Chorda tympani nerve transection at different developmental ages produces differential effects on taste bud volume and papillae morphology in the rat
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Chorda tympani nerve transection (CTX) results in morphological changes to fungiform papillae and associated taste buds. When transection occurs during neonatal development in the rat, the effects on fungiform taste bud and papillae structure are markedly more severe than observed following a comparable surgery in the adult rat. The present study examined the potential "sensitive period" for morphological modifications to tongue epithelium following CTX. Rats received unilateral transection at 65, 30, 25, 20, 15, 10, or 5 days of age. With each descending age at the time of transection, the effects on the structural integrity of fungiform papillae were more severe. Significant losses in total number of taste buds and filiform-like papillae were observed when transection occurred 5–30 days of age. Significant reduction in the number of taste pores was indicated at every age of transection. Another group of rats received chorda tympani transection at 10, 25, or 65 days of age to determine if the time course of taste bud degeneration differed depending on the age of the rat at the time of transection. Taste bud volumes differed significantly from intact sides of the tongue at 2, 8, and 50 days posttransection after CTX at 65 days of age. Volume measurements did not differ 2 days posttransection after CTX at 10 or 25 days of age, but were significantly reduced at the other time points. Findings demonstrate a transitional period throughout development wherein fungiform papillae are highly dependent upon the chorda tympani for maintenance of morphological integrity. © 2005 Wiley Periodicals, Inc. J Neurobiol, 2005Keywords:
Lingual papilla
Taste bud
Chorda
Abstract Using rat's circumvallate papillae, ATPase, alk. Pase and acid Pase of taste buds were observed after the transection of the glossopharyngeal nerve. The taste buds began to disappear after the nerve was cut and were completely lost after ten days. Following the regeneration of the glossopharyngeal nerve, taste buds reappeared from the bottom of the gutters of circumvallate papillae about 25 days after the operation. ATPase was strongly present on the cell membrane of taste bud cells as far as they existed during degeneration and regeneration. Alk. Pase, which is normally localized on the superficial layers of the epithelium overlying the gutters of circumvallate papilla, gradually diminished as the taste buds degenerated and reappeared as the taste buds regenerated; that is, the activity began to diminish three days after the operation, became feeble after ten days and reappeared after 25 days. It is concluded that taste bud cells secrete alk. Pase in the gutters of circumvallate papillae. Acid Pase activity, usually found in the supranuclear portion of taste bud cells, was intensely reactive during degeneration but did not reappear at the early stage of regeneration of taste bud cells.
Lingual papilla
Taste bud
Taste receptor
Glossopharyngeal nerve
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Major duodenal papilla
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Lingual papilla
Taste bud
Major duodenal papilla
Taste receptor
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In normal rats there is one taste bud on the apical surface of each fungiform papilla. These taste buds are innervated by the chorda tympani proper nerve (CT). According to general consensus, after cutting the nerve the taste buds should disappear. In this study, performed on 24 rats divided in six groups, the CT nerve on the left side (singly denervated) and the combined chorda-lingual (CT-L) nerve on the other side (doubly denervated were permanently interrupted. The animals were sacrificed after 5, 10, 20, 35,60 and 100 days and their tongues serially sectioned for light microscope examiation. Some papillae were examined under an electron microscope. The papillae were categorized into three groups: papillae with a normal looking taste bud, with an abnormal looking taste bud and without a taste bud. The results showed a substantial number of papillae with a normal looking taste bud present at all time intervals in all animals. More specifically, on the singly denervated side the proportion of normal looking taste buds stayed below 10% until day 60, when it increased to 15% and to 23% on day 100. The proportion of abnormal looking taste buds decreased from above 92% by day 5 to 49% on day 100. The percentage of fungiform papillae without signs of a taste bud was relatively low on the singly denervated side at times (1, 5, 16, 29, 34 and 28%). On the doubly denervated side fewer than than 4% normal looking taste buds were found throughout the time period. The proportion of abnormal looking taste buds decreased from ˜ 96% by day 5 to 35% on day 100. A significantly higher proportion of papillae with no taste bud was observed on this side from day 10 onwards. (1, 29, 32, 52, 60 and 63%). The reasons for the difference in tast bud number between the doubly and singly denervated sides are unknown, but it is possible that collaterals from other (non-gustatory) nerves have an ability, although limited, to induce and maintain fungiform taste buds. In other words, the capacity to induce taste bud formation is not limited exclusively to gustatory nerves.
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Lingual papilla
Chorda
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Major duodenal papilla
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Taste bud
Lingual papilla
Major duodenal papilla
Taste receptor
Epiglottis
Medulla
Aftertaste
Chorda
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Taste bud
Lingual papilla
Soft palate
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Abstract Taste buds and papillae in tongues of rhesus monkeys were examined and counted to determine if there are age‐related differences in general morphology or numbers of receptor organs. Tongues from 15 monkeys in five groups aged 4–31 years were studied with light microscopy. Fungiform, circumvallate, and foliate papillae were examined and taste buds in each papilla type were counted. Numbers of papillae did not differ with age through 31 years; however, at 24 years and older, fungiform papillae were reduced in number in some animals that had lost tongue tips due to trauma. There were no age‐related differences in numbers of taste buds in any of the three gustatory papilla types, nor did taste bud diameter alter with age. From data on each papilla type, estimates were made of total numbers of lingual taste buds. Totals ranged from about 8,000 to 10,000 and there were no agerelated differences. These results support other recent reports that taste buds are not decreased in number in old rats or humans. Since taste bud numbers and general morphology are maintained even in old age, any age‐related differences in taste behavior cannot be attributed to gross degenerative changes in lingual taste buds.
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The G-protein subunit alpha-gustducin, which is similar to rod transducin, has been implicated in the transduction of both sweet- and bitter-tasting substances. In rodents, there are differences in sensitivity to sweet and bitter stimuli in different populations of taste buds. Rat fungiform taste buds are more responsive to salts than to sweet stimuli, whereas those on the palate respond predominantly to sweet substances. In contrast, hamster fungiform taste buds are more sensitive to sweet-tasting stimuli. Taste buds in the vallate and foliate papillae of both species are sensitive to bitter compounds. These differences in sensitivity should be reflected in the numbers of gustducin-containing cells in different taste bud populations. We examined taste buds in the rat and hamster for immunoreactivity to an antibody against alpha-gustducin. Immunofluorescence of labeled taste cells was examined by confocal microscopy, and the cells were counted. Gustducin-positive cells were seen in all taste bud regions; they were spindle-shaped, with circular cross-sections and apical processes that extended to the taste pore. Cells with this characteristic shape in rat vallate taste buds are Type II (light) cells. In the rat, taste buds of the fungiform papillae had fewer gustducin-positive cells (3.1/taste bud) than those of other regions, including the posterior tongue and palate (>8.9/taste bud). Hamster fungiform taste buds contained twice as many gustducin-expressing cells (6.8/taste bud) as those of the rat. These data support the hypothesis that alpha-gustducin is involved in the transduction of both sweet- and bitter-tasting stimuli by mammalian taste receptor cells.
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Golden hamster
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Taste receptor
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The number of basic taste qualities registered by single human fungiform papillae is correlated with the number of taste buds borne on these papillae. Multiple sensitivity was demonstrated both in single fungiform papillae and in single taste buds, with response to all four of the basic taste qualities occurring in a single taste bud.
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Abstract Many common chemotherapeutics produce disruptions in the sense of taste which can lead to loss of appetite, nutritional imbalance, and reduced quality of life, especially if taste loss persists after treatment ends. Cyclophosphamide (CYP), an alkylating chemotherapeutic agent, affects taste sensitivity through its cytotoxic effects on mature taster receptor cells (TRCs) and on taste progenitor cell populations, retarding the capacity to replace TRCs. Mechanistic studies have focused primarily on taste cells, however, taste signaling requires communication between TRCs and the gustatory nerve fibers which innervate them. Here, we evaluate the effect of CYP on the peripheral gustatory nerve fibers that innervate the taste bud. Following histological analysis of tongue tissues, we find that CYP reduces innervation within the fungiform and circumvallate taste buds within 4-8 days after administration. To better understand the dynamics of the denervation process, we used 2-photon intravital imaging to observe the peripheral gustatory neuron arbors within individual fungiform taste buds before and after CYP treatment. We find that gustatory fibers retract from the taste bud proper but are maintained within the central papilla core. These data indicate that, in addition to TRCs, gustatory nerve fibers are also affected by CYP treatment. Because the connectivity between TRCs and gustatory neurons must be re-established for proper function, gustatory fibers should continue to be included in future studies to understand the mechanisms leading to chemotherapy-induced persistent taste loss.
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