altered. Such a change should be accompanied by a shift in orotopic representation and increased NH(4)Cl responses. This hypothesis was not supported. After CT denervation, orotopy was unaltered, NH(4)Cl responsiveness declined, and no other changes occurred that could simply explain the behavioral effects. Indeed, the most pronounced consequence of CT denervation was a 68% reduction in NaCl responses, supporting previous evidence for a critical role of this nerve in coding sodium salts. In addition, we found "reorganizational" changes similar to, albeit smaller than, those observed in other sensory systems after deafferentation. There was a trend for increased responses elicited by stimulation of receptor subpopulations innervated by the GL and greater superficial petrosal nerves. In addition, the spontaneous rate of nasoincisor duct-responsive cells increased significantly. This effect on spontaneous rate is opposite to that produced by CT anesthesia, suggesting that acute versus chronic denervation may affect central taste neurons differently. In conclusion, the taste system at the medullary level seems more resistant to large-scale plasticity than other sensory systems, but nevertheless reacts to lost afferent input. Because the most robust plastic changes have been documented at cortical levels in other sensory pathways, the substrate for the behavioral effect of neonatal CT transection may be located more centrally in the gustatory system.

Afferent Pathways↗
PubMed2000

Glycerol metabolism in Lactobacillus collinoides: production of 3-hydroxypropionaldehyde, a precursor of acrolein.

Lactobacillus collinoides is a lactic acid bacterium commonly found in fermenting apple juice. Although this bacterium is not particularly involved in malolactic conversion, the presence of L. collinoides in cider may have serious consequences on the product. L. collinoides is indeed considered to be responsible for the transformation of glycerol to 3-hydroxypropionaldehyde (3-HPA), a precursor of acrolein that spoils the product quality by generating bitter tastes. The purpose of our work was to evaluate the influence of environmental and culture conditions on the conversion of glycerol to 3-HPA in L. collinoides, and to obtain a DNA probe of the gene coding for glycerol dehydratase, the enzyme responsible for this conversion.

Acrolein↗
PubMed1989

Neural coding of gustatory information in the thalamus of Macaca mulatta.

1. Extracellular action potentials were recorded from single neurons in the parvicellular division of the ventroposteromedial (VPMpc) nucleus of the thalamus of restrained, but alert, Old World monkeys during gustatory, tactile, and thermal stimulation of the oral cavity. In contrast to previous reports in anesthetized or paralyzed rats, the spontaneous activity of these neurons was brisk and their evoked responses robust. 2. Each of 50 taste-responsive neurons was tested with 1.0 M sucrose, 0.1 M NaCl, 0.003 M HCl, and 0.001 M QHCl before other concentrations of the same stimuli were used. Sucrose, which was effective in 80% of the neurons tested, evoked the largest responses of the 4 standard gustatory stimuli (16.1 spikes/s). The average response to NaCl, an effective stimulus for 44% of the neurons in the sample, was 7.5 spikes/s. HCl and QHCl, which few neurons responded to, typically evoked smaller responses. 3. Most of the neurons tested showed monotonic intensity-response (I-R) functions. The power functions showed about the same degree of compression (range = 0.39-0.53), which has been described previously for brain stem neurons in anesthetized rodents. Only 9.1% of the responses were inhibitory, and there was no tendency for these responses to be associated with either specific neurons or stimuli. These data suggest that quality coding of gustatory information in the thalamus is not radically different from that seen among lower-order neurons in other species. 4. Through the use of hierarchical cluster analysis, it was possible to divide the neuron sample into 2 groups, one of which consisted of sucrose-best neurons that had an average entropy value of 0.56. The neurons in the other group, though more heterogeneous, showed either primary or side-band sensitivity to NaCl. The average breadth of responsiveness of the 50 thalamic neurons as described by the entropy coefficient was 0.73. 5. In addition to gustatory neurons, tactile (n = 15), thermal (n = 1), and nonresponsive (n = 25) neurons also were located within VPMpc. An additional 48 neurons that could not be classified as either sensory or motor in nature, inhibited their bursting spontaneous discharge just prior to the onset of fluid stimulation. Only 2 of these neurons demonstrated differential chemical sensitivity. The presence of these nongustatory neurons within the thalamic taste area suggests that the traditional characterization of VPMpc as a gustatory relay may understate its role in ingestive behavior and ignore other noningestive functions of the area.

Animals↗
PubMed1997

Studies of human olfaction from the University of Pennsylvania Smell and Taste Center.

This paper, presented in part as an invited lecture on the occasion of Professor E.P. Köster's retirement from Utrecht University, summarizes a large body of human studies performed at the University of Pennsylvania Smell and Taste Center during the last 17 years. Details of the development of standardized olfactory tests are provided, including their validation and application in a wide variety of clinical and laboratory settings. Included are studies related to transduction mechanisms in olfactory coding and factors that adversely influence olfactory function (e.g. age, gender, smoking, exposure to environmental chemicals, numerous diseases). A brief discussion of the strengths and weaknesses of the olfactory vector hypothesis for neurodegenerative diseases is also presented.

Humans↗
PubMed1999

Gustatory neural coding in the cortex of the alert cynomolgus macaque: the quality of bitterness.

We sought to define the gustatory neural representation in primates for stimuli that humans describe as predominantly bitter. Thus we analyzed the responses of single neurons from the insular cortex of two alert, male cynomolgus macaques in response to the oral application of four basic taste stimuli (glucose, NaCl, HCl, and quinine HCl) and fruit juice, and to a series of 15 other chemicals to which humans ascribe a bitter component. Gustatory neurons occupied a volume of 109 mm3 across an area of 4.0 mm in the anterposterior plane, 4.4 mm in the mediolateral, and 6.2 mm in the dorsoventral. Taste cells represented 161 (8.6%) of the 1881 neurons tested for chemical sensitivity. Fifty of these could be monitored throughout the delivery of the entire stimulus series, and their responses constitute the data of this study. The mean spontaneous discharge rate of the cortical gustatory cells was 3.2 +/- 3.3 spikes/s (range = 0.2-17.7 spikes/s). The mean breadth-of-tuning coefficient was a moderate 0.77 +/- 0.15 (range = 0.25-0.99). Forty-eight neurons responded to taste stimuli with excitation, and two responded with inhibition. Forty-one of the 50 neurons were able to be classified into one of four functional types based on their responses to the four basic stimuli used here. These were sugar (n = 22), salt (n = 7), acid (n = 7), and quinine (n = 5). A two-dimensional space was generated from correlations among the response profiles elicited by the stimuli array. The 16 bitter chemicals formed a coherent group that was most closely related to HCl, moderately to NaCl, and bore no relationship with glucose. Within the bitter stimuli, six formed a subgroup that was most separated from all nonbitter chemicals: quinine HCl, phenlythiocarbamide, propylthiouracil, caffeine, theophylline, and phenylalanine. Humans describe these stimuli as rather purely bitter. Of the remaining 10 bitter compounds, 4 were on the fringe of the bitter group leading to NaCl: MgCl2, CaCl2, NH4Cl, and arginine. Humans characterize these as bitter-salty. Three were on the fringe leading to HCl: urea, cysteine and vitamin B1. Humans call these bitter-sour. The remaining three (nicotine, histidine, and vitamin B2) occupied the center of the bitter group. Taste quality, inferred from the position of each stimulus in the space, correlated well with human descriptions of the same stimuli, reinforcing the value of the macaque as a neural model for human gustation.

Action Potentials↗
PubMed2005

Positive selection on a high-sensitivity allele of the human bitter-taste receptor TAS2R16.

BACKGROUND: During periods of human expansion into new environments, recognition of bitter natural toxins through taste may have conferred an important selective advantage. The G protein-coupled receptor encoded by TAS2R16 mediates response to salicin, amygdalin, and many bitter beta-glucopyranosides. beta-glucopyranosides are ubiquitous in nature, with many having a highly toxic cyanogenic activity. RESULTS: We examined evidence for natural selection on the human receptor TAS2R16 by sequencing the entire coding region, as well as part of the 5' and 3' UTRs, in 997 individuals from 60 human populations. We detected signatures of positive selection, indicated by an excess of evolutionarily derived alleles at the nonsynonymous site K172N and two linked sites and significant values of Fay and Wu's H statistics in 19 populations. The estimated age range for the common ancestor of the derived N172 variant is 78,700-791,000 years, placing it in the Middle Pleistocene and before the expansion of early humans out of Africa. Using calcium imaging in cells expressing different receptor variants, we showed that N172 is associated with an increased sensitivity to salicin, arbutin, and five different cyanogenic glycosides. CONCLUSION: We have detected a clear signal of positive selection at the bitter-taste receptor gene TAS2R16. We speculate that the increased sensitivity that is shown toward harmful cyanogenic glycosides and conferred by the N172 allele may have driven the signal of selection at an early stage of human evolution.

Alleles↗