Anatomy of the Tongue and Taste Buds

American Journal of Otolaryngology, 1983

Microscopy Research and Technique, 1993

We have examined developing taste buds in fungiform papillae of rats from the 18th day of gestation (El81 to the 15th postnatal day (P15). Nerve processes were seen in the epithelium of El8 rats before taste buds were obvious. At E20, early taste buds were visible, but were embedded within the epithelium, i.e., their cells were shielded from the oral cavity by overlying squamous epithelium. At this stage, the epithelium on the lateral aspects of the fungiform papillae was keratinized, but that overlying the taste bud was not. Some taste bud cells at E20 contained synapse-like structures near their contacts with nerve processes. In postnatal animals, keratinized epithelial cells were seen overlying taste buds, but taste pores were not observed until P10. How, then, do stimuli reach the taste cells and elicit physiological and behavioral responses as reported by others? The keratinized epithelium overlying the buds was unlike that on the lateral aspect of the papilla in at least one significant way. Few lamellated bodies were present in intercellular spaces beneath the stratum corneum, whereas these were abundant in the corresponding location within epithelium on the slope of the papilla. Although some were present within the squamous epithelium overlying the bud, they apparently were not released into the intercellular space. These lipid-rich lamellated bodies are thought to represent the water barrier of the epithelium, i.e., the barrier which prevents aqueous solutions from passing through the epithelium. We determined that the keratinized epithelium overlying the taste bud was permeable to a tracer, lanthanum nitrate, whereas that on the lateral surface was not. Lanthanum was visualized around taste cells and around nerve profiles within and near the taste bud. We propose that the absence of an aqueous permeability barrier in the epithelium overlying taste buds likely explains the ability of tastants to reach the taste bud cells and nerves in the developmental period before pore Taste bud, Taste pore, Fungiform papilla formation.

The Journal of Comparative Neurology, 1993

Innervation of the axolotl lingual epithelium by the glossopharyngeal nerve was examined to reveal its sensory target cells. The carbocyanine dye diI was applied to the nerve stump in the tongue fixed with paraformaldehyde. After a diffusion period of several months, the tongues were examined with a conventional epifluorescence microscope and a confocal laser scanning microscope (LSM) in wholemounts or preparations sectioned with a vibratome. Beneath the epithelium the labeled nerve fibers spread horizontally to form a meshwork of fibers, from which fascicles of fibers extended upward perpendicularly to the epithelium to innervate taste buds. Numerous taste buds were labeled by possible transcellular diffusion of diI. At the base of the taste bud, the nerve fibers branched and formed a basal plexus of fine fibers, on which numerous varicosities were seen. One or a t most several taste cells were labeled in a taste bud. In the basal part of taste buds, the cell without an apical process, the basal cell, was also labeled. In the epithelium, between the taste buds, a few solitary cells were labeled. In some cases, a single fascicle of fibers innervating these cells was clearly shown by the LSM. In addition, fine fibers apparently formed free nerve endings in the epithelial cell layer. The results showed that the IX nerve innervated not only taste cells, but also presumed mechanosensory basal cells in the taste bud and the solitary cells of unknown function in the non-taste lingual epithelium. Afferent nerve responses to mechanical stimulation of the tongue may be explained by these non-taste cellular elements in the epithelium.

Advances in Oto-Rhino-Laryngology, 2006

The anatomy, physiology and psychology of taste provide a glimpse into a uniquely heterogeneous sensory world; a world that is robust in its importance to flavor, redundant in its transductive heterogeneity and complexity, requisite in that feeding and hence life usually depend upon taste input, regenerative in that taste cells constantly turn over and regrow after tissue damage, and resistant to disease, loss of neural innervation and epithelial destruction. This chapter considers our current state of knowledge in anatomy, taste bud physiology, molecular biology of bitter, sweet, sour, savory and salty tastes, afferent signaling and quality coding, human perception, and pathophysiology and senescence of taste. We highlight some of the advances made in molecular biology of taste and point out areas where further research is needed ranging from taste bud development and regeneration, to within-taste bud processing, to central/perceptual coding networks for taste. Our hope is that this chapter will provide a background for greater understanding of taste physiology, perception, disease, and future sensory research.

Annals of the New York Academy of Sciences, 1989

* The authors' research summarized here was supported by grants from the National Institutes of Health (NS 20397 and NS 24884) and the National Institute of Mental Health (MH 43787). Dr. Norgren is the recipient of a Research Scientist Development Award, Level 11, also from the National institute of Mental Health (MH 00653). Receptor Subpopulation Number Percentageb InnervationC Anterior tongue Fungiform papillae 185 13.7 CT Posterior tongue Foliate papillae 460 Circumvallate papilla 350 34.2 26.0 IX IX Anterior (hard) palate Nasoincisor ducts 67 5.0 GSP Posterior (soft) palate Geshmacksstrieffen 66 Posterior palatal field 88 4.9 6.5 GSP GSP Buccal wall 46 3.4 CT

Brain Research, 1975

The pontine taste area relays gustatory intbrmation from the rostral pole of the solitary nucleus to both the thalamus and ventral forebrain. An electrophysiological investigation of this area was carried out in 3 stages. First, multiunit responses from the dorsal pons were mapped using sapid, thermal, and tactile stimuli applied to the anterior tongue. The gustatory zone lies within and just dorsal and ventral to the brachium conjunctivum as it enters the pons from the cerebellum. Second, gustatory stimuli were applied independently to the anterior and posterior tongue to determine whether receptors in both fields are represented in the pons. Responses with characteristics similar to those obtained from the glossopharyngeal nerve were located on the dorsal edge of the pontine gustatory zone. More ventrally the responses from the posterior tongue mimicked anterior tongue responses, but were of lesser amplitude than the largest anterior responses occurring at the ventral edge of the gustatory zone. Third, 71 single units were isolated in the dorsal pons, and tested for sensitivity to gustatory stimulation of the anterior and posterior tongue separately. More than half the units responded to gustatory stimuli-some from the anterior tongue alone, some from the posterior alone, but most responded to stimuli applied to either field. In the latter instance 7 of 10 units tested continued to respond after anesthetizing the chorda tympani with Xylocaine instilled into the middle ear, thus demonstrating a true glossopharyngeal input. This proves that gustatory information from two distinct receptive fields may converge on the same central neuron.

Zeitschrift f�r Zellforschung und Mikroskopische Anatomie, 1965

The taste buds of the circumvallate papillae have been examined by electron microscopy in OsOa-fixed, PTA stained material or after KMnOt fixation. The microvilli of the receptor cells have terminal dilatations which presumably give an increased surface area for transduction. The extracellular spaces at the necks of the receptor cells near the bases of the microvilli are interrupted by closed contacts. The synapses have a well defined synaptic cleft suggesting a chemical rather than an electrical mode of transmission. Synaptie membrane specialisations differ from the membrane "thickenings" of other types of synapse. Presynaptic "dense projections" are present but there is no well define postsynaptic "thickening". Vesicles occur in both pre-and postsynaptic components, but it is debatable whether or not they should be termed "synaptic vesicles".

Neuroscience, 1982

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 Iibres were closely associated with the taste buds in these structures, they assumed a perigemmal rather than an intragemmel 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.

Physiological Reviews

The tongue is a complex multifunctional organ that interacts and senses both interoceptively and exteroceptively. Although it is easily visible to almost all of us it is relatively understudied and what is in the literature as regards taste mechanisms is often contradictory or is not comprehensively reported. The tongue is both a motor and a sensory organ: motor in that it is required for speech and mastication, and sensory in that it receives information to be relayed to the central nervous system pertaining to the safety and quality of the contents of the oral cavity. Additionally, the tongue and its taste apparatus form part of an innate immune surveillance system. For example, loss or alteration in taste perception can be an early indication of infection as became evident during the present global SARS-CoV-2 pandemic. Here we particularly emphasize the latest updates in the mechanisms of taste perception, taste bud formation and adult taste bud renewal, the presence, and effects...

Egyptian Journal of Histology, 2019

Background: A correlative characterization of oral mucosa was carried out in common animal species. Objective: This work aimed to correlate the histological structure of lingual gustatory papillae as well as the immunohistochemical reactivity to a particular umami receptor among different animal species to categorize the best experimental animal models for research. Methods: The dorsal lingual mucosal specimens were obtained from four species (orders) including; chicken (Galliformes), frogs (Anura), camels (Artiodactyla) and rabbits (Lagomorpha). They were processed for routine histological examination; histochemical staining using periodic acid Schiff (PAS) and Masson's trichrome in addition to immunohistochemical localization of umami metabotropic glutamate receptor-4 (mGluR4) antibody. Results: Chicken, camels and rabbits exhibited keratinized stratified epithelium on the dorsal lingual mucosa with statistically greatest thickness in anterior lingual epithelium of chicken. For frogs, filiform and fungiform papillary walls were formed of mucous secreting columnar monolayer epithelium with a subjacent spindle cell layer. Insignificant differences in PAS staining intensity of dorsal lingual epithelium were noted between chicken anteriorly and rabbits as well as between chicken posteriorly and camels with the greatest significant intensity in frogs reflecting the highest content of glycogen and mucin. Likewise, the density of lamina propria and degree of collagen fibers bundling detected by Masson's trichrome were significantly different among species greatest in chicken and least in frogs. Intraepithelial taste buds were found in chicken while frogs displayed on top of fungiform papillae the largest gustatory disc among vertebrates. Camels and rabbits presented conventional papillary taste buds with the absence of foliate papillae in camels. Chicken and camel were negatively immunoreacted to mGluR4; frogs and rabbits were positively immunoreacted with the strongest reaction in rabbits. Conclusion: It was concluded that the direct association between histological variations of masticatory lingual mucosa and diverse environmental factors would reflect the adaptation capability of the lingual tissue.