Leucine-enkephalin-, neurokinin A- and cholecystokinin-like immunoreactivities in the guinea pig tongue

The occurrence of these neuropeptides was examined by immunofluorescence. Leu-Enk-like immunoreactivity was seen in nerve fibres associated with the epithelium, blood vessels and lingual salivary glands as well as in ganglionic cells within the tongue. Neuropeptide A-like immunoreactivity was found in nerve fibres associated with the epithelium, taste buds, blood vessels and lingual salivary glands. Cholecystokinin-like immunoreactivity was found in some nerve fibres around blood vessels as well as in ganglionic cells. The coexistence of these neuropeptides and substance P was also demonstrated in some nerve fibres and ganglionic cells within the tongue. Like substance P, these neuropeptides could be involved in blood flow regulation, salivation and as trophic factors for taste buds.

Lipid characterization and 14C-acetate metabolism in catfish taste epithelium

The catfish, Ictalurus punctatus is an important model system for the study of the biochemical mechanisms of taste reception. A detailed lipid analysis of epithelial tissue from the taste organ (barbel) of the catfish has been performed. Polar lipids account for 62 +/- 1% of the total, neutrals for 38 +/- 1%. Phosphatidyl-cholines, serines and ethanolamines are the major constituents of the polar fraction. Plasmalogen concentration is high relative to that of non-neural tissues. [14C]-Acetate is incorporated into cell lipid fractions after incubation of barbel tissue at 37 degrees C for 60 min. Percentage amounts of most lipids change with time during this in vitro incubation. The phospholipids are the most metabolically active fractions. This work yields information for continuing reconstitution experiments and indicates that the taste epithelium of this important model system is a metabolically active tissue capable of supporting lipid turnover/synthesis.

Lectin cytochemistry of the dark granules in the type 1 cells of Syrian hamster circumvallate taste buds

Lectin-gold complexes in the dark granules (DGs) and the dense substance (DS) of vallate taste buds were localized. Both the DGs and the DS were labelled with wheat-germ agglutinin, Ulex europeus agglutinin-I and peanut agglutinin. Their common reaction to these lectins suggested that the DGs contain carbohydrate components similar to those of the DS. The results provide cytochemical evidence that the DS in the taste pit represents, at least in part, the content of the DGs in the type 1 cells.

A comparative study of three methods for the estimation of total plasmalogens in lingual taste epithelium and other tissues

The total plasmalogen content of lingual and other tissues was analyzed using the iodine-addition (Method 1), the p-nitrophenylhydrazone (Method 2), and the two-dimensional thin layer chromatography procedure (Method 3). Methods 1 and 2 were simple, rapid and reproducible, yielding values usually in close agreement with each other, and values higher than those of Method 3. Method 3 exhibited poor reproducibility. All three methods were of comparable sensitivity (less than 20 nmol of total plasmalogen per sample). According to Methods 1 and 2, there was more total plasmalogen in lingual epithelium containing taste buds compared with lingual epithelium devoid of taste buds. Plasmalogen content of bovine and rat brain, heart and liver agreed with literature values.

Immunohistochemical localization of keratin in the taste buds of rat vallate papillae

Keratin detected with anti-human whole keratin serum, raised in rabbits by injection of the isolated human whole keratin, was used as a histologic marker to study the origin of the cells in taste buds. Rat vallate papillae, including surrounding tissue, were processed for indirect immunofluorescent staining of ketatin. In the taste buds, most basal cells and some of the elongated cells were immunoreactive with anti-keratin serum, showing that most taste-bud cells, if not all, originate from cells of epithelial origin.

[The presence of calmodulin in chemosensory structures, its purification and content]

Chemosensory tissues, bovine olfactory epithelium and barbel of dwarf sheat-fish (Ictalurus nebulosus) rich in gustatory buds were shown to contain calmodulin. The fraction of thermostable proteins which activate brain phosphodiesterase of cyclic nucleotides was purified to homogeneity by stepwise ion-exchange chromatography on DEAE-cellulose and gel filtration on Sephacryl S-300. Some properties of calmodulin from chemosensory tissues (e. g., content, molecular weight, electrophoretic mobility, degree of activation of phosphodiesterase) are similar to those of brain calmodulin.

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.

Influence of innervation on the levels of noradrenaline and serotonin in the circumvallate papilla of the rat

The levels and the distribution of monoamines within the rat circumvallate papilla have been studied. Noradrenaline was found in the connective tissue underlying the taste buds, whereas serotonin was located in the basal area of the gustatory epithelium but not inside the taste buds. Following denervation, noradrenaline levels decreased and serotonin levels increased. These results suggest that both neurotransmitters may have some mutual interaction in modulating transmission at the papilla.

[Lingual taste buds following application of colchicine to the glossopharyngeal nerve in the rat]

Dissection of the glossopharyngeal nerve and application to it of colchicine that blocks axoplasmic drug transport were performed to study the effect of the nerves on the taste buds of foliate lingual papillae. It was observed that colchicine application to the nerve gave rise to destruction of the taste buds. The process of destruction proceeded more slowly as compared to that induced by nerve dissection. Colchicine application led to changes in the protein spectrum of the epithelium of foliate papillae. The absence of changes in the protein spectrum of the epithelium of foliate papillae and the presence of nerve fibers in the epithelium of the taste buds on exposure to colchicine provide evidence against its direct toxic effect on the taste buds, giving rise to their destruction. The changes seen in the taste buds result from the blocked transport of factors that participate in neurotropic control of the taste buds.

The occurrence of taste buds in the palate of human adults as evidenced by light microscopy

There is some uncertainty in the literature as to the existence of taste buds in the palate of the human adult. In those histologic studies in which the ages of the individuals have been reported, taste buds have not been found in the palates of adults, but have been found in fetuses or newborn. However, clinical studies have demonstrated taste perception in the palate of the human adult. Thus, the aim of the present study was to attempt to find taste buds in the human palate in subjects of different ages. In serial sections of selected areas of the palatal mucosa from autopsy material from individuals 0--80 years of age no taste buds could be demonstrated. However, in four of seven subjects aged 25--44 years, one or two taste buds were found in biopsies from areas of the soft palate where taste perception had been demonstrated clinically just prior to excision. Thus the present study indicates that scattered taste buds exist also in the soft palate of human adults.

Location of taste buds in intact taste papillae by a selective staining method

Taste buds were found to stain strongly and selectively in intact papillae with highly acidic dyes such as ponceau S. In intact tongues the taste buds in the fungiform, circumvallate and foliate papillae of the cynomolgus monkey and in the fungiform papillae of the rat as well as the taste discs in the fungiform papillae of the frog could be visualized. This method enables a rapid location and counting of taste buds in taste papillae without preparing histological sections. In cynomolgus tongue material fixed in formalin, the dyes penetrate into the buds. In fresh tongues only the taste pore region of the buds stains, which suggests that in vivo taste buds are impenetrable underneath the pore.

Three-dimensional mapping of the sweet taste receptor site

The active sites of the receptors for sweet and bitter tastants are shown to be related by a simple symmetry operation. This relationship, in turn, allows the identification of the critical geometrical features of both receptor sites. The model proposed for the sweet site is shown to be consistent with a large number of (conformationally rigid) sweet molecules.

Histochemical studies on the mucins of the vertebrate tongues. XI. Histochemical analysis of mucosubstances in the lingual glands and taste buds of some birds

The tongues of six birds were investigated histochemically to determine the distribution and nature of mucosubstances in the lingual glands and taste buds. The anterior lingual glands in sparrow, kingfisher, parrot and pigeon hawk contained only one type of cells (seromucous) elaborating a mixture of neutral mucosubstances, sialomucins and sulfomucins. The anterior lingual glands in fowl and owl contained three distinct types of cells elaborating separately neutral mucosubstances, sialomucins and sulfomucins. The posterior lingual glands in most of the birds investigated except fowl contained only seromucous cells identical to the cells in the anterior lingual glands, while in fowl two distinct cell types were identified: one elaborating sulfomucins and the other sialomucins. Taste buds were found to be restricted in the glandular areas of the tongue in all the birds and always in close association with the gland ducts. Special adenomere cavities were seen only in the tongue of sparrow.

Pharmaco-histochemical studies on a specific monoamine in the gustatory epithelia of the rabbit

The foliate, vallate and fungiform papillae of the rabbit's tongue were studied fluorescence-histochemically under normal and experimental conditions. In normal animals a yellow fluorescence suggesting the presence of a serotonin-like monoamine was demonstrated only in taste bud cells of the foliate papilla, though its intensity was very weak. The fluorescence disappeared completely following reserpine treatment, while it was significantly enhanced by the treatment with nialamide. The fluorescence of taste bud cells could be clearly distinguished from that of catecholamines by the treatment with alpha-MMT followed by nialamide. When 5-HTP, 5-HT and 5,6-DHT were administered separately, each of these drugs was selectively taken up in taste bud cells of the foliate and vallate papillae, but no fluorescent cells were observed in the fungiform papilla. From the present results, it seems reasonable to conclude that the fluorigenic amine of taste bud cells may be 5-HT (serotonin), or at least an indoleamine derivative. Also, it is suggested that the taste bud of the vallate papilla contains a cell type which can potentially synthesize a biogenic amine in situ, or is actually synthesizing it in a very small amount just like in the case of the taste bud of the foliate one.

Histochemical studies on the mucins of the vertebrate tongues. VII. Histochemical analysis of mucosubstances in the tongues of some fishes

The tongues of three fishes were investigated histochemically to determine the distribution and nature of mucosubstances by employing recent techniques and the results were considered comparatively with the lingual mucosubstances of other vertebrates. A heterogenous distribution of neutral mucosubstances, sulfomucins and sialomucins in various lingual sites was noted. The taste buds and/or free nerve endings were found to be restricted in the areas containing abundance of goblet cells. In non-gustatory areas of tongue, the goblet cells were very few or absent. Importance of lingual histology in establishing phylogenetic relationships and the possible functional significance of the mucosubstances in the physiology of gustation is discussed in detail.

Specific effect of 5,6-dihydroxytryptamine on the monoamine fluorophore of the frog's gustatory cells

A specific formaldehyde-induced yellow fluorescence, suggesting the presence of serotonin-like monoamine has been demonstrated in the gustatory cells of the frog. The fungiform papillae of frogs were examined fluorescence-histochemically after intraperitoneal injection of 5,6-dihydroxytryptamine. The results indicated that the fluorophore of gustatory cells was affected selectively by the drug injection: the yellow fluorescence was transiently enhanced 3 hours after the drug injection, thereafter being reduced rapidly. The effect of 5,6-dihydroxytryptamine was long-lasting with the reduction of the yellow fluorophore persisting at least for the experimental duration of 14 days. A single injection of 6-hydroxydopamine induced a complete depletion of noradrenaline fluorescence from adrenergic nerve terminals, while the fluorescence of gustatory cells was not affected by a high dose of the drug. The present results with pharmacologic treatments further support the view that the gustatory cell of the frog contains a serotonin-like monoamine.

The occurrence of the cell type containing a specific monoamine in the taste bud of the rabbit's foliate papila

The fluorescence histochemical examination on biogenic amines of the rabbit's foliate papilla revealed that a specific monoamine exhibiting an yellow fluorescence was present in a certain cell type of taste buds. The fluorescence had the emission maximum at 520 mmu and faded rapidly under the influence of the UV-irradiation. The green fluorescence of adrenergic nerve had the emission maximum at 480 mmu and was fairly stable upon the UV-irradiation. The yellow fluorescence disappeared completely following reserpine treatment, while it was markedly enhanced by nialamide treatment. From the observations, it is suggested that certain taste bud cells of the foliate papilla contain a biogenic monoamine, probably 5-hydroxytryptamine (serotonin).

A monoamine in the gustatory cell of the frog's taste organ: a fluorescence histochemical and electron microscopic study

Fluorescence histochemistry reveals that in the frog's taste organ a yellow fluorescence is regularly observed at the most basal region of the sensory epithelium. The fluorescence has a strong intensity, but it fades rapidly upon the UV-irradiation. The peak of the emission spectrum is at 520 mmug. Following reserpine treatment the yellow fluroescence is markedly reduced, but not depleted completely. From these characteristics the monoamine fluorescence is regarded as representing 5-HT (serotonin). The ultrastructural study on sensory epithelia shows that the terminal portions of gustatory cell processes are localized at the basal region. These portions are filled with dense cored vesicles (700-1000 angstrom in diameter) and frequently opposed with nerve fibers penetrating into the epithelium. The gustatory cell processes are also interposed between the terminal portions of nerve fibers. The cytoplasm of the gustatory cell process is characterized by many mitochondria, fine filaments and glycogen particles, but contains few cored vesicles. The distribution of terminal portions of gustary cell processes seems to correspond fairly well to that of the monoamine fluorescence observed discontinuously along the basal lamina. Accordingly it is concluded that the fluorigenic monoamine is localized in the cored vesicles of the gustatory cell.

Fine structure of taste buds in the rat

The taste buds of rat circumvallate papillae contain three distinct types of cells. The type I (dark) cell is characterized by the presence of dense round granules, which are precursor to the dense substance of the taste pore. The granules are discharged into the pore by exocytosis. The type II (light) cell is filled with numerous vesicles and smooth-surfaced endoplasmic reticulum. The type III cell contains in its basal cytoplasm characteristic dark-cored vesicles and masses of clear vesicles, and makes synapse-like contacts with nerve fibers. The fine structure of foliate buds corresponds to that of circumvallate papillae, while fungiform buds differ in their apical regions. In the latter the pore is filled with vesicles alone, and the type I cell contains rod-shaped granules of moderate density. When polysaccharides were examined by means of the periodic acid-silver methenamine and the periodic acid-thiocarbohydrazide methods, slightly positive reactions were found on the dense granules of the type I cell and the dense substance in the pore, whereas the membranes of the pore vesicles, apical cytoplasmic processes and cytoplasmic vesicles in type II cells showed intense reactions.

The effect of transection of the glossopharyngeal nerve upon the structure, cholinesterase activity and innervation of taste buds in rabbits

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Disc electrophoresis of extracts from the taste buds located in circumvallate papillae of rat tongues

The epithelium of the circumvallate papillae of rat tongues was stripped off by treatment with 0.005% elastase in a state when many taste buds were present. The taste buds were isolated from the stripped epithelium by further treatment with 0.005% elastase and 0.08% trypsin. A protein which was thought to be characteristic of taste buds was found from semimicro disc polyacrylamide gel electrophoretic studies of the stripped epithelia with and without taste buds. This result was supported by micro disc polyacrylamide gel electrophoretic studies of isolated taste buds.

Sweet-sensitive protein from bovine taste buds: isolation and assay

Using refractometry and ultraviolet-difference spectroscopy to indicate interaction between proteins and coinpounds of low molecular weight, we found a protein fraction in bovine tongue extracts that coinplexes sugars and saccharin. The strengths of the coinzplexes parallel the degrees of sweetness of the compounds, and the effects of pH upon formation of complexes parallel the effects of pH upon sensitivity of taste buds to sweet compounds in vivo.