Scanning-electron-microscopic study of the dorsal lingual surface of the squirrel monkey

The structure of the lingual papillae and the ultrastructure of the surface of the lingual dorsal epithelial cells of squirrel monkeys were observed by scanning electron microscopy. Filiform papillae were distributed over the entire dorsal surface of the tongue, except for the radix zone. Fungiform papillae were scattered among these filiform papillae. In the middle of the posterior end of the lingual body, a single vallate papilla was located. Higher magnification of the lingual dorsal epithelium revealed that prominent microridges and elevated intercellular borders occurred widely in the basofrontal area of the filiform papillae, interpapillar area and lingual radix zone. On the surface of the upper part of the filiform papillae, fine pits and hollows were observed. Indistinct microridges were distributed over the surface of the fungiform papillae.     

Fine structure of the filiform papilla of beagle dogs

Light and electron microscopic examination of the dorsal lingual epithelium of beagle dogs (Canis domesticus) revealed three different regions: that anterior to the filiform papillae, that posterior to the papillae, and an interpapillary region. Whereas the basal and suprabasal cells are similar throughout, differences characterize the intermediate and surface layers. Keratohyalin granules are common in the intermediate layers in the anterior and interpapillary regions, tonofibrils are prominent in the posterior region, and no keratohyalin granules occur. The surface layer of the interpapillary region is not keratinized, that of the anterior region shows soft keratinization, and that of the posterior region shows hard keratinization. The perimeter of keratohyalin granules is composed of ribosomes 10-20 nm in diameter.     

Comparative studies of the dorsal surface of the tongue in three mammalian species by scanning electron microscopy

Comparative features of the dorsal tongue epithelia in musk shrews, mongooses and rats were described. The shapes of the filiform papillae were different in each of the species. The distribution pattern of filiform papillae was similar both in the musk shrews and mongoose, in that the form of filiform papillae changed gradually from the lingual apex to the posterior part of the lingual body. By contrast, the different types of filiform papillae were distributed on definite areas of the dorsal lingual surface in the rat. Microridges on the interpapillar surface in the musk shrew and mongoose presented a clear outline, but those of the rat were not so distinct. In all species, the upper surface of filiform papillae did not show any distinct microridges.     

Fine structure of the dorsal lingual epithelium of the frog, Rana rugosa

Scanning and transmission electron microscopy was employed to investigate the ultrastructure of the lingual dorsal epithelial cells of the frog, Rana rugosa. The specimens for scanning electron microscopy were prepared by a method that involved osmium postfixation and treatment with acid to remove extracellular material that adhered to the surface of the tongue. Over almost the entire dorsal surface, filiform papillae, consisting of a large number of non-ciliated cells with microridges and a very small number of ciliated cells, were compactly distributed. Fungiform papillae were scattered among these filiform papillae. A round sensory disk was located on the top of each fungiform papilla. Each sensory disk was encircled by a band of ciliated cells. Transmission electron microscopy revealed that a large part of the filiform papillar epithelium was composed of cells that contained numerous electron-dense granules. These cells were coincident with the non-ciliated cells observed by scanning electron microscopy. In these cells, the nucleus was located on the basal side, and the ergastoplasm was well-developed on the basal side of the nucleus.     

An ultrastructural study of the dorsal lingual epithelium of the crab-eating frog,Rana cancrivora

The amphibian tongue contains two types of papilla which are believed to function in gustation and in the secretion of salivary fluid. Scanning electron microscopy reveals that columnar, filiform papillae are compactly distributed over nearly the entire dorsal surface of the tongue of the frog, Rana cancrivora, and fungiform papillae are scattered among the filiform papillae. Microridges and microvilli are distributed on the epithelial cell surface of the extensive area of the filiform papillae. Light microscopy shows that the apex of each filiform papilla is composed of stratified columnar and/or cuboidal epithelium and its base is composed of simple columnar epithelium. Transmission electron microscopy reveals that most of the epithelium of the filiform papillae is composed of cells that contain numerous round electron-dense granules 1–3 μm in diameter. Cellular interdigitation is well developed between adjacent cells. On the free-surface of epithelial cells, microridges or microvilli are frequently seen. Between these granular cells, a small number of ciliated cells, mitochondria-rich cells and electron-lucent cells are inserted. In some cases, electron-dense granules are present in the ciliated cells. At higher magnification, the electron-dense granules appear to be covered with patterns of spots and tubules. Overall, the morphology and ultrastructure of the lingual epithelium of the three species of Rana that have been studied are quite similar, but they can be easily distinguished from those of Bufo japonicus. Therefore, it appears that lingual morphology is phylogenetically constrained among members of the predominantly freshwater genus Rana to produce uniformity of papillary structure and this morphology persists in Rana cancrivora despite the distinct saline environment in which it lives. © 1993 Wiley-Liss, Inc.     

Fine structure of the dorsal lingual epithelium of the little tern, Sterna albifrons Pallas (Aves, Lari).

The dorsal surface of the tongue of the little tern, Sterna albifrons, has a distinctive anterior region for five-sixths of its length and a terminal posterior region. The anterior region observed by scanning electron microscopy is distinguished along its forward half by a median line from which median papillae protrude. The hind half of the anterior region has a median sulcus without papillae. The deciduous epithelium on both sides of the median line and sulcus bears scattered epithelial protrusions. The posterior lingual region has neither median papillae nor deciduous epithelium. So-called giant conical papillae are located in a transverse row between anterior and posterior regions. Delicate microridges adorn the surfaces of all outer epithelial cells in both regions. Examination of the dorsal lingual epithelium by light and electron microscopy provides histologic and cytologic criteria for distinguishing anterior and posterior regions. Basal cells are nearly alike throughout the dorsal epithelium. Intermediate layer cells of the anterior region contain numerous tonofibrils in electron-dense bundles composed of 10 nm tonofilaments. The outer layer is composed of electron-dense, well-keratinized cells, and electron-lucent epithelial protrusions are present on the exposed surface of the outermost cells. Median papillae are composed of typical keratinized cells, which are nearly filled with keratin filaments. Intermediate layer cells in the posterior region of the tongue are nearly filled with unbundled tonofilaments. There is only a very thin outer keratinized layer in this region.     

Ultrastructural study of the precursor to fungiform papillae prior to the arrival of sensory nerves in the fetal rat.

The structure of precursors to fungiform papillae without taste buds, prior to the arrival of sensory nerve fibers at the papillae, was examined in the fetal rat on embryonic day 13 (E13) and 16 (E16) by light and transmission electron microscopy in an attempt to clarify the mechanism of morphogenesis of these papillae. At E13, a row of rudiments of fungiform papillae was arranged along both sides of the median sulcus of the lingual dorsal surface, and each row consisted of about 10 rudiments. There was no apparent direct contact between papillae rudiments and sensory nerves at this time. Bilaterally towards the lateral side of the tongue, adjacent to these first rudiments of fungiform papillae, a series of cord-like invaginations of the dorsal epithelium of the tongue into the underlying connective tissue, representing additional papillary primordia parallel to the first row, was observed. The basal end of each invagination was enlarged as a round bulge, indented at its tip by a mound of fibroblasts protruding into the bulge. At E16 there was still no apparent direct contact between rudiments of fungiform papillae and sensory nerves. Each rudiment apically contained a spherical core of aggregating cells, which consisted of a dense assembly of large, oval cells unlike those in other areas of the lingual dorsal epithelium. The differentiation of these aggregated cells was unclear. The basal lamina was clearly recognizable between the epithelium of the rudiment of fungiform papillae and the underlying connective tissue. Spherical structures, which appeared to be sections of the cord-like invaginations of the lingual epithelium that appeared on E13, were observed within the connective tissue separated from the dorsal lingual epithelium. Transverse sections of such structures revealed four concentric layers of cells: a central core, an inner shell, an outer shell, and a layer of large cells. Bundles of fibers were arranged in the central core, and the diameters of bundles varied somewhat depending on the depth of the primordia within the connective tissue and their distance from the median sulcus. Ultrastructural features of cells in the outer shell differed significantly in rudiments close to the lingual epithelium as compared to those in deeper areas of connective tissue. Around the outer shell there was a large-cell layer consisting of one to three layers of radially elongated, oval cells that contained many variously sized, electron-dense, round granules. Large numbers of fibroblasts formed dense aggregates around each spherical rudiment, and were separated by the basal lamina from the large-cell epithelial layer. Progressing from deep-lying levels of the rudiments of the papillae to levels close to the lingual surface epithelium, the central core, inner shell, and outer shell gradually disappeared from the invaginated papillary cords.     

Fine structure of the dorsal lingual epithelium of the lizard, Gekko japonicus (Lacertilia, Gekkonidae)

Three different types of lingual papilla were observed by scanning electron microscopy on the dorsal lingual epithelium of the lizard Gekko japonicus. Dome-shaped lingual papillae were located at the apex. Flat, fan-shaped lingual papillae were seen in the widest area of the lingual body. Long, scale-like lingual papillae were arranged on the latero-posterior dorsal surface. At higher magnification, microvilli and microridges were seen to be widely distributed over the surface of the papillae. By light microscopy, the epithelium of the dome-shaped papillae was composed of single, columnar epithelial cells filled with secretory granules. The tip of the epithelium of the fan-shaped and scale-like papillae was composed of stratified squamous epithelial cells without granules. The major part of the epithelium of these two types of papilla, except the tip area, was also composed of single, columnar epithelial cells with secretory granules. By transmission electron microscopy, a nucleus without a defined shape was seen to be located in the basal part of each of the single, columnar epithelial cells. Rough-surfaced endoplasmic reticulum and Golgi apparatus were well developed around the nucleus. The other, major part of the cytoplasm was filled with the spherical secretory granules, a large number of which had very electron-dense cores and moderately electron-dense peripheral regions. In the stratified squamous epithelium, a nucleus, which tended to be condensed on the free-surface side, was located in the center of each cell. Mitochondria, endoplasmic reticulum, and vesicles were observed in the cytoplasm.     

Spacing patterns on tongue surface-gustatory papilla

The dorsal surface of the mammalian tongue is covered with four kinds of papillae, fungiform, circumvallate, foliate and filiform papillae. With the exception of the filiform papillae, these types of papillae contain taste buds and are known as the gustatory papillae. The gustatory papillae are distributed over the tongue surface in a distinct spatial pattern. The circumvallate and foliate papillae are positioned in the central and lateral regions respectively and the fungiform papillae are distributed on the anterior part of the tongue in a stereotyped array. The patterned distribution and developmental processes of the fungiform papillae indicate some similarity between the fungiform papillae and the other epithelial appendages, including the teeth, feathers and hair. This is because 1) prior to the morphological changes, the signaling molecules are expressed in the fungiform papillae forming area with a stereotyped pattern; 2) the morphogenesis of the fungiform papillae showed specific structures in early development, such as epithelial thickening and mesenchymal condensation and 3) the fungiform papillae develop through reciprocal interactions between the epithelium and mesenchymal tissue. These results led us to examine whether or not the early organogenesis of the fungiform papillae is a good model system for understanding both the spacing pattern and the epithelial-mesenchymal interaction during embryogenesis.     

Blood vascular architecture of the rat lingual papillae with special reference to their relations to the connective tissue papillae and surface structures: a light and scanning electron microscope study

Subepithelial blood vessels of the rat lingual papillae and their spatial relations to the connective tissue papillae and surface structures were demonstrated by light and scanning electron microscopy. In the rat, four types of papillae were distinguished on the dorsal surface of the tongue, i.e. the filiform, fungiform, foliate and circumvallate papillae. Vascular beds of various appearance were found in all four types of lingual papillae: a simple or twisted capillary loop in the filiform papilla; a basket- or petal-like network in the fungiform papilla; a ring-like network in the foliate papilla, and a conglomerated network surrounded by double heart-shaped capillary networks in the circumvallate papilla. These characteristic vascular beds corresponded to the shape of the connective tissue papillae and surface structures. The vascular bed beneath the gustatory epithelium in the fungiform, foliate and circumvallate papilla consisted of fine capillary networks next to the taste buds.     

SEM study on the dorsal lingual surface of the common tree shrew, Tupaia glis.

The dorsal lingual surface of the common tree shrew was examined by SEM after treating it with HCl to remove the mucous substance. Filiform (FI), fungiform (FU) and circumvallate papillae (CI) were observed. The FI exhibited a small circular bulge surrounded by anterior and posterior filamentous processes. FU were scattered among the FI. There were 3 CI separating the anterior 4/5 from the posterior 1/5 of the tongue. In addition, a group of conical projections with caudal orientation was found anterior to the palatoglossal fold on each side of the tongue. Microridges were widely observed on the entire dorsal lingual surface, except on the free surface of FI processes.     

The surface structure of the completely and incompletely orthokeratinized oral epithelium in the rat: a light, scanning and transmission electron microscope study.

Mucosa from the hard and soft palates, molar gingiva, cheek and dorsal surface of the tongue of the rat was examined in the light microscope, following Mallory's triple connective tissue stain, and in the scanning and transmission electron microscopes. The epithelium covering the hard palate, gingiva, the smooth band of mucosa at the junction of the hard and soft palates, intermediate zones of the soft palate, fungiform papilla-like structures in the central zone of the soft palate, the fungiform papillae, and the more superficial part and posterior surfaces of the filiform papillae of the tongue all exhibited complete orthokeratinization. The oral surfaces of the epithelial cells in all these areas had a honeycomb pattern of interconnecting ridges surrounding depressions. Imprints of the overlying cells that had been desquamated were apparent, and the lateral boundaries between the cells were formed by two raised ridges separated by a gap. The epithelium covering the cheek, central zone of the soft palate apart from the fungiform papilla-like structures, lateral zones of the soft palate, gingival crevice, and the mucosa between the fungiform and filiform papillae of the tongue all exhibited incomplete orthokeratinization. The oral surfaces of the epithelial cells in all these areas were relatively smooth and did not exhibit a honeycomb pattern of interconnecting ridges. Imprints of the overlying cells that had been desquamated and the lateral boundaries between the cells were only very occasionally found. In the transmission electron microscope the outlines of the cells were compatible with the surface patterns seen in the scanning electron microscope. The possible relationships between the degree of orthokeratinization and ultrastructure of the various epithelia are discussed.     

Immunohistochemical localization of carbonic anhydrase isozyme II in the gustatory epithelium of the adult rat.

The distribution of carbonic anhydrase isozyme II (CA II)-like immunoreactivity (-LI) in the gustatory epithelium was examined in the adult rat. In the circumvallate and foliate papillae, CA II-LI was observed in the cytoplasm of the spindle-shaped taste bud cells, with weak immunoreaction in the surface of the gustatory epithelium. No neuronal elements displayed CA II-LI in these papillae. There was no apparent difference in the distribution pattern between the anterior and posterior portions of the foliate papillae. In immunoelectron microscopy, immunoreaction products for CA II were diffusely distributed in the entire cytoplasm of the taste bud cells having dense round granules at the periphery of the cells. No taste bud cells displaying CA II-LI were detected in the fungiform papillae, but a few thick nerve fibers displayed CA II-LI. In the taste buds of the palatal epithelium, neither taste bud cells nor neuronal elements exhibited CA II-LI. The present results indicate that CA II was localized in the type I cells designated as supporting cells in the taste buds located in the posterior lingual papillae of the adult animal.     

Differential localization of distinct keratin mRNA-species in mouse tongue epithelium by in situ hybridization with specific cDNA probes

The tongue of the adult mouse is covered by a multilayered squamous epithelium which is continuous on the ventral surface, however interrupted on the dorsal surface by many filiform and few fungiform papillae. The filiform papillae themselves are subdivided into an anterior and posterior unit exhibiting different forms of keratinization. Thus, the entire epithelium shows a pronounced morphological diversity of well recognizable tissue units. We have used a highly sensitive in situ hybridization technique to investigate the differential expression of keratin mRNAs in the tongue epithelium. The hybridization probes used were cDNA restriction fragments complementary to the most specific 3'-regions of any given keratin mRNA. We could show that independent of the morphologically different tongue regions, all basal cells uniformly express the mRNA of a type I 52-kD keratin, typical also for basal cells of the epidermis. Immediately above the homogenous basal layer a vertically oriented specialization of the keratin expression occurs within the morphological tissue units. Thus the dorsal interpapillary and ventral epithelium express the mRNAs of a type II 57-kD and a type I 47-kD keratin pair. In contrast, in the anterior unit of the filiform papillae, only the 47-kD mRNA is present, indicating that this keratin may be coexpressed in tongue epithelium with different type II partners. In suprabasal cells of both, the fungiform papillae and the posterior unit of the filiform papillae, a mRNA of a type I 59-kD keratin could be detected; however, its type II 67-kD epidermal counterpart seems not to be present in these cells. Most surprisingly, in distinct cells of both types of papillae, a type I 50-kD keratin mRNA could be localized which usually is associated with epidermal hyperproliferation. In conclusion, the in situ hybridization technique applied has been proved to be a powerful method for detailed studies of differentiation processes, especially in morphologically complex epithelia.     

Three-dimensional and surface structures of rat filiform papillae

The three-dimensional and surface structures of the simple conical papillae of the rat tongue have been demonstrated with scanning electron microscopy. The papillary projection was organized into the anterior, posterior and central core cell populations, whereas the basal region of the papilla which consisted of circularly arranged cells showed no differentiation into three autonomic cell populations. It is considered that the anterior and posterior cell populations around the central core tend to be mutually attached at the bilateral sides, and that the posterior and core cell contacts are rather close than the anterior one. The anterior papillary cells showed relatively smooth surface with little micropits and without microridges. The reticular microridges on the basal cell surface of the posterior papillary cells appear to later develop the micropits and linear microridges on the tip cell surface. These suggest that the anterior cell surface is more highly keratinized than the posterior one. The microridges or micropits on the outer cell surface and the microprojections on the inner cell surface organizing filiform papilla are considered to be the structures for the purpose of cell adhesion.     

Study by transmission and scanning electron microscopy of the morphogenesis of three types of lingual papillae in the albino rat (Rattus rattus)

El‐Bakry, A.M. 2010. Study by transmission and scanning electron microscopy of the morphogenesis of three types of lingual papillae in the albino rat (Rattus rattus).—Acta Zoologica (Stockholm) 91 : 267–278 Tongues were removed from albino rat foetus on days 12 (E12) and 16 (E16) of gestation and from newborns (P0) and from juvenile rats on days 7 (P7), 14 (P14) and 21 (P21) postnatally for investigation by light, scanning, and transmission electron microscopy. Significant changes appeared during the morphogenesis of the papillae. At E12, two rows of rudiments of fungiform papillae were extended bilaterally on the anterior half of the tongue. At E16, the rudiments of fungiform papillae were regularly arranged in a lattice‐like pattern. A rudiment of circumvallate papillae could be recognized. No rudiment of filiform papillae was visible. No evidence of keratinization was recognizable. At P0, rudiments of filiform papillae were visible but had a more rounded appearance, with keratinization. The fungiform and circumvallate papillae were large and their outlines were somewhat irregular as that found in the adult rat. At P7, the filiform papillae were large and slender. The fungiform papillae became large and the shape of circumvallate papillae was almost similar to that observed in the adult. At P14 and P21, the shape and structure of the three types of papillae were irregular as those found in the adult. In conclusion, the rudiments of the fungiform and circumvallate papillae were visible earlier than those of the filiform papillae. The morphogenesis of filiform papillae advanced in a parallel manner with the keratinization of the lingual epithelium, in the period from just before birth to a few weeks after birth.     

Scanning electron microscopic study on the structure of the lingual papillae of the Saanen goat

The morphology of lingual papillae of the ten male mature Saanen goats (11 months old, approximately 42 kg in weight and of a known pedigree) was examined by scanning electron microscopy. Tissues were taken from the dorsal and ventral surfaces of the apex, body and root of the tongue, and were prepared accordingly and observed under the scanning electron microscope. On the dorsal and ventro-lateral surfaces of the lingual mucosa, three types of mechanical papillae (filiform, lenticular, and conical) and two types of gustatory papillae (vallate and fungiform) were observed. The structure and density of the filiform papillae differentiated on the anterior, posterior and ventro-lateral aspects of the tongue. Two types of lenticular papillae, both possessing a prominent surrounding papillary groove, were determined. The pyramidal-shaped type I lenticular papilla had a pointed apex while the round-shaped type II lenticular papilla possessed a blunt apex. Certain number of the type I lenticular papillae had double apices. The larger conical papillae were hollow structures, differing structurally from the filiform papillae with their larger size, a tip without projections and lack of the secondary papillae. The vallate papillae were present on both rims of the torus linguae, were encircled by a prominent gustatory furrow which was also surrounded by a thick annular fold. The fungiform papillae were scattered among the filiform papillae in the anterior two-thirds of the dorsal and lateral surfaces, and each of them was highly protected by surrounding filiform papillae, yet encircled by a papillary groove. Our findings indicate that Saanen goat have profuse distribution of papillae on the tongue displaying morphological features characteristic of mechanical function.     

Fine structure of the dorsal epithelium of the tongue of the freshwater turtle,Geoclemys reevesii (Chelonia,Emydinae)

Scanning electron microscopy shows that lingual papillae occur all over the dorsal surface of the tongue of the freshwater turtle, Geoclemys reevesii. The surface of each papilla is composed of compactly distributed hemispherical bulges, each composed of a single cell. Microvilli are widely distributed over the surface of cells. Histological examination reveals that the connective tissue penetrates deep into the center of papillae and that the epithelium is stratified columnar. Under the transmission electron microscope, the cells of the basal and the deep intermediate layers of the epithelium appear rounded. A large nucleus lies in the central area of each cell. The cytoplasm contains mitochondria, endoplasmic reticulum and free ribosomes. The cell membrane form numerous processes. The shallow intermediate layer contains two types of cell. The cytoplasm of the first has numerous fine granules, in addition to mitochondria, ribosomes, and endoplasmic reticulum. The other type of cell contains highly electron-dense granules. The surface layer shows two cell types. One type consists of typical mucous cells. The other type of cell contains fine, electron-lucent granules. The latter cells lie on the free-surface side, covering the mucous cells, and have microvilli on their free surfaces.