Embryonic taste buds develop in the absence of innervation

Development ◽  
1996 ◽  
Vol 122 (4) ◽  
pp. 1103-1111 ◽  
Author(s):  
L.A. Barlow ◽  
C.B. Chien ◽  
R.G. Northcutt
Keyword(s):  
Embryonic Development ◽  
Taste Receptor ◽  
Nerve Fibers ◽  
Taste Buds ◽  
Taste Bud ◽  
Taste Cells ◽  
Experimental Approaches ◽  
Well Differentiated ◽  
Serotonin Immunoreactivity

It has been hypothesized that taste buds are induced by contact with developing cranial nerve fibers late in embryonic development, since descriptive studies indicate that during embryonic development taste cell differentiation occurs concomitantly with or slightly following the advent of innervation. However, experimental evidence delineating the role of innervation in taste bud development is sparse and equivocal. Using two complementary experimental approaches, we demonstrate that taste cells differentiate fully in the complete absence of innervation. When the presumptive oropharyngeal region was taken from a donor axolotl embryo, prior to its innervation and development of taste buds, and grafted ectopically on to the trunk of a host embryo, the graft developed well-differentiated taste buds. Although grafts were invaded by branches of local spinal nerves, these neurites were rarely found near ectopic taste cells. When the oropharyngeal region was raised in culture, numerous taste buds were generated in the complete absence of neural elements. Taste buds in grafts and in explants were identical to those found in situ both in terms of their morphology and their expression of calretinin and serotonin immunoreactivity. Our findings indicate that innervation is not necessary for complete differentiation of taste receptor cells. We propose that taste buds are either induced in response to signals from other tissues, such as the neural crest, or arise independently through intrinsic patterning of the local epithelium.

A paracrine signaling role for serotonin in rat taste buds: expression and localization of serotonin receptor subtypes

2004 ◽  
Vol 286 (4) ◽  
pp. R649-R658 ◽  
Author(s):  
Namik Kaya ◽  
Tiansheng Shen ◽  
Shao-gang Lu ◽  
Fang-li Zhao ◽  
Scott Herness
Keyword(s):  
Serotonin Receptor ◽  
Taste Receptor ◽  
Nerve Fibers ◽  
Taste Buds ◽  
Taste Bud ◽  
Receptor Subtype ◽  
Receptor Subtypes ◽  
Double Labeling ◽  
Receptor Cells ◽  
Taste Receptor Cells

Recent advances in peripheral taste physiology now suggest that the classic linear view of information processing within the taste bud is inadequate and that paracrine processing, although undemonstrated, may be an essential feature of peripheral gustatory transduction. Taste receptor cells (TRCs) express multiple neurotransmitters of unknown function that could potentially participate in a paracrine role. Serotonin is expressed in a subset of TRCs with afferent synapses; additionally, TRCs respond physiologically to serotonin. This study explored the expression and cellular localization of serotonin receptor subtypes in TRCs as a possible route of paracrine communication. RT-PCR was performed on RNA extracted from rat posterior taste buds with 14 primer sets representing 5-HT1 through 5-HT7 receptor subtype families. Data suggest that 5-HT1A and 5-HT3 receptors are expressed in taste buds. Immunocytochemistry with a 5-HT1A-specific antibody demonstrated that subsets of TRCs were immunopositive for 5-HT1A. With the use of double-labeling, serotonin- and 5-HT1A-immunopositive cells were observed exclusively in nonoverlapping populations. On the other hand, 5-HT3-immunopositive taste receptor cells were not observed. This observation, combined with other data, suggests 5-HT3 is expressed in postsynaptic neural elements within the bud. We hypothesize that 5-HT release from TRCs activates postsynaptic 5-HT3 receptors on afferent nerve fibers and, via a paracrine route, inhibits neighboring TRCs via 5-HT1A receptors. The role of the 5-HT1A-expressing TRC within the taste bud remains to be explored.

Combining HVEM and computer-assisted reconstructions to elucidate the three-dimensional structure of taste buds

1987 ◽  
Vol 45 ◽  
pp. 584-587
Author(s):  
John C. Kinnamon
Keyword(s):  
Developmental Process ◽  
Sensory Nerve ◽  
Nerve Fibers ◽  
Taste Buds ◽  
Taste Bud ◽  
Dimensional Structure ◽  
Computer Assisted ◽  
Oral Epithelium ◽  
Synaptic Connections ◽  
Taste Cells

The vertebrate taste bud contains 50 to 150 spindle-shaped cells assembled in an onion-shaped structure approximately 60 μm wide and 80-100 μm tall. Located on the tongue and other portions of the oral epithelium, taste buds are always in a state of flux, with new cells continually entering the bud and moving from the periphery to the core as they mature. During the developmental process, young taste cells form afferent synaptic connections with sensory nerve fibers which enter the taste bud at the base and course tortuously throughout the bud. As taste cells age and become senescent, they lose their synaptic connections with the nerve fibers, degenerate, and eventually disappear. All of the processes described above result in the complete turnover of the cells within a taste bud in a period of from 10 days to two weeks in the rat.

Taste buds develop autonomously from endoderm without induction by cephalic neural crest or paraxial mesoderm

Development ◽  
1997 ◽  
Vol 124 (5) ◽  
pp. 949-957 ◽  
Author(s):  
L.A. Barlow ◽  
R.G. Northcutt
Keyword(s):  
Epithelial Cells ◽  
Neural Crest ◽  
Explant Culture ◽  
Nerve Fibers ◽  
Taste Buds ◽  
Paraxial Mesoderm ◽  
Culture Techniques ◽  
Well Differentiated ◽  
Neural Crest Migration

Although it had long been believed that embryonic taste buds in vertebrates were induced to differentiate by ingrowing nerve fibers, we and others have recently shown that embryonic taste buds can develop normally in the complete absence of innervation. This leads to the question of which tissues, if any, induce the formation of taste buds in oropharyngeal endoderm. We proposed that taste buds, like many specialized epithelial cells, might arise via an inductive interaction between the endodermal epithelial cells that line the oropharynx and the adjacent mesenchyme that is derived from both cephalic neural crest and paraxial mesoderm. Using complementary grafting and explant culture techniques, however, we have now found that well-differentiated taste buds will develop in tissue completely devoid of neural crest and paraxial mesoderm derivatives. When the presumptive oropharyngeal region was removed from salamander embryos prior to the onset of cephalic neural crest migration, taste buds developed in grafts and explants coincident with their appearance in intact control embryos. Similarly, explants from neurulae in which movement of paraxial mesoderm had not yet begun also developed taste buds after 9–12 days in vitro. We conclude that neither cranial neural crest nor paraxial mesoderm is responsible for the induction of embryonic taste buds. Surprisingly, the ability to develop taste buds late in embryonic development seems to be an intrinsic feature of the oropharyngeal endoderm that is determined by the completion of gastrulation.

scholarly journals Expression of Taste Receptor 2 Subtypes in Human Testis and Sperm

2020 ◽  
Vol 9 (1) ◽  
pp. 264 ◽  
Author(s):  
Laura Governini ◽  
Bianca Semplici ◽  
Valentina Pavone ◽  
Laura Crifasi ◽  
Camilla Marrocco ◽  
...  
Keyword(s):  
Taste Receptor ◽  
Receptor Activation ◽  
Taste Buds ◽  
The Body ◽  
Semen Parameters ◽  
Human Testis ◽  
Taste Receptors ◽  
Organ Systems

Taste receptors (TASRs) are expressed not only in the oral cavity but also throughout the body, thus suggesting that they may play different roles in organ systems beyond the tongue. Recent studies showed the expression of several TASRs in mammalian testis and sperm, indicating an involvement of these receptors in male gametogenesis and fertility. This notion is supported by an impaired reproductive phenotype of mouse carrying targeted deletion of taste receptor genes, as well as by a significant correlation between human semen parameters and specific polymorphisms of taste receptor genes. To better understand the biological and thus clinical significance of these receptors for human reproduction, we analyzed the expression of several members of the TAS2Rs family of bitter receptors in human testis and in ejaculated sperm before and after in vitro selection and capacitation. Our results provide evidence for the expression of TAS2R genes, with TAS2R14 being the most expressed bitter receptor subtype in both testis tissue and sperm cells, respectively. In addition, it was observed that in vitro capacitation significantly affects both the expression and the subcellular localization of these receptors in isolated spermatozoa. Interestingly, α-gustducin and α-transducin, two Gα subunits expressed in taste buds on the tongue, are also expressed in human spermatozoa; moreover, a subcellular redistribution of both G protein α-subunits to different sub-compartments of sperm was registered upon in vitro capacitation. Finally, we shed light on the possible downstream transduction pathway initiated upon taste receptor activation in the male reproductive system. Performing ultrasensitive droplets digital PCR assays to quantify RNA copy numbers of a distinct gene, we found a significant correlation between the expression of TAS2Rs and TRPM5 (r = 0.87), the cation channel involved in bitter but also sweet and umami taste transduction in taste buds on the tongue. Even if further studies are needed to clarify the precise functional role of taste receptors for successful reproduction, the presented findings significantly extend our knowledge of the biological role of TAS2Rs for human male fertility.

scholarly journals Identification of electrophysiologically distinct cell subpopulations in Necturus taste buds.

1993 ◽  
Vol 102 (1) ◽  
pp. 143-170 ◽  
Author(s):  
A Bigiani ◽  
S D Roper
Keyword(s):  
Lucifer Yellow ◽  
Taste Buds ◽  
Taste Bud ◽  
Basal Cells ◽  
Patch Clamp Technique ◽  
Lingual Epithelium ◽  
Voltage Gated ◽  
Receptor Cells ◽  
Taste Cells ◽  
K Currents

We used the patch clamp technique to record from taste cells in thin transverse slices of lingual epithelium from Necturus maculosus. In this preparation, the epithelial polarity and the cellular organization of the taste buds, as well as the interrelationships among cells within the taste bud, were preserved. Whole-cell recording, combined with cell identification using Lucifer yellow, allowed us to identify distinct subpopulations of taste cells based on their electrophysiological properties. Receptor cells could be divided in two groups: one group was characterized by the presence of voltage-gated Na+, K+, and Ca2+ currents; the other group was characterized by the presence of K+ currents only. Therefore, receptor cells in the first group would be expected to be capable of generating action potentials, whereas receptor cells in the second group would not. Basal taste cells could also be divided into two different groups. Some basal cells possessed voltage-gated Na+, K+, and Ca2+ conductances, whereas other basal cells only had K+ conductance. In addition to single taste cells, we were able to identify electrically coupled taste cells. We monitored cell-cell coupling by measuring membrane capacitance and by observing Lucifer yellow dye coupling. Electrical coupling in pairs of dye-coupled taste receptor cells was strong, as indicated by experiments with the uncoupling agent 1-octanol. Electrically coupled receptor cells possessed voltage-gated currents, including Na+ and K+ currents. The electrophysiological differentiation among taste cells presumably is related to functional diversifications, such as different chemosensitivities.

Specification of pharyngeal endoderm is dependent on early signals from axial mesoderm

Development ◽  
2001 ◽  
Vol 128 (22) ◽  
pp. 4573-4583
Author(s):  
Linda A. Barlow
Keyword(s):  
Embryonic Development ◽  
Taste Buds ◽  
Taste Bud ◽  
General View ◽  
Bud Development ◽  
Pharyngeal Endoderm ◽  
Prechordal Mesoderm

The development of taste buds is an autonomous property of the pharyngeal endoderm, and this inherent capacity is acquired by the time gastrulation is complete. These results are surprising, given the general view that taste bud development is nerve dependent, and occurs at the end of embryogenesis. The pharyngeal endoderm sits at the dorsal lip of the blastopore at the onset of gastrulation, and because this taste bud-bearing endoderm is specified to make taste buds by the end of gastrulation, signals that this tissue encounters during gastrulation might be responsible for its specification. To test this idea, tissue contacts during gastrulation were manipulated systematically in axolotl embryos, and the subsequent ability of the pharyngeal endoderm to generate taste buds was assessed. Disruption of both putative planar and vertical signals from neurectoderm failed to prevent the differentiation of taste buds in endoderm. However, manipulations of contact between presumptive pharyngeal endoderm and axial mesoderm during gastrulation indicate that signals from axial mesoderm (the notochord and prechordal mesoderm) specify the pharyngeal endoderm, conferring upon the endoderm the ability to autonomously differentiate taste buds. These findings further emphasize that despite the late differentiation of taste buds, the tissue-intrinsic mechanisms that generate these chemoreceptive organs are set in motion very early in embryonic development.

scholarly journals Electron Microscopic Observations on the Taste Buds of the Rabbit

1958 ◽  
Vol 4 (2) ◽  
pp. 143-150 ◽  
Author(s):  
A. J. de Lorenzo
Keyword(s):  
Plasma Membranes ◽  
Supporting Cell ◽  
Nerve Fibers ◽  
Taste Buds ◽  
Taste Bud ◽  
Electron Microscopic ◽  
Gustatory Receptors ◽  
Sustentacular Cells ◽  
Granular Cytoplasm ◽  
Dense Substance

An examination of the fine structure of the taste buds in the rabbit was undertaken. Gustatory epithelium was fixed in OsO4 or 1 per cent KMnO4 solution, containing polyvinylpyrrolidone (PVP). Thick sections were examined in the phase microscope and contiguous sections prepared for the electron microscope. The bud contains two types of cells, gustatory receptors and sustentacular cells. The receptors are characterized by a dark nucleus and densely granular cytoplasm. The apical processes bear numerous microvilli which extend into the taste pore. Imbedded between the microvilli there is a dense substance, which is also present in the apical cytoplasm of the receptors. The sustentacular cells contain a large pale nucleus and less dense cytoplasm. Their basal surfaces rest upon a basement membrane. The subepithelial nerve plexuses comprise the fibers which innervate the gustatory receptors. The nerve fibers vary in diameter from 500 A to 0.3 µ, and are ensheathed by Schwann cells. The intragemmal fibers enter the taste bud between adjacent cells, and are ensheathed by the plasma membranes of the supporting cell until they synapse upon the gustatory cell. The synaptic terminals contain synaptic vesicles, which at this junction reside in the postsynaptic element. This observation is discussed with reference to synapses described elsewhere in the nervous system.

scholarly journals Proton currents through amiloride-sensitive Na channels in hamster taste cells. Role in acid transduction.

1992 ◽  
Vol 100 (5) ◽  
pp. 803-824 ◽  
Author(s):  
T A Gilbertson ◽  
P Avenet ◽  
S C Kinnamon ◽  
S D Roper
Keyword(s):  
Citric Acid ◽  
Taste Receptor ◽  
Taste Bud ◽  
Disulfonic Acid ◽  
Dependent Manner ◽  
Na Channels ◽  
Transient Currents ◽  
Receptor Cells ◽  
Taste Cells ◽  
Taste Receptor Cells

The activity of taste cells maintained in the intact hamster tongue was monitored in response to acid stimulation by recording action currents from taste receptor cells with an extracellular "macro" patch pipette: a glass pipette was pressed over the taste pore of fungiform papillae and perfused with citric acid, hydrochloric acid, or NaCl. Because this technique restricted stimulus application to the small surface area of the apical membranes of the taste cells, many nonspecific, and potentially detrimental, effects of acid stimulation could be avoided. Acid stimulation reliably elicited fast transient currents (action currents of average amplitude, 9 pA) which were consistently smaller than those elicited by NaCl (29 pA). The frequency of action currents elicited by acid stimuli increased in a dose-dependent manner with decreasing pH from a threshold of about pH 5.0. Acid-elicited responses were independent of K+, Na+, Cl-, or Ca2+ at physiological (salivary) concentrations, and were unaffected by anthracene-9-carboxylic acid, tetraethylammonium bromide, diisothiocyanate-stilbene-2,2'-disulfonic acid, vanadate, or Cd2+. In contrast, amiloride (< or = 30 microM) fully and reversibly suppressed acid-evoked action currents. At submaximal amiloride concentrations, the frequency and amplitude of the action currents were reduced, indicating a reduction of the taste cell apical conductance concomitant with a decrease in cell excitation. Exposure to low pH elicited, in addition to transient currents, an amiloride-sensitive sustained d.c. current. This current is apparently carried by protons instead of Na+ through amiloride-sensitive channels. When citric acid was applied while the taste bud was stimulated by NaCl, the action currents became smaller and the response resembled that produced by acid alone. Because of the strong interdependence of the acid and salt (NaCl) responses when both stimuli are applied simultaneously, and because of the similarity in the concentration dependence of amiloride block, we conclude that amiloride-sensitive Na+ channels on hamster taste receptor cells are permeable to protons and may play a role in acid (sour) taste.

Acid-Sensitive Two-Pore Domain Potassium (K2P) Channels in Mouse Taste Buds

2004 ◽  
Vol 92 (3) ◽  
pp. 1928-1936 ◽  
Author(s):  
Trevor A. Richter ◽  
Gennady A. Dvoryanchikov ◽  
Nirupa Chaudhari ◽  
Stephen D. Roper
Keyword(s):  
Ion Channels ◽  
Potassium Channels ◽  
Taste Receptor ◽  
Taste Buds ◽  
Confocal Imaging ◽  
Intracellular Acidification ◽  
Pharmacological Characterization ◽  
Taste Cells ◽  
Pore Domain ◽  
And Task

Sour (acid) taste is postulated to result from intracellular acidification that modulates one or more acid-sensitive ion channels in taste receptor cells. The identity of such channel(s) remains uncertain. Potassium channels, by regulating the excitability of taste cells, are candidates for acid transducers. Several 2-pore domain potassium leak conductance channels (K2P family) are sensitive to intracellular acidification. We examined their expression in mouse vallate and foliate taste buds using RT-PCR, and detected TWIK-1 and -2, TREK-1 and -2, and TASK-1. Of these, TWIK-1 and TASK-1 were preferentially expressed in taste cells relative to surrounding nonsensory epithelium. The related TRESK channel was not detected, whereas the acid-insensitive TASK-2 was. Using confocal imaging with pH-, Ca2+-, and voltage-sensitive dyes, we tested pharmacological agents that are diagnostic for these channels. Riluzole (500 μM), selective for TREK-1 and -2 channels, enhanced acid taste responses. In contrast, halothane (≤ ∼17 mM), which acts on TREK-1 and TASK-1 channels, blocked acid taste responses. Agents diagnostic for other 2-pore domain and voltage-gated potassium channels (anandamide, 10 μM; Gd3+, 1 mM; arachidonic acid, 100 μM; quinidine, 200 μM; quinine, 100 mM; 4-AP, 10 mM; and TEA, 1 mM) did not affect acid responses. The expression of 2-pore domain channels and our pharmacological characterization suggest that a matrix of ion channels, including one or more acid-sensitive 2-pore domain K channels, could play a role in sour taste transduction. However, our results do not unambiguously identify any one channel as the acid taste transducer.

Mouse mandibular retromolar taste buds associated with a mucus salivary gland

2021 ◽  
Author(s):  
Quan T Nguyen ◽  
Grace E Beck Coburn ◽  
Amber Valentino ◽  
Bekir Karabucak ◽  
Marco Tizzano
Keyword(s):  
Salivary Gland ◽  
Fluorescent Protein ◽  
Minor Salivary Gland ◽  
Immunohistochemical Analysis ◽  
Taste Buds ◽  
Taste Bud ◽  
Neuronal Marker ◽  
Taste Cells ◽  
Green Fluorescent ◽  
A Minor

Abstract We have characterized a recently rediscovered chemosensory structure at the rear of the mandibular mucosa in the mouse oral cavity originally reported in the 1980s. This consists of unorganized taste buds, not contained within troughs, associated with the ducts of an underlying minor salivary gland. Using whole-mount preparations of transgenic mice expressing green fluorescent protein under the promoter of taste-signaling-specific genes, we determined that the structure contains taste bud clusters and salivary gland orifices at the rear of each mandible, distal to the last molar and anterior to the ascending ramus. Immunohistochemical analysis show in the retromolar taste buds expression of the taste receptors Tas2R131 and T1R3 and taste cascade molecules TrpM5, PLCβ2, and GNAT3, consistent with type II taste cells, and expression of GAD1, consistent with type III taste cells. Furthermore, the neuronal marker CGRP in retromolar mucosa tissue wrapping around TrpM5+ taste buds was observed. RT-PCR showed that retromolar taste buds express all three mouse tas1r genes, 28 of the 35 tas2r genes, and taste transduction signaling genes gnat3, plcb2, and trpm5, making the retromolar TBs similar to other lingual and palate taste buds. Finally, histochemistry demonstrated that the mandibular retromolar secretory gland is a minor salivary gland of mucous type. The mandibular retromolar taste structure may thus play a role in taste sensation and represent a potential novel pharmacological target for taste disorders.

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