Taste Fibers Research Articles

Symptoms: Sudden Sensorineural Hearing Loss and Aural Fullness

Symptoms: Sudden Sensorineural Hearing Loss and Aural Fullness

Use of Suweg (Amorphopallus campanulatus )Tuber Flour Substitute bread flour on the quality of sweet bread

Healthy food is food that is rich in fiber, therefore this study was conducted to see the difference in the making of sweet bread by substituting wheat flour to Suweg tuber flour which is believed to be higher in fiber and better, besides that the treatment is to add CMC concentration in the manufacture of sweet bread. The Objective of this study was to obtain the best substitution effect of wheat flour and Suweg tuber flour in terms of nutritional value and quality of sweet bread and to determine the effect of CMC concentration in the manufacture of sweet bread. This study used a completely randomized design (CRD) method with two factorials. Factor I is the ratio of wheat flour and flour (T) consisting of 5 levels, namely T0 = 200: 0, T1 = 180: 20, T2 = 160: 30, T3 = 140: 60, T4 = 120: 80. Factor II is CMC concentration (C) consists of 3 levels, C1 = 0.37, C2 = 0.75, C3 = 1.12. Observational parameter tests carried out were color organoleptic tests, texture organoleptic tests, flavour organoleptic tests, taste organoleptic tests, expansion volume, water content, ash content, fat content, fiber content, and protein content. The results showed that the ratio of wheat flour and Suweg tuber flour had a very significant difference (p<0.01) on color organoleptic, flavour organoleptic, texture organoleptic, taste organoleptic, dough volume expansion, moisture content, content fat content, protein content and crude fiber content, while the concentration of CMC was very significant (p<0.01) on color organoleptic, texture organoleptic, dough volume expansion organoleptic, water content, protein content, fat content, and crude fiber content.

Identifying elements of a ready-to-eat meal desired by older adults

The population of older adults is rapidly growing, and undernutrition remains a concern. Properly formulated ready to eat (RTE) meals can provide older adults with convenient, nutritious meals that require minimal preparation. The study objective of this work was to uncover which properties and components of RTE meals were most important to older adults. 285 participants (mean age = 68.3 years) from Canada (n = 167) and the United States (n = 118) completed a two-part online survey. First, demographic information, including oral health survey and medication history was gathered. Rating-based conjoint analysis was then employed to identify RTE meal preferences. Meal ideas (n = 24) were created via a half-factorial design comprised of four concepts: taste theme (Asian, Latin, Mediterranean), protein source (chicken, fish, alternative protein, egg), spice (presence/absence), and fiber source (grains/vegetables). Participants indicated their expected liking and purchase intent of each meal idea. Results from the oral health survey found significant correlations between age and medication intake (R = 0.219, p = 0.0002), and frequencies of loss of taste and loss of smell (R = 0.800, p < 0.0001). Regarding meal components, protein source had the greatest importance to the total population (relative importance = 51.5%) with chicken having the greatest positive influence on liking (utility value = 0.31). A greater preference for the Mediterranean taste theme was observed in the Canadian respondents (p = 0.0002). Segmentation of the full dataset revealed four clusters based on relative importance of meal components. Cluster 1 (n = 25) contained participants preferring the presence of chicken and not fish, Cluster 2 (n = 190) was positively affected by the inclusion of chicken and fish, Cluster 3 (n = 42) contained individuals negatively affected by the presence of spice, and Cluster 4 (n = 23) contained individuals who preferred vegetarian options. In future research, meals that contain chicken or are vegetarian-friendly will be pursued.

Probing the multimodal fungiform papilla: complex peripheral nerve endings of chorda tympani taste and mechanosensitive fibers before and after Hedgehog pathway inhibition

The fungiform papilla (FP) is a gustatory and somatosensory structure incorporating chorda tympani (CT) nerve fibers that innervate taste buds (TB) and also contain somatosensory endings for touch and temperature. Hedgehog (HH) pathway inhibition eliminates TB, but CT innervation remains in the FP. Importantly, after HH inhibition, CT neurophysiological responses to taste stimuli are eliminated, but tactile responses remain. To examine CT fibers that respond to tactile stimuli in the absence of TB, we used Phox2b-Cre; Rosa26LSL−TdTomato reporter mice to selectively label CT fibers with TdTomato. Normally CT fibers project in a compact bundle directly into TB, but after HH pathway inhibition, CT fibers reorganize and expand just under the FP epithelium where TB were. This widened expanse of CT fibers coexpresses Synapsin-1, β-tubulin, S100, and neurofilaments. Further, GAP43 expression in these fibers suggests they are actively remodeling. Interestingly, CT fibers have complex terminals within the apical FP epithelium and in perigemmal locations in the FP apex. These extragemmal fibers remain after HH pathway inhibition. To identify tactile end organs in FP, we used a K20 antibody to label Merkel cells. In control mice, K20 was expressed in TB cells and at the base of epithelial ridges outside of FP. After HH pathway inhibition, K20 + cells remained in epithelial ridges but were eliminated in the apical FP without TB. These data suggest that the complex, extragemmal nerve endings within and disbursed under the apical FP are the mechanosensitive nerve endings of the CT that remain after HH pathway inhibition.

Whole-Mount Staining, Visualization, and Analysis of Fungiform, Circumvallate, and Palate Taste Buds.

Taste buds are collections of taste-transducing cells specialized to detect subsets of chemical stimuli in the oral cavity. These transducing cells communicate with nerve fibers that carry this information to the brain. Because taste-transducing cells continuously die and are replaced throughout adulthood, the taste-bud environment is both complex and dynamic, requiring detailed analyses of its cell types, their locations, and any physical relationships between them. Detailed analyses have been limited by tongue-tissue heterogeneity and density that have significantly reduced antibody permeability. These obstacles require sectioning protocols that result in splitting taste buds across sections so that measurements are only approximated, and cell relationships are lost. To overcome these challenges, the methods described herein involve collecting, imaging, and analyzing whole taste buds and individual terminal arbors from three taste regions: fungiform papillae, circumvallate papillae, and the palate. Collecting whole taste buds reduces bias and technical variability and can be used to report absolute numbers for features including taste-bud volume, total taste-bud innervation, transducing-cell counts, and the morphology of individual terminal arbors. To demonstrate the advantages of this method, this paper provides comparisons of taste bud and innervation volumes between fungiform and circumvallate taste buds using a general taste-bud marker and a label for all taste fibers. A workflow for the use of sparse-cell genetic labeling of taste neurons (with labeled subsets of taste-transducing cells) is also provided. This workflow analyzes the structures of individual taste-nerve arbors, cell type numbers, and the physical relationships between cells using image analysis software. Together, these workflows provide a novel approach for tissue preparation and analysis of both whole taste buds and the complete morphology of their innervating arbors.

Facial nerve paralysis

Abstract The facial nerve, the seventh pair of cranial nerves, has an essential role in non-verbal communication through facial expression. Besides innervating the muscles involved in facial expression, the complex structure of the facial nerve contains sensory fibres involved in the perception of taste and parasympathetic fibres involved in the salivation and tearing processes. Damage to the facial nerve manifested by facial paralysis translates into a decrease or disappearance of mobility of normal facial expression. Facial nerve palsy is one of the common causes of presenting to the Emergency Room. Most facial paralysis are idiopathic, followed by traumatic, infectious, tumor causes. A special place is occupied by the child’s facial paralysis. Due to the multitude of factors that can determine or favour its appearance, it requires a multidisciplinary evaluation consisting of otorhinolaryngologist, neurologist, ophthalmologist, internist. Early presentation to the doctor, accurate determination of the cause, correctly performed topographic diagnosis is the key to proper treatment and complete functional recovery.

Taste bud-derived BDNF maintains innervation of a subset of TrkB-expressing gustatory nerve fibers.

Taste receptor cells transduce different types of taste stimuli and transmit this information to gustatory neurons that carry it to the brain. Taste receptor cells turn over continuously in adulthood, requiring constant new innervation from nerve fibers. Therefore, the maintenance of innervation to taste buds is an active process mediated by many factors, including brain-derived neurotrophic factor (BDNF). Specifically, 40% of taste bud innervation is lost when Bdnf is removed during adulthood. Here we speculated that not all gustatory nerve fibers express the BDNF receptor, TrkB, resulting in subsets of neurons that vary in their response to BDNF. However, it is also possible that the partial loss of innervation occurred because the Bdnf gene was not effectively removed. To test these possibilities, we first determined that not all gustatory nerve fibers express the TrkB receptor in adult mice. We then verified the efficiency of Bdnf removal specifically in taste buds of K14-CreER:Bdnf mice and found that Bdnf expression was reduced to 1%, indicating efficient Bdnf gene recombination. BDNF removal resulted in a 55% loss of TrkB-expressing nerve fibers, which was greater than the loss of P2X3-positive fibers (39%), likely because taste buds were innervated by P2X3+/TrkB- fibers that were unaffected by BDNF removal. We conclude that gustatory innervation consists of both TrkB-positive and TrkB-negative taste fibers and that BDNF is specifically important for maintaining TrkB-positive innervation to taste buds. In addition, although taste bud size was not affected by inducible Bdnf removal, the expression of the γ subunit of the ENaC channel was reduced. So, BDNF may regulate expression of some molecular components of taste transduction pathways.

Immunohistochemical Analysis of Human Vallate Taste Buds.

The morphology of the vallate papillae from postmortem human samples was investigated with immunohistochemistry. Microscopically, taste buds were present along the inner wall of the papilla, and in some cases in the outer wall as well. The typical taste cell markers PLCβ2, GNAT3 (gustducin) and the T1R3 receptor stain elongated cells in human taste buds consistent with the Type II cells in rodents. In the human tissue, taste bud cells that stain with Type II cell markers, PLCβ2 and GNAT3, also stain with villin antibody. Two typical immunochemical markers for Type III taste cells in rodents, PGP9.5 and SNAP25, fail to stain any taste bud cells in the human postmortem tissue, although these antibodies do stain numerous nerve fibers throughout the specimen. Car4, another Type III cell marker, reacted with only a few taste cells in our samples. Finally, human vallate papillae have a general network of innervation similar to rodents and antibodies directed against SNAP25, PGP9.5, acetylated tubulin and P2X3 all stain free perigemmal nerve endings as well as intragemmal taste fibers. We conclude that with the exception of certain molecular features of Type III cells, human vallate papillae share the structural, morphological, and molecular features observed in rodents.

CALHM1 Deletion in Mice Affects Glossopharyngeal Taste Responses, Food Intake, Body Weight, and Life Span.

Stimulation of Type II taste receptor cells (TRCs) with T1R taste receptors causes sweet or umami taste, whereas T2Rs elicit bitter taste. Type II TRCs contain the calcium channel, calcium homeostasis modulator protein 1 (CALHM1), which releases adenosine triphosphate (ATP) transmitter to taste fibers. We have previously demonstrated with chorda tympani nerve recordings and two-bottle preference (TBP) tests that mice with genetically deleted Calhm1 (knockout [KO]) have severely impaired perception of sweet, bitter, and umami compounds, whereas their sour and salty tasting ability is unaltered. Here, we present data from KO mice of effects on glossopharyngeal (NG) nerve responses, TBP, food intake, body weight, and life span. KO mice have no NG response to sweet and a suppressed response to bitter compared with control (wild-type [WT]) mice. KO mice showed some NG response to umami, suggesting that umami taste involves both CALHM1- and non-CALHM1-modulated signals. NG responses to sour and salty were not significantly different between KO and WT mice. Behavioral data conformed in general with the NG data. Adult KO mice consumed less food, weighed significantly less, and lived almost a year longer than WT mice. Taken together, these data demonstrate that sweet taste majorly influences food intake, body weight, and life span.

Bilateral lingual nerve injury associated with classic laryngeal mask airway

Editor, A 36-year-old American Society of Anesthesiologists physical status Class I woman underwent a myomectomy for uterine fibroid. A size 4 classic laryngeal mask airway (LMA) was easily and atraumatically inserted and cuff inflated. Positive pressure ventilation started with no detectable air leak. Anaesthesia was maintained with sevoflurane 2–3% in O2/air. Procedure was prolonged due to surgical difficulties and intraoperative bleeding to a total time of 180 min. In recovery, patient reported tongue numbness and abnormal taste sensation over the anterior two thirds of the tongue. No obvious swelling, haematoma or bleeding in the oral cavity was noticed. After 3 weeks, she felt that 90% of the tongue sensation had returned to normal. It took 6 weeks for complete resolution of her symptoms; a diagnosis of lingual nerve damage was made based on the clinical presentation and relevant clinical examination. Patient consent was obtained for publication of this case report. Lingual nerve is a branch of the third division of the trigeminal nerve; it carries taste fibres from the facial nerve, namely the chorda tympani, supplying the anterior two thirds of the tongue. During its course, it lies in close proximity to the mandible, making it vulnerable to compression and damage. Injury could present with varying symptoms of neuropathic pain.1 Several reports of cranial nerve damage (lingual, hypoglossal and recurrent laryngeal nerve)2 as well as submandibular and parotid gland swellings3 have been published. The majority are related to the classic LMA, a few are related to ProSeal LMA. The mechanism of injury to the lingual nerve has been described before as a pressure neuropraxia when it enters the oral cavity below the inferior border of the superior constrictor muscle. Potential predisposing factors include traumatic insertion, high cuff pressures, use of small-size LMA, use of nitrous oxide, malpositioning including lateral position and extreme head-side rotation. Small-size LMA and the use of nitrous oxide were a common factor in most of the cases. Nitrous oxide diffuses into the cuff, leading to an increase in its pressure. This is likely to build up with time. Anaesthetists should be vigilant in monitoring cuff pressures during the procedure if nitrous oxide to be used. The classic LMA should be inflated according to manufacturer's guidelines using a volume-controlled technique aiming to achieve an adequate seal and avoiding intracuff pressure above 60 cmH2O. In this case, the only indeterminate was cuff pressure. If a manometer is not readily available, the use of a 10-ml syringe connected to the pilot balloon and allowed to equilibrate could give a good estimate of correct cuff pressure.4 To avoid nerve damage, the following conditions must be considered: Use the appropriate size LMA for the case, 4 for women and 5 for men. Gentle airway manipulation. Avoid cuff pressure above 60 cmH2O. Ensure cuff pressure measurement every 30 min, if using nitrous oxide. Avoid extreme neck positions. Have a low threshold of suspicion for lingual nerve damage if patient reports abnormal sensation/taste. What to do if it happens: Early referral to a specialist is required. Tests for light touch, pin prick and two-point discrimination could be used to identify the baseline and monitor progress. Clear documentation of patient complaints and clinical findings helped with schematic illustration to the areas of damage for further assessment and follow-up. If problems of neuropathic pain are encountered, a referral to a pain specialist might be required. In summary, cranial nerve damage related to the use of supraglottic airway devices is a rare but well described occurrence. Despite avoiding all known risk factors damage may still occur. We cannot overemphasis the need for cuff pressure measurement by some validated means. Close monitoring for improvement is vital, as without signs of improvement early intervention is essential. Acknowledgements The authors would like to declare that they have not received any assistance, financial support or sponsorship in relation to above publication and have no conflicts of interest.

Distinct neural ensembles in the rat gustatory cortex encode salt and water tastes

The gustatory cortex (GC) is important for perceiving the intensity of tastants but it remains unclear as to how single neurons in the region carry out this function. Previous studies have shown that taste-evoked activity from single neurons in GC can be correlated or anticorrelated with tastant concentration, yet whether one or both neural responses signal intensity is poorly characterized because animals from these studies were not trained to report the intensity of the concentration that they tasted. To address this issue, we designed a two-alternative forced choice (2-AFC) task in which freely licking rats distinguished among concentrations of NaCl and recorded from ensembles of neurons in the GC. We identified three neural ensembles that rapidly (<300 ms or ∼2 licks) processed NaCl concentration. For two ensembles, their NaCl evoked activity was anticorrelated with NaCl concentration but could be further distinguished by their response to water; in one ensemble, water evoked the greatest response while in the other ensemble the lowest tested NaCl concentration evoked the greatest response. However, the concentration sensitive activity from each of these ensembles did not show a strong association with the behaviour of the rat in the 2-AFC task, suggesting a lesser role for signalling tastant intensity. Conversely, for a third neural ensemble, its neural activity was well correlated with increases in NaCl concentration, and this relationship best matched the intensity perceived by the rat. These results suggest that this neuronal ensemble in GC whose activity monotonically increases with concentration plays an important role in signalling the intensity of the taste of NaCl.

Imaging of the facial nerve

The facial nerve is responsible for the motor innervation of the face. It has a visceral motor function (lacrimal, submandibular, sublingual glands and secretion of the nose); it conveys a great part of the taste fibers, participates to the general sensory of the auricle (skin of the concha) and the wall of the external auditory meatus. The facial mimic, production of tears, nasal flow and salivation all depend on the facial nerve. In order to image the facial nerve it is mandatory to be knowledgeable about its normal anatomy including the course of its efferent and afferent fibers and about relevant technical considerations regarding CT and MR to be able to achieve high-resolution images of the nerve.

Responses of Single Chorda Tympani Taste Fibers of the Calf (Bos taurus)

In spite of a wealth of information on feed and nutrition in cattle, there little is published of what they actually can taste. Here, we attempt to remedy some of this deficiency by presenting recordings of the chorda tympani proper nerve of young Holstein calves during stimulation of approximately 30 compounds. Hierarchical cluster analysis of 46 single taste fibers separated 4 fiber clusters: N (salt best), H (sour best), and 2 clusters, which could not be related to any human taste quality. The N fibers responded best to LiCl, NaCl, urea, monosodium glutamate, and KCl, whereas the H fibers responded strongly to citric and ascorbic acid. Interestingly, propionic and butyric acid stimulated best the 3rd cluster, whereas the 4th cluster responded best to denatonium benzoate and only to a small extent to quinine hydrochloride. Sweeteners stimulated moderately all clusters. Beginning with the largest response to sweet, the order between the responses was: acesulfame-K, saccharin, D-phenylalanine, glycine, sucrose, fructose, erythritol, cyclamate, and lactose. Alitame, aspartame, and super-aspartame evoked no or little responses. Three and 5 M ethanol stimulated all clusters. Comparison with taste fibers in other species suggests that the taste world of cattle is quite different from other species'.

Major Differences in the Proportion of Amino Acid Fiber Types Transmitting Taste Information From Oral and Extraoral Regions in the Channel Catfish

The present study investigates for the first time in any teleost the amino acid specificity and sensitivity of single glossopharyngeal (cranial nerve IX) fibers that innervate taste buds within the oropharyngeal cavity. These results are contrasted with similar data obtained from facial (cranial nerve VII) fibers that innervate extraoral taste buds. The major finding is that functional differences are clearly evident between taste fibers of these two cranial nerves. Catfish possess the most extensive distribution of taste buds found in vertebrates. Taste buds on the external body surface are exclusively innervated by VII, whereas IX, along with the vagus (X), innervate the vast majority of taste buds within the oropharyngeal cavity. Responses to the l-isomers of alanine (Ala), arginine (Arg), and proline (Pro), the three most stimulatory amino acids that bind to independent taste receptors, were obtained from 90 single VII and 64 single IX taste fibers. This study confirmed a previous investigation that the amino acid responsive VII fibers consist of two major groups, the Ala and Arg clusters containing taste fibers having thresholds in the ηM range. In contrast, the present study indicates the amino acid responsive IX taste system is dominated by taste fibers responsive to Pro and to Pro and Arg, respectively, has a reduced percentage of Ala fibers, and is less sensitive than VII. The present electrophysiological results are consistent with previous experiments, indicating that the extraoral taste system is essential for appetitive behavior, whereas oropharyngeal taste buds are critical for consummatory behavior.

Effects of dietary Na+ deprivation on epithelial Na+ channel (ENaC), BDNF, and TrkB mRNA expression in the rat tongue

BackgroundIn rodents, dietary Na+ deprivation reduces gustatory responses of primary taste fibers and central taste neurons to lingual Na+ stimulation. However, in the rat taste bud cells Na+ deprivation increases the number of amiloride sensitive epithelial Na+ channels (ENaC), which are considered as the "receptor" of the Na+ component of salt taste. To explore the mechanisms, the expression of the three ENaC subunits (α, β and γ) in taste buds were observed from rats fed with diets containing either 0.03% (Na+ deprivation) or 1% (control) NaCl for 15 days, by using in situ hybridization and real-time quantitative RT-PCR (qRT-PCR). Since BDNF/TrkB signaling is involved in the neural innervation of taste buds, the effects of Na+ deprivation on BDNF and its receptor TrkB expression in the rat taste buds were also examined.ResultsIn situ hybridization analysis showed that all three ENaC subunit mRNAs were found in the rat fungiform taste buds and lingual epithelia, but in the vallate and foliate taste buds, only α ENaC mRNA was easily detected, while β and γ ENaC mRNAs were much less than those in the fungiform taste buds. Between control and low Na+ fed animals, the numbers of taste bud cells expressing α, β and γ ENaC subunits were not significantly different in the fungiform, vallate and foliate taste buds, respectively. Similarly, qRT-PCR also indicated that Na+ deprivation had no effect on any ENaC subunit expression in the three types of taste buds. However, Na+ deprivation reduced BDNF mRNA expression by 50% in the fungiform taste buds, but not in the vallate and foliate taste buds. The expression of TrkB was not different between control and Na+ deprived rats, irrespective of the taste papillae type.ConclusionThe findings demonstrate that dietary Na+ deprivation does not change ENaC mRNA expression in rat taste buds, but reduces BDNF mRNA expression in the fungiform taste buds. Given the roles of BDNF in survival of cells and target innervation, our results suggest that dietary Na+ deprivation might lead to a loss of gustatory innervation in the mouse fungiform taste buds.

The sweet taste quality is linked to a cluster of taste fibers in primates: lactisole diminishes preference and responses to sweet in S fibers (sweet best) chorda tympani fibers of M. fascicularis monkey

BackgroundPsychophysically, sweet and bitter have long been considered separate taste qualities, evident already to the newborn human. The identification of different receptors for sweet and bitter located on separate cells of the taste buds substantiated this separation. However, this finding leads to the next question: is bitter and sweet also kept separated in the next link from the taste buds, the fibers of the taste nerves? Previous studies in non-human primates, P. troglodytes, C. aethiops, M. mulatta, M. fascicularis and C. jacchus, suggest that the sweet and bitter taste qualities are linked to specific groups of fibers called S and Q fibers. In this study we apply a new sweet taste modifier, lactisole, commercially available as a suppressor of the sweetness of sugars on the human tongue, to test our hypothesis that sweet taste is conveyed in S fibers.ResultsWe first ascertained that lactisole exerted similar suppression of sweetness in M. fascicularis, as reported in humans, by recording their preference of sweeteners and non- sweeteners with and without lactisole in two-bottle tests. The addition of lactisole significantly diminished the preference for all sweeteners but had no effect on the intake of non-sweet compounds or the intake of water. We then recorded the response to the same taste stimuli in 40 single chorda tympani nerve fibers. Comparison between single fiber nerve responses to stimuli with and without lactisole showed that lactisole only suppressed the responses to sweeteners in S fibers. It had no effect on the responses to any other stimuli in all other taste fibers.ConclusionIn M. fascicularis, lactisole diminishes the attractiveness of compounds, which taste sweet to humans. This behavior is linked to activity of fibers in the S-cluster. Assuming that lactisole blocks the T1R3 monomer of the sweet taste receptor T1R2/R3, these results present further support for the hypothesis that S fibers convey taste from T1R2/R3 receptors, while the impulse activity in non-S fibers originates from other kinds of receptors. The absence of the effect of lactisole on the faint responses in some S fibers to other stimuli as well as the responses to sweet and non-sweet stimuli in non-S fibers suggest that these responses originate from other taste receptors.

Bitter taste markers explain variability in vegetable sweetness, bitterness, and intake

Intake of vegetables falls short of recommendations to lower risk of chronic diseases. Most research addresses bitterness as a sensory deterrent to consuming vegetables. We examined bitter and sweet sensations from vegetables as mediators of vegetable preference and intake as well as how these tastes vary with markers of genetic variation in taste (3.2 mM 6- n-propylthiouracil bitterness) and taste pathology (1.0 mM quinine bitterness, chorda tympani nerve relative to whole mouth). Seventy-one females and 39 males (18–60 years) reported prototypical tastes from and preference for Brussels sprouts, kale and asparagus as well as servings of vegetables consumed, excluding salad and potatoes. Intensity and hedonic ratings were made with the general Labeled Magnitude Scale. Data were analyzed with multiple linear regression and structural equation modeling. Vegetable sweetness and bitterness were independent predictors of more or less preference for sampled vegetables and vegetable intake, respectively. Those who taste PROP as most bitter also tasted the vegetables as most bitter and least sweet. The spatial pattern of quinine bitterness, suggestive of insult to chorda tympani taste fibers, was associated with less bitterness and sweetness from vegetables. Via structural equation modeling, PROP best explained variability in vegetable preference and intake via vegetable bitterness whereas the quinine marker explained variability in vegetable preference and intake via vegetable bitterness and sweetness. In summary, bitterness and sweetness of sampled vegetables varied by taste genetic and taste function markers, which explained differences in preference for vegetables tasted in the laboratory as well as overall vegetable intake outside the laboratory.

Elucidating coding of taste qualities with the taste modifier miraculin in the common marmoset

To investigate the relationships between the activity in different types of taste fibers and the gustatory behavior in marmosets, we used the taste modifier miraculin, which in humans adds a sweet taste quality to sour stimuli. In behavioral experiments, we measured marmosets’ consumption of acids before and after tongue application of miraculin. In electrophysiological experiments responses of single taste fibers in chorda tympani and glossopharyngeal nerves were recorded before and after tongue application of miraculin. We found that after miraculin marmosets consumed acids more readily. Taste nerve recordings showed that after miraculin taste fibers which usually respond only to sweeteners, S fibers, became responsive to acids. These results further support our hypothesis that the activity in S fibers is translated into a hedonically positive behavioral response.

Expression of P2Y1 receptors in rat taste buds.

Extracellular nucleotides such as ATP are the signaling molecules which bind to membrane receptors (P2X ligand-gated ion channels and G-protein-coupled P2Y families). In the gustatory system, it is known that P2X receptors are expressed exclusively in nerve fibers innervating the taste buds. Also, P2Y receptors are suggested to play some important roles in taste signal transductions on the basis of the physiological studies. In the present study, we examined the expression patterns of P2Y1 receptor subtype by using reverse transcript polymerase chain reaction (RT-PCR), in situ hybridization, and immunohistochemistry. RT-PCR analyses showed that P2Y1 receptor mRNAs appeared in circumvallate papillae. P2Y1 receptor mRNA was detected in a subset of taste bud cells by in situ hybridization. By immunohistochemical analyses, P2Y1 receptor was detected in a subset of taste bud cells of fungiform, foliate, and circumvallate papillae. We showed that ATP induced a biphasic intracellular Ca2+ increase in taste cells by a Ca2+ imaging method. Furthermore, we showed by double-immunolabeling methods that P2Y1-expressing cells coexpressed both IP3R3 and SNAP-25. These results suggest that ATP may activate P2Y receptors resulting in Ca2+ release from internal stores via IP3R3. Since many SNAP-25-immunoreactive taste bud cells coexpressed P2Y1 immunoreactivity, it is suggested that P2Y1-expressing cells may possess synapses with afferent nerve fibers. The results of the present study suggest that P2Y1 receptor may play some roles in ATP-mediated signal transductions between taste bud cells and afferent taste fibers.

Sense of taste in a New World monkey, the common marmoset. II. Link between behavior and nerve activity.

In a previous study, we characterized the gustatory system of a New World monkey the common marmoset, Callithrix jacchus jacchus, with electrophysiological techniques by recording from taste fibers of the chorda tympani proper (CT) and glossopharyngeal (NG) nerves. Hierarchical cluster analysis identified three clusters of taste fibers: S fibers, responding predominantly to sweeteners, Q fibers, responding predominantly to bitter stimuli, and H fibers, responding predominantly to acids. In this study, we employed two behavioral techniques, the two-bottle preference (TBP) and conditioned taste aversion (CTA), to study the taste of the compounds used in the previous electrophysiological study. The results showed that compounds that did not stimulate any taste fibers were neither preferred nor rejected. Compounds that activated only S fibers were always preferred over water. When aversion to sucrose was created by the CTA method, these compounds were rejected. Compounds that activated Q fibers were rejected and consumed less than water. We studied the relationship between intake and net response from S and Q fibers in the CT and NG nerves. Intake was measured as a preference ratio in TBP test. The net response was defined as: (S(CT) + S(NG)) - (Q(CT) + Q(NG)), where S(CT) + S(NG) denotes the sum of the responses in S fibers of the CT and NG nerves. Similarly, Q(CT) + Q(NG) represents the sum of the responses in Q fibers of the CT and NG nerves. The relationship between intake and the Net response was linear with a Pearson correlation coefficient 0.85. This study supports our hypothesis that intake is influenced by S and Q fibers, where S fibers serve as a hedonically positive input and Q fibers as a hedonically negative input.