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.     

Three-dimensional architecture of the connective tissue papillae of the mouse tongue as viewed by scanning electron microscopy

The morphological relationship between lingual papillae and underlying connective tissue papillae of mouse was studied because it is conceivable that the differentiation of epithelium may be affected by its connective tissue. Tongues of adult male mice were fixed in formol or Karnovsky's fixative. After removal of the epithelium by long-term hydrochloric acid treatment at room temperature, the surface of the connective tissue papillae was observed by scanning electron microscopy. Connective tissue papillae that were fungiform in shape and which were distributed at the anterior part of the tongue showed barnacle-like protrusion after removal of the epithelium. Their surface was covered by numerous long filaments running vertically and there was a round depression on the top of each fungiform papilla that may be found to correspond to a taste bud when the results of light and electron microscopy are compared. Filiform papillae in a narrow sense were closely distributed in the anterior part of the tongue. They had a tapered tip declining posteriorly. Each filiform connective tissue papilla was conical in shape and had a round depression that slightly declined antero-downward, and a long narrow depression ran along the anterior edge of each connective tissue papilla. Large conical papillae which distributed at the anterior margin of the intermolar prominence had shovel-like connective tissue papillae which had a depression at the posterior surface unlike that of the filiform papillae. Branched papillae distributed in the posterior part of the prominence had a depression at the anterior surface. Under the light microscope, numerous keratohyaline granules were seen to be contained only in the posterior epithelial cell line of the large conical papillae distributed in the anterior margin of the prominence, while these granules were found only in the anterior epithelial cell line of both filiform and branched papillae. It became clear that the axes of each connective tissue papilla of large conical papillae distributed radically around a single midpoint. Connective tissue papillae of vallate papillae had a beehive-like shape and in follicate papillae there were several vertical elliptical gaps, seen when the epithelium was peeled from the connective tissue.     

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.     

Taste placodes are primary targets of geniculate but not trigeminal sensory axons in mouse developing tongue

Tongue embryonic taste buds begin to differentiate before the onset of gustatory papilla formation in murine. In light of this previous finding, we sought to reexamine the developing sensory innervation as it extends toward the lingual epithelium between E 11.5 and 14.5. Nerve tracings with fluorescent lipophilic dyes followed by confocal microscope examination were used to study the terminal branching of chorda tympani and lingual nerves. At E11.5, we confirmed that the chorda tympani nerve provided for most of the nerve branching in the tongue swellings. At E12.5, we show that the lingual nerve contribution to the overall innervation of the lingual swellings increased to the extent that its ramifications matched those of the chorda tympani nerve. At E13.0, the chorda tympani nerve terminal arborizations appeared more complex than those of the lingual nerve. While the chorda tympani nerve terminal branching appeared close to the lingual epithelium that of the trigeminal nerve remained rather confined to the subepithelial mesenchymal tissue. At E13.5, chorda tympani nerve terminals projected specifically to an ordered set of loci on the tongue dorsum corresponding to the epithelial placodes. In contrast, the lingual nerve terminals remained subepithelial with no branches directed towards the placodes. At E14.5, chorda tympani nerve filopodia first entered the apical epithelium of the developing fungiform papilla. The results suggest that there may be no significant delay between the differentiation of embryonic taste buds and their initial innervation.     

Fungiform papilla pattern: EGF regulates inter-papilla lingual epithelium and decreases papilla number by means of PI3K/Akt, MEK/ERK, and p38 MAPK signaling

Fungiform papillae are epithelial taste organs that form on the tongue, requiring differentiation of papillae and inter-papilla epithelium. We tested roles of epidermal growth factor (EGF) and the receptor EGFR in papilla development. Developmentally, EGF was localized within and between papillae whereas EGFR was progressively restricted to inter-papilla epithelium. In tongue cultures, EGF decreased papillae and increased cell proliferation in inter-papilla epithelium in a concentration-dependent manner, whereas EGFR inhibitor increased and fused papillae. EGF preincubation could over-ride disruption of Shh signaling that ordinarily would effect a doubling of fungiform papillae. With EGF-induced activation of EGFR, we demonstrated phosphorylation in PI3K/Akt, MEK/ERK, and p38 MAPK pathways; with pathway inhibitors (LY294002, U0126, SB203580) the EGF-mediated decrease in papillae was reversed, and synergistic actions were shown. Thus, EGF/EGFR signaling by means of PI3K/Akt, MEK/ERK, and p38 MAPK contributes to epithelial cell proliferation between papillae; this biases against papilla differentiation and reduces numbers of papillae.     

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.     

Taste cell formation does not require gustatory and somatosensory innervation

Dependency of taste buds and taste papillae on innervation has been debated for a long time. Previous research showed neurotrophins, brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3), play an important role for the establishment of the lingual gustatory and somatosensory innervation. BDNF null mutant mice showed severe deficits in gustatory innervation and loss of taste buds while NT-3 null mutation reduced lingual somatosensory innervation to tongue papillae. These results proved BDNF or NT-3 null mutations affected different sensory modalities (i.e. gustatory and somatosensory, respectively). In this study, we analyzed taste bud development in BDNF × NT-3 double knockout mice to examine the relationship between taste bud development and gustatory/somatosensory innervation. Our results demonstrate that, at the initial stage, before nerve fibers reached the appropriate areas in the papilla, taste bud formation did not require innervation. However, at the synaptogenic stage, after nerve fibers ramified into the apical epithelium, innervation was required and played an essential role in the development of taste buds/papillae.     

Neural control of ectopic filiform spines in adult tongue

The tongue surface directly above a fungiform taste bud is flat, thinly keratinized, and free of filiform spines. We examined fungiform papillae in serial sections of rat and gerbil tongues after unilateral transection of the chorda-lingual nerve had caused many fungiform taste buds to degenerate. Such empty fungiform papillae often formed a solitary keratinized outgrowth that closely resembled the spine of an ordinary filiform papilla. By six months an ectopic spine was found on 61% of empty fungiform papillae, but never on fungiform papillae that contained a taste bud. Experimental innervation of the tongue reduced the incidence of ectopic filiform spines in proportion to the cross-sectional area of the trigeminal nerve branches tested (the mylohyoid nerve, the lingual nerve, lingual + mylohyoid or lingual + auriculotemporal nerves). The chorda tympani nerve was 60 times more effective than trigeminal nerves in preventing ectopic filiform spines. We suggest that positive and negative trophic actions are normal characteristics of taste axons, for they promote the formation of taste buds and prevent the expression of ectopic filiform spines. By preventing the outgrowth of ectopic spines on fungiform papillae, taste axons maintain a thinly keratinized apical surface that can be breached by the taste receptor cells.     

Comparative morphological study on the lingual papillae and their connective tissue cores (CTC) in reeves’ muntjac deer (Muntiacus reevesi)

The lingual papillae and their connective tissue cores (CTC) from Reeves’ muntjac deers (herbivorous artiodactyla) were studied using light and scanning electron microscopy and then compared to those of other mammalian species. At the posterior portion of the tongue, the Reeves’ muntjac has a lingual prominence on which large conical papillae are distributed. On the dorsal surface of the anterior tongue, numerous filiform papillae were found. Externally, each filiform papilla consists of a rod-shaped main process and several small accessory processes. Their CTCs consist of 10 or more rod-shaped processes arranged in a horseshoe pattern and several posterior processes forming a small circular pattern. This structure is a common characteristic of artiodactyla, through which Reeves’ muntjac deer can be categorized in a position in the artiodactyla class lying between the bighorn sheep and the East African bongo. Fungiform papillae are distributed among the filiform papillae on the anterior portion of the tongue. Large fungiform papillae are also sparsely distributed on the lingual prominence and have several taste buds in the epithelium on the surface. Ten or more vallate papillae are distributed at the postero-lateral area of the lingual prominence and numerous taste buds are distributed in the epithelium of their side.     

Building sensory receptors on the tongue

Neurotrophins, neurotrophin receptors and sensory neurons are required for the development of lingual sense organs. For example, neurotrophin 3 sustains lingual somatosensory neurons. In the traditional view, sensory axons will terminate where neurotrophin expression is most pronounced. Yet, lingual somatosensory axons characteristically terminate in each filiform papilla and in each somatosensory prominence within a cluster of cells expressing the p75 neurotrophin receptor (p75NTR), rather than terminating among the adjacent cells that secrete neurotrophin 3. The p75NTR on special specialized clusters of epithelial cells may promote axonal arborization in vivo since its over-expression by fibroblasts enhances neurite outgrowth from overlying somatosensory neurons in vitro. Two classical observations have implicated gustatory neurons in the development and maintenance of mammalian taste buds—the early arrival times of embryonic innervation and the loss of taste buds after their denervation in adults. In the modern era more than a dozen experimental studies have used early denervation or neurotrophin gene mutations to evaluate mammalian gustatory organ development. Necessary for taste organ development, brain-derived neurotrophic factor sustains developing gustatory neurons. The cardinal conclusion is readily summarized: taste buds in the palate and tongue are induced by innervation. Taste buds are unstable: the death and birth of taste receptor cells relentlessly remodels synaptic connections. As receptor cells turn over, the sensory code for taste quality is probably stabilized by selective synapse formation between each type of gustatory axon and its matching taste receptor cell. We anticipate important new discoveries of molecular interactions among the epithelium, the underlying mesenchyme and gustatory innervation that build the gustatory papillae, their specialized epithelial cells, and the resulting taste buds.     

Light and scanning electron microscopic study on the lingual papillae and their connective tissue cores of the Cape hyrax Procavia capensis

We examined the epithelial surface and connective tissue cores (CTCs) of each lingual papilla on the Paenungulata, Cape hyrax (Procavia capensis), by scanning electron microscopy and light microscopy. The tongue consisted of a lingual apex, lingual body and lingual root. Filiform, fungiform and foliate papillae were observed on the dorsal surface of the tongue; however, fungiform papillae were quite diminished on the lingual prominence. Moreover, no clearly distinguishable vallate papillae were found on the tongue. Instead of vallate papillae, numerous dome-like large fungiform papillae were arranged in a row just in front of the rather large foliate papillae. Foliate papillae were situated in the one-third postero-lateral margin of the lingual body. The epithelium of filiform papillae was covered by a keratinized layer with kerato-hyaline granules, whereas weak keratinization was observed on the interpapillary epithelium. The external surface of the filiform papillae was conical in shape. CTCs of the filiform papillae were seen as a hood-like core with a semicircular concavity in the anterior portion of each core. Large filiform papillae were distributed on the lingual prominence. The CTCs of large filiform papillae after exfoliation of their epithelium consisted of a concave primary core and were associated with several small protrusions. The surface of fungiform papillae was smooth and dome-like. After removal of the epithelium, CTCs appeared as a flower bud-like primary core and were associated with several protrusions that were arranged on the rim of the primary core. Several taste buds were found on the top of the dorsal part of the epithelium of both fungiform and large fungiform papillae. Well-developed foliate papillae were seen and numerous taste buds could be observed in the lateral wall of the epithelium in a slit-like groove. The morphological characteristics of the tongue of the Cape hyrax had similarities with other Paenungulata such as Sirenia. However, three-dimensional characteristics, especially CTCs of lingual papillae, exhibited multiple similarities with rodents, insectivores and artiodactyls.     

Stereo architecture of the connective tissue cores of the lingual papillae in the treeshrew (Tupaia glis).

Summary The stereo architecture of the lingual connective tissue cores (CTC) in the treeshrew (Tupaia glis) (which has the primitive characteristics of primates) was observed by scanning electron microscopy, and compared to that of other animal orders. The tongue of the treeshrew has three vallate papillae which are situated in the posterior part of the tongue, while some macaques have several vallate papillae. Among numerous filiform papillae, fungiform papillae are sporadically distributed. A filiform papilla consists of a bundle of several slender spine-like processes arranged in a circle at the basal margin. After removal of the epithelium, the CTC of the filiform papilla looks like a human hand raised with the palm facing towards the tongue tip. The fungiform CTC in the threeshrew is columnar in shape (rather similar to that of Insectivora and Rodentia) and at the top there are several round depressions for taste buds. In the treeshrew several large rod-shaped processes are derived from the postero-lateral margin of the tongue, as in Carnivora (dogs and cats), where foliate papillae are located in many other animal species. The treeshrew has numerous characteristics similar to those of the crab-eating macaque (Primates), but at the same time it has some characteristics similar to those of Insectivora, Rodentia, Carnivora and Artiodactyla.     

Morphology of the lingual papillae in the roan antelope

We examined the dorsal lingual surfaces of an adult roan antelope (Hippotragus equinus) by scanning electron microscopy. Filiform, fungiform and vallate papillae were observed. The filiform papillae consisted of a larger main papilla and smaller secondary papillae. A top of the connective tissue core of the filiform papilla showed several depressions. The connective tissue core of the papilla with a long process was rarely observed. The fungiform papillae were round in shape. The connective tissue core of the fungiform papilla was flower-bud shaped. The lenticular papillae of large size were limited on the torus lingua. The connective tissue core of the lenticular papilla consisted of numerous small spines. The vallate papillae were located on both sides of the posterolateral aspects. The vallate papillae were flattened oval shaped and the papillae are surrounded by circular trench. The connective tissue core of the vallate papilla was covered with numerous small spines.     

Distribution of taste buds on fungiform and circumvallate papillae of bovine tongue

The distribution of taste buds on the fungiform and circumvallate papillae of the cow tongue has been determined. The two tongues studied were from Holstein-Friesian cows four to six years of age; they contained 14,765 and 21,691 taste buds, respectively. The tip of the tongue is well supplied with fungiform papillae, and the posterior portion contains the circumvallate papillae. The midportion of the tongue contains relatively few taste papillae. The fungiform papillae contained 1,580 and 1,838 taste buds on the two tongues, respectively, and the circumvallate papillae were estimated to contain 13,185 and 19,853 taste buds. The highest concentration of taste buds therefore occurs in the circumvallate papillae; these relatively few papillae contain approximately 90% of the taste buds. On a circumvallate papilla, taste buds are found only on the papillary sidewall, with none either on the apical surface of the papilla or on the outer wall of the moat.     

Sox2 is required for development of taste bud sensory cells

Sox2 is expressed in basal epithelial cells of the tongue, with high levels in taste bud placodes, fungiform papillae, and mature taste cells, and low levels in filiform papillae. High Sox2 expression appears to lie downstream from canonical Wnt signaling. In hypomorphic Sox2(EGFP/LP) embryos, placodes form but no mature taste buds develop. In contrast, transgenic overexpression of Sox2 in the basal cells inhibits differentiation of filiform keratinocytes. Together, our loss-of-function and gain-of-function studies suggest that Sox2 functions in a dose-dependent manner to regulate the differentiation of endodermal progenitor cells of the tongue into taste bud sensory cells versus keratinocytes.     

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.     

Morphology of the lingual papillae in the Patagonian cavy

We examined the dorsal lingual surfaces of an adult Patagonian cavy (Dolichotis patagonum) by scanning electron microscopy. The tongue of the Patagonian cavy is about 8 cm long and the lingual body had lingual prominence on the posterior third. There were no fungiform papillae in the lingual dorsal surface. The fungiform papillae were observed in both lateral sides of the lingual apex. The filiform papilla of the lingual body consisted of a large conical papilla. The connective tissue core of the filiform papilla showed many slender processes. The fungiform papillae were round in shape. The connective tissue core of the fungiform papilla was flower-bud shaped. Two vallate papillae were located on between lingual body and root, and insert in two grooves. The connective tissue core of the vallate papilla was covered with numerous small spines. Many foliate papillae were observed on the posterolateral regions of the tongue. After removing epithelium from the foliate papillae many vertical depressions became apparent. These findings suggest that in the structure of the lingual papillae of the Patagonian cavy there is similar to that of the capybara.     

The nature of the substance P-containing nerve fibres in taste papillae of the rat tongue

The nature of the association of substance P (SP) with taste buds in the rat tongue was investigated by immunohistochemical and radioimmunoassay techniques. Both the circumvallate and fungiform papillae were found to receive a rich innervation by substance P-containing fibres. Although these fibres were closely associated with the taste buds in these structures, they assumed a perigemmal rather than an intragemmal location. Bilateral lesions of the glossopharyngeal nerve resulted in the depletion of taste buds from the vallate papilla and a large reduction in substance P immunoreactive fibres in this area. Lesions of the chorda tympani, which led to the degeneration of taste buds in fungiform papillae, had no effect on the immunohistochemical appearance of substance P in these papilla or on the substance P levels in the anterior part of the tongue. Lesions of the mandibular division of the trigeminal nerve or neonatal capsaicin treatment had no effect on the structural integrity of taste buds in fungiform papillae but led to the depletion of substance P-immunoreactive fibres from these papillae. Both of these procedures caused a 71% reduction in the substance P content of the anterior tongue, ipsilaterally after the nerve lesion and bilaterally after capsaicin treatment. The results are discussed in relation to the possible functional role of substance P-containing fibres within nerves supplying taste structures of the tongue.     

Morphology of the lingual papillae in the sitatunga

We examined the dorsal lingual surfaces of an adult sitatunga (Tragelaphus spekei) by scanning electron microscopy. Filiform, fungiform and vallate papillae were observed. The filiform papillae consisted of a larger main papilla and smaller secondary papillae. The filiform papilla contained connective tissue core consisting of several processes. The fungiform papillae were round in shape. The connective tissue core of the fungiform papilla was flower-bud shaped. Lenticular papillae were limited on the torus lingua. The connective tissue core of the lenticular papilla consisted of numerous small spines, or these spines and rod-shaped processes. The vallate papillae were flattened-oval shaped and the papillae were surrounded by a circular trench. The connective tissue core of the vallate papilla was covered with numerous small spines. These findings indicate that the tongue of the sitatunga is similar to that of the blackbuck and Barbary sheep.