Capsaicin receptors are colocalized with sweet/bitter receptors in the taste sensing cells of circumvallate papillae

Diet Preference, Feed Efficiency and Expression of the Sodium-Dependent Glucose Transporter Isoform 1 and Sweet Taste Receptors in the Jejunum of Lambs Supplemented with Different Flavours

This study investigated the effect of dietary flavour supplements on the preference, feed efficiency and expression of the sweet taste receptor family 1 members 2 and 3 (T1R2 + T1R3), and sodium-glucose linked transporter 1 (SGLT1) genes in the lambs' small intestines. Eight, five-month-old, Israeli crossbred Assaf lambs were offered 16 different non-nutritive commercial flavours in rolled barley and ground corn. Capsicum and sucram were the most preferred non-aroma flavours (p = 0.020), while milky (p < 0.001) was the most preferred powder-aroma flavour. For the metabolic and relative gene expression study, eight lambs were randomly assigned to either sucram, capsicum, a mix containing sucram and capsicum at 1:1 ratio or no flavour for control in a 4 × 2 cross-over design. The total collection of urine (females only), faeces and refusals was carried out, and T1R2, T1R3 and SGLT1 relative gene expression evaluated from the proximal jejunum biopsies. Flavour had no significant effect on the feed intake (p = 0.934), but capsicum increased the average daily weight gain per metabolic body weight (p = 0.049). The T1R3 gene was expressed highest in the mix treatment (1.7; p = 0.005). Collectively, our findings indicate that flavours can be used to motivate feed acceptance and improve the weight gain in lambs.

Sucrose alleviates capsaicin-induced tongue burning: An in vivo study

Background

Spicy foods are flavorful and stimulate salivation, which is beneficial for individuals with poor appetite. They are also ubiquitous in many regional cuisines, but the chemical compounds in such foods, especially capsaicin from chili peppers, can cause tissue inflammation and generate intolerable burning pain in the oral cavity.

Material and Methods

To identify a potential method to reduce capsaicin-induced burning pain without influencing food flavor, we tested the effects of mouth rinsing with various concentrations of sucrose. Inclusion criteria were good general and oral health, while exclusion criteria were poor baseline smell or taste, capsaicin allergy, and current orofacial pain complaints. To define an appropriate capsaicin dose, participants placed filter paper strips impregnated with 0.003%–0.3% capsaicin on the tip of the tongue and rated burning sensation by visual analog scale (VAS) score.

Results

A 0.1% capsaicin solution induced tongue burning in the midrange (VAS = 6.33 ± 0.52) and so was used for subsequent tests. We then examined the efficacy concentration of sucrose for reducing tongue burning by recording VAS scores at multiple time points following a 15-s oral rinse with various aqueous sucrose solutions (5%, 10%, and 20%), milk, or pure water (control) after 0.1% capsaicin application. Scores were compared at each time point by one-way ANOVA with post hoc Dunnett’s tests. A 15-s rinse with 20% sucrose significantly alleviated burning pain compared to water rinse at 45, 60, 120, and 180 s after capsaicin exposure.

Conclusions

Thus, periodic rinsing with 20% aqueous sucrose may help promote spicy food consumption among individuals with poor appetite.

Key words:Capsaicin, sucrose, burning sensation.

Cannabinoids Drugs and Oral Health-From Recreational Side-Effects to Medicinal Purposes: A Systematic Review

Background: marijuana, the common name for cannabis sativa preparations, is one of the most consumed drug all over the world, both at therapeutical and recreational levels. With the legalization of medical uses of cannabis in many countries, and even its recreational use in most of these, the prevalence of marijuana use has markedly risen over the last decade. At the same time, there is also a higher prevalence in the health concerns related to cannabis use and abuse. Thus, it is mandatory for oral healthcare operators to know and deal with the consequences and effects of cannabis use on oral cavity health. This review will briefly summarize the components of cannabis and the endocannabinoid system, as well as the cellular and molecular mechanisms of biological cannabis action in human cells and biologic activities on tissues. We will also look into oropharyngeal tissue expression of cannabinoid receptors, together with a putative association of cannabis to several oral diseases. Therefore, this review will elaborate the basic biology and physiology of cannabinoids in human oral tissues with the aim of providing a better comprehension of the effects of its use and abuse on oral health, in order to include cannabinoid usage into dental patient health records as well as good medicinal practice. Methods: the paper selection was performed by PubMed/Medline and EMBASE electronic databases, and reported according to the PRISMA guidelines. The scientific products were included for qualitative analysis. Results: the paper search screened a total of 276 papers. After the initial screening and the eligibility assessment, a total of 32 articles were considered for the qualitative analysis. Conclusions: today, cannabis consumption has been correlated to a higher risk of gingival and periodontal disease, oral infection and cancer of the oral cavity, while the physico-chemical activity has not been completely clarified. Further investigations are necessary to evaluate a therapeutic efficacy of this class of drugs for the promising treatment of several different diseases of the salivary glands and oral diseases.

Peri-threshold Trigeminal Stimulation with Capsaicin Increases Taste Sensitivity in Humans

Introduction

Taste perception is affected by trigeminal stimuli, i.e., capsaicin. This has been studied at suprathreshold concentrations. However, little is known about taste perception at threshold level in the presence of low concentration of capsaicin. The aim of the study was to explore whether taste sensitivity for sweet, sour, salt, bitter, and umami is modulated by the presence of capsaicin in the peri-threshold range.

Methods

Fifty-seven adults (age range 19–85 years; 32 women) with functional gustation participated in the study. Based on their perception of phenylthiocarbamide (PTC), the group was stratified into non-tasters (n = 20) and tasters (n = 37). Threshold for sweet (sucrose), sour (citric acid), salty (sodium chloride), bitter (quinine-hydrochloride), and umami (sodium-glutamate) tastes was estimated using a single-staircase paradigm (3-alternative forced choice; volume per trial 0.1 ml) with or without 0.9-µM capsaicin added. This capsaicin concentration had been determined in pilot studies to be in the range of oral perception thresholds.

Results

The addition of capsaicin produced lower taste thresholds for sweet, sour, salty, and bitter but not for umami. In contrast, neither PTC taster status nor sex affected these results.

Conclusion

The current results indicate that a low concentration of capsaicin increases gustatory sensitivity.

Implications

The current findings provide evidence supporting different effects of capsaicin on taste perception at threshold level. It has implications for boosting taste sensitivity or flavor enjoyment with low concentration of capsaicin.

Kokumi Taste Active Peptides Modulate Salt and Umami Taste

Kokumi taste substances exemplified by γ-glutamyl peptides and Maillard Peptides modulate salt and umami tastes. However, the underlying mechanism for their action has not been delineated. Here, we investigated the effects of a kokumi taste active and inactive peptide fraction (500-10,000 Da) isolated from mature (FII_m) and immature (FII_im) Ganjang, a typical Korean soy sauce, on salt and umami taste responses in humans and rodents. Only FII_m (0.1-1.0%) produced a biphasic effect in rat chorda tympani (CT) taste nerve responses to lingual stimulation with 100 mM NaCl + 5 μM benzamil, a specific epithelial Na⁺ channel blocker. Both elevated temperature (42 °C) and FII_m produced synergistic effects on the NaCl + benzamil CT response. At 0.5% FII_m produced the maximum increase in rat CT response to NaCl + benzamil, and enhanced salt taste intensity in human subjects. At 2.5% FII_m enhanced rat CT response to glutamate that was equivalent to the enhancement observed with 1 mM IMP. In human subjects, 0.3% FII_m produced enhancement of umami taste. These results suggest that FII_m modulates amiloride-insensitive salt taste and umami taste at different concentration ranges in rats and humans.

Mammalian Taste Cells Express Functional Olfactory Receptors

The peripheral taste and olfactory systems in mammals are separate and independent sensory systems. In the current model of chemosensation, gustatory, and olfactory receptors are genetically divergent families expressed in anatomically distinct locations that project to disparate downstream targets. Although information from the 2 sensory systems merges to form the perception of flavor, the first cross talk is thought to occur centrally, in the insular cortex. Recent studies have shown that gustatory and olfactory receptors are expressed throughout the body and serve as chemical sensors in multiple tissues. Olfactory receptor cDNA has been detected in the tongue, yet the presence of physiologically functional olfactory receptors in taste cells has not yet been demonstrated. Here we report that olfactory receptors are functionally expressed in taste papillae. We found expression of olfactory receptors in the taste papillae of green fluorescent protein-expressing transgenic mice and, using immunocytochemistry and real-time quantitative polymerase chain reaction experiments, the presence of olfactory signal transduction molecules and olfactory receptors in cultured human fungiform taste papilla (HBO) cells. Both HBO cells and mouse taste papilla cells responded to odorants. Knockdown of adenylyl cyclase mRNA by specific small inhibitory RNA and pharmacological block of adenylyl cyclase eliminated these responses, leading us to hypothesize that the gustatory system may receive olfactory information in the periphery. These results provide the first direct evidence of the presence of functional olfactory receptors in mammalian taste cells. Our results also demonstrate that the initial integration of gustatory and olfactory information may occur as early as the taste receptor cells.

Development of a Regional Taste Test that uses Edible Circles for Stimulus Delivery

Introduction

Measurements of chemosensory function within specific regions of the tongue can yield important information about the sensitivity of lingual areas to chemosensory stimuli, and may identify possible nerve damage. A novel regional chemosensory test that uses thin edible circles was developed for human testing.

Methods

Edible circles placed at six different regions of the tongue were used to examine regional sensitivity to quinine for bitter taste, NaCl for salt taste, sucralose for sweet taste, and capsaicin for pungency. The six regions included the anterior tip of the tongue, the left and right lateral margins of the tongue (anterior and posterior), and the circumvallate region. Testing was completed with the mouth open, and the mouth closed.

Results

Intensity ratings at all sites were higher in the closed mouth condition for the three taste stimuli. Quinine intensity was highest at the circumvallate region with the mouth closed. NaCl and sucralose intensity were highest at the anterior tip and circumvallate regions. Capsaicin intensity was most highly perceived at the anterior tip of the tongue, but open and closed mouth intensity ratings showed no significant differences.

Conclusions

Regional differences in chemosensory perception were observed on the tongue, and these differences were dependent on the chemosensory stimulus, tongue region, and tasting mode.

Implications

Edible circles show minimal diffusion with saliva, can be used to examine both taste and irritation, and may be used to identify regional papillae counts on the tongue. Finally, edible circles should be invaluable for examining damage to the oral cavity.

Deconvoluting physical and chemical heat: Temperature and spiciness influence flavor differently

Flavor is an essential, rich and rewarding part of human life. We refer to both physical and chemical heat in similar terms; elevated temperature and capsaicin are both termed hot. Both influence our perception of flavor, however little research exists into the possibly divergent effect of chemical and physical heat on flavor. A human sensory panel was recruited to determine the equivalent level of capsaicin to match the heat of several physical temperatures. In a subsequent session, the intensities of multiple concentrations of tastant solutions were scaled by the same panel. Finally, panelists evaluated tastants plus equivalent chemical or physical "heat". All basic tastes aside from umami were influenced by heat, capsaicin, or both. Interestingly, capsaicin blocked bitter taste input much more powerfully than elevated temperature. This suggests that despite converging percepts, chemical and physical heat have a fundamentally different effect on the perception of flavor.

Integrating TRPV1 Receptor Function with Capsaicin Psychophysics

Capsaicin is a naturally occurring vanilloid that causes a hot, pungent sensation in the human oral cavity. This trigeminal stimulus activates TRPV1 receptors and stimulates an influx of cations into sensory cells. TRPV1 receptors function as homotetramers that also respond to heat, proinflammatory substances, lipoxygenase products, resiniferatoxin, endocannabinoids, protons, and peptide toxins. Kinase-mediated phosphorylation of TRPV1 leads to increased sensitivity to both chemical and thermal stimuli. In contrast, desensitization occurs via a calcium-dependent mechanism that results in receptor dephosphorylation. Human psychophysical studies have shown that capsaicin is detected at nanomole amounts and causes desensitization in the oral cavity. Psychophysical studies further indicate that desensitization can be temporarily reversed in the oral cavity if stimulation with capsaicin is resumed at short interstimulus intervals. Pretreatment of lingual epithelium with capsaicin modulates the perception of several primary taste qualities. Also, sweet taste stimuli may decrease the intensity of capsaicin perception in the oral cavity. In addition, capsaicin perception and hedonic responses may be modified by diet. Psychophysical studies with capsaicin are consistent with recent findings that have identified TRPV1 channel modulation by phosphorylation and interactions with membrane inositol phospholipids. Future studies will further clarify the importance of capsaicin and its receptor in human health and nutrition.

Anxiolytic efficacy of repeated oral capsaicin in rats with partial aberration of oral sensory relay to brain

OBJECTIVE

This study was conducted to examine if taste over load with oral capsaicin improves the adverse behavioural effects induced by partial aberration of oral sensory relays to brain with bilateral transections of the lingual and chorda tympani nerves.

DESIGN

Male Sprague-Dawley rats received daily 1 ml of 0.02% capsaicin or water drop by drop into the oral cavity following the bilateral transections of the lingual and chorda tympani nerves. Rats were subjected to ambulatory activity, elevated plus maze and forced swim tests after 11th, 14th and 17th daily administration of capsaicin or water, respectively. The basal and stress-induced plasma corticosterone levels were examined after the end of behavioural tests.

RESULTS

Ambulatory counts, distance travelled, centre zone activities and rearing were increased, and rostral grooming decreased, during the activity test in capsaicin treated rats. Behavioural scores of capsaicin rats during elevated plus maze test did not differ from control rats. Immobility during the swim test was decreased in capsaicin rats with near significance (P = 0.0547). Repeated oral capsaicin increased both the basal level and stress-induced elevation of plasma corticosterone in rats with bilateral transections of the lingual and chorda tympani nerves.

DISCUSSION

It is concluded that repeated oral administration of capsaicin reduces anxiety-like behaviours in rats that received bilateral transections of the lingual and chorda tympani nerves, and that the increased corticosterone response, possibly modulating the hippocampal neural plasticity, may be implicated in the anxiolytic efficacy of oral capsaicin.

TRPs in taste and chemesthesis

TRP channels are expressed in taste buds, nerve fibers, and keratinocytes in the oronasal cavity. These channels play integral roles in transducing chemical stimuli, giving rise to sensations of taste, irritation, warmth, coolness, and pungency. Specifically, TRPM5 acts downstream of taste receptors in the taste transduction pathway. TRPM5 channels convert taste-evoked intracellular Ca(2+) release into membrane depolarization to trigger taste transmitter secretion. PKD2L1 is expressed in acid-sensitive (sour) taste bud cells but is unlikely to be the transducer for sour taste. TRPV1 is a receptor for pungent chemical stimuli such as capsaicin and for several irritants (chemesthesis). It is controversial whether TRPV1 is present in the taste buds and plays a direct role in taste. Instead, TRPV1 is expressed in non-gustatory sensory afferent fibers and in keratinocytes of the oronasal cavity. In many sensory fibers and epithelial cells lining the oronasal cavity, TRPA1 is also co-expressed with TRPV1. As with TRPV1, TRPA1 transduces a wide variety of irritants and, in combination with TRPV1, assures that there is a broad response to noxious chemical stimuli. Other TRP channels, including TRPM8, TRPV3, and TRPV4, play less prominent roles in chemesthesis and no known role in taste, per se. The pungency of foods and beverages is likely highly influenced by the temperature at which they are consumed, their acidity, and, for beverages, their carbonation. All these factors modulate the activity of TRP channels in taste buds and in the oronasal mucosa.

Genetics of taste receptors

Taste receptors function as one of the interfaces between internal and external milieus. Taste receptors for sweet and umami (T1R [taste receptor, type 1]), bitter (T2R [taste receptor, type 2]), and salty (ENaC [epithelial sodium channel]) have been discovered in the recent years, but transduction mechanisms of sour taste and ENaC-independent salt taste are still poorly understood. In addition to these five main taste qualities, the taste system detects such noncanonical "tastes" as water, fat, and complex carbohydrates, but their reception mechanisms require further research. Variations in taste receptor genes between and within vertebrate species contribute to individual and species differences in taste-related behaviors. These variations are shaped by evolutionary forces and reflect species adaptations to their chemical environments and feeding ecology. Principles of drug discovery can be applied to taste receptors as targets in order to develop novel taste compounds to satisfy demand in better artificial sweeteners, enhancers of sugar and sodium taste, and blockers of bitterness of food ingredients and oral medications.

Effects of early intraoral acesulfame-K stimulation to mice on the adult's sweet preference and the expression of α-gustducin in fungiform papilla

Exposure to artificial sweetener acesulfame-K (AK) at early development stages may influence the adult sweet preference and the periphery gustatory system. We observed that the intraoral AK stimulation to mice from postnatal day 4 (P4) to weaning decreased the preference thresholds for AK and sucrose solutions in adulthood, with the preference pattern unchanged. The preference scores were increased in the exposure group significantly when compared with the control group at a range of concentrations for AK or sucrose solution. Meanwhile, more α-Gustducin-labeled fungiform taste buds and cells in a single taste bud were induced from week 7 by the early intraoral AK stimulation. However, the growth in the number of α-Gustducin-positive taste bud or positive cell number per taste bud occurred only in the anterior region, the rostral 1-mm part, but not in the intermediate region, the caudal 4-mm part, of the anterior two-third of the tongue containing fungiform papillae. This work extends our previous observations and provides new information about the developmental and regional expression pattern of α-Gustducin in mouse fungiform taste bud under early AK-stimulated conditions.

Characterization of the expression pattern of adrenergic receptors in rat taste buds

Taste buds signal the presence of chemical stimuli in the oral cavity to the central nervous system using both early transduction mechanisms, which allow single cells to be depolarized via receptor-mediated signaling pathways, and late transduction mechanisms, which involve extensive cell-to-cell communication among the cells in the bud. The latter mechanisms, which involve a large number of neurotransmitters and neuropeptides, are less well understood. Among neurotransmitters, multiple lines of evidence suggest that norepinephrine plays a yet unknown role in the taste bud. This study investigated the expression pattern of adrenergic receptors in the rat posterior taste bud. Expression of alpha1A, alpha1B, alpha1D, alpha2A, alpha2B, alpha2C, beta1, and the beta2 adrenoceptor subtypes was observed in taste buds using RT-PCR and immunocytochemical techniques. Taste buds also expressed the biosynthetic enzyme for norepinephrine, dopamine beta-hydroxylase (DbetaH), as well as the norepinephrine transporter. Further, expression of the epinephrine synthetic enzyme, phenylethanolamine N-methyltransferase (PNMT), was observed suggesting a possible role for this transmitter in the bud. Phenotyping adrenoceptor expression patterns with double labeling experiments to gustducin, synaptosomal-associated protein 25 (SNAP-25), and neural cell adhesion molecule (NCAM) suggests they are prominently expressed in subsets of cells known to express taste receptor molecules but segregated from cells known to have synapses with the afferent nerve fiber. Alpha and beta adrenoceptors co-express with one another in unique patterns as observed with immunocytochemistry and single cell reverse transcription polymerase chain reaction (RT-PCR). These data suggest that single cells express multiple adrenergic receptors and that adrenergic signaling may be particularly important in bitter, sweet, and umami taste qualities. In summary, adrenergic signaling in the taste bud occurs through complex pathways that include presynaptic and postsynaptic receptors and likely play modulatory roles in processing of gustatory information similar to other peripheral sensory systems such as the retina, cochlea, and olfactory bulb.