Taste bud development in the zebrafish, Danio rerio.

Taste buds are chemosensory endorgans consisting of modified epithelial cells. Fish and other vertebrates use their taste bud cells to sample potential food, either selecting or rejecting substances according to their edibility. The adult gustatory system in fish has been studied thoroughly, including regeneration experiments. Taste buds occur in the epithelia of the lips, the mouth cavity, the oropharyngeal cavity, and also in the skin of the barbels, the head, and sometimes even all over the body surface. Despite its importance for feeding, little is known about the ontogeny of the fish taste system. We examined the development of taste buds in the zebrafish on the light microscopical and the scanning and transmission electron microscopical levels. Taste buds develop later than the olfactory organ and the solitary chemosensory cells, two other chemosensory systems in aquatic vertebrates. The first few taste bud primordia are visible within the epithelia of lips and gill arches 3 to 4 days after fertilization, and the first few taste buds with open receptor areas appear on the lips and simultaneously on the gill arches 4-5 days after fertilization, which coincides with the onset of feeding. Taste buds in the mouth cavity, on the head, and on the barbels are formed later in development. As seen in other fish, zebrafish taste buds contain elongate dark and light cells, termed according to their electron density. Dark cells with a cell apex of many short microvilli appear first, followed by the light cells with one large microvillus. In addition, the zebrafish has a third fusiform cell type, which appears last. This cell type is low in electron density and has a brush-like apical ending with several small microvilli. This cell type has not been described previously. Furthermore, in zebrafish, the ontogenetic processes of taste bud formation differ from regenerative processes described in the literature.     

Immunohistochemical distribution of growth-associated protein 43 (GAP-43) in developing rat nasoincisor papilla

We employed immunohistochemistry of growth-associated protein 43 (GAP-43) to trace the early development of gustatory nerves and alpha-gustducin to demonstrate mature taste buds in the rat nasoincisor papilla (NP). The sequential changes of gustatory structures revealed eight characteristic stages. One, at embryonic day 16 (E16), GAP-43-immunoreactive (IR) nerve fibers were observed in close relation with presumptive taste buds in the lateral apical epithelium on each side of NP; meanwhile, no immunoreactivity could be observed in the papillary epithelium. Two, at E17, fine GAP-43-IR nerve fibers first invaded the apical epithelium of the papilla. Three, at E19, GAP-43-IR nerve fibers were extensive in apical epithelium and colonized in immature taste buds. Four, at E20, GAP-43-IR nerve fibers were first observed in ductal epithelium (lining the medial wall of nasoincisor ducts). Five, at postnatal day 1 (P1), immunoreactive nerve fibers first coincided with immature taste buds in the ductal epithelium. Six, at P3, alpha-gustducin-IR cells identical for mature taste buds were simultaneously demonstrated in both apical and ductal epithelium. Seven, at P14, progressive taste bud proliferation and maturation as well as neural invasion were demonstrated in all regions of the epithelium. Eight, during advanced stage in adult animals, extensive innervation was traced especially in close relation with taste buds. The sequential topographic patterns of NP gustatory structures seem very specific as compared to those in other locations of mammalian gustatory system. The present study reveals that gustatory nerves preceded the development of taste buds. However, further investigations are required to examine such a characteristic model for the neurogenic theory of taste induction.     

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.     

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.     

江豚味蕾的分布及超微结构

目的：了解江豚味觉器官味蕾在口腔中的分布方式和味蕾的超微结构。方法：用石蜡切片观察江豚味蕾的分布，用透射电镜观察味蕾的超微结构。结果：江豚味蕾仅分布于舌小窝侧壁上皮层及舌小窝内疣状突起上皮层中；江豚味蕾主要包括明细胞和暗细胞，味孔表面由暗细胞细胞体的上行突起构成，明细胞细胞体上行突起不到达味孔表面。结论：脊椎动物味蕾在体内外的分布特点与动物的分类地位相关，而脊椎动物舌表面的形态学特点与动物的栖息环境相关。     

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 alpha-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). alpha-gustducin-like immunoreactivity (-LI) was not expressed in the pored taste buds of either prenatal or newborn rats. The earliest expression of alpha-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 alpha-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.     

云豹味蕾的分布与结构

目的：了解云豹味觉器官味蕾在口腔中的分布和结构。方法：用光镜观察云豹舌的形态结构和味蕾的分布，并用透射电镜观察味蕾的结构。结果：云豹味蕾分布于舌尖及轮廓乳突的上皮层中，主要由明细胞和暗细胞组成。结论：云豹味蕾的分布及舌的形态学特点与它的捕食和吞咽习性相适应。     

Chorda tympani innervation of anterior mandibular taste buds in the chicken (Gallus gallus domesticus)

While the mammalian chorda tympani innervates taste buds on the anterior two-thirds of the tongue, the chorda tympani of chickens does not enter the tongue, but rather is reported to supply the oral epithelium of the lower beak subjacent to the tongue. This study in the chicken investigated whether the integrity of taste buds in the lower beak is normally dependent upon innervation by the chorda tympani. Following unilateral ligation and removal of a large section of the chorda tympani, animals were sacrificed at 11, 14, and 21 days postoperatively. Oral tissue between the lingual frenulum and beak tip was serially examined, and the presence of each bud was recorded, noting the point at which the bud opened into the oral cavity. No buds were observed on the operated side in any of the cases, while the average bud count on the unoperated side was 33 +/- 10 (SD). On the unoperated side, taste buds were generally associated with anterior mandibular salivary gland ducts that reached surface epithelium and opened into the oral cavity. On the operated side, the cellular organization adjacent to gland ducts and in duct-free epithelium appeared as in control (i.e., bud-free) epithelium. The number of salivary gland duct openings into the oral cavity was equivalent on the operated and control sides. It is concluded that the chorda tympani of chickens innervates taste buds in the anterior lower beak epithelium and that it functions to maintain the structural integrity of these buds.     

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.     

The distribution of PGP9. 5, BDNF and NGF in the vallate papilla of adult and developing mice

The development and innervation of vallate papillae and taste buds in mice were studied using antibodies against the neuronal marker, protein gene product 9.5 (PGP 9.5), and against nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF). PGP 9.5 immunohistochemical studies revealed that the earliest sign of median vallate papilla formation was an epithelial bulge at embryonic day 13 (E13), and at E14, a dense nerve plexus was found within the connective tissue core of the papilla. Thin nerve fibers penetrated the apical and medial trench wall epithelium of the papilla at E16 and a few of these began to invade the lateral trench wall epithelium at E17. At postnatal day 1 (P1), the newly formed taste buds were recognizable and a small number of PGP 9.5-immunoreactive (IR) cells appeared on the medial trench wall epithelium. The number of PGP 9.5-IR taste bud cells then increased gradually and reached the adult level at postnatal week 2. PGP 9.5 immunoreactivity increased systematically with age. NGF and BDNF immunoreactivity was first seen at the boundary between the columnar cells in the apical epithelium of the developing vallate papilla at E13, then in the medial and lateral trench walls at E15 (BDNF) or E18 (NGF). At P1, BDNF immunoreactivity was exclusively present in the newly formed taste buds of the medial trench wall. The number of BDNF-IR taste bud cells then increased gradually, reaching the adult level at P7. Similar degrees of NGF and BDNF immunoreactivity were seen in the developing vallate papilla. In the present study, we found that the vallate papilla was formed prior to its innervation, and we propose that initiation of papilla formation does not require any direct influence from the specific gustatory nerve. We also suggest that neurotrophins in the early developing vallate papillae might act as local tropic factors for the embryonic growth of nerve fibers to induce differentiation of the taste buds.     

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.     

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.     

Morphology of the buccopharyngeal portion of the gill in the fathead minnow Pimephales promelas (Rafinesque)

Buccopharyngeal epithelium covering gill arches and gill rakers of the fathead minnow was studied by light microscopic, scanning, and transmission electron microscopic techniques. Mature mucous cells in goblet pattern and nonmucus containing cells were in the apical one-third of the tissue. The latter cells contributed to a surface microridge system which overlapped apices of goblet cells. The bottom of the epithelium was comprised of a continuous row of darkly stained basal epithelial cells. In this region, two to three epithelial cells of similar staining characteristics were piled up forming apical columns which partially encircled nests of lightly stained cells. A basal lamina and thick basement lamella of about 20 plies of orthogonally arranged collagen supported the epithelium. Numerous taste buds were seen in gill arches and rakers. Taste bud cellular components included marginal cells, light receptor cells, dark receptor cells, and basal cells. These were identical in all taste buds. Taste bud surface morphology differed between gill arch and raker. Pores of the former were depressed, while those of the latter were raised. Thick microvilli of taste pores were apical extensions of light cells, while smaller, more numerous microvilli were projections from dark cells.     

Role of bursin in the development of B lymphocytes in chicken embryonic Bursa of Fabricius

Localization and role of bursin during Bursa of Fabricius (BF) ontogeny were examined by immunohistochemical staining and by in ovo injection with anti-bursin antibody. Mouse monoclonal anti-bursin antibody HU2 was generated by immunization with synthetic bursin. It recognized reticular cells (REC), follicular associated epithelium (FAE), FAE-supporting cells, and the basal layer of interfollicular epithelium (IFE) in the mature BF. Bu-1(+) cells were first detectable in the mesenchyme area at 13 days of embryogenesis (E13) before bud formation, then lined up along the bud, and homed into the bud at around E15. IgM(+) cells were detected in the bud after E13. Bursin was first observed at the under edge of the bud. Injection of HU2 into embryonal vein at E13 suppressed the appearance of IgM(+) cells in the Bursa at E17. These results indicate that bursin exists beneath the bud and may act on the appearance of IgM(+) cells during BF ontogeny.     

Immunocytochemical localization of the L1 and N-CAM cell adhesion molecules and their shared carbohydrate epitope L2/HNK-1 in the developing and differentiated gustatory papillae of the mouse tongue

Summary The localization of the cell adhesion molecules L1 and N-CAM, and their shared carbohydrate epitope L2/HNK-1, was investigated at the light and electron microscopic levels in developing and adult fungiform and circumvallate gustatory papillae of the mouse tongue.At embryonic day 13, the earliest stage investigated, the tongue epithelium was still undifferentiated and was not yet innervated by sensory fibres. At this stage none of the three molecules was detectable within the tongue epithelium. At embryonic day 15 the primordia of the gustatory papilla became unequivocally discernible when the papillary epithelium was already innervated by few sensory axons. At this stage N-CAM was the first molecule expressed on epithelial cells and was confined to those parts of the papillary epithelium destined to become the chemosensory cells of the taste buds. The sensory axons were N-CAM-, L1- and L2/HNK-1-positive when fasciculating or contacting their accompanying Schwann cells or the cells of the papillary epithelium. Contacts between Schwann cells were also prominently labelled by antibodies to the three antigens. The mesenchymal tissue underlying the prospective sensory epithelium expressed N-CAM at all embryonic stages, but ceased to be N-CAM positive within the first six postnatal days. From embryonic day 16 onward a weak L1 immunoreactivity was detectable within the basal and intermediate layers of the lingual epithelium and remained present in adulthood.Cytodifferentiation of epithelial cells into spindle-shaped sensory cells and organization into taste buds began at postnatal day two. Simultaneously, L1 and L2/HNK-1 immunoreactivity increased on taste bud cells and N-CAM disappeared from the non-sensory extragemmal parts of the papillary epithelium. At approximately postnatal day six, taste bud formation was complete and the pattern of cell adhesion molecule expression was comparable to that found in the adult in that L1 was strongly expressed on the apposing surfaces of all cells, whereas N-CAM was confined to cell contacts between a subpopulation of intragemmal cells. The L2/HNK-1 epitope was visible on the surfaces of taste bud cells, on intragemmal axons, and in a small portion of extracellular matrix directly underlying the taste buds, but was no longer expressed on those parts of the sensory fibres embedded in the subepithelial mesenchyme. The L2/HNK-1 epitope may thus be regarded as a cell surface marker for the cellular elements of mature taste buds. The highly sialylated form of N-CAM was not detectable at any stage investigated.The observations suggest that the expression of the three molecules within the papillary epithelium follows rather than precedes the innervation by sensory axons and does not, therefore, reflect the gustatory epithelium's susceptibility to innervation as found for N-CAM in the neuromuscular system. The spatio-temporal expression of N-CAM, however, is suggestive of its influence on the differentiation of taste bud cells. Apart from axon-axon and axon-Schwann cell interactions L1 might be involved in interactions between gustatory cells and sensory nerve terminals and, surprisingly, also between non-sensory epithelial cells, whereas the L2/HNK-1 epitope may be implicated in the maintenance of the characteristic cytoarchitecture of the differentiated taste buds.     

Distribution of taste and general sensory nerve endings in fungiform papillae of the hamster

Sensory endings of chorda tympani and lingual (trigeminal) nerve fibers were identified by selective denervation and localized within specific regions of fungiform pipillae in the hamster. The chorda tympani was resected from the middle ear and the peripheral fibers were allowed to degenerate for 1, 3, or 8 days prior to perfusion-fixation and electron-microscopic examination of the anterior tongue. Taste buds were virtually devoid of intact nerves by 3 days following chorda tympani denervation. Remnants of the fibers were restricted to taste buds. Lingual fibers, on the other hand, persist in normal numbers after chorda tympani resection and populate perigemmal areas of connective tissue and extragemmal areas located apically in the squamous, nontaste epithelium surrounding the taste bud. This study provides evidence of a segregation of chorda tympani fibers in the taste bud and lingual nerve fibers in the apical fungiform papilla. The lingual nerve-epithelial arrangement and superficial location, near the least cornified area of the tongue, may be well suited for relatively sensitive somatosensation, possibly mechanoreception. Thus, the apical fungiform papilla appears to be a site where both taste and tactile oral stimuli interact with receptors.     

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.     

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