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PubMed2000

Lack of functional and morphological susceptibility of the greater superficial petrosal nerve to developmental dietary sodium restriction.

Restriction of dietary sodium during gestation has major effects on taste function and anatomy in the offspring. The chorda tympani nerve of offspring that are maintained on sodium-reduced chow throughout life (NaDep) has reduced neurophysiological responses to sodium and altered morphology of its terminal field in the nucleus of the solitary tract. There are many anatomical and physiological similarities between the chorda tympani nerve that innervates taste buds on the anterior tongue and the greater superficial petrosal nerve (GSP) that innervates taste buds on the palate. To determine if the GSP is similarly susceptible to the effects of dietary sodium restriction, the present study examined neurophysiological responses and the terminal field of the GSP in NaDep and control rats. Neurophysiological responses of the GSP to a variety of sodium and non-sodium stimuli did not differ between NaDep and control rats. Furthermore, the volume and shape of the GSP terminal field in the nucleus of the solitary tract did not differ between the groups. Therefore, despite the high degree of functional and anatomical correspondence between the chorda tympani nerve and the GSP, the GSP does not appear to be susceptible to the effects of lifelong dietary sodium restriction.

Amiloride↗
PubMed1983

Developmental changes in taste responses from glossopharyngeal nerve in sheep and comparisons with chorda tympani responses.

To learn whether there are developmental changes in salt and acid taste responses from the posterior tongue, we recorded from the glossopharyngeal nerve, which innervates taste buds in circumvallate papillae, in sheep fetuses, lambs and adults. Multifiber responses to NH4Cl, KCl, NaCl, LiCl, citric and hydrochloric acids were expressed as ratios, relative to responses for two standard chemicals, NH4Cl and KCl. Response ratios for NaCl and LiCl, relative to either standard, increased during development, but the magnitude of the change was small. KCl elicited very large magnitude responses, relative to NH4Cl, in the youngest fetuses, and then decreased by 50% in stimulating effectiveness. Relative responses to both acids also decreased developmentally. The general shapes of KCl response-concentration functions did not change throughout development; however, in the youngest fetuses, the NH4Cl responses-concentration function was not similar to that in older animals. These developmental changes are different than those for responses from anterior tongue taste buds recorded from the chorda tympani nerve. Anterior tongue responses to NaCl and LiCl change most substantially and those to KCl change very little; acid responses do not change. The developmental differences for anterior versus posterior tongue responses suggest that membrane composition and maturational changes of taste buds in the two locations are not the same. Response-concentration functions from both tongue areas support the proposition that specific membrane components interacting with various salts are added during development.

Aging↗
PubMed1981

Access to the cerebral cortex of extra-lingual taste inputs in the rat.

Rats with their intra-lingual taste nerves (the chorda tympani and the glossopharyngeal nerve) sectioned were trained to avoid drinking 0.5 M NaCl solution by associating NaCl drinking with subsequent LiCl poisoning. The acquired learned aversion in these rats was abolished after ablations of the neocortical area for the intra-lingual taste nerves. This result indicates that extra-lingual taste inputs from the palatine and epiglottal taste buds share the neocortical taste area with intra-lingual taste inputs.

Animals↗
PubMed2001

Secretion of carbonic anhydrase isoenzyme VI (CA VI) from human and rat lingual serous von Ebner's glands.

Salivary carbonic anhydrase VI (CA VI) appears to contribute to taste function by protecting taste receptor cells (TRCs) from apoptosis. The serous von Ebner's glands locating in the posterior tongue deliver their saliva into the bottom of the trenches surrounding the TRC-rich circumvallate and foliate papillae. Because these glands deliver their saliva directly into the immediate vicinity of TRCs, we investigated whether CA VI is secreted by the von Ebner's glands, using immunochemical techniques. The immunohistochemical results showed that CA VI is present in the serous acinar cells, ductal cells, and ductal content of von Ebner's glands and in the demilune and ductal cells plus ductal content of rat lingual mucous glands. More importantly, CA VI was also detected in taste buds and in the taste pores. Western blotting of saliva collected from the orifices of human von Ebner's glands and CAs purified from rat von Ebner's glands confirmed that CA VI is expressed in these glands and secreted to the bottom of the trenches surrounding the circumvallate and foliate papillae. These findings are consistent with the hypothesis that locally secreted CA VI is implicated in the paracrine modulation of taste function and TRC apoptosis. (J Histochem Cytochem 49:657-662, 2001)

Animals↗
PubMed1979

Light and scanning microscopy of the taste organs and vascularization of the tongue of the spotted salamander, Salamandra salamandra (L.).

The mucosa of the spotted salamander tongue and its taste organs were investigated by means of light and scanning electron microscopy. The most striking feature of the salamander tongue is an almost complete lack of papillae which are replaced by long, radially disposed folds with linear arrays of taste organs along their ridges. In respect of morphology, the taste organs of the salamander occupy an intermediate position between the taste buds of Urodela and taste discs of Salientia. Scanning electron microscopic examination of microcorrosion casts of the blood vessels of the tongue has revealed that the structure of subepidermal capillary network reflects the topography of the tongue surface and the distribution of its taste organs. In the core regions of the folds the capillary loops accompanying gustatory receptors empty via their shorter, descending arms into the draining vessels, the initial segments of which retain a course parallel to that of the folds. In the few fungiform papillae the capillary vessels form single loops whose distal ends come to lie in the vicinity of taste discs.

Animals↗
PubMed2006

Wnt-beta-catenin signaling initiates taste papilla development.

Fungiform taste papillae form a regular array on the dorsal tongue. Taste buds arise from papilla epithelium and, unusually for epithelial derivatives, synapse with neurons, release neurotransmitters and generate receptor and action potentials. Despite the importance of taste as one of our five senses, genetic analyses of taste papilla and bud development are lacking. We demonstrate that Wnt-beta-catenin signaling is activated in developing fungiform placodes and taste bud cells. A dominant stabilizing mutation of epithelial beta-catenin causes massive overproduction of enlarged fungiform papillae and taste buds. Likewise, genetic deletion of epithelial beta-catenin or inhibition of Wnt-beta-catenin signaling by ectopic dickkopf1 (Dkk1) blocks initiation of fungiform papilla morphogenesis. Ectopic papillae are innervated in the stabilizing beta-catenin mutant, whereas ectopic Dkk1 causes absence of lingual epithelial innervation. Thus, Wnt-beta-catenin signaling is critical for fungiform papilla and taste bud development. Altered regulation of this pathway may underlie evolutionary changes in taste papilla patterning.

Animals↗
PubMed1997

Ontogeny of taste sense.

Developmental changes in the taste receptors and CNS, in physiological and behavioural patterns in fetus and postnatal animals constitute the ontogeny of taste. Tongue epithelial cells are modified into taste buds only with innervation and are seen to degenerate on denervation. On removal of a portion of the tongue, with its taste buds, the central projections of gustation also atrophy, indicating an interdependence of taste receptors and central areas for their development. Gradual transitions in electrical responses to taste stimuli are shown from fetal to adult stage. While responses to ammonium chloride are marked in early fetus, with advancements in age responses to a wide variety of chemicals are shown. Again, early in the development, fibers responsive to chloride are predominant while at a later stage fibers responsive to sodium increase in number. Behaviourally, human fetus and neonatal mammals showed increased swallowing movements on sweet taste and decreased movements on bitter taste which is somewhat at variance with electrophysiological evidence and reflects on the multimodal involvement of taste cell functional and behavioural dynamics with age.

Animals↗
PubMed2005

Electrical taste thresholds established on the medial tongue using two sizes of electrodes.

OBJECTIVES/HYPOTHESIS: The present study determined whether a 125 mm electrode would produce lower and more reliable electrical taste thresholds than a 25 mm electrode when measurement occurred in a medial tongue region relatively sparse in taste bud numbers. We hypothesized this would be the case and that the obtained threshold values would be higher than those previously reported for anterior and lateral tongue regions. STUDY DESIGN AND METHODS: Sixteen college-age subjects were tested twice, once using the 25 mm electrode and once using the 125 mm electrode on each of two sessions separated by 2 to 16 days. The order of presentation of the sessions was counterbalanced across subjects. Measurement was confined to the medial tongue, 0.7 cm lateral to the median furrow. RESULTS: As hypothesized, the larger electrode resulted in lower and more reliable threshold values than the smaller electrode (respective median threshold values = 20.06 microA & 33.59 microA, P = .001; respective test-retest rs = 0.78 [P < .001] and 0.46 [P < .05]). Also as hypothesized, the threshold values were higher (i.e., sensitivity lower) than previously reported for anterior and lateral tongue regions. CONCLUSIONS: The magnitude and reliability of electrical taste thresholds depends on the tongue region examined and the size of the electrodes used. These results suggest that relatively large electrodes should be considered for electrogustometric threshold testing, particularly when lingual regions not highly populated with taste buds are evaluated.

Adult↗
PubMed1977

Taste areas of the plica sublingualis of Alouatta and Aotus (Primates, Platyrrhini).

A conspicuous accumulation of taste buds occurs in the rostral part of the plica sublingualis ("frenal lamella") of Alouatta and Aotus forming taste areas (area gustatoria) superficially situated in the oral mucous membrane. They are found in close vicinity to the orifices of the sublingual salivary glands, but are lacking in the aboral part of the plica sublingualis. They do not occur in all primate species studied. A taste area does not projects above the surface of the surrounding tissue like a papilla. The taste buds open not in crypts of furrows of the oral mucosa, but directly into the spatium sublinguale of the oral cavity proper. In the anterior part of the cavum oris proprium different kinds and very differentiated qualities of sensoral information are perceived (touch, olfaction, temperature). It is conceivable that the taste areas play an important role in perceiving fresh saliva, together with the other sensorial structures in this part of the mouth. This problem can be solved experimentally and by behavioral studies, In addition to its topographical relation to the tongue, the organon sublinguale of Callicebus is structurally very similar to the plica sublingualis of Aotus and Alouatta. Since a sublingua does not occur in New World monkeys, it can be concluded that this organ represents a plica sublingualis which became adherent to the undersurface of the tongue.

Alouatta↗
PubMed1987

Autonomic control of von Ebner's lingual salivary glands and implications for taste sensation.

To learn the nature of the autonomic control of the serous lingual salivary glands of von Ebner, parasympathetic and sympathetic agonists were injected into rats, and the extent of depletion of the secretory granules in gland acini was measured. Injection of the beta-adrenergic agonist isoproterenol caused a concentration-dependent reduction of the secretory granule content of the acinar cells. Injection of the beta-adrenergic antagonist propranolol, combined with isoproterenol, blocked the reduction in secretory granule content seen with isoproterenol alone. Injection of the parasympathetic agonist carbachol also produced a concentration-dependent reduction in granule content of the acini. This reduction was partially blocked by injection of atropine, and completely blocked by injection of atropine and propranolol. beta-Adrenergic and parasympathetic agonists alone did not cause total degranulation of the acini. However, this was achieved by injection of both agonists. It is concluded that protein secretion in von Ebner's glands is under both sympathetic and parasympathetic nervous control. It is hypothesized that the glands contain two sets of granules with different compositions, each under the control of either the parasympathetic or sympathetic nervous system. Because von Ebner's glands are closely associated with taste buds and because the glands supply the microenvironment of these taste buds the secretion of these glands may be very important in the mechanism of taste transduction.

Adrenergic Fibers↗
PubMed1982

Influence of innervation on the levels of noradrenaline and serotonin in the circumvallate papilla of the rat.

The levels and the distribution of monoamines within the rat circumvallate papilla have been studied. Noradrenaline was found in the connective tissue underlying the taste buds, whereas serotonin was located in the basal area of the gustatory epithelium but not inside the taste buds. Following denervation, noradrenaline levels decreased and serotonin levels increased. These results suggest that both neurotransmitters may have some mutual interaction in modulating transmission at the papilla.

Animals↗
PubMed1997

Taste: the neglected nutritional factor.

Scientists now think that every taste bud has some degree of sensitivity to all the primary taste sensations. The brain detects the type of taste by the ratio of stimulation of different taste buds. Many different substances have flavor-enhancing capacity, including ingredients that represent the primary tastes. Medications, chronic disorders, and radiation therapy can alter taste perception, resulting in loss of appetite. Individualizing nutrition advice, with consideration of taste, health needs, and personal preferences, is a "signature dish" of quality dietetics practice.

Aged↗
PubMed1994

Olfaction and gustation in fish: an overview.

Living in an aquatic environment, often devoid of light but rich in dissolved compounds, fish have highly developed chemosensory and chemical signalling systems. The olfactory and gustatory systems comprise the major chemosensory pathways. Despite considerable variations in structural organization of the peripheral olfactory organ throughout fish species, ultrastructural organization of the olfactory sensory epithelium is extremely consistent. The olfactory receptor cell is a bipolar neurone which is directly exposed to the external environment and sends information to the brain by its own axon (cranial nerve I). Four major classes of chemicals have been identified as specific olfactory stimuli and their stimulatory effectiveness characterized: amino acids, sex steroids, bile acids/salts and prostaglandins. Olfactory signals such as those involved in reproduction and feeding may be processed independently through two distinct subsystems: the lateral and medial olfactory systems. The taste buds constitute the structural basis of the gustatory organ. Taste buds may occur not only in the oropharyngeal cavity, but on the whole body surface. Chemical information detected by specialized epithelial cells, gustatory cells, is transmitted to the central nervous system by cranial nerve VII (facial), IX (glossopharyngeal), and X (vagal). Besides diverse sensitivities and specificities for amino acids, fish gustatory receptors detect various organic acids, nucleotides and bile salts. Putative receptors, molecular mechanisms of transduction and the role played by olfaction and gustation in feeding, reproduction, migration and other fish behaviours are discussed.

Animals↗
PubMed2000

Gustatory innervation and bax-dependent caspase-2: participants in the life and death pathways of mouse taste receptor cells.

In the adult mouse tongue, an average of 11% of the gustatory receptor cells are replaced each day. In investigating homeostatic cell death mechanisms in gustatory renewing epithelium, we observed that taste receptor cells were selectively immunopositive for the bcl-2 family death factor, Bax, and for the protease Caspase-2 (Nedd2/Ich1). We determined that 8-10% of the taste receptor cells of the vallate papilla were Bax positive and that 11% were Caspase-2 positive. Some of these immunopositive taste cells had apoptotic morphological defects. Within the subset of vallate taste cells immunopositive for either Caspase-2 or Bax, up to 79% coexpressed both death factors. Bax and Caspase-2 first appeared in occasional vallate taste receptor cells on the same postnatal day-the day after birth. bax null mutation markedly reduced gustatory Caspase-2 immunoexpression. These observations suggest that taste cell death pathways utilize p53, Bax, and Caspase-2 to dispose of aged receptor cells. Apart from reducing Caspase-2 expression, Bax deficiency also altered taste organ development. bax(-/-) mice had a more profusely innervated vallate papilla, which grew to be 25% longer and taller, with the mean taste bud containing more than twice the normal number of taste cells. This augmentation of taste organ development with increased innervation is complementary to the well-documented reduction in taste organ development with sparse innervation. We propose that additional taste neurons survived programmed cell death in Bax-deficient mice, thereby providing an inductive boost to vallate gustatory development.

Afferent Pathways↗
PubMed1992

The effect of neonatal capsaicin treatment on gustatory behavior in the albino rat.

Small-diameter fibers present in gustatory peripheral nerves have historically been suspected of relaying information about the bitter quality of a taste stimulus. Neonatally injected capsaicin irreversibly destroys a proportion of unmyelinated C- and some A delta-fibers. Consummatory responses to increasing concentrations of quinine and other chemical solutions following neonatal capsaicin injection were compared to those of untreated and vehicle-injected control Sabra albino rats. Capsaicin-treated rats significantly increased their withdrawal thresholds to noxious, CO2 laser-generated heat pulses verifying treatment effectiveness. Furthermore, neonatal capsaicin treatment diminished sensitivity to pungent capsaicin solutions in mature rats. However, there were no group differences in quinine intake, suggesting that the full array of unmyelinated fibers associated with taste buds is not essential for the transmission of bitter taste. Capsaicin-treated animals showed a significant reduction in intake of normally highly preferred sodium chloride and sucrose concentrations. These results were probably not due to loss of peripheral unmyelinated afferent fibers per se, but rather to secondary central changes.

Animals↗
PubMed1993

Fungiform papillae of the pig and the wild boar analyzed by scanning electron microscopy.

Fungiform papillae of wild boar and pig were studied by scanning electron microscopy (SEM). Four regions were defined on the tongue: rostral, medial and caudal thirds and lateral sides. Morphologically the fungiform papillae correspond with their denomination. Rostral and lateral tongue regions presented the largest average number of fungiform papillae. Taste pores opened onto the upper surface of the papillae and were easily identifiable by SEM. The total number of fungiform taste pores from both animals was the highest reported in the literature. The lateral papillae of wild boar and pig contained the largest average number of pores per papilla. This region must be important in taste sensitivity. Lateral and rostral papillae from both animals can provide a source of taste buds for study since each fungiform papilla presents numerous taste buds and these papillae are very abundant.

Animals↗
PubMed1995

Immunohistochemical correlates of peripheral gustatory sensitivity to sodium and amiloride.

In mammals, transduction of sodium stimuli occurs via amiloride-sensitive sodium channels. In rat, gustatory physiological sensitivity to sodium stimuli develops gradually during the early postnatal period. In addition, if pregnant rats are subjected to dietary sodium restriction during gestation, their offspring fail to develop normal gustatory physiological responses to sodium and sensitivity to amiloride. In the present study, we used polyclonal antibodies raised against amiloride-sensitive sodium channels to ascertain whether gustatory function is correlated with the immunological presence of the transduction apparatus for sodium stimuli in the taste buds of neonatal rats and adult offspring of sodium-restricted dams. The results indicate that antiamiloride-sensitive sodium channel antisera bind cells within taste buds of neonatal and adult rats, regardless of maternal dietary condition. Therefore, despite the functional absence of taste system amiloride-sensitive sodium channels, the antigenic determinants of these channels are expressed. These data suggest that the onset of normal gustatory sodium sensitivity in neonatal normal rats results from the progressive activation of existing, quiescent channels. Furthermore, they rule out the possibility that the failure to synthesize channel protein underlies the lack of gustatory sodium and amiloride sensitivity in the offspring of sodium-restricted rats.

Amiloride↗
PubMed1996

Recovery of chorda tympani nerve function following injury.

The chorda tympani (CT) nerve carries taste information from the anterior tongue to the brain stem. Injury to the chorda tympani may result in loss or distortion of taste information. This study examined changes occurring in the hamster peripheral taste system during recovery from injury. The hamster chorda tympani nerve was crushed in the middle ear and the animals were allowed to survive from 2 to 16 weeks. At 2 weeks, CT fibers had degenerated distal to the crush site. Up to 16 weeks after crush, there were 67% fewer myelinated fibers in regenerated nerves than in controls. The mean area of the Ca(2+)-ATPase-stained core of the fungiform taste buds was significantly smaller than in controls 2 weeks after injury, but recovered to control values by 4 weeks. Electrophysiological responses to taste stimuli were recorded from the chorda tympani distal to the injury. No responses were seen after 2 weeks; weak and unstable responses were seen after 3 weeks. By 4-8 weeks, relative responses to taste stimuli were similar to control responses, but the variability of the responses to sucrose was significantly greater than that in controls. The frequency of responses to the water rinse following taste stimuli, particularly sucrose, was also greater in the regenerated nerves. The abnormal electrophysiological responses to sucrose may be the result of the differential rate of return of fiber types and/or the transduction mechanisms. In some ways, recovery of the peripheral gustatory system after damage to the chorda tympani nerve recapitulates the later stages of taste bud development.

Animals↗