Development and maturation of taste buds of the palatal epithelium of the rat: Histological and immunohistochemical study

Palatal taste buds are intriguing partners in the mediation of taste behavior and their spatial distribution is functionally important for suckling behavior, especially in the neonatal life. Their prenatal development has not been previously elucidated in the rat, and the onset of their maturation remains rather controversial. We delineated the development and frequency distribution of the taste buds as well as the immunohistochemical expression of α‐gustducin, a G protein closely related to the transduction of taste stimuli, in the nasoincisor papilla (NIP) and soft palate (SP) from the embryonic day 17 (E17) till the postnatal day 70 (PN70). The main findings in the present study were the development of a substantial number of taste pores in the SP of fetal rats (60.3 ± 1.7 out of 122.8 ± 5.5; mean ± SD/animal at E19) and NIP of neonatal rats (9.8 ± 1.0 out of 44.8 ± 2.2 at PN4). α‐gustducin‐like immunoreactivity (‐LI) was not expressed in the pored taste buds of either prenatal or newborn rats. The earliest expression of α‐gustducin‐LI was demonstrated at PN1 in the SP (1.5 ± 0.5 cells/taste bud; mean ± SD) and at PN4 in the NIP (1.4 ± 0.5). By age the total counts of pored taste buds continuously increased and their morphological features became quite discernible. They became pear in shape, characterized by distinct pores, long subporal space, and longitudinally oriented cells. Around the second week, a remarkable transient decrease in the total number of taste buds was recorded in the oral epithelium of NIP and SP, which might be correlated with the changes of ingestive behaviors. The total counts of cells showing α‐gustducin‐LI per taste bud gradually increased till the end of our investigation (14.1 ± 2.7 in NIP and 12.4 ± 2.5 in SP at PN70). We conclude that substantial development of taste buds began prenatally in the SP, whereas most developed entirely postnatal in the NIP. The present study provides evidence that the existence of a taste pore which is considered an important criterion for the morphological maturation of taste buds is not enough for the onset of the taste transduction, which necessitates also mature taste cells. Moreover, the earlier maturation of palatal taste buds compared with the contiguous populations in the oral cavity evokes an evidence of their significant role in the transmission of gustatory information, especially in the early life of rat. Anat Rec 263:260–268, 2001. © 2001 Wiley‐Liss, Inc.     

Differentiation of the lingual and palatal gustatory epithelium of the rat as revealed by immunohistochemistry of alpha-gustducin.

We used alpha-gustducin, a taste-cell-specific G protein to investigate the onset of taste transduction and its relation to the development of the palatal and lingual taste buds. Frozen cryostat and paraffin sections were prepared from the palatal and lingual gustatory epithelium of the rat from birth till postnatal day 21 (PN 21d). At PN 1-7d, alpha-gustducin-immunoreactive solitary ovoid or bipolar cells were scattered among the oral epithelium either horizontally along the oral surface or vertically oriented between the basal lamina and oral surface. In the circumvallate and foliate papillae, these cells became wrapped in alpha-gustducin-immunonegative cells surrounded by an extracellular space forming a bud-like structure. Simultaneously, different stages of typical taste buds were recognized, but alpha-gustducin was only expressed in some neonatally developed pored buds. At PN 1d, alpha-gustducin was expressed in pored taste buds with a relatively higher frequency recorded in the soft palate as compared with the nasoincisor, circumvallate, and foliate papillae. The immunoreactive cells were spindle shaped with elongated processes extending from the base to the pore of the taste buds. During the second week, the solitary cells could no longer be recognized while the total counts of immunoreactive cells within the taste buds gradually increased. We argue that taste transduction is essentially required from the time of birth and can be fulfilled by both of the solitary chemosensory cells, which are immunoreactive for alpha-gustducin and scattered in the oral epithelium, and the taste cells within the mature taste buds. Moreover, the onset of taste transduction accomplished by the palatal taste buds developed earlier than that achieved by taste buds in the circumvallate and foliate papillae.     

Postnatal development of the vallate papilla and taste buds in rats

The postnatal maturation of the vallate papilla and its taste buds was quantitatively investigated in rats by ligh microscopy. Specifically, we measured postnatal increases in the size of mature vallate taste buds and the vallate papilla, increases in the thickness of the gustatory epidermis, and increases in the number of mature taste buds and taste cells per bud. Mature taste buds, defined as those having a taste pore, are rare at birth but proliferate rapidly during the first postnatal month until an average of 610 mature taste buds has accumulated by 90 days. Throughout this postnatal period, mature taste buds adjust to the developmental thickening of the epidermis by continuously increasing in length. Mature taste buds also increase in width, in part due to a threefold increase from 10 and 45 days in the number of taste cells per bud. From 10 to 21 days there is an average daily net increase of three cells per mature taste bud. The maturational increase in taste buds and cells may contribute to the functional changes in taste nerve responses known to occur over the course of several generations of taste receptor cells. The dimensions of the vallate papilla and the surface area of the gustatory epithelium increase logarithmically with age. Although mature taste buds continue to increase in number until 90 days, both taste bud density (178/mm2) and the number of cells per mature taste bud (70-75 cells) reach ceilings by 45 days. Thus, density-dependent factors appear to control vallate taste bud maturation. The immaturity of lingual taste buds in newborn rats supports the view that odor, rather than taste, is the chemosensory signal that guides suckling in altricial rodents.     

Developmental change of alpha-gustducin expression in the mouse fungiform papilla

Developmental changes in the distribution pattern of taste buds in newborn mouse have not been previously elucidated, and little work has been done to examine the postnatal alteration of the expression of α-gustducin in the mouse taste buds. In the present paper, we delineated the development and frequency distribution of the taste buds as well as the immunohistochemical expression of α-gustducin, a G protein closely related to the transduction of taste stimuli in the fungiform papilla from the birthday till the age of week 9. At birth, more than 45 taste buds (with or without pores) were observed on the fungiform papilla, then the number of mature taste buds increased rapidly, and resulted in 66% (80.2 ± 0.6 of 122.2 ± 1.3) of fungiform papilla taste buds containing taste pores at week 3. By age the total counts of pored taste buds continuously increased and their morphological features became quite discernible. They became ellipse in shape, characterized by distinct pores. Quantitative analysis of α-gustducin expression at different postnatal ages revealed a significant increase in the number of immunolabeled taste buds and α-gustducin-positive cells in single taste buds from week 1 to 7, by week 7, the number reached the value found in adults (99.3 ± 0.9 and 8.3 ± 0.3, respectively). These results indicated that taste buds within fungiform papilla play an important role in the detection of nutrients in the postnatal mouse. Grant sponsor: National Natural Science Foundation of China; Grant number: 30060025.     

Ontogeny and innervation of taste buds in mouse palatal gustatory epithelium

We investigated the relationship between mouse taste bud development and innervation of the soft palate. We employed scanning electron microscopy and immunohistochemistry using antibodies against protein gene product 9.5 and peripherin to detect sensory nerves, and cytokeratin 8 and α-gustducin to stain palatal taste buds. At E14, nerve fibers were observed along the medial border of the palatal shelves that tracked toward the epithelium. At E15.5, primordial stages of taste buds in the basal lamina of the soft palate first appeared. At E16, the taste buds became large spherical masses of columnar cells scattered in the soft palate basal lamina. At E17, the morphology and also the location of taste buds changed. At E18–19, some taste buds acquired a more elongated shape with a short neck, extending a variable distance from the soft palate basal lamina toward the surface epithelium. At E18, mature taste buds with taste pores and perigemmal nerve fibers were observed on the surface epithelium of the soft palate. The expression of α-gustducin was demonstrated at postnatal day 1 and the number of pored taste buds increased with age and they became pear-shaped at 8 weeks. The percent of pored fungiform-like papillae at birth was 58.3% of the whole palate; this increased to 83.8% at postnatal day 8 and reached a maximum of 95.7% at 12 weeks. The innervation of the soft palate was classified into three types of plexuses in relation to taste buds: basal nerve plexus, intragemmal and perigemmal nerve fibers. This study reveals that the nerve fibers preceded the development of taste buds in the palate of mice, and therefore the nerve fibers have roles in the initial induction of taste buds in the soft palate.     

Developmental change of α-gustducin expression in the mouse fungiform papilla

Developmental changes in the distribution pattern of taste buds in newborn mouse have not been previously elucidated, and little work has been done to examine the postnatal alteration of the expression of α-gustducin in the mouse taste buds. In the present paper, we delineated the development and frequency distribution of the taste buds as well as the immunohistochemical expression of α-gustducin, a G protein closely related to the transduction of taste stimuli in the fungiform papilla from the birthday till the age of week 9. At birth, more than 45 taste buds (with or without pores) were observed on the fungiform papilla, then the number of mature taste buds increased rapidly, and resulted in 66% (80.2 ± 0.6 of 122.2 ± 1.3) of fungiform papilla taste buds containing taste pores at week 3. By age the total counts of pored taste buds continuously increased and their morphological features became quite discernible. They became ellipse in shape, characterized by distinct pores. Quantitative analysis of α-gustducin expression at different postnatal ages revealed a significant increase in the number of immunolabeled taste buds and α-gustducin-positive cells in single taste buds from week 1 to 7, by week 7, the number reached the value found in adults (99.3 ± 0.9 and 8.3 ± 0.3, respectively). These results indicated that taste buds within fungiform papilla play an important role in the detection of nutrients in the postnatal mouse.     

Variations in human taste bud density and taste intensity perception

Some variations in human taste sensitivity may be due to different numbers of taste buds among subjects. Taste pores were counted on the tongue tips of 16 people with videomicroscopy, and the subjects were divided into two groups (N = 8) by the rank order of their taste bud densities. The "higher" density group averaged 374 +/- 134 taste pores/cm2, while the "lower" density group averaged 135 +/- 43 tp/cm2. The higher density group had an average fungiform papilla density which was 1.8 times greater than the lower density group and an average of 1.5 times more taste pores/papilla. The subjects also rated the intensity for 4 suprathreshold concentrations of 5 taste stimuli placed on the same region of the tongue where taste pores were counted. The group with higher taste bud densities gave significantly higher average intensity ratings for sucrose (196%), NaCl (135%) and PROP (142%), but not for citric acid (118%) and quinine HCl (110%) than the lower density group. Thus, the subjects with higher fungiform taste bud densities also reported some tastes as more intense than subjects with fewer fungiform taste buds.     

Differentiation of alpha-gustducin in taste buds of the mouse soft palate and fungiform papillae

We used alpha-gustducin, a type II taste-cell-specific G protein, to investigate the onset of taste transduction and its relation to the development of the soft palate (SP) and fungiform (FF) papillae taste buds in the mouse. Paraffin wax embedded sections were prepared from the SP and anterior region of the tongue of the mouse from birth until postnatal day (PD) 63. No alpha-gustducin-immunoreactive cells were observed on the day of birth. One day later, alpha-gustducin was immunolocalised in taste buds with pores with a relatively higher frequency recorded in the SP as compared with the FF papillae. The immunoreactive cells were spindle shaped with elongated processes extending from the base to the pore of the taste buds. On PD 7, the number of taste buds containing alpha-gustducin-immunoreactive cells in the SP was three times greater than that of FF papillae. Our results indicate that taste transduction is essentially acquired from the time of birth. Moreover, the onset of taste transduction by the SP taste buds developed earlier than that achieved by taste buds in the FF papillae.     

Expression of BDNF and TrkB in mouse taste buds after denervation and in circumvallate papillae during development

BDNF (brain-derived neurotrophic factor) is a member of the neurotrophin family which affects the proliferation and survival of neurons. Using an immunocytochemical method, we examined the expression of BDNF and its receptor, TrkB, in the taste bud cells of the circumvallate papillae of normal mice and of mice after transection of the glossopharyngeal nerves. We additionally observed the expression of BDNF and TrkB in the developing circumvallate papillae of late prenatal and early postnatal mice. In normal untreated mice, BDNF was expressed in most of the taste bud cells; TrkB was detected in the plasma membrane of taste bud cells and in the nerve fibers. Double-labeling studies showed that BDNF and NCAM (neural cell adhesion molecule) or TrkB and NCAM colocalized in some of the taste bud cells, but that most taste bud cells were immunopositive for only BDNF or TrkB. NCAM-immunoreactive cells are known to be type-III cells, which have afferent synaptic contacts with the nerve terminals. Five days after denervation, the number of taste buds and nerve fibers markedly decreased; however, the remaining taste bud cells still expressed BDNF and TrkB. By 10 days after denervation, most of the taste buds had disappeared, and there were a few TrkB-immunoreactive nerve fibers in the connective tissue core. By 4 weeks after denervation, numerous TrkB-immunoreactive nerve fibers had invaded the papillae, and a few taste buds expressing BDNF and TrkB had regenerated. At E (embryonic day) 15 during development, the circumvallate papillae appeared, and then TrkB-immunoreactive nerve fibers entered the connective tissue core, and some of these fibers further invaded among the dorsal epithelial cells of the papillae. TrkB-immunoreactive oval-shaped cells were occasionally found in the dorsal epithelium. Such TrkB-immunoreactive nerve fibers and cells were also observed at E16-18. However, BDNF was not expressed in the papillae through the late prenatal days of E15 to E18. At P (postnatal day) 0, a cluster of BDNF-and TrkB-immunoreactive cells appeared in the dorsal epithelium of the papillae, and was presumed to be primitive taste buds. We conclude that TrkB-immunoreactive nerve fibers are necessary for papillary and taste bud formation during development and for the regeneration of taste buds after denervation. BDNF in the taste bud cells may act as a neurotrophic factor for innervating sensory neurons--through TrkB receptors of the axons of those neurons, and also may exert autocrine and paracrine trophic actions on neighboring taste bud cells by binding to their TrkB receptors.     

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.     

Maturation of taste buds on the soft palate of the postnatal rat

Taste bud distribution on the soft palate and within three types of tongue papillae (fungiform, foliate, and circumvallate) were examined histologically in the rat at different postnatal ages. After paraffin embedding, serial sections (10 microm) were made and stained by HE, and digitized images of each section were examined. The existence of a taste pore was used to identify mature taste buds. At birth, 53% (68 of 127 observed) of the taste buds on the soft palate, but only 14% (14 of 110 observed) within fungiform papillae, contained a taste pore. One week after birth, the number of mature taste buds increased rapidly, resulting in 90% of soft palate taste buds and 80% of fungiform taste buds containing taste pores. In contrast, no taste buds with pores were observed at birth within foliate and circumvallate papillae; however, at two weeks after birth 52% (71 of 132 observed) of the foliate and 68% (180 of 267 observed) of the circumvallate taste buds examined contained taste pores. These results suggest that taste buds within the soft palate play an important role in the detection of nutrients in the neonatal rat.     

Immunohistochemical observation on substance P in regenerating taste buds of the rat

The present study was performed to investigate the relationship between substance P-positive (SP-positive) nerve fibers and regeneration of taste buds in the foliate papillae of the rat by means of immunohistochemistry. It was confirmed by neurotomy that taste buds in the foliate papillae of the rat were innervated mostly (90%) by the glossopharyngeal (IXth) nerve and partly (10%) by the chorda tympani. In this experiment, the IXth nerve was sectioned distal to the petrosal ganglion. The rats were sacrificed at various intervals from 20 days to 80 days after the operation. In the course of degeneration and disappearance of taste buds, both SP-positive fibers and taste buds disappeared completely from the posterior folds of the foliate papillae 7 days after the operation. Within 22 days, regenerated SP-positive fibers began to appear in the lamina propria, and following the penetration of the fibers into the epithelium, taste bud anlagen reappeared at the bottom of the trench, and in the posterior folds at 24 days. The process of new taste bud formation extended toward the apex of the trench and to the anterior folds, which seemed to follow the regeneration in the nerve trunk. Quantitative data showed a gradual increase in the number of taste buds and taste buds containing SP-positive fibers. These findings indicate that SP might have a role in regeneration of taste buds.     

Organization of geniculate and trigeminal ganglion cells innervating single fungiform taste papillae: a study with tetramethylrhodamine dextran amine labeling.

Single gustatory nerve fibers branch and innervate several taste buds. In turn, individual taste buds may receive innervation from numerous gustatory nerve fibers. To evaluate the pattern of sensory innervation of fungiform papilla-bearing taste buds, we used iontophoretic fluorescent injection to retrogradely label the fibers that innervate single taste papillae in the hamster. For each animal, a single taste papilla was injected through the gemmal pore with 3.3% tetramethylrhodamine dextran amine. Fungiform papillae either at the tongue tip (0.5-1.5 mm from the tip) or more posteriorly (1.5-3.0 mm from the tip) were injected. After one to seven days survival, the geniculate and trigeminal ganglia and the tongue were sectioned and examined for labeled cells and fibers, respectively. Analysis of the number and topographic distribution of geniculate cells innervating single taste papillae, shows that: (i) 15 +/- 4 (S.D.) ganglion cells converge to innervate a single fungiform taste bud; (ii) more ganglion cells innervate anterior- (range: 13-35 cells) than posterior-lying buds (range: five to 12 cells), which, in part, may be related to bud volume (microm3); and (iii) ganglion somata innervating a single taste bud are scattered widely within the geniculate ganglion. Analysis of labeled fibers in the tongue demonstrated that two to eight taste buds located within 2 mm of the injected taste bud share collateral innervation with the injected taste bud. Since all buds with labeled fibers were located in close proximity (within a 2-mm radius), widely dispersed geniculate ganglion cells converge to innervate closely spaced fungiform taste buds. Trigeminal ganglion (mandibular division) cells were also labeled in every case and, as with the geniculate ganglion, a dispersed cell body location and collateralization pattern among papillae were observed. This study shows that iontophoresis of tetramethylrhodamine dextran amine, selectively applied to individual peripheral receptor end-organs, effectively locates sensory ganglion cells in two different ganglia that project to these sites. Moreover, the marker demonstrates collateral branches of sensory afferents associated with the labeled fibers and the nearby receptor areas innervated by these collaterals. The labeling of single or clusters of receptor cells, as well as identified sensory afferents, affords future possibilities for combining this technique with immunocytochemistry to establish the relationships of innervation patterns with neurotransmitters and neurotropic substances within identified cells.     

Long-term effects of gustatory neurectomy on fungiform papillae in the young rat

Recent evidence from mature hamster fungiform papillae indicates that following denervation taste buds are present from 21 to 330 days in the absence of discernible intragemmal nerve fibers. In contrast, most prior taste bud degeneration studies focused on shorter survival times. The present inquiry in young rats examined the issue of postneurectomy buds, in which regeneration of the resected chorda tympani or facial nerves was prevented and anterior tongue tissue examined over a range of relatively long survival times (30-90 days). Conditions for observing potential taste buds used three histologic stains and a definition of the taste bud not necessarily requiring pore identification. In each case, serial section examination of the anterior-most 2-3 mm of lingual epithelium revealed 29-56 bud-containing fungiform papillae on the unoperated side. In contrast, ipsilateral to the neurectomy, only zero-7 medially-placed, mature-looking buds were observed per case, as well as zero-3 more laterally situated fungiform papillae containing small clusters of cells in basal epithelium that lacked the vertical organization and cytoplasmic staining intensity of mature taste buds. These cell aggregates were distributed evenly across survival time and stain used. Therefore, in young rats following gustatory neurectomy, longer survival times, per se, would not appear to be a prerequisite for sustaining fungiform taste buds. The appearance of "midline" buds postsurgery may be attributed to either normal contralateral or a net bilateral innervation, and/or ipsilateral denervation and bud loss inducing neural sprouting from the contralateral side.     

Initial innervation of the palatal gustatory epithelium in the rat as revealed by growth-associated protein-43 (GAP-43) immunohistochemistry

We studied the earliest stages of the palate in rat embryos using scanning electron microscopy and immunohistochemistry of growth-associated protein-43 (GAP-43) to investigate the role of nerves in the development of the palatal taste buds. Chronological sequences of the palatal gustatory structures revealed characteristic several stages: 1) At embryonic day 13.5 (E13.5), the palatal shelves were widely separated, and no nerves could be observed in the vicinity of their epithelium which was formed of an undifferentiated single cell layer. 2) At E14, intraepithelial GAP-43-immunoreactive fine nerves were first observed along the medial border of the palatal shelves which became several layers thick but still separate along their entire length. 3) At E15, the fusion process resulted in the formation of cranial parts of the soft palate, the epithelium of which was heavily innervated and revealed small fungiform-like papillae devoid of nerves. 4) As the fusion process continued more caudally at E15, there was a substantial increase in palatal innervation and number of fungiform-like papillae. Primordial stages of taste buds were first distinguished in the papillae where they coincided with sparsely distributed GAP-43-immunoreactive nerve fibers. 5) At E16, the whole soft palate was eventually differentiated and attained its definitive morphology. Different stages of taste buds (i.e. pored and non-pored) were recognized, and an extensive subgemmal plexus characteristic for the adult palatal taste buds was observed. 6) Mature taste buds with alpha-gustducin-immunopositive cells were observed at E18, and their numbers increased gradually with age. The present study reveals that the gustatory nerves preceded the development of taste buds in the palate of rats, and therefore may have some roles in the initial induction of taste buds as proposed in lingual taste buds.     

Taste bud development and patterning in sighted and blind morphs of Astyanax mexicanus

In the blind cave‐dwelling morph of A. mexicanus, the eye degenerates while other sensory systems, such as gustation, are expanded compared to their sighted (surface‐dwelling) ancestor. This study compares the development of taste buds along the jaws of each morph. To determine whether cavefish have an altered onset or rate of taste bud development, we fluorescently labeled basal and receptor cells within taste buds over a developmental series. Our results show that taste bud number increases during development in both morphs. The rate of development is, however, accelerated in cavefish; a small difference in taste bud number exists at 5 dpf reaching threefold by 22 dpf. The expansion of taste buds in cavefish is, therefore, detectable after the onset of eye degeneration. This study provides important insights into the timing of taste bud expansion in cavefish as well as enhances our understanding of taste bud development in teleosts in general. Developmental Dynamics 238:3056–3064, 2009. © 2009 Wiley‐Liss, Inc.     

Expression of ATP-gated P2X3 receptors in rat gustatory papillae and taste buds

It has recently become evident that ATP and other extracellular nucleotides could play an important role in signal transductions. ATP mediates excitatory signaling by means of P2X receptors. P2X3, one of its subtypes, a membrane ligand-gated ion channel, is strongly expressed in peripheral sensory neurons. The aim of the present study was to examine the distribution of nerve fibers expressing P2X3 receptors in taste buds in the gustatory papillae and soft palate of rats by immunohistochemistry. We found that the fluorescence ATP marker quinacrine stained subsets of taste bud cells. Numerous nerve fibers innervating taste buds were intensely immunostained with the P2X3 receptor antibody. These nerve fibers ascended among intragemmal cells and terminated just below the taste pores. In order to examine whether P2X3 receptors are involved in signal modulation within taste buds, we used fluorescent double stainings to analyze the distribution of P2X3 receptors and their relationship to alpha-gustducin immunopositive taste receptor cells. Many varicose nerve fibers expressing P2X3 receptor-immunoreactivities were entangled with alpha-gustducin-immunopositive taste receptor cells and ended closely below the taste pores. In fungiform papillae, nerve fibers expressing both P2X3 receptors and PGP 9.5 were observed. In contrast, only PGP 9.5 immunoreactive nerve fibers were recognized in filiform papillae. These results suggest that P2X3 receptors might be involved in taste transmission pathways within taste buds. ATP may act as a neurotransmitter, co-transmitter, or neuromodulator at P2X3 receptors to generate activating gustatory nerve fibers.     

Variation in human fungiform taste bud densities among regions and subjects

Taste sensitivity is known to vary among regions of the tongue and between subjects. The distribution of taste buds on the human tongue is examined in this report to determine if interregional and intersubject variation of taste bud density might account for some of the variation in human taste sensitivity. The subjects were ten males, aged 22-80 years, who died from acute trauma or an acute cardiovascular episode. Specimens were obtained as anatomical gifts or from autopsy. A sample of tissue about 1 cm2 was taken from the tongue tip and midlateral region; frozen sections were prepared for light microscopy; and serial sections were examined by light microscopy to count the taste buds. The average taste bud (tb) density on the tongue tip was 116 tb/cm2 with a range from 3.6 to 514 among subjects. The number of gustatory papillae on the tip averaged 24.5 papillae/cm2 with a range from 2.4 to 80. Taste bud density in the midregion averaged 25.2 tb/cm2 (range: 0-85.9), and the mean number of gustatory papillae was 8.25/cm2 (range: 0-28). The mean number of taste buds per papilla was 3.8 +/- 2.2 (s.d.) on the tip and 2.6 +/- 1.5 (s.d.) on the midregion. Subjects with the highest taste bud densities on the tip also had the highest densities in the midregion and the highest number of taste buds per papilla. Taste bud density was 4.6 times higher on the tip than the midregion, which probably accounts for some of the regional difference in taste sensitivity.(ABSTRACT TRUNCATED AT 250 WORDS)     

Distribution of cytokeratin filaments and vimentin in developing human taste buds

 Taste buds in humans originate from approximately the 8th postovulatory week under the influence of ingrowing nerve fibers. Since they develop from local epithelium, it is of interest whether or not prospective taste cells maintain or develop characteristics of epithelial cells that are different from those of the adjacent epithelium during differentiation. The aim of this study was to monitor changes of the distribution of the cytokeratin filaments (CKs) 8, 18, 19 and 20 (”gastrointestinal” type), CK 7 (”ductal” type), and CK 13 (maturation ”mucosa type”), as well as vimentin in developing human taste buds and adjacent squamous epithelium. With the exception of CK13, which remains negative in taste bud anlagen and adult taste buds, all cytokeratins tested were present in taste cells. With the progress of development, the distribution of CKs becomes more and more restricted to taste cells and salivatory ducts as well as Ebner gland cells. Only CK20 is exclusively specific to taste bud anlagen and sometimes to individual bipolar cells occurring in early stages (week 8–9). Vimentin was located mainly in mesodermal derivatives but also in perigemmal epithelial cells during all stages of development. The occurrence of vimentin in ”borderline” epithelia that interface with underlying connective tissue, i.e., in a region of discontinuity, may be associated with particular events in development, cell migration or even dedifferentiation. Accepted: 17 September 1998     

Fine structure of the taste bud in the mud puppy,Necturus maculosus

The taste receptor of Necturus was studied because of its potential usefulness in electrophysiological intracellular recording. The taste bud has about twice the length and twice the diameter of buds in most other vertebrates. The large size can be attributed to both a greater number of cells and a greater size of the individual cells. The cells of Necturus taste buds appear to be homologous to those in other vertebrates. Three distinct cell types were found: dark cells (60%), light cells (30%), and basal cells (10%). Dark cells contained granular endoplasmic reticulum, Golgi bodies, and many clusters of characteristic granules that reacted positively when treated with the periodic acid-silver methenamine technique. They are probably secretory cells. Light cells, found in the center of the taste bud, were virtually filled with agranular endoplasmic reticulum, mitochondria and Golgi bodies. Their morphology is similar to that of chloride cells in fish gills, and they may have an ion transport function important in the gustatory response. Basal cells, located at the periphery in the basal half of the bud, contained characteristic dense-core vesicles about 70–90 mμ in diameter. The lower half of the taste bud contained many intraepithelial nerve processes adjacent to the cells.