Expression of alpha-gustducin in the circumvallate papillae of taste buds of diabetic rats

Taste impairment is a complication of Diabetes mellitus and some studies have shown this taste disorder in diabetes. Diabetes can decrease the ability of individuals to detect and recognize sweet, salty and bitter tastes. alpha-Gustducin is a transducin-like G-protein selectively expressed in 20 - 30% of taste receptor cells, which has been shown to be involved in bitter, sweet and umami taste responses. The present study was performed to explore the protein and mRNA expression of alpha-gustducin in the taste buds of diabetic and control rat circumvallate papillae. Our results showed that the positive expression of alpha-gustducin in diabetic rat taste bud cells is higher than that in normal controls as shown by both immunohistochemistry and RT-PCR. There may be some variant of bitter, sweet or umami taste transduction during diabetes and that taste transduction variant may be one cause of diabetic taste impairment.     

On the taste of umami in chimpanzee.

Whole and single fiber chorda tympani nerve recordings were obtained in 5 chimpanzees to stimulation with MSG (monosodium phosphate) and GMP (guanosine 5'-monophosphate, disodium salt) alone and in combination. The overall chorda tympani nerve activity was recorded to 5 concentrations of MSG, ranging from 1 to 100 mM with and without 0.3 mM GMP, and to 5 concentrations of GMP, ranging from 0.1 to 10 mM, with and without 30 mM MSG. A synergistic effect was recorded between MSG and GMP in 3 out of 4 animals. The effect of stimulation with MSG and GMP alone and mixed was studied in approximately 25 single fiber recordings against a background of the stimulating effects of 11 different sweeteners, 3 acids, 3 bitter compounds and 3 different salts. The fibers showed a high taste specificity and fell into groups which corroborated with the human concepts of the taste qualities. The umami compounds elicited moderate responses which were largest in the sweet fibers. In the 6 sweet fibers that responded to the umami compounds. 0.3 mM GMP was a more effective stimulus than 10 mM MSG. In 3 of these fibers a synergistic effect was recorded to the mixture of GMP and MSG. It is interesting that the response to GMP and MSG was unaffected by gymnemic acid, although it blocked the response to the sweet compounds. Three out of 10 salt fibers responded to MSG and GMP but no synergistic effect was recorded. No specific umami fibers were recorded. However, more data must be collected before the final conclusion on the presence or absence of specific umami fibers can be drawn.     

Gustatory neural responses to umami stimuli in the parabrachial nucleus of C57BL/6J mice

Umami is considered to be the fifth basic taste quality and is elicited by glutamate. The mouse is an ideal rodent model for the study of this taste quality because of evidence that suggests that this species, like humans, may sense umami-tasting compounds as unique from other basic taste qualities. We performed single-unit recording of taste responses in the parabrachial nucleus (PbN) of anesthetized C57BL/6J mice to investigate the central representation of umami taste. A total of 52 taste-responsive neurons (22 sucrose-best, 19 NaCl-best, 5 citric acid-best, and 6 quinine-best) were recorded from stimulation period with a large panel of basic and umami-tasting stimuli. No neuron responded best to monopotassium glutamate (MPG) or inosine 5'-monophosphate (IMP), suggesting convergence of input in the central nervous system. Synergism induced by an MPG-IMP mixture was observed in all sucrose-best and some NaCl-best neurons that possessed strong sensitivity to sucrose. In more than half of sucrose-best neurons, the MPG-IMP mixture evoked stronger responses than those elicited by their best stimulus. Furthermore, hierarchical cluster analysis and multidimensional analysis indicated close similarity between sucrose and the MPG-IMP mixture. These results strongly suggest the mixture tastes sweet to mice, a conclusion consistent with previous findings that show bidirectional generalization of conditioned taste aversion between sucrose and umami mixtures, and suppression of taste responses to both sucrose and mixtures by the antisweet polypeptide gurmarin in the chorda tympani nerve. The distribution pattern of reconstructed recording sites of specific neuron types suggested chemotopic organization in the PbN.     

Skn-1a (Pou2f3) specifies taste receptor cell lineage

Functional diversification of taste cells is crucial for proper discrimination of taste qualities. We found the homeodomain protein Skn-1a (Pou2f3) to be expressed in sweet, umami and bitter taste cells. Skn-1a-deficient mice lacked electrophysiological and behavioral responses to sweet, umami and bitter tastes, as a result of a complete absence of sweet, umami and bitter cells and the concomitant expansion of sour cells. Skn-1a is critical for generating and balancing the diverse composition of taste cells.     

Comparison of L-monosodium glutamate and L-amino acid taste in rats

T1R2/T1R3 heterodimers are selectively responsive to sweet substances whereas T1R1/T1R3 receptors are selective for umami substances, represented by monosodium glutamate (MSG), and for L-amino acids. If a single receptor is responsible for detection of umami and L-amino acids, then it would be predicted that MSG and L-amino acids elicit similar tastes in rats. The present study compared the taste profile of MSG with four amino acids (glycine, L-proline, L-serine and L-arginine) using conditioned taste aversion, detection threshold, and taste discrimination methods. These experiments were designed to either reduce or neutralize the taste of sodium associated with MSG and the other amino acids. Detection threshold studies showed that rats were most sensitive to L-arginine and least sensitive to L-proline. Glycine and L-serine thresholds were similar to those previously reported for MSG. Like MSG, a conditioned taste aversion to each of the four amino acids generalized to sucrose in the presence of amiloride, a sodium channel blocker. Rats showed moderate generalization of aversion between MSG and L-arginine, suggesting that these two amino acids taste only moderately alike. However, the taste aversion experiments indicated that glycine, L-serine, and L-proline elicit taste sensations similar to MSG when amiloride is present. Discrimination experiments further compared the tastes of these three amino acids with MSG. When the sodium taste associated with MSG was reduced or neutralized, glycine and L-proline elicited tastes very similar but not identical to the taste of MSG. Low (but not higher) concentrations of L-serine were also difficult for rats to discriminate from MSG. While there are taste qualities common to all of these amino acids, the perceptual differences found in this study, combined with previous reports, suggest either multiple taste receptors and/or multiple signaling pathways may be involved in umami and amino acid taste perception in rats.     

Unilateral nasal obstruction alters sweet taste preference and sweet taste receptors in rat circumvallate papillae

Nasal obstruction causes mouth breathing, and affects the growth and development of craniofacial structures, muscle function in the stomatognathic system, and the taste perceptive system. However, the detailed mechanism underlying the effects of nasal obstruction on taste perception has not been fully elucidated. In this study, we investigated this mechanism using the two-bottle taste preference test, immunohistological analysis, and quantification of the mRNA expression of taste-related molecules in the circumvallate papillae. Neonatal male Wistar rats were divided randomly into control and experimental groups. Rats in the experimental group underwent unilateral nasal obstruction by cauterization of the external nostril at the age of 8 days. Arterial oxygen saturation (SpO₂) was recorded in awake rats using collar clip sensors. Taste preference for five basic taste solutions was evaluated. Immunohistochemical analysis and quantitative real-time polymerase chain reaction (RT-PCR) were conducted to evaluate the expressions of taste-related molecules in the taste cells of the circumvallate papillae. Body weights were similar between the two groups throughout the experimental period. The SpO₂ in the 7- to 12-week-old rats in the experimental group was significantly lower than that in the age-matched rats in the control group. In the two-bottle taste preference test, the sensitivities to sweet taste decreased in the experimental group. The mRNA expression of T1R2, T1R3, α-gustducin, and PLCβ2 was significantly lower in the experimental group than in the control group as determined by quantitative RT-PCR, and the immunohistochemical staining for α-gustducin and PLCβ2 was less prominent. These findings suggest that nasal obstruction may affect sweet taste perception via the reduced expression of taste-related molecules in the taste cells in rat circumvallate papillae.     

Strain differences in the neural, behavioral, and molecular correlates of sweet and salty taste in naive, ethanol- and sucrose-exposed P and NP rats

Strain differences between naive, sucrose- and ethanol-exposed alcohol-preferring (P) and alcohol-nonpreferring (NP) rats were investigated in their consumption of ethanol, sucrose, and NaCl; chorda tympani (CT) nerve responses to sweet and salty stimuli; and gene expression in the anterior tongue of T1R3 and TRPV1/TRPV1t. Preference for 5% ethanol and 10% sucrose, CT responses to sweet stimuli, and T1R3 expression were greater in naive P rats than NP rats. The enhancement of the CT response to 0.5 M sucrose in the presence of varying ethanol concentrations (0.5-40%) in naive P rats was higher and shifted to lower ethanol concentrations than NP rats. Chronic ingestion of 5% sucrose or 5% ethanol decreased T1R3 mRNA in NP and P rats. Naive P rats also demonstrated bigger CT responses to NaCl+benzamil and greater TRPV1/TRPV1t expression. TRPV1t agonists produced biphasic effects on NaCl+benzamil CT responses, enhancing the response at low concentrations and inhibiting it at high concentrations. The concentration of a TRPV1/TRPV1t agonist (Maillard reacted peptides conjugated with galacturonic acid) that produced a maximum enhancement in the NaCl+benzamil CT response induced a decrease in NaCl intake and preference in P rats. In naive P rats and NP rats exposed to 5% ethanol in a no-choice paradigm, the biphasic TRPV1t agonist vs. NaCl+benzamil CT response profiles were higher and shifted to lower agonist concentrations than in naive NP rats. TRPV1/TRPV1t mRNA expression increased in NP rats but not in P rats exposed to 5% ethanol in a no-choice paradigm. We conclude that P and NP rats differ in T1R3 and TRPV1/TRPV1t expression and neural and behavioral responses to sweet and salty stimuli and to chronic sucrose and ethanol exposure.     

The role of sucrose-sensitive neurons in ingestion of sweet stimuli by hamsters

The relationship between sweet preference and activity in sucrose-sensitive chorda tympani nerve fibers was investigated in hamsters (Mesocricetus auratus). Without exception, hamsters increased consumption of aqueous solutions of nonsweet 0.1 M NaCl, 0.001 M quinine-HCl, 0.01 M citric acid, 0.001 M dithiothreitol, 0.01 M pyridine, 0.01 M 2-phenylethanol, 0.005 M i-amyl acetate, 0.01 M vanillin, half-saturated 1-menthol and 0.033 mM capsaicin if they were made sweet by adding 0.5 M sucrose. Since sucrose activates chorda tympani S fibers, activity in these nerve fibers may be sufficient for increased preference. To determine if S-fiber activity is necessary for preference, equally preferred sweet stimuli were presented to the tongue while recording responses of single chorda tympani fibers. S fibers were clearly activated by 0.03 M sucrose, 0.001 M Na saccharin, 0.01 M D-phenylalanine, 0.1 M glycine, 0.005 M dulcin and 0.03 M Na 2-mercaptoethanesulfonate but not by 0.01 M Ca cyclamate and 0.003 M Na 3-nitrobenzenesulfonate. Ca cyclamate weakly activated H fibers and Na 3-nitrobenzenesulfonate weakly activated N fibers. Thus, S-fiber chorda tympani activity may be sufficient but not necessary for sweet preference, which may be influenced by activity in fibers of other taste nerves.     

Electrophysiological and behavioral studies on the taste of umami substances in the rat.

Electrophysiological and behavioral experiments were performed to reveal taste properties of "umami" substances such as monosodium glutamate (MSG) and disodium inosine monophosphate (IMP) in rats. To eliminate the taste effects of Na ions contained in these umami substances, we dissolved them in 0.01 mM amiloride, which is known to block sodium responses. In the electrophysiological study, taste responses of the whole chorda tympani nerve were recorded. The magnitude of responses to MSG (or IMP) at concentrations below 0.1 M (or 0.01 M) was less than 10% of that to 0.1 M NaCl. On the other hand, the mixtures of MSG and IMP showed responses 2-7 times larger than the arithmetric sum of the responses to each component of the mixtures. A new sweet taste inhibitor (Gymnema sylvestre extract) strongly suppressed neural responses to mixtures of MSG and IMP as well as sucrose, but only weakly or negligibly to individual solutions of these umami substances. In the behavioral study, the brief exposure two-bottle preference test and conditioned taste aversion paradigm were used. MSG was most preferred at 0.3 M (preference ratio = 57%), IMP, at 0.01 M (61%), and both were less preferred or rejected at higher concentrations. In contrast, mixtures of MSG and IMP were more preferred at a broad concentration range (e.g., 82% for 0.1 M MSG + 0.01 M IMP). Aversive conditioning to umami substances was generalized to sucrose, and vice versa, but not to 0.1 M NaCl, 0.01 M HCl, and 0.1 mM quinine hydrochloride.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Acute anosmia in the mouse: behavioral discrimination among the four basic taste substances

The importance of taste and smell in discrimination of tastes was examined in normal and anosmic mice. We studied the influence of olfaction on taste sensation using behavioral and electrophysiological methods in both normal animals and animals made anosmic mice by destroying their olfactory receptor cells with zinc sulfate (ZnSO(4)) solution. Electrophysiological responses from chorda tympani nerves showed that peripheral taste receptor cells transmitted taste signals normally to the central nervous system, even when the olfactory senses were abnormal. Behavioral observations showed that mice with abnormal olfaction could not differentiate tastes.     

Are umami taste receptor sites structurally related to glutamate CNS receptor sites?

Umami tasting substances, MSG (monosodium glutamate), HG (glutamic acid), LGDE (1-glutamic acid diethyl ester), DLHCA (dl-homocysteic acid), DLAAA (dl-aminoadipic acid) and 5'GMP, were tested on the hamster and the human. Ten mM MSG was routinely used in the hamster as it elicited strong chorda tympani responses. Similar response amplitudes were found for MSG, HG, LGDE, DLAAA 10 mM, DLHCA 8 mM and sucrose 100 mM. A 5 microM concentration of 5'GMP eventually was an efficient stimulus on a few preparations. Such a low concentration is very seldom efficient as a taste stimulus in rodents, indicating a higher specificity of receptor mechanisms than what is usually found for sweet taste, for example. The synergy between MSG and 5'GMP was found in the hamster CT only for concentrations lower than those of the literature, i.e., a mixture of 12 microM 5'GMP and 2.5 mM MSG showed a reinforcement of 50% in response amplitude equivalent to a 100% increase in concentration. We take this as an evidence of an umami component in the hamster CT response to glutamate; in accordance with literature data, we could not find reinforcement for higher concentrations which were in fact near saturation. Responses to MSG, HG, LGDE, DLAAA and DLHCA, among 38 other organic stimuli, were studied in 42 hamster chorda tympani. Responses to HG, LGDE and 5'GMP, among chemoreception of these compounds used as umami tasting stimuli.(ABSTRACT TRUNCATED AT 250 WORDS)     

Gustatory information of umami substances in three major taste nerves

The chorda tympani (CT), glossopharyngeal (GL), and greater superficial petrosal (GSP) nerves, the three major branches of cranial nerves innervating taste buds, respond with considerable differences to various taste stimuli. To examine which nerve is responsible for transmitting umami taste in rats, we conducted electrophysiological and behavioral experiments. In the electrophysiological study, responses to umami substances were compared among these three nerves. The CT and GSP were more responsive to mixtures of monosodium L-glutamate (MSG) and 5'-inosine monophosphate (IMP) than the GL. Synergistic effects by the mixture of MSG and IMP were the most prominent in the CT followed by the GSP, whereas it was negligible in the GL. In the behavioral study, rats with a combined transection of the CT and GSP could not acquire conditioned taste aversions to umami substances. These results suggest that umami taste is conveyed more dominantly via the CT and GSP than the GL in the rat.     

The mammalian amiloride-insensitive non-specific salt taste receptor is a vanilloid receptor-1 variant

The amiloride-insensitive salt taste receptor is the predominant transducer of salt taste in some mammalian species, including humans. The physiological, pharmacological and biochemical properties of the amiloride-insensitive salt taste receptor were investigated by RT-PCR, by the measurement of unilateral apical Na⁺ fluxes in polarized rat fungiform taste receptor cells and by chorda tympani taste nerve recordings. The chorda tympani responses to NaCl, KCl, NH₄Cl and CaCl₂ were recorded in Sprague-Dawley rats, and in wild-type and vanilloid receptor-1 (VR-1) knockout mice. The chorda tympani responses to mineral salts were monitored in the presence of vanilloids (resiniferatoxin and capsaicin), VR-1 antagonists (capsazepine and SB-366791), and at elevated temperatures. The results indicate that the amiloride-insensitive salt taste receptor is a constitutively active non-selective cation channel derived from the VR-1 gene. It accounts for all of the amiloride-insensitive chorda tympani taste nerve response to Na⁺ salts and part of the response to K⁺, NH₄⁺ and Ca²⁺ salts. It is activated by vanilloids and temperature (> 38°C), and is inhibited by VR-1 antagonists. In the presence of vanilloids, external pH and ATP lower the temperature threshold of the channel. This allows for increased salt taste sensitivity without an increase in temperature. VR-1 knockout mice demonstrate no functional amiloride-insensitive salt taste receptor and no salt taste sensitivity to vanilloids and temperature. We conclude that the mammalian non-specific salt taste receptor is a VR-1 variant.     

Perception and hedonic value of basic tastes in domestic ruminants

Taste is one of the five senses that give ruminants and other animals an awareness of their environment, especially for food selection. The sense of taste, which recognizes sweet, bitter, salty, sour and umami basic tastes, is often considered of paramount importance as it is the last sense in use before foods are swallowed. It thus plays a fundamental biological role in aiding animals to regulate intake of suitable food and reject unsuitable food. However, despite potentially relevant production and welfare issues, only a few studies have investigated how ruminants perceive and evaluate the basic tastes. Here we review current knowledge on tasting abilities and hedonic value of basic tastes in domestic ruminants via the analysis of both their anatomical and neurological structures and their behavioral preferences.Studies of the organization and functioning of the anatomical and neurological structures responsible for the perception of taste in ruminants have shown that sheep, cattle and goats all have lingual receptors for all five basic tastes. However, these studies have mainly focused on the sweet and bitter tastes. They have shown in particular that cows have fewer genes coding for the bitter receptors than other mammals, making them more tolerant to this taste. This pattern has been linked to the differences in the range of toxins and so potentially in the occurrence of bitterness encountered by different species in their environment, depending on the nature of their diet. Studies of ruminant feeding behavior have shown that the taste inducing the greatest consensus in preferences is the umami taste, with a high positive hedonic value. The bitter taste seems to have a rather negative hedonic value, the salty taste either a positive or a negative one depending on body needs, while the sweet taste seems to have a positive value in cattle and goats but not in sheep. Finally, the hedonic value of the sour taste is uncertain. Besides the hedonic value, the animal may assign a signal value to the tastes. In ruminants, the unanimous preference for the umami taste, the need dependent preference for the salty taste, and the reluctance of sheep to associate a positive reward with the bitter taste suggest that these tastes would signal the presence of proteins, minerals and toxins, respectively.     

Relationships between insulin release and taste

Tasting sweet food elicits insulin release prior to increasing plasma glucose levels, known as cephalic phase insulin release (CPIR). The characteristic of CPIR is that plasma insulin secretion occurs before the rise of the plasma glucose level. In this experiment, we examined whether taste stimuli placed on the tongue could induce CPIR. We used female Wistar rats and five basic taste stimuli: sucrose (sweet), sodium chloride (salty), HCl (sour), quinine (bitter) or monosodium glutamate (umami). Rats reliably exhibited CPIR to sucrose. Sodium chloride, HCl, quinine, or monosodium glutamate did not elicit CPIR. The non-nutritive sweetener saccharine elicited CPIR. However, starch, which is nutritive but non-sweet, did not elicit CPIR although rats showed a strong preference for starch which is a source of glucose. In addition, we studied whether CPIR was related to taste receptor cell activity. We carried out the experiment in rats with bilaterally cut chorda tympani nerves, one of the gustatory nerves. After sectioning, CPIR was not observed for sweet stimulation. From these results, we conclude that sweetness information conducted by thistaste nerve provides essential information for eliciting CPIR.     

Gustatory neural responses in preweanling mice.

Taste sensitivity of preweanling mice was studied by examining responses of the chorda tympani (CT) and glossopharyngeal (GL) nerves to various taste stimuli, and was compared to that of adult mice. In mice of 7-10 days of age, comparing to that of the CT nerve, threshold of the GL nerve for monosodium l-glutamate (MSG) was low, but those for sucrose and NaCl were high. Sensitivities to HCl and quinine-HCl were similar between the CT and GL nerves, although that to quinine-HCl was larger in the GL nerve than in the CT nerve in adult mice. Enhancement of MSG responses by addition of GMP was observed in the CT nerve but not in the GL nerve in this age group. In mice of 8-16 weeks of age, threshold of the GL nerve for MSG became higher but that for NaCl became lower. Enhancement of MSG responses by addition of GMP appeared also in the GL nerve. Inhibition of NaCl responses by amiloride was observed in the CT nerve. These results suggest that, in mice, the GL nerve is important taste input for umami substances especially during the preweanling period, whereas the CT nerve is for sweet and salty substances. Properties of umami and salt receptor systems change during the postweanling period.     

Chorda tympani and lingual nerve responses to astringent compounds in rodents.

A wide variety of compounds in foods and beverages produce astringent sensations when introduced into the oral cavity. There is controversy, however, whether "astringency," with its associated puckering and drying sensations, is a fundamental taste quality or is a tactile sensation. To address this issue, electrophysiological recordings were made from the gerbil chorda tympani nerve and the rat lingual nerve. The chorda tympani nerve transmits taste information from the anterior 2/3 of the tongue, whereas the lingual nerve transmits tactile, thermal and pain sensations from the anterior 2/3 of the tongue. The astringent compounds tested were: tannic acid, tartaric acid, gallic acid, aluminum ammonium sulfate and aluminum potassium sulfate. Tannic acid, tartaric acid, and gallic acids were tested at concentrations up to 120 mM over a pH range from approximately 2 to 6. The aluminum salts were tested at concentrations up to 160 mM only at low pH's. All compounds rapidly (and at lower concentrations, reversibly) stimulate the chorda tympani nerve in a concentration-dependent manner at all pH's tested. The rapidity and reversibility of the chorda tympani responses suggest that astringent-tasting compounds interact directly with taste cells rather than indirectly by precipitating salivary proteins. At pH 6, tannic acid, tartaric acid, and gallic acid all elicit robust chorda tympani responses, implying that the ionized forms of these compounds produce taste sensations. None of these compounds stimulate lingual nerves over the same concentration and pH ranges used in the chorda tympani experiments.(ABSTRACT TRUNCATED AT 250 WORDS)     

Distribution of taste and general sensory nerve endings in fungiform papillae of the hamster

Sensory endings of chorda tympani and lingual (trigeminal) nerve fibers were identified by selective denervation and localized within specific regions of fungiform pipillae in the hamster. The chorda tympani was resected from the middle ear and the peripheral fibers were allowed to degenerate for 1, 3, or 8 days prior to perfusion-fixation and electron-microscopic examination of the anterior tongue. Taste buds were virtually devoid of intact nerves by 3 days following chorda tympani denervation. Remnants of the fibers were restricted to taste buds. Lingual fibers, on the other hand, persist in normal numbers after chorda tympani resection and populate perigemmal areas of connective tissue and extragemmal areas located apically in the squamous, nontaste epithelium surrounding the taste bud. This study provides evidence of a segregation of chorda tympani fibers in the taste bud and lingual nerve fibers in the apical fungiform papilla. The lingual nerve-epithelial arrangement and superficial location, near the least cornified area of the tongue, may be well suited for relatively sensitive somatosensation, possibly mechanoreception. Thus, the apical fungiform papilla appears to be a site where both taste and tactile oral stimuli interact with receptors.