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PubMed1991

Mediation of responses to calcium in taste cells by modulation of a potassium conductance.

Calcium salts are strong taste stimuli in vertebrate animals. However, the chemosensory transduction mechanisms for calcium are not known. In taste buds of Necturus maculosus (mud puppy), calcium evokes depolarizing receptor potentials by acting extracellularly on the apical ends of taste cells to block a resting potassium conductance. Therefore, divalent cations elicit receptor potentials in taste cells by modulating a potassium conductance rather than by permeating the cell membrane, the mechanism utilized by monovalent cations such as sodium and potassium ions.

Animals↗
PubMed1987

Labeling of sweet taste binding sites using a colloidal gold-labeled sweet protein, thaumatin.

Thaumatin, an intensely sweet tasting protein, was bound to colloidal gold and applied to the taste bud-bearing foliate papillae of Rhesus monkeys. Examination of thin sections of taste pores showed that gold particles were bound to merocrine secretions of Type I taste bud cells, to some cell remnants of lysed cells, and, most importantly, to small, membrane bounded blebs of cytoplasm. These blebs are thought to be shed into the pore from the tips of taste bud cell microvilli, particularly those arising from Type II cells. The binding of gold particles to microvillus tips and to the blebs suggest that this may be an important means by which taste bud cells rid themselves of taste stimulus-receptor complexes.

Animals↗
PubMed1982

Lipid profiles of taste and non-taste epithelial tissues from steer tongues.

Some hypotheses on taste reception have implicated lipids of taste cells as major receptor constituents. This study reports detailed lipid profiles of the taste bud-containing epidermis from circumvallate papillae and fungiform papillae as well as profiles from two non-taste bud tissues: circumvallate papillae dermis and epidermis from the lateral posterior of the tongue. Differences in levels of triglycerides and phosphatidylcholines were observed but these were not directly related to the presence of taste buds. At this level of analysis, it is evident that there are no unusual distributions of phospholipid classes in the taste bud epidermis when compared with the non-taste bud lingual epidermis.

Animals↗
PubMed1988

Influences of dietary sodium on functional taste receptor development: a sensitive period.

Restriction of maternal dietary sodium on or before embryonic day 8 reduced taste responses of the chorda tympani nerve to sodium chloride in the offspring. The response attenuation was substantial; responses to sodium chloride in the offspring of deprived rats were approximately 40 percent of those in control animals. Instituting the low sodium diet at embryonic day 10 or later did not produce functional changes. Thus, a sensitive period for the gustatory system exists, and the abrupt transition from maximal environmental susceptibility to no susceptibility occurs during a 2-day prenatal period. Moreover, events important in determining the developmental fate of taste membrane components occur before the initial formation of taste buds.

Amiloride↗
PubMed2006

Chorda tympani nerve transection alters linoleic acid taste discrimination by male and female rats.

Taste is intimately associated with food choice, yet little is known about the role of taste in preferences for dietary fat, a major component of many foods. We measured the taste threshold for linoleic acid (LA), an essential free fatty acid found in dietary fat, before and after bilateral transections of the chorda tympani nerve (CTX) in adult male and female rats. We conditioned a taste aversion to 88 microM LA and assessed the generalization of the aversion to lower LA concentrations to determine LA discrimination thresholds. We discovered that female rats had a lower LA discrimination threshold (approximately 2.75 microM LA) than did male rats (approximately 11 microM LA). In another set of animals, we performed CTX and found that CTX elevated LA threshold to the same level (approximately 22 microM LA) in male and female rats. Finally, we evaluated licking responses to 11, 22, 44 and 88 microM LA mixed in sucrose by male rats and ovariectomized (OVX) female rats treated with estradiol benzoate or oil vehicle. All rats increased licking to increasing LA concentrations, but OVX rats responded to a lower LA concentration (22 microM) than did males (44 microM) in 10-s trials. However, estradiol did not affect this outcome. Collectively, these experiments show that male and female rats use taste to discriminate LA and that the chorda tympani nerve, which innervates taste buds on the anterior tongue, plays a role in this discrimination. Furthermore, sex differences in fat preferences may depend on differences in fatty acid taste thresholds as well as on the taste stimuli with which fat is combined.

Analysis of Variance↗
PubMed2003

Some sweet and bitter tastants stimulate inhibitory pathway of adenylyl cyclase via melatonin and alpha 2-adrenergic receptors in Xenopus laevis melanophores.

The sweeteners saccharin, D-tryptophan, and neohesperidin dihydrochalcone (NHD) and the bitter tastant cyclo(Leu-Trp) stimulated concentration-dependent pigment aggregation in a Xenopus laevis melanophore cell line similar to melatonin. Like melatonin, these tastants inhibited (by 45-92%) cAMP formation in melanophores; pertussis toxin pretreatment almost completely abolished the tastant-induced cAMP inhibition, suggesting the involvement of the inhibitory pathway (Gi) of adenylyl cyclase. The presence of luzindole (melatonin receptor antagonist) almost completely abolished the inhibition of cAMP formation induced by saccharin, D-tryptophan, and cyclo(Leu-Trp) but only slightly affected the inhibitory effect of NHD. In contrast, the presence of an alpha2-adrenergic receptor antagonist, yohimbine, almost completely abolished the inhibition of cAMP formation induced by NHD but had only a minor effect on that induced by the other tastants. Thus saccharin, D-tryptophan, and cyclo(Leu-Trp) are melatonin receptor agonists whereas NHD is an alpha2-adrenergic receptor agonist, but both pathways lead to the same transduction output and cellular response. Formation of D-myo-inositol 1,4,5-trisphosphate (IP3) in melanophores was reduced (15-58%, no concentration dependence) by saccharin, D-tryptophan, and cyclo(Leu-Trp) stimulation but increased by NHD stimulation. Tastant stimulation did not affect cGMP. Although some of the above tastants were found to be membrane permeant, their direct activation of downstream transduction components in this experimental system is questionable. MT1 and MT2 melatonin receptor mRNAs were identified in rat circumvallate papilla taste buds and nonsensory epithelium, suggesting the occurrence of MT1 and MT2 receptors in these tissues. Melatonin stimulation reduced the cellular content of cAMP in taste cells, which may or may not be related to taste sensation.

Adenylyl Cyclases↗
PubMed1987

Salt consumption and nutritional state especially dietary protein level.

To examine the background of excessive salt intake by the people who live in the northeastern district of the mainland of Japan, statistical analysis was carried out on salt consumption with nutritional status with data from the National Nutrition Survey of Japan and prefectural reports. We found that the dietary protein level (using the index animal-protein calorie intake:total calorie intake) was inversely proportional to the salt intake. To clarify the relationship between taste preference and nutritional status, the effects of dietary protein levels on the preference for salt were studied in spontaneously hypertensive rats (SHR), Wistar-Slc rats, and Sprague-Dawley (SD) rats. We found that the appetite or preference for sodium chloride depends not only on a genetic factor but also on the nutritional status, ie, dietary protein levels. We also observed that the preference for the monosodium glutamate solution was not induced in animals fed a low-protein diet. From these observations we speculated that the threshold of taste sensation is increased in rats fed a low-protein diet. To determine the threshold of taste sensation for NaCl, we calculated the turnover time of taste buds, which was lengthened in rats fed a low-protein diet. The findings from statistical analysis and the results from animal experiments suggest that taste preference is influenced not only by genetic factors but also by the nutritional status. Our hypothesis is that dietary protein level is one of the important factors affecting the taste preference for sodium chloride.

Animals↗
PubMed2000

Taste(s) and olfaction(s) in fish: a review of specialized sub-systems and central integration.

Evidence from comparative morphology and electrophysiology suggests that both, olfaction and taste in fish serve different ecological roles. The lateral olfactory system (dorsolateral olfactory bulb glomeruli and lateral olfactory tract) and the external taste buds are probably specialized for food search and amino acid discrimination. The medial olfactory system (basomedial olfactory bulb glomeruli and medial olfactory tract) and the solitary chemosensory taste cells, however, may have their roles in intra- and interspecific interactions (discriminating pheromones by olfaction, bile components by both olfaction and taste). Whereas stimulation of the taste systems alone triggers reflexes, complex, conditional or conditioned behaviours are only released when the olfactory system is intact. This points at the importance of telencephalic and diencephalic integration of olfactory and taste inputs. Consequently, caution is appropriate concerning simplistic interpretations of deprivation experiments.

Animals↗
PubMedDate not supplied

[Dysgeusias].

This is a review of multiple pathologic conditions associated with altered taste perception and identification. We stated the steps and the molecular basis of this sense. This paper includes two cases that exemplify two distinct types of dysgeusia; case, 1 a 48 year old man who had clinical manifestations of hypogeusia and dysgeusia for one year, probably secondary to air pollutants. Case 2, a 37 year old man who worked in the same factory and also had dysgeusia; we concluded that it was secondary to thermal and chemical agression of the oropharynx; his plasma and urinary levels of zinc were normal. Many medications and contaminants of air and water are related with changes in serum and urine levels of zinc, which is a determinant at several levels for the correct integration of the taste system. Namely it is important for synthesis of the metalloprotein, gustin, a parotid gland protein secreted into saliva, which in turns is very important to make union of the sapid substance (SS) with its receptor in the surface of the gustatory epithelium a the taste buds. Zinc is also related with neurotransmission of the electrical stimulus generated in the bud cell and ending in the central nervous system. There is an acute zinc loss syndrome, seen in patients treated with histidine, which simulates the steps in which taste sensation is integrated. A clinical approach for diagnosis of hypogeusic or dysgeusic patients must include a careful evaluation of the diat elements, an assesment of hereditary disorders, the type of work and contact with pollutants known to be related with dysgeusia. A special care regarding physical examination must be considered in particular a meticulous review of the oropharynx in order to diagnose inflammatory, neoplastic or neurological disorders. The levels of perception an identification of flavors: sweet, bitter, sour and salt, must be determined using the forced scale triple choice technic. Serum and urinary levels of zinc should be determined in each patient using a flameless atomic absorption spectrophotometer. A quantification of the activity of leucocyte alkaline phosphatase, a zinc metalloenzyme, is a useful aid, liver function tests. 13 and 14 determinations and serum protein electrophoresis are mandatory because many pathologic states of these organ systems are known to be related with disorders of taste. We wish to remark the important function of zinc in the taste system, the role of essential trace elements is receiving increased atention and these alterations are good examples of their clinical importance.

Adult↗
PubMed1997

Feeding patterns and brain evolution in ostariophysean fishes.

The sense of taste plays a crucial role in a fish's ability to locate and select appropriate food. Functionally, the taste system is divisible into two subsystems, with external taste, utilized to locate food in the environment, being mediated by the facial nerve while intraoral taste, crucial for triggering swallowing, is mediated by the vagus nerve. Each of these nerves connects to its own portion of the medullary viscerosensory column. In most teleosts, the viscerosensory column forms a continuous, relatively undifferentiated column of neuropil in the dorsomedial medulla. The taste bud-bearing surfaces of the fish are mapped onto this column with external taste buds being represented anteriorly and pharyngeal taste buds caudally. Taste information reaching the vagal taste area, the "vagal lobe", is relayed directly to motoneurons that control the oropharyngeal musculature. In goldfish, unlike most teleosts, the vagal lobe is laminated, highly differentiated structure containing both sensory and motor layers. This derived neural structure is related to the specialized palatal food sorting apparatus utilized by the fish to separate food from substrate material. Despite the complex morphology of the vagal lobe in goldfish, the underlying circuitry is essentially identical to that of other fishes, i.e. after an obligatory synapse in the sensory layers, the gustatory input is relayed to the oropharyngeal motoneurons comprising the motor layer. Thus evolution of the derived, laminated brain structure did not entail generation of new connectivity but merely involved rearrangement of previously existing neuronal populations.

Animals↗
PubMed1993

Primary structure and cell-type specific expression of a gustatory G protein-coupled receptor related to olfactory receptors.

We have reported on the partial structures of a multigene family encoding GTP-binding protein (G protein)-coupled, seven-transmembrane receptors expressed in the tongue (Abe, K., Kusakabe, Y., Tanemura, K., Emori, Y., and Arai, S. (1993) FEBS Lett. 316, 253-256). Here we describe a full-length cDNA clone encoding a tongue cell-type specific receptor. The encoded protein consists of 312 amino acid residues. In overall structure, the protein is similar to known G protein-coupled, seven-transmembrane receptors such as an olfactory receptor (56% identity) but is significantly different in part, particularly in NH2-terminal extracellular and COOH-terminal cytoplasmic domain structures. Northern analysis showed that the mRNA for this protein is expressed only in the epithelium of the tongue, not in other organs. In situ hybridization experiments clearly indicated that the mRNA is expressed exclusively on the tongue apical surface, not on the reverse side of the tongue nor in its muscle layer. Expression was also detected in the taste buds and surrounding cellular tissues of the fungiform and circumvallate papillae. It is suggested that this gustatory receptor structurally related to olfactory receptors may be a candidate for a taste receptor.

Amino Acid Sequence↗
PubMed2002

Rats fail to discriminate quinine from denatonium: implications for the neural coding of bitter-tasting compounds.

Recent molecular findings indicate that many different G-protein-coupled taste receptors that bind with "bitter-tasting" ligands are coexpressed in single taste receptor cells in taste buds, leading to the prediction that mammals can respond behaviorally to structurally diverse "bitter" tastants but cannot discriminate among them. However, recent in situ calcium-imaging findings imply that rat taste receptor cells are more narrowly tuned to respond to bitter-tasting compounds than had been predicted from molecular findings, suggesting that these animals can discriminate among these chemicals. Using an operant conditioning paradigm, we demonstrated that rats cannot discriminate between two structurally dissimilar bitter compounds, quinine hydrochloride and denatonium benzoate, despite the fact that these tastants are thought to stimulate different taste receptor cells. These rats were nonetheless able to show concentration-dependent avoidance responses to both compounds in brief-access tests and to discriminate among other taste stimuli, including quinine versus KCl, denatonium versus KCl, and NaCl versus KCl. Importantly, the concentrations were varied in the discrimination tests to render intensity an irrelevant cue. We conclude that denatonium and quinine produce a unitary taste sensation, leaving open the likely possibility that other compounds fall into this class. Although a broader array of compounds needs to be tested, our findings lend support to the hypothesis that there is only one qualitative type of bitterness. These results also highlight the need to confirm predictions about the downstream properties of the gustatory system, or any sensory system, based on upstream molecular and biophysical events.

Animals↗
PubMed1979

Decline and disappearance of taste response after interruption of the chorda tympani proper nerve of the rat.

The response amplitude in the chorda tympani proper nerve of rats to taste stimulation has been studied at different times after interruption of the nerve in the middle ear. The results show that the reponse in the nerve declined and disappeared completely within 15 h after the nerve was interrupted. As a first sign of deteriorating function a stage of hypersensitivity was observed. Results obtained during applications of local anesthetic or colchicine and section at different distances from the tongue indicate that the decreased response was the result of an interruption of axoplasmic flow from the nerve cell bodies in the geniculate ganglion to the taste buds.

Anesthesia, General↗
PubMed1999

Merkel cells are responsible for the initiation of taste organ morphogenesis in the frog.

Taste organs in the frog have a distinctive cell type located exclusively in the basal portion. In the same fashion as type III cells in mammalian taste buds, these basal cells show immunoreactivity for serotonin antibody. Further, these cells are morphologically similar to epidermal Merkel cells. To determine the significance of these serotonergic basal cells, we examined the early development of taste organs during metamorphosis of the frog by focusing on the origin and possible roles of serotonergic basal cells. For convenience of description, five stages of development (metamorphic stage to climax stages A-D) are defined. In the metamorphic stage, a few noninnervated Merkel cells appear at the upper layer of the lingual epithelium. No neuronal elements are seen in the epithelium at this stage. At climax stages A-B, immature fungiform papillae become discernible in the dorsal surface of the tongue, where the Merkel cells are located. Merkel cells then move downward and extend their cytoplasmic processes toward the basal lamina. These cells are identified by their intense immunoreactivity for serotonin. During the later stages, many nerve fibers in the subepithelial connective tissue approach the epithelium containing Merkel cells. At climax stages C-D, Merkel cells extend cytoplasmic processes along the basal lamina toward the center of the newly forming fungiform papillae. The morphology of these Merkel cells exactly coincides with that of serotonergic basal cells in adult taste organs. Profuse exocytotic release of dense-cored granules of Merkel cells toward the nerve fibers through the basal lamina is frequently seen in these stages. The present study indicates that serotonergic basal cells are derived from intraepithelial Merkel cells, which act as target sites for growing nerves and may be responsible for the initiation of taste organ morphogenesis.

Animals↗
PubMed1981

Axonal transport maintains taste responses.

Transection of the gerbil's IXth nerve causes gustatory action potentials to decline in 1-6 h; the rate of decline is a linear function of the length of the nerve stump remaining attached to the tongue. To test the implication that taste discharge mechanisms depend upon axonal transport in the IXth nerve, we injected 40 nl of [3H]leucine into the petrosal ganglion of one IXth nerve of the gerbil, Meriones unguiculatus. Subsequent liquid scintillation counting of the petrosal ganglion, IXth nerve segments, and representative areas of the tongue indicated that labeled materials were transported down the IXth nerve primarily to the vallate and ipsilateral foliate taste papillae of the tongue. A significant impairment of axonal transport and a substantial decline in summated IXth nerve taste responses occurred within 2-3 h after colchicine was applied to the IXth nerve trunk between the tongue and the petrosal ganglion. Similarly, cooling the IXth nerve with a 3-10 degrees C thermocouple junction or metal probe impaired axonal transport and caused a taste response decline. Since impulse mechanisms of the nerve trunk continued to function distal to these sites of treatment, we concluded that the maintenance of taste discharges at the level of the taste bud depends upon unimpeded axonal transport.

Action Potentials↗
PubMed1997

Bitter taste of monosaccharide pentaacetate esters.

The pentaacetate esters of several, but not all, monosaccharides were recently found to stimulate insulin release from rat pancreatic islets. We have now compared the taste of solutions of either these esters or the corresponding unesterified monosaccharides. The sweet taste of the latter monosaccharides (0.22 M) ranged as follows: D-glucose approximately or = D-galactose approximately or = D-mannoheptulose > L-glucose. None of the esters (1.7 mM) displayed a sweet taste. However, the alpha- and beta-anomer of D-glucose pentaacetate, the alpha-anomer of D-mannose pentaacetate and the beta-anomer of L-glucose pentaacetate all displayed a bitter taste, whilst both alpha- and beta-D-galactose pentaacetate yielded doubtful results. Since such a situation is comparable to that characterizing the islet B-cell response to these esters, it is proposed that the intracellular interaction between the esters or their hydrolytic products and a protein involved in the recognition of bitter taste in taste buds may participate in their insulinotropic action.

Acetates↗
PubMed1992

Difference in receptive field features of taste neurons in rat granular and dysgranular insular cortices.

Receptive fields (RFs) of 59 cortical taste neurons (35 in the granular insular area, area GI, 21 in the dysgranular insular area, area DI, and 3 in the agranular insular area, area AI) were identified in the oral cavity of the rat. The fraction of the neurons with RFs in the anterior oral cavity only was significantly larger in area GI (74.3%) than in area DI (42.9%). On the other hand, the fraction of neurons with RFs in both the anterior and posterior oral cavity was larger in area DI (42.9%) than in area GI (11.4%). On the whole, it is suggested that area GI is involved in discrimination of several taste stimuli in the oral cavity, whereas in area DI taste information originating from various regions of the oral cavity is integrated. When neurons were classified according to the best stimulus which most excited the neuron among the four basic tastes, different categories of taste neurons had RFs in different parts of the oral cavity. It is suggested that, in either taste area, different categories of taste neurons are involved in different sorts of taste coding. The majority of neurons in both areas had bilateral RFs. In area GI, neurons with RFs on single subpopulations of taste buds were significantly more numerous at the rostral region of the cortex than at the caudal region. There was no such relation between RF types and cortical localization in area DI. Otherwise, topographic representation of the oral cavity by taste neurons on the cortical surface was not obvious. RF features of taste neurons did not differ across layers in either cortical area.

Animals↗
PubMed1982

Sucrose taste thresholds: age-related differences.

Sucrose taste detection thresholds were measured in 71 adults aged 20 to 88 years. A forced-choice, tracking procedure was used to eliminate subject response bias and rinses were included between all stimuli. A significant age-related decrease in sensitivity was observed. However, the loss of sensitivity was not great and elderly people had highly variable thresholds. A similar study on salt taste acuity has been reported from this laboratory demonstrating a small, but statistically significant threshold increment with age. The observation that age-related differences in taste sensitivity are not large is consistent with biological information that taste bud cells are continuously replaced in adult mammals.

Adult↗