Structure Of Taste Buds Research Articles

Gustatory dysfunction in relation to circumvallate papilla’s taste buds structure upon unilateral maxillary molar extraction in Wistar rats: an in vivo study

Background: The interaction between taste sensation and dentoalveolar innervation is still under research. teeth loss can alter taste thresholds in humans, but the underlying mechanisms are still obscure. This study investigated the effect of unilateral maxillary molars extraction on the structure of circumvallate papilla in rats. Methods: Thirty-two male Wister rats, aged 3-4 months were randomly distributed into four groups (one control and 3 experimental ) each including 8 animals. The rats were euthanized 3, 6 or 9 weeks following the procedure. The changes in trough length and the taste buds structure and number of both sides of CVP were investigated using routine histological examination followed by statistical analysis. Results: the trough toward the extraction side was obviously shorter with a noticeable decrease of taste buds’ number than the non-extraction side. Taste buds were reduced in size and most of them showed signs of degeneration which was more evident in group II followed by group III, less deformity detected in group IV in comparison to the preceding 2 experimental groups. the non-extraction side of all experimental groups showed normal trough length and generally normal histology of taste buds. Conclusions: Maxillary molars extraction has a degenerative effect on the structure of taste buds and gustatory epithelium which were more marked at the extraction side and showed improvement upon elongation of follow up period

Gustatory dysfunction in relation to circumvallate papilla's taste buds structure upon unilateral maxillary molar extraction in Wistar rats: an in vivo study.

Background: The interaction between taste sensation and dentoalveolar innervation is still under research. teeth loss can alter taste thresholds in humans, but the underlying mechanisms are still obscure. This study investigated the effect of unilateral maxillary molars extraction on the structure of circumvallate papilla in rats. Methods: Thirty-two male Wister rats, aged 3-4 months were randomly distributed into four groups (one control and 3 experimental ) each including 8 animals. The rats were euthanized 3, 6 or 9 weeks following the procedure. The changes in trough length and the taste buds structure and number of both sides of CVP were investigated using routine histological examination followed by statistical analysis. Results: the trough toward the extraction side was obviously shorter with a noticeable decrease of taste buds' number than the non-extraction side. Taste buds were reduced in size and most of them showed signs of degeneration which was more evident in group II followed by group III, less deformity detected in group IV in comparison to the preceding 2 experimental groups. the non-extraction side of all experimental groups showed normal trough length and generally normal histology of taste buds. Conclusions: Maxillary molars extraction has a degenerative effect on the structure of taste buds and gustatory epithelium which were more marked at the extraction side and showed improvement upon elongation of follow up period.

AP1 transcription factors are required to maintain the peripheral taste system.

The sense of taste is used by organisms to achieve the optimal nutritional requirement and avoid potentially toxic compounds. In the oral cavity, taste receptor cells are grouped together in taste buds that are present in specialized taste papillae in the tongue. Taste receptor cells are the cells that detect chemicals in potential food items and transmit that information to gustatory nerves that convey the taste information to the brain. As taste cells are in contact with the external environment, they can be damaged and are routinely replaced throughout an organism's lifetime to maintain functionality. However, this taste cell turnover loses efficiency over time resulting in a reduction in taste ability. Currently, very little is known about the mechanisms that regulate the renewal and maintenance of taste cells. We therefore performed RNA-sequencing analysis on isolated taste cells from 2 and 6-month-old mice to determine how alterations in the taste cell-transcriptome regulate taste cell maintenance and function in adults. We found that the activator protein-1 (AP1) transcription factors (c-Fos, Fosb and c-Jun) and genes associated with this pathway were significantly downregulated in taste cells by 6 months and further declined at 12 months. We generated conditional c-Fos-knockout mice to target K14-expressing cells, including differentiating taste cells. c-Fos deletion caused a severe perturbation in taste bud structure and resulted in a significant reduction in the taste bud size. c-Fos deletion also affected taste cell turnover as evident by a decrease in proliferative marker, and upregulation of the apoptotic marker cleaved-PARP. Thus, AP1 factors are important regulators of adult taste cell renewal and their downregulation negatively impacts taste maintenance.

Insulin-Like Growth Factors Are Expressed in the Taste System, but Do Not Maintain Adult Taste Buds.

Growth factors regulate cell growth and differentiation in many tissues. In the taste system, as yet unknown growth factors are produced by neurons to maintain taste buds. A number of growth factor receptors are expressed at greater levels in taste buds than in the surrounding epithelium and may be receptors for candidate factors involved in taste bud maintenance. We determined that the ligands of eight of these receptors were expressed in the E14.5 geniculate ganglion and that four of these ligands were expressed in the adult geniculate ganglion. Of these, the insulin-like growth factors (IGF1, IGF2) were expressed in the ganglion and their receptor, insulin-like growth factor receptor 1 (IGF1R), were expressed at the highest levels in taste buds. To determine whether IGF1R regulates taste bud number or structure, we conditionally eliminated IGF1R from the lingual epithelium of mice using the keratin 14 (K14) promoter (K14-Cre::Igf1rlox/lox). While K14-Cre::Igf1rlox/lox mice had significantly fewer taste buds at P30 compared with control mice (Igf1rlox/lox), this difference was not observed by P80. IGF1R removal did not affect taste bud size or cell number, and the number of phospholipase C β2- (PLCβ2) and carbonic anhydrase 4- (Car4) positive taste receptor cells did not differ between genotypes. Taste buds at the back of the tongue fungiform taste field were larger and contained more cells than those at the tongue tip, and these differences were diminished in K14-Cre::Igf1rlox/lox mice. The epithelium was thicker at the back versus the tip of the tongue, and this difference was also attenuated in K14-Cre::Igf1rlox/lox mice. We conclude that, although IGFs are expressed at high levels in the taste system, they likely play little or no role in maintaining adult taste bud structure. IGFs have a potential role in establishing the initial number of taste buds, and there may be limits on epithelial thickness in the absence of IGF1R signaling.

TASTE MASKING OF DONEPEZIL HYDROCHLORIDE USING DIFFERENT ION EXCHANGE RESINS- A COMPARATIVE STUDY

Taste mainly depends on the physiology, sensitivity and structure of taste buds. It is an important parameter in administering drugs orally. Bitter taste is a major limitation to patient compliance. Donepezil hydrochloride (DH) is a bitter drug used in Alzheimer's disease. Amongst the many techniques for taste masking, using ion exchange resins has been extensively reported. The technique of forming tasteless complexes with bitter drugs involves selection of most appropriate exchanger and optimization of complexing ratio. The aim of the present work was to select the best cationic exchanger amongst Indion 414, Indion 234 and Indion 214. All parameters were optimized to produce drug-loaded tasteless complexes. Complexation was carried out using batch process prior to which, acid-alkali activation was performed to remove adsorbed impurities from the resin bed surface and hence improve loading efficiency. UV-spectrophotometric method was used to determine percent drug loading. The molecular properties of drug resin complexes were studied using Fourier Transform Infra-red Spectroscopy, Differential Scanning Calorimetry and Xray Powder Diffraction which confirmed complexation. Indion 414 was found to give highest drug loading and minimal drug was released from the complex at salivary pH. Key words: Donepezil HCl, Ion exchange resins, Molecular properties, Taste masking

Reduction of type II taste cells correlates with taste dysfunction after X-ray irradiation in mice

Taste dysfunction that develops after radiotherapy for head and neck cancer impairs patients' quality of life. Although taste cells have been shown to degenerate after exposure to X-ray irradiation, the alteration in taste cell population is unclear. This study investigated the histopathological change of taste bud structure and the taste cell population in X-ray irradiated mice. The head and neck region of C57BL/6J male mice was exposed to a single 15 Gy dose of X-ray irradiation and a chronological histopathological analysis of the circumvallate papilla was performed. Preference for sweet taste was measured using the two-bottle preference method. The histological analysis of the circumvallate papilla revealed that the basal cells had almost disappeared, but that there was not clear change in the spindle-shaped taste cells on day 4 after irradiation. The number of taste cells had decreased on day 8, and then remained unchanged until day 20, after which they increased and recovered to their original number by day 24. There was a more marked decrease in the number of alpha-gustducin-positive type II taste cells than in the number of serotonin-positive type III taste cells. Preference for sweet taste measured by the two-bottle preference method was decreased in parallel with taste cell number. These findings suggest that X-ray irradiation disrupts the basal cells, resulting in a decrease of the number of taste cells, particularly type II taste cells, which may be the cause of radiotherapy-induced taste dysfunction.

Volumetry of human taste buds using laser scanning microscopy

In vivo laser scanning confocal microscopy is a relatively new, non-invasive method for assessment of oral cavity epithelia. The penetration depth of approximately 200-400 microm allows visualisation of fungiform papillae and their taste buds. This paper describes the technique of in vivo volumetry of human taste buds. Confocal laser scanning microscopy used a diode laser at 670 nm for illumination. Digital laser scanning confocal microscopy equipment consisted of the Heidelberg Retina Tomograph HRTII and the Rostock Cornea Module. Volume scans of fungiform papillae were used for three-dimensional reconstruction of the taste bud. This technique supplied information on taste bud structure and enabled measurement and calculation of taste bud volume. Volumetric data from a 23-year-old man over a nine-day period showed only a small deviation in values. After three to four weeks, phenomenological changes in taste bud structures were found (i.e. a significant increase in volume, followed by disappearance of the taste bud and appearance of a new taste bud). The data obtained indicate the potential application of this non-invasive imaging modality: to evaluate variation of taste bud volume in human fungiform papillae with ageing; to study the effects of chorda tympani nerve transection on taste bud volume; and to demonstrate recovery of taste buds in patients with a severed chorda tympani nerve who show recovery of gustatory sensibility after surgery.

Expression of the voltage-gated potassium channel KCNQ1 in mammalian taste bud cells and the effect of its null-mutation on taste preferences.

Vertebrate taste buds undergo continual cell turnover. To understand how the gustatory progenitor cells in the stratified lingual epithelium migrate and differentiate into different types of mature taste cells, we sought to identify genes that were selectively expressed in taste cells at different maturation stages. Here we report the expression of the voltage-gated potassium channel KCNQ1 in mammalian taste buds of mouse, rat, and human. Immunohistochemistry and nuclear staining showed that nearly all rodent and human taste cells express this channel. Double immunostaining with antibodies against type II and III taste cell markers validated the presence of KCNQ1 in these two types of cells. Co-localization studies with cytokeratin 14 indicated that KCNQ1 is also expressed in type IV basal precursor cells. Null mutation of the kcnq1 gene in mouse, however, did not alter the gross structure of taste buds or the expression of taste signaling molecules. Behavioral assays showed that the mutant mice display reduced preference to some umami substances, but not to any other taste compounds tested. Gustatory nerve recordings, however, were unable to detect any significant change in the integrated nerve responses of the mutant mice to umami stimuli. These results suggest that although it is expressed in nearly all taste bud cells, the function of KCNQ1 is not required for gross taste bud development or peripheral taste transduction pathways, and the reduced preference of kcnq1-null mice in the behavioral assays may be attributable to the deficiency in the central nervous system or other organs.

Confocal microscopy of the Peripheral Gustatory System: Comparison between Healthy Subjects and Patients Suffering from Taste Disorders during Radiochemotherapy

Laser-scanning microscopy (LSM) was used to compare taste buds and epithelia of fungiform papillae of healthy subjects with those of patients suffering from taste disorders during/after radiochemotherapy (RCT). Aim of the study was to investigate effects responsible for taste loss at a microscopic level. Prospective study. Data from 12 healthy subjects (mean age 52.4, SD 9.5 years) were compared with those of 12 patients (mean age 54.7, SD 8.5 years) with head and neck cancer suffering from taste disorders during RCT. Four parameters from LSM were selected for analysis: 1) distance between the pore of the taste buds of fungiform papillae and the crest of the papillary vessels; 2) epithelial cells of each taste bud at 34 mum; 3), cell density, and 4) area of the taste pore at 4 mum. These data were correlated to measures of gustatory sensitivity obtained with both the validated "taste strips" test kit and electrogustometry. Patients complaining from taste disorders during RCT exhibited a significant decrease of taste function assessed with both natural and electric stimuli. In these patients, we found thicker epithelia and smaller areas of the taste pores compared with healthy subjects. In 30% of those patients, no taste pores were detectable; in deeper sections, however, normal taste buds were present. In conclusion, in RCT patients with taste disorders, LSM indicates changes of epithelia of fungiform papilla but no changes of the taste bud structure. Damage of the chorda tympani nerve by scattered rays, direct or indirect mucotoxic effects of chemotherapeutic agents, and covering of taste pores by epithelial cells are likely reasons for taste loss during RCT.

Postnatal development of the mouse volatile papilla taste bud cells.

In the present study, we examined specific markers for taste bud cells in the mouse and the postnatal development of volatile papilla taste bud cells in ddY mice. We examined the immunoreactivity of 4 types of carbonic anhydrase isoenzymes, CA I, CA II, CA III and CA VI, as specific markers for taste bud cells, and K8.13 cytokeratin antibody as a specific marker for the lingual epithelial cells. Of the carbonic anhydrase isoenzymes, only CA III immunoreactivity was clearly detected in the spindle shaped gustatory cells. CA VI immunoreactivity was detectable in suspentacular cells. CA I and CA II antibodies did not recognize any taste bud cell specifically. K8.13 cytokeratin immunoreactivity was detected in the lingual epithelial cells, but not in taste bud cells. At 7 days after birth, the suckling phase, very small taste buds developed from the anaplastic gustatory cells. At 14 days after birth, the taste buds showed larger size than those at 7 days after birth. At 21 days birth, after the weaning phase, taste bud structure approximated the mature structure. These results demonstrate the specificity of anti-CA III and anti-CA VI for gustatory cells and suspentacular cells, respectively. These markers should be useful for an analysis of taste bud development in mice.

Fine structure of taste buds located on the lamb epiglottis

Taste buds located on the aryepiglottal folds and laryngeal surface of the epiglottis are the principal receptors responsible for the initiation of the laryngeal chemoreflex. In contrast to the wealth of information available concerning the ultrastructure of oral taste buds, little comparable data exists for taste buds located at the entrance to the larynx. Therefore, the present study was designed to investigate the fine structure of taste buds located on the lamb epiglottis. Stained thick and semi-serial thin sections from taste buds located on the lamb epiglottis were examined with light and electron microscopy. Based on morphological criteria, three types of cells could be identified in the taste bud: Type I, Type II, and basal cells. Both Type I and Type II cells extended into the apical taste pore, but there were differences between these two cell types with regard to nuclear profiles, electron density, and the relative density of ribosomes, apical mitochondria, and rough and smooth endoplasmic reticulum. Basal cells did not extend a process into the taste pore. Nerve processes were observed throughout the taste bud. Synapses were observed between both Type I and Type II cells and nerve fibers. These synapses exhibited membrane thickenings and accumulations of clear and dense-cored vesicles of varying proportions in the taste cell cytoplasm adjacent to membrane specializations. The taste buds located on the lamb epiglottis share several structural similarities to taste buds located in the oral cavity and other regions of the pharynx and larynx of many mammalian species. The presence of synapses on both Type I and Type II cells of the lamb epiglottal taste bud suggests that both cell types are involved in laryngeal chemoreception.

Fixation and occurrence of dark and light cells in taste buds of fungiform papillae.

The fine structure of taste buds of the fungiform papillae of the Old World monkey Cynomolgus (Macaca fascicularis) was found to vary with the primary fixative solution used. Standard primary fixative solutions of glutaraldehyde as well as fixatives containing both formaldehyde and glutaraldehyde gave non-reproducible and usually poor results. Osmium tetroxide in distilled water gave reproducible fixation of acceptable quality. Further, when fixed in osmium tetroxide in distilled water, taste buds of the fungiform papillae did not show the dark and light cells well known from other studies. It is therefore suggested that the terms dark and light cells not be used as synonyms for receptor or support cells, since the appearance of taste bud cells is affected by fixation.

Combining HVEM and computer-assisted reconstructions to elucidate the three-dimensional structure of taste buds

The vertebrate taste bud contains 50 to 150 spindle-shaped cells assembled in an onion-shaped structure approximately 60 μm wide and 80-100 μm tall. Located on the tongue and other portions of the oral epithelium, taste buds are always in a state of flux, with new cells continually entering the bud and moving from the periphery to the core as they mature. During the developmental process, young taste cells form afferent synaptic connections with sensory nerve fibers which enter the taste bud at the base and course tortuously throughout the bud. As taste cells age and become senescent, they lose their synaptic connections with the nerve fibers, degenerate, and eventually disappear. All of the processes described above result in the complete turnover of the cells within a taste bud in a period of from 10 days to two weeks in the rat.

Taste bud development in chickens (Gallus gallus domesticus).

Oral epithelium in the anterior mandibular glands region was examined in embryonic, hatchling, and mature chickens to establish the timing of morphologic events during taste bud ontogeny. Hematoxylin-and-eosin-stained sections (10 microns) from 27 Anak (broiler breed) chickens were examined serially, and buds were quantified at 16-20 days of incubation (E) and, posthatch days 1 and 50-60. Taste buds were first recognized at the beginning of E17 as small clusters of cells in the basal epithelium. Only spherical-shaped buds were observed on E17 and E18, and these spherical clusters never penetrated to the surface of the stratified epithelial layer. E19 marked a transitional stage when mature bud features began to emerge: the buds assumed a more elongate shape, several kinds of cells comprising the bud were distinguishable and the first taste pores were observed. During the ensuing embryonic days, buds continued to elongate commensurate with the deepening oral epithelium and by hatching virtually all buds opened to the oral cavity. No marked morphological changes in taste bud structure were observed on the day of hatching and at 50-60 days posthatching. Taste bud numbers increased dramatically during E17 and E18, peaked on E19, and remained relatively constant thereafter. It is concluded that the morphological sequence of taste bud development in chickens is similar to that in mammals. The timing of bud ontogeny, though initiated only during the third trimester in ovo, essentially is completed by hatching, thus providing the precocial hatchling with the sensory apparatus essential for gustatory experience.

Persistence of taste buds in denervated fungiform papillae

Taste buds in hamster fungiform papillae persist in an atrophic state for as long as 330 days after chorda tympani denervation or 50 days after combined chorda tympani-lingual nerve resection. Although taste bud structure depends on innervation, there is no absolute neural requirement for taste bud survival.

Fine structure of taste buds in the minnow.

The distribution, external surface morphology and ultrastructure of taste buds (TB) in the minnow, Pseudorasboraparva, were studied using scanning (SEM) and transmission (TEM) electron microscopy. SEM analysis revealed that TBs were widely dispersed on the skin of the head and lips as well as the mucosa within the oropharyngeal cavity, esophagus and branchial apparatus. The density of TBs was especially high on the lips, gill rakers, and palatal organ, reaching over 140 per mm2. Each TB showed two kinds of processes on the apical surface: thick rod shaped processes and microvilli. TEM analysis showed the presence of three distinct cell types in each TB: tubular (t), filament-ous (f) and basal (b) cells. Their general morphology appears to be homologous to that of other species of fishes. The most striking find of this study, compared to previous studies of the mor-phology of fish TBs, is that a rod shaped process of t-cells contains tubules. Adirect opening ofthe tubules to the outer surface was sometimes observed at the base of the process. Typical synaptic contacts were seldom found, but somewhat thickened pazallel membranes with a few or no vesicular accumulation were sometimes found between nerves and either t-or b-cells.

Fine structure of taste buds in the tongue, palatal mucosa and gill arch of the axolotl, Ambystoma mexicanum.

Fine structure of taste buds in the tongue, palatal mucosa and gill arch of the axolotl, Ambystoma mexicanum.

Structure of taste buds in foliate papillae of the rhesus monkey, Macaca mulatta.

Taste buds in foliate papillae of the rhesus monkey were examined by electron microscopy. Three distinct cell types were identified. Type I cells were narrow elongated cells containing an oval nucleus, bundles of intermediate filaments, several Golgi bodies, and characteristic apical membrane-bounded dense granules. These cells exhibited morphological variations: some had a moderately dense cytoplasm, perinuclear free ribosomes, and flattened sacs of rough endoplasmic reticulum; others had a more lucent cytoplasm, dilated irregular rough endoplasmic reticulum, lysosome-like dense bodies, and lipid droplets. Type II cells typically contained a spherical, pale nucleus, a prominent nucleolus, supranuclear and infranuclear Golgi bodies, mitochondria with tubular cristae, and one or two centrioles. This cell type, too, showed some variation in the relative amounts of ribosomes and smooth endoplasmic reticulum, which varied inversely with each other. Type III cells were characterized by a clear apical cytoplasm essentially devoid of ribosomes and containing microtubules. In a few type III cells, the peri- and infranuclear regions contained many ribosomes and some rough endoplasmic reticulum. In most Type III cells, there were large numbers of dense and clear vesicles in the peri- and infranuclear regions; some of the vesicles were grouped in synapse-like arrangements with adjacent nerves. The morphological variations exhibited by all three cell types could be accounted for by age differences in each of the cells. This would be consistent with the notion that cell renewal occurs in each of the three cell populations.

Effects of tryptophan and 5-hydroxytryptophan on the number of monoamine-containing cells in the frog taste buds

Effects of serotonin precursors on the metabolism of 5-hydroxytryptamine (5-HT) in dumbbell shaped cells of the frog taste buds were studied using fluorescence microscopy. The injection of DL-tryptophan and 5-hydroxytryptophan (5-HTp) resulted in an increase in the cells' fluorescence intensity and in the number of cells in the taste bud. Pyromycin, in doses not affecting the taste bud structure, prevented the tryptophan-induced increase in the number of fluorescent cells. The participation of specific proteins in the mechanism underlying this phenomenon is suggested.

Fine structure of taste buds in te human fungiform papilla

The fine structure of taste buds on fungiform papillae from man was examined with particular reference to different cell types and to cell-nerve contacts. Most of the elongated cells of the taste bud extended from the basal lamina to the apical pore, terminating in irregular microvilli. The cells contained clear apical vesicles, mitochondria, filament bundles and Golgi cisternae. Unmyelinated nerve fibers, containing mitochondria as well as both dense-cored and clear synaptic-type vesicles, were scattered throughout the whole taste bud but were most numerous at the base. The nerve fibers were either in simple appositional contact or in mesaxonal contact with the taste bud cell. Typical synapses with the postsynaptic densities in the taste bud cell were sometimes seen. In addition, single taste bud cells were observed to have more than one type of contact with nerve fibers. As in the Old World monkey Cynomolgus it was not possible to distinguish different cell types described earlier in other species.