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PubMed2000

The effects of sialoadenectomy and exogenous EGF on taste bud morphology and maintenance.

Taste buds on the dorsal tongue surface are continually bathed in saliva rich in epidermal growth factor (EGF). In the following experiment, taste bud number and morphology were monitored following submandibular and sublingual salivary gland removal (sialoadenectomy), to determine if EGF plays a role in the maintenance and formation of taste buds. Adult male rats were divided into four groups: sialoadenectomized (SX, n = 4); sialoadenectomized with EGF replacement (SX + EGF, n = 5); sham-operated (SH, n = 4); and sham-operated with exogenous EGF (SH + EGF, n = 5). After a 3 week recovery, SX + EGF and SH + EGF animals were given 50 microg/day EGF in their drinking water for 14 days. At day 14, saliva was collected, the animals were killed and the presence of EGF determined by radioligand-binding assay. Tongues were removed and histologically examined for the presence and morphology of taste buds on fungiform and circumvallate papillae, or immunostained for the presence of EGF, TGFalpha (transforming growth factor alpha) and EGFR (EGF receptor). The removal of submandibular and sublingual salivary glands resulted in the loss of fungiform taste buds and normal fungiform papillae morphology. These effects were reversed by EGF supplementation, indicating a role for EGF in fungiform taste bud maintenance. In addition, supplementation of EGF to sham-operated animals increased the size of fungiform taste buds. In contrast, removal of salivary glands had no effect on the size, numbers, or morphology of circumvallate taste buds, suggesting that the formation and maintenance of taste buds in fungiform and circumvallate papillae may involve different and distinct processes. EGF, TGFalpha and EGFR were localized to distinct layers of the dorsal epithelium and to within both fungiform and circumvallate taste buds. Their expression within the epithelium or taste buds was not altered with sialoadenectomy, indicating that the actions of endogenous EGF and TGFalpha are distinct and not regulated by exogenous EGF and TGFalpha supplied in saliva.

Animals↗
PubMed1998

Intracellular free calcium concentration in human taste bud cells increases in response to taste stimuli.

We examined changes of intracellular free calcium concentration [Ca2+]i elicited by taste stimuli of sucrose, denatonium and NaCl in the taste buds of seven human fungiform papillae. In one taste bud we observed an increase in [Ca2+]i induced by only NaCl. In another bud an increase of [Ca2+]i in response to both NaCl and sucrose was found. The Ca2+ responses to NaCl and sucrose occurred in differential areas within the one taste bud. In the other five fungiform papillae [Ca2+]i was not changed by the taste stimuli. These results suggest that an increase of [Ca2+]i participates in taste transduction mechanisms for sucrose and NaCl, and that taste cells in one taste bud may respond to differential stimuli.

Adult↗
PubMed1981

Long-term effects of surgical desalivation upon taste acuity, fluid intake, and taste buds in the rat.

Taste bud structure and taste preferences in intact and desalivated animals were evaluated to ascertain whether there was a structure-function relationship. Thirty-three totally desalivated rats and 30 sham-operated controls were tested between 95 and 110 d after surgery with a 48-hour two-bottle preference paradigm; they were then sacrificed, and the tongue epithelium and circumvallate papillae taste buds were examined histologically. Desalivated rats manifested significantly increased preferences for normally avoided solutions. Histological study of the dorsal tongue epithelium revealed increased keratosis. There were qualitative changes in the taste buds of the circumvallate papillae with some taste buds appearing shrunken and disorganized.

Animals↗
PubMed1980

Quantitative analysis of developing epiglottal taste buds in sheep.

Epiglottal taste buds of the sheep increase in number during development, and continue to increase until the epiglottis has reached its adult size. However, since the increase in taste bud numbers is paralleled by increase in the surface area of the epiglottis, the density of taste buds decreases progressively in the fetus and newborn. After birth the density remains relatively constant. From examination of the morphological stages of epiglottal taste bud development, we conclude that taste buds are originally produced by de novo formation, but that further increase in numbers is effected by division of existing, developing taste buds. Because of the large number of taste buds, and the maintenance of their density on the epiglottis, it is concluded that they have an important functional role in upper airway protective reflexes.

Aging↗
PubMed1990

Postnatal development of palatal and laryngeal taste buds in the hamster.

Mammalian taste buds are distributed within several distinct subpopulations, innervated by branches of three cranial nerves. These taste bud populations originate and mature at different times in various mammalian species and are thought to play differential roles in the control of taste-mediated behaviors. The hamster is a common animal for the electrophysiological study of the gustatory system, and it has been shown that taste buds innervated by the IXth nerve develop postnatally in this species. To delineate further the development of the gustatory system of hamsters, we quantified the number of taste buds appearing on the palatal, nasopharyngeal, and laryngeal epithelium from birth through 120 days of age. Taste buds are present in almost adult numbers on the soft palate at birth, but only 39% of these are mature. Distinct taste pores, indicative of mature taste buds, increase in number until about 20-30 days of life, at which time all of the taste buds on the soft palate and on the nasoincisive papillae are fully developed. Taste buds are concentrated primarily on the posterior and medial portions of the soft palate. Taste buds located on the laryngeal surface of the epiglottis and the aryepiglottal folds are absent at birth and originate and mature over the following 120 days. Laryngeal taste buds are more concentrated on the aryepiglottal folds than on the epiglottis. On the soft palate and in the epiglottal region, the maturation of taste buds is well characterized by a logarithmic function (Y = a log X + B) relating the number of mature taste buds to postnatal age. On the soft palate, the length of the taste buds from base to apex correlates with the thickness of the epithelium, which increases with development. The diameter of mature taste buds on the soft palate does not change with age. In contrast to many mammalian species, in rodents taste bud development occurs mostly after birth. Rapid postnatal development progresses at a time when ingestive behavior is undergoing a number of significant changes. Taste buds in the larynx have been implicated in a number of laryngeal reflexes (i.e., apnea, swallowing) in several nonrodent species. The electrophysiological properties of superior laryngeal nerve fibers would suggest a similar function for epiglottal taste buds in the hamster.

Animals↗
PubMed1998

Biology of taste buds and the clinical problem of taste loss.

Taste buds are the anatomical structures that mediate the sense of taste. They comprise taste cells and nerve fibers within specialized epithelial structures. Taste cells are traditionally described by histologic methods as basal, dark, intermediate, and light cells, with the nerve fibers surrounding and infiltrating the taste buds. By means of immunohistochemical methods, taste cells and gustatory nerve fibers can be classified in functional groups based on the expression of various cell adhesion molecules and other proteins. When taste buds become damaged, the loss of the ability to taste results. This loss is not uncommon and can impact health and quality of life. Patients who receive radiation therapy for head and neck cancer often experience taste loss, which leads to compromised nutritional intake and a worse outcome than patients who do not experience taste loss. The mode of radiation damage to taste cells and nerve fibers has been investigated using cell adhesion molecules, synaptic vesicle proteins, and other cell markers. The light and intermediate cells are preferentially affected by ionizing radiation, whereas the nerve fibers remain structurally intact. Experimental studies of radiation-induced taste loss are performed via a unique animal/human model.

Ageusia↗
PubMed1994

Expression of the neural cell adhesion molecule (NCAM) and polysialic acid during taste bud degeneration and regeneration.

Taste receptor cells are replaced throughout life, accompanied by continuing synaptogenesis between newly formed taste cells and first-order gustatory fibers. The neural cell adhesion molecule (NCAM) is expressed by a subset of taste cells in adult rodents and appears on gustatory nerve fibers during development prior to differentiation of the taste buds. We employed antibodies against the extracellular domain of the NCAM polypeptide (mAb 3F4) and against polysialic acid (PSA) residues found on embryonic forms of NCAM (mAb 5A5) to investigate the relationship between the expression of these molecules and the innervation of taste buds in adult rats. In unoperated rats, anti-NCAM recognized a subset of cells within the vallate taste buds and also the fibers of the glossopharyngeal (IXth) nerve, including those innervating the gustatory epithelium. Taste bud cells did not express PSA but mAb 5A5 immunoreactivity was observed on some fibers of the IXth nerve, including a few that entered the taste buds. Bilateral crush of the IXth nerve resulted in the loss of NCAM expression from the gustatory epithelium within 8 days. As IXth nerve fibers reinnervated the epithelium, NCAM expression was seen first in the nerve, followed by increased expression in the epithelium as the taste cells differentiated from their precursors. PSA expression by fibers of the IXth nerve did not return to normal until well after the regeneration of the vallate taste buds. The present results demonstrate that taste cell expression of NCAM is dependent upon innervation by the IXth nerve and that NCAM expression appears in the nerve prior to its expression in the differentiating epithelium during regeneration.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Ultrastructure of mouse foliate taste buds: synaptic and nonsynaptic interactions between taste cells and nerve fibers.

High voltage electron microscopy and conventional transmission electron microscopy were used to examine the ultrastructure of foliate taste buds of mice. Computer-assisted, three-dimensional reconstructions from serial sections were used to visualize regions of interaction between taste cells and nerve fibers. Based on criteria previously established for murine vallate taste buds (Kinnamon et al., '85), foliate taste cells were classified as dark, light, or intermediate depending on their cytoplasmic content and the characteristics of their nuclei. Cells of foliate taste buds display a continuous range of morphologies, from "typical" dark cells to "typical" light cells. Cells of dark, intermediate, and light morphologies all make afferent synapses onto nerve processes, suggesting that cells of all 3 types are sensory in function. Synapses between taste cells and nerve processes may be either macular or fingerlike in shape. No efferent synapses were found. In addition to conventional synapses, taste cells exhibit 2 other types of specializations at sites of apposition with nerve fibers: subsurface cisternae and atypical mitochondria. Subsurface cisternae are narrow sacs of endoplasmic reticulum that are closely apposed to the inner leaflet of the taste cell membrane. Possible functions of subsurface cisternae include synthesis of synaptic membrane components, modification of the electrical or adhesive properties of the taste cell membrane, and exchange of trophic factors with nerve processes. Atypical mitochondria are usually much larger than typical taste cell mitochondria, and their cristae often display a swollen, twisted configuration. These mitochondria are closely apposed to the inside of the taste cell membrane adjacent to nerve fibers. Atypical mitochondria may be providing unusual amounts of energy for metabolic reactions in their vicinities or participating in calcium buffering in the taste cell. Within taste cells, presynaptic specializations, subsurface cisternae, and mitochondria are often clustered together to form "synaptic ensembles." We hypothesize that the functions served by the subsurface cisternae and mitochondria, as well as synaptic transmission, may be important in interactions between taste cells and nerve fibers.

Animals↗
PubMed1994

Bidirectional synaptic transmission in Necturus taste buds.

Pairs of taste cells were impaled with intracellular recording microelectrodes in intact taste buds in slices of Necturus lingual epithelium. Applying short pulses of 140 mM KCl or 200 mM CaCl2 solutions to the apical pore elicited receptor potentials in taste receptor cells. Chemostimulation of receptor cells elicited postsynaptic responses in basal cells in the taste bud. Postsynaptic responses in basal cells had a threshold for activation and did not saturate with increasing doses of chemical stimulus applied to the receptor cells. We directly depolarized individual receptor cells and tested whether this would evoke postsynaptic responses in basal cells. Depolarizing receptor cells to approximately 0 mV evoked small depolarizing responses in basal cells in 16% of the experiments. The properties of these responses were consistent with their being mediated by a chemical synapse. A comparison of the responses in basal cells evoked by depolarizing single receptor cells, with responses evoked by stimulating the entire receptor cell population with KCl suggests that there is extensive synaptic convergence from receptor cells onto each basal cell. We also tested whether electrical excitation of basal cells would elicit (retrograde) synaptic responses in receptor cells. Single depolarizing pulses (up to 1 sec duration) applied to basal cells through the intracellular recording microelectrode never evoked synaptic responses in receptor cells. However, when repetitive electrical stimuli were applied to basal cells (four to six 1 sec depolarizations to approximately 0 mV every 12 sec) we observed prolonged effects on receptor cells in 11 of 23 experiments. These effects included an increase in the amplitude of receptor potentials elicited by KCI (mean +/- SD = +19 +/- 5%), an increase in membrane input resistance of receptor cells (+27 +/- 11%), and a hyperpolarization of receptor cells (3-10 mV). In control experiments, repetitive stimulation of one receptor cell never elicited such effects in another receptor cell. We investigated the possibility that serotonin (5-HT), released from basal cells, mediated the above modulatory effects on receptor cells. Bath-applied 5-HT (100 microM) mimicked the effects produced by repetitive basal cell stimulation (KCI responses increased by 23 +/- 12%; input resistance increased by 24 +/- 11%; hyperpolarization of 5-15 mV; N = 14). We conclude that basal cells release 5-HT onto adjacent taste receptor cells and that this enhances the electrotonic propagation of receptor potentials from the apical (chemosensitive) tip to the basal (synaptic) processes of receptor cells. The net effect is that activation of basal cells effectively increases the chemosensitivity of taste receptor cells.

Animals↗
PubMed1994

Analysis of the embryonic lineage of vertebrate taste buds.

In all vertebrates, taste buds are the last sensory receptors to appear late in embryonic development. They are thought to arise locally from the oropharyngeal epithelium, although this hypothesis has not been tested experimentally. Alternatively, taste buds have been proposed to arise from neuroectodermal cells that migrate from peripheral neurogenic sources to the oropharyngeal epithelium and give rise to taste bud precursor cells. In order to determine the exact embryonic lineage of the cells of vertebrate taste buds, we have employed a combination of endogenous and exogenous cell marking techniques to follow neuroectodermal and endodermal cells through development. We find, in the ambystomatid salamander used in our studies, taste buds arise locally within the endodermally-derived epithelium lining the oropharyngeal cavity, and do not receive a contribution from neuroectodermal sources, i.e. ectodermal placodes or cephalic neural crest.

Animals↗
PubMed1997

Mice with a targeted disruption of the neurotrophin receptor trkB lose their gustatory ganglion cells early but do develop taste buds.

The alleged ability of taste afferents to induce taste buds in developing animals is investigated using a mouse model with a targeted deletion of the tyrosine kinase receptor trkB for the neurotrophin BDNF. This neurotrophin was recently shown to be expressed in developing taste buds and the receptor trkB has been shown to be expressed in the developing ganglion cells that innervate the taste buds. Our data show a reduction of geniculate ganglion cells to about 5% of control animals in neonates. Degeneration of ganglion cells starts when processes reach the central target (solitary tract) but before they reach the peripheral target (taste buds). Degeneration of ganglion cells is almost completed in trkB knockout mice before taste afferents reach in control animals the developing fungiform papillae. Four days later the first taste buds can be identified in fungiform papillae of both control and trkB knockout mice in about equal number and density. Many taste buds undergo a normal maturation compared to control animals. However, the more lateral and caudal fungiform papillae grow less in size and become less conspicuous in older trkB knockout mice. No intragemmal innervation can be found in trkB knockout taste buds but a few extragemmal fibers enter the apex and end between taste had cells without forming specialized synapses. Taste buds of trkB knockout mice appear less well organized than those of control mice, but some cells show similar vesicle accumulations as control taste bud cells in their base but no synaptic contact to an afferent. These data strongly suggest that the initial-development of many fungiform papillae and taste buds is independent of the specific taste innervation. It remains to be shown why others appear to be more dependent on proper innervation.

Animals↗
PubMed2000

Erb and c-Kit receptors have distinctive patterns of expression in adult and developing taste papillae and taste buds.

Twenty four different protein tyrosine kinases (PTKs) were amplified from a taste-enriched cDNA library using PCR. The expression of four protein tyrosine kinase receptors (EGFR, ErbB2, ErbB3, and c-kit) was examined in adult and developing rat taste papillae. All four of these receptors were expressed in overlapping populations of differentiated taste cells within adult taste buds. Taste bud basal cells were ErbB2(+) but did not express the other Erb receptors. During prenatal development, the Erb receptors were expressed extensively in the basal cells around developing papillae, and ErbB2 and c-kit immunoreactive neuronal fibers were seen in close association with taste papillae. In early postnatal stages, ErbB2(+) and c-kit(+) neuronal fibers were often seen entering the taste papillae epithelium, where new taste buds form, and by postnatal day 2 (P2), individual ErbB2(+) and c-kit(+) cells were seen in this region as well. Between P3 and P8, c-kit was highly expressed at the bottom of foliate papillae trenches. The extensive expression of the Erb and c-kit receptors in adult taste buds and in and around developing papillae suggests that these receptors may play a role in the prenatal and postnatal development of gustatory papillae and taste buds.

Age Factors↗
PubMed1997

Porcine lingual taste buds: a quantitative study.

BACKGROUND: Taste buds on the pig tongue have been neither studied in detail nor quantified. We have counted the numbers of fungiform and vallate papillae, estimated their taste bud densities, and computed numbers of taste buds per volume of papilla on porcine tongue. Pig was chosen for this work because it is an omnivorous animal, and is one of the better models for study of nutrition-related problems in omnivorous human beings. METHODS: Tongues from three adult pigs were obtained from the local abattoir, fixed in 10% neutral buffered formalin, and mapped for the fungiform and vallate papillae. Serial 15 microns sections were prepared from blocks containing the papillae, and were stained by H & E. Density and volume of the taste buds were estimated using a Bioquant system. RESULTS: Eight hundred fifty and 826 fungiform papillae were observed on tongue I and II, respectively; numerically vallate papillae were 1, 2, and 2 for tongue I, II and III, respectively. Number of taste buds per fungiform papilla was considerably less on the dorsal surface of the tongue (3.88/papilla) than on the lateral side (22.11/papilla). Vallate papillae contained significantly more taste buds, a mean of 732.67 per papilla (t = 14.27; df = 6; P = < 0.05), than in the fungiform papillae. Density of the buds per volume of fungiform papilla was notably less on the dorsum (13.69) than on the lateral border (30.08). The density of vallate papillae taste buds per volume of the papilla was significantly greater than the lateral and dorsal papillae taste bud density (t = 4.28; df = 6; P < or = 0.05). CONCLUSIONS: The present results are relevant to studies on variations of taste sensitivity among regions of the tongue.

Animals↗
PubMed2001

Expression of cyclin-dependent kinase inhibitors in taste buds of mouse and hamster.

Taste buds are specialized epithelial cell clusters in the oral squamous cell epithelium. Although taste buds have been reported to renew rapidly, the mechanism of cell cycle control in these specialized structures remains unresolved. To clarify the cell cycle status and role of cyclin-dependent kinase inhibitors (CDKI) for cell cycle control in the taste buds, we analyzed cell proliferation activity using bromodeoxyuridine (BrdU) and Ki-67 immunostainings and the expression of the Cip/Kip family of CDKI (p21Cip1, p27Kip1, and p57Kip2) in the circumvallate papillae of mouse and hamster. BrdU-positive cells were detected in the basal layer of the oral epithelium. In the taste buds, Ki-67-positive cells were seen in the basal area, with only a very few positive cells in the taste buds. Both p21Cip1 and p27Kip1 positive cells were seen in the suprabasal layer of the non-gustatory oral epithelium. In the taste buds, stronger p27Kip1 staining was detected than in the non-gustatory epithelium. Western blotting analysis revealed that p27Kip1 was abundant in the mucosal tissues from circumvallate papillae. Thus, our study suggests that the taste bud cells except for basal cells are post-mitotic cells and that the cell cycle arrest associated with taste bud cell differentiation could be regulated predominantly by p27Kip1.

Animals↗
PubMed1989

Immunocytochemistry of neuron-specific proteins and neuropeptides in taste buds and associated nerves.

The taste buds and associated nerves in the guinea pig, rat, cat, and mouse were investigated by immunocytochemistry and formaldehyde-induced fluorescence histochemistry. The antisera used were against spot 35 protein, neuron-specific enolase (NSE), neurofilament protein (NFP), and substance P. The spot 35 protein immunoreactivity was confined to taste bud cells in the guinea pig and rat; the immunoreactive cells, slender in shape, comprised half the number of the total taste bud cells in the guinea pig but were fewer in the rat. For NSE, on the other hand, taste bud cells as well as neural elements localized in both the taste bud and the subepithelial connective tissue were immunoreactive in all the species investigated. Furthermore, all of the spot 35 protein-immunoreactive cells proved to be NSE-immunoreactive in the guinea pig and rat. For NFP, neither the bud cells nor the nerves in the taste bud were reactive, whereas a part of nerves in the connective tissue was immunostained in all the species. The antiserum against substance P exclusively detected some parts of nerves in and out of the taste buds in the cat, rat, and mouse. The aminergic innervation was rather meager and appeared in the nerve fibers localized in the taste buds and connective tissue of the cat and mouse.

Animals↗
PubMed1979

The fine structural effect of sialectomy on the taste bud cells in the rat.

Taste buds in the rat and other mammals share a secretory activity with their transduction function as taste receptor. The present work shows the effect of bilateral removal of the main salivary glands on taste bud cells' components related to secretion in the vallate papilla of the rat. In the sialectomized rats remarkable changes were evidence in the dark and intermediate types of taste bud cells, which are known to be the secretory components. Such changes involve hypertrophy of either the protein synthetizing machinery, the smooth endoplasmic reticulum or the Golgi complex. Lucent and coated vesicles associated to Golgi cisternae increased in number but the amount of dense-core vesicles (secretory vesicles) at the apical cytoplasm of cells decreased. Images of exocytosis of secretory products were observed. The hypertrophy of Golgi complex components was clearly detected with the OsO4 impregnation method for light and electron microscopy. Alteration in the acid phosphatase activity of taste bud cells was not observed in the sialectomized rats. These findings suggest that sialectomy stimulates the entire secretory cycle of dark and intermediate taste bud cells. The light taste bud cells, which are not engaged in secretion, are hardly affected by the treatment. Although taste buds in mammals are neuro-dependent structures, present evidence indicates that they are also sensitive to non-neural influences.

Animals↗