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PubMed1990

Possible role for salivary gland protein in taste reception indicated by homology to lipophilic-ligand carrier proteins.

Sensory transduction in taste and olfaction, the principal chemical senses, seems to be mediated by membrane-associated proteins on the apical surfaces of the respective receptor cells. The recent isolation and characterization of soluble 'odorant-binding proteins' secreted from the nasal glands of rat, cow and frog, led to the hypothesis that these proteins function as necessary cofactors in olfactory transduction by concentrating and delivering odorants to the receptors. The primary reception of taste stimuli occurs in specialized neuroepithelial receptor cells bundled in taste buds that are clustered in various types of papillae in the lingual epithelium of the tongue. Small tubulo-alveolar salivary glands, the von Ebner's glands, are located beneath the circumvallate and the foliate papillae. Their ducts open exclusively into the trough at the base of the papillae. Taste buds located in the medial and lateral walls of the papillae open with their taste pores into the trough and consequently are in direct contact with the secretions of von Ebner's glands. Here we report the molecular cloning and characterization of a protein of relative molecular mass 18,000 that is highly expressed in von Ebner's glands. Like the odorant-binding proteins, this protein shows similarity to members of a protein superfamily of hydrophobic molecule transporters, indicating that pre-receptor events could also be necessary for the concentration and delivery of sapid molecules in the gustatory system, and emphasizing the close relationship of taste and olfaction.

Amino Acid Sequence↗
PubMed1999

Depressed taste and smell in geriatric patients.

BACKGROUND: Geriatric patients have a number of dental care problems that younger patients do not encounter. The oral changes associated with aging can have a significant effect on the efficacy of dental treatment. TYPES OF STUDIES REVIEWED: The authors reviewed studies dealing with the causes of depressed sense of taste and smell; the causes included aging, disease, medications and dental problems. Based on their findings, the authors described the location and anatomy of taste buds and receptor cells for smell and explored appetite, saliva, food seasonings, nutrition and dietary recommendations. They also discussed the relationship of smoking and tongue cleaning to taste sensations. RESULTS: The authors found that considerable differences exist between elderly people and young people in regards to sensory perception and pleasantness of food flavors. Salt and bitter taste acuity declines with age, but sweet and sour perceptivity does not. Olfactory acuity also declines with age. The authors found that most of the studies reviewed suggested that the sense of smell is more impaired by aging compared with the sense of taste. Smoking diminishes the taste of food and makes flavorful foods taste flat, while tongue brushing can increase taste sensation for geriatric patients. CLINICAL IMPLICATIONS: Food can become tasteless and unappetizing for geriatric patients as the result of declining taste and smell perception. Geriatric patients should be encouraged to add seasonings to their food instead of relying on excessive consumption of salt and sugar to give their food flavor. Adequate nutrition, tongue cleaning and smoking cessation are recommended for geriatric dental patients.

Aged↗
PubMed2006

Prion infection of oral and nasal mucosa.

Centrifugal spread of the prion agent to peripheral tissues is postulated to occur by axonal transport along nerve fibers. This study investigated the distribution of the pathological isoform of the protein (PrP(Sc)) in the tongues and nasal cavities of hamsters following intracerebral inoculation of the HY strain of the transmissible mink encephalopathy (TME) agent. We report that PrP(Sc) deposition was found in the lamina propria, taste buds, and stratified squamous epithelium of fungiform papillae in the tongue, as well as in skeletal muscle cells. Using laser scanning confocal microscopy, PrP(Sc) was localized to nerve fibers in each of these structures in the tongue, neuroepithelial taste cells of the taste bud, and, possibly, epithelial cells. This PrP(Sc) distribution was consistent with a spread of HY TME agent along both somatosensory and gustatory cranial nerves to the tongue and suggests subsequent synaptic spread to taste cells and epithelial cells via peripheral synapses. In the nasal cavity, PrP(Sc) accumulation was found in the olfactory and vomeronasal epithelium, where its location was consistent with a distribution in cell bodies and apical dendrites of the sensory neurons. Prion spread to these sites is consistent with transport via the olfactory nerve fibers that descend from the olfactory bulb. Our data suggest that epithelial cells, neuroepithelial taste cells, or olfactory sensory neurons at chemosensory mucosal surfaces, which undergo normal turnover, infected with the prion agent could be shed and play a role in the horizontal transmission of animal prion diseases.

Animals↗
PubMedDate not supplied

Age-related changes in sensory and secretomotor nerve endings in the larynx of F344/N rat.

The aim of the present study was to define the age-related changes in sensory and secretomotor nerve endings in the larynx of F344/N rats. For this purpose, laryngeal tissue sections obtained from 12-, 24- and 35-month-old F344/N rats were compared with respect to the density, distribution and morphology of various types of sensory and secretomotor nerve endings immunoreactive for protein gene product 9.5 (PGP 9.5), calcitonin gene-related peptide (CGRP) and substance P (SP). Two distinct forms of PGP 9.5-immunoreactive motor end-plates were noted; the large sized motor end-plates localized in thyroarytenoid and cricoarytenoid muscles were degenerated in aged rats, while the small sized motor end-plates, localized predominantly in vocal muscles, did not show any age-related changes. CGRP- and SP-immunoreactive nerve fibres of the laryngeal glands did not show any age-related changes. Subepithelial laminar nerve endings immunoreactive to PGP 9.5 showed degeneration with ageing. Aggregates of terminal arborisations in the subepithelial region were smaller in aged animals. PGP 9.5-immunostained taste cells and well-developed subgemmal network were abundant in 12- and 24-month-old rats, but only a few were noted in aged rats. The total number of taste buds decreased significantly with ageing. CGRP- and SP-immunostained taste bud-nerve endings were noted in 12- and 24-month-old rats, but only rarely in 35-month-old rats. The laryngeal epithelium contained PGP 9.5-, CGRP- and SP-immunoreactive thin free nerve endings with many varicosities; their number and distribution were similar between 12- and 24-month-old rats, while only a few endings were observed in 35-month-old rats. Our results indicated that ageing is associated with the reduction of laryngeal sensory and secretomotor nerve endings.

Aging↗
PubMed1991

Organization of gustatory sensitivities in hamster superior laryngeal nerve fibers.

1. Mammalian taste receptors are distributed within several distinct subpopulations, innervated by branches of cranial nerves VII, IX, and X. Most gustatory electrophysiology has focused on input from the fungiform papillae on the anterior portion of the tongue, carried by the chorda tympani branch of the VIIth nerve. However, laryngeal taste buds in the hamster are as numerous as those in the fungiform papillae. Gustatory fibers in the hamster's chorda tympani and glossopharyngeal nerves have been well characterized. In comparison with these taste fibers, much less is known about the chemical sensitivities of fibers innervating laryngeal taste buds. 2. Action potentials were recorded from 65 individual fibers in the superior laryngeal nerve (SLN) of the hamster. Stimuli were distilled H2O and five concentrations each of sucrose, NaCl, HCl, and quinine hydrochloride (QHCl). All stimuli except the NaCl series were made in physiological saline (0.154 M NaCl) and were delivered from the laryngeal side of the epiglottis via a tracheal cannula. Responses were quantified as the number of impulses in 10 s minus the responses in the preceding 10 s of baseline activity during a rinse with physiological saline. 3. Distilled H2O, HCl, and NaCl were by far the most excitatory stimuli, with mean responses across all cells 5-10 times greater than those evoked by sucrose or QHCl. The order of effectiveness of the strongest concentrations of the stimuli was H2O greater than 0.03 M HCl greater than 1.0 M NaCl much greater than 0.03 M QHCl greater than 1.0 M sucrose. 4. The mean concentration-response function for NaCl was U shaped, with the greatest number of impulses to distilled H2O and 1.0 M NaCl. The responses diminished as the concentrations approached physiological levels (0.154 M NaCl), where there was no response, and increased as NaCl concentration rose above this level. Increasing concentrations of HCl above 0.0003 M elicited increasing responses in these fibers. 5. The mean time course of the responses to distilled H2O and to hypotonic NaCl solutions (0.01 and 0.03 M) peaked in the first few seconds and then declined slowly. This was distinct from the time course of the responses to hypertonic NaCl concentrations (0.3 and 1.0 M), which increased gradually throughout the 10-s response period. Responses to HCl peaked in the initial second and then decayed rapidly to a slowly declining plateau. These distinctively different time courses suggest different receptor mechanisms for water, salt, and acid stimuli. 6. The across-fiber pattern of the responses to hypotonic NaCl solutions correlated strongly to that elicited by distilled H2O.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1993

Spinal and facial innervation of the skin in the gadid fish Ciliata mustela (Teleostei).

The pattern of innervation of the skin of the rockling Ciliata mustela was investigated to sort out spinal from facial nerve innervation of cutaneous chemosensory and mechanosensory systems. This fish has a variety of appendages with different functional sensory specializations, i.e., the chin barbel, pelvic fin, anterior dorsal fin, and dorsal trunk skin. The carbocyanine dye, diI, was applied to nerve stumps in dissected aldehyde-fixed tissue. In the case of the chin barbel, the dye was applied to both the trigeminal and facial nerve components. In the other cases, the dye was applied either selectively to the spinal nerves, to the facial nerves, or to both components. In the chin barbel, diI labeled nerve fibers associated with taste buds (TBs) and solitary chemosensory cells (SCCs) as well as relatively blunt free nerve endings, which closely approach the epidermal surface. In the pelvic fin, anterior dorsal fin, and dorsal trunk skin, taste buds, solitary chemosensory cells, and their innervation were labeled only after diI was applied to the facial nerve stumps. Application of diI to spinal nerves labeled delicate, free nerve endings and nerve fibers associated with small cells deep in the epidermis with features characteristic of Merkel cells. Transmission electron microscopy supports these results; after denervation of the facial component of the anterior dorsal fin, synaptic contacts with Merkel cells remained intact, whereas the synapses with the SCCs vanished.

Animals↗
PubMed1992

Salt taste discrimination after bilateral section of the chorda tympani or glossopharyngeal nerves.

Gustatory deafferentation of the anterior tongue by bilateral section of the chorda tympani nerve, which removes only 15% of the total taste buds in the rat, severely impaired the rat's ability to discriminate NaCl from KCl. The discrimination deficit was selective. Denervated rats were able to discriminate sucrose from quinine. Despite eliminating four times as many taste buds by bilateral section of the glossopharyngeal nerve, posterior lingual deafferentation had no effect on NaCl vs. KCl discrimination performance. Collectively, these data suggest that afferents in the chorda tympani nerve provide the highest degree of disparity between the peripheral signals representing NaCl and KCl. Electrophysiological findings of others implicate the sodium-specific afferents that appear to exclusively exist in the chorda tympani nerve as the critical elements subserving the NaCl vs. KCl discrimination.

Animals↗
PubMed1988

Cholinergic innervation of the tongue of the one humped camel, Camelus dromedarius.

Distribution of adrenergic and cholinergic nerve profiles in the tongue of camel has been studied by histochemical methods. The tongue is richly innervated by cholinergic nerve profiles as is evidenced by the presence of numerous nerve fibres at different levels. There is noted strong cholinesterase positive reaction close to the lateral border of the circumvallate papillae (in the region of the taste buds) and the upper border of the fungiform papillae. Numerous nerve fibres have been observed in the connective tissue core of all the lingual papillae. Adrenergic nerve terminals could not be observed in the taste buds though numerous adrenergic nerve fibres could be seen in and around the blood vessels. Rich cholinergic innervation of the blood vessels has also been noted in the tongue.

Animals↗
PubMed2001

NaCl thresholds: relationship to anterior tongue locus, area of stimulation, and number of fungiform papillae.

NaCl detection thresholds were determined for 12.5- and 50-mm(2) lingual areas at four anterior tongue locations in eight subjects using a device that allowed for accurate temporal and spatial presentation of tastants to small regions of the anterior tongue. The locations, all on the right side of the tongue, were the tongue tip, an area 1.7 cm posterior to the tongue tip, and regions 1.7 and 3.4 cm posterior to the tip along the tongue's lateral margin. Stimulus duration was 0.75 s. Thresholds were established using a two-alternative forced-choice single-staircase procedure, and the number of fungiform papillae at each stimulation site was counted with the aid of videomicroscopy. NaCl thresholds were lower for the 50-mm(2) than the 12.5-mm(2) stimulation area at all target sites, and were directly related to papillary number among and within the stimulated regions. For a given number of papillae, thresholds were lower within the 12.5-mm(2) than within the 50-mm(2) stimulation region, likely reflecting taste bud density and activation of common afferent pathways. The tongue tip was more sensitive than any other tongue region, and the lateral margins were seemingly more sensitive than the lingual centrum. Large individual differences in taste sensitivity and tongue papilla numbers were noted, and some subjects were insensitive to the highest tastant concentrations at the nontip loci. This study empirically demonstrates that NaCl detection sensitivity varies across discrete regions of the anterior tongue and is related to the relative number and density of fungiform papillae.

Adult↗
PubMed1990

A search for the cortical gustatory area in the hamster.

The gustatory area was searched in the cerebral cortex of the hamster by means of a combined approach using electrophysiological, behavioral, and histological experiments. The chorda tympani (CT), which innervates taste buds on the anterior part of the tongue, projected to a confined area anterior to the middle cerebral artery and just dorsal to the rhinal fissure. The trigeminal component of the lingual nerve (LN) area was located anterodorsal to the CT area, and the glossopharyngeal nerve (GN), which innervates taste buds on the posterior part of the tongue, was posterior to the CT area. The center of the CT and GN areas belonged to the dorsal part of the dysgranular insular cortex, and the LN area was within the primary somatosensory granular cortex. Bilateral symmetrical ablations of the CT and GN areas abolished the conditioned taste aversion (to sodium saccharin) that had been acquired before ablations, indicating a role of these areas in some cognitive processes of taste perception. Injections of horseradish peroxidase conjugated with wheat germ agglutinin (WGA-HRP) in the CT and GN areas, centered in the dysgranular insular cortex, revealed that this cortical region had major fiber connections with the contralateral homotypical cortical area, ipsilateral amygdala (central, lateral and basolateral nuclei), ipsilateral parvicellular part of the posteromedial ventral nucleus of the thalamus, bilateral parabrachial nucleus, contralateral nucleus of the solitary tract, raphe nuclei, and the locus ceruleus. Conversely, injections of WGA-HRP in these target areas showed anterograde and/or retrograde transport in the similar dysgranular insular cortex and additionally in the ventral part of the granular insular cortex. The present results suggest that the cortical gustatory area of the hamster is about 1.5 X 1.5 mm in size with the topographic organization between anterior and posterior parts of the tongue, and is located mainly in the dysgranular insular cortex around the middle cerebral artery.

Afferent Pathways↗
PubMed2002

Electron microscopic observations of glossal circumvallate papillae in dysgeusic patients.

A number of reports have been published describing the ultrastructure of normal taste buds but few have discussed their pathology, particularly in patients with gustatory abnormalities. We therefore conducted an electron microscopic study of biopsy specimens of glossal circumvallate papillae from patients with dysgeusia. We found depletion of microvilli and dense substance in the taste pores, vacuolation and hyaline degeneration of the taste bud cells and condensation of nuclear material and cytoplasm in cells of indeterminate histological type. In one patient with idiopathic dysgeusia, disruption of subsurface cisternae contiguous with the nerve endings was evident in Type II cells. In another patient, who had undergone radiotherapy, the number of cored vesicles in Type III cells was reduced.

Adult↗
PubMed1990

The effects of hetero-reinnervation within the rat tongue.

This study centred on the effects of hetero-reinnervation within the rat tongue. Lingual, greater auricular and vagus nerves were used. Proximal segments of each of these nerves were joined to the distal hypoglossal stump using 10/0 nylon suture. Histological sections of the tongue were examined. In lingual hypoglossal cross-union, histological evidence indicated that neuromuscular junction (nmj) reinnervation was present to some degree in all intrinsic tongue muscles and within geniohyoid. Lingual nerve fibres were also found within the dorsal keratinised lingual epithelium, reinnervating taste buds and intralingual ganglia. Greater auricular nerve fibres were unable to make contact with nmjs, nor were they found to any appreciable degree within the lingual mucosa. Vagal nerve fibres were found close to, but not innervating, nmjs, but did reinnervate taste buds, lingual vasculature and intralingual ganglia. It was concluded that nodose cells are unable to reinnervate vacated nmjs, but like lingual fibres can reinnervate lingual mucosa, intralingual ganglia and vasculature.

Animals↗
PubMed1997

Development of membrane properties in taste cells of fungiform papillae: functional evidence for early presence of amiloride-sensitive sodium channels.

Behavioral and physiological studies have demonstrated a reduced sensitivity to several taste stimuli early in development. It has been suggested that this reduced sensitivity results from a late maturation of underlying transduction mechanisms. Little is known, however, about maturation of membrane properties of taste cells early in development. We have obtained whole-cell recordings from single fungiform taste cells of rat pups to examine the development of the NaCl transduction system. Although taste buds undergo a considerable increase in size during development, membrane capacitance measurements revealed no change in membrane surface area of individual taste cells, suggesting that the increase in size results from an increase in the total number of cells per bud. Whole-cell recordings showed that taste cells from very young pups [postnatal day 2 (PND2)] already possessed voltage-activated Na+ and K+ currents with no apparent differences in size or kinetics compared with adults. Surprisingly, amiloride-sensitive Na+ responses, important for Na+ transduction, were found as early as PND2. The magnitude of responses to amiloride and the percentage of amiloride-sensitive cells remained the same throughout all age groups. Furthermore, the similarity of amiloride inhibition constants suggested that the channel in neonates is the same channel that is expressed in adult taste buds. Our results indicate that taste cells at PND2 already have acquired the transduction elements necessary for signaling NaCl responses to the afferent nerve. We hypothesize that complete functionality of the salt taste transduction system, however, may not be reached until amiloride-sensitive Na+ channels become selectively localized at the apical membrane. This would explain previous studies indicating that amiloride sensitivity cannot be detected before PND12 in the intact tongue. Apical clustering of channels along with the opening of the taste pore and an increase in the total number of taste cells per bud likely constitute additional important steps toward a fully functional sensory system.

Amiloride↗
PubMed2002

Taste dysfunction in irradiated patients with head and neck cancer.

Taste disorders caused by radiation therapy for head and neck cancer are common. This prospective study of 40 patients with head and neck cancer assessed changes in taste sensations during radiation therapy. The relationship between the time course and the degree of taste disorder was studied. The taste recognition threshold and supra-threshold taste intensity performance for the four basic tastes were measured using the whole-mouth taste method before, during, and after radiation therapy. Bitter taste was affected most. An increase in threshold for sweet taste depended upon whether the tip of tongue was included within the radiation field. The slope of the taste intensity performance did not change during or after radiotherapy. The pattern of salivary dysfunction was different from that of taste dysfunction. The main cause of taste disorders during radiation support the hypothesis that taste dysfunction is due to damage to the taste buds in the radiation field.

Adult↗
PubMed2006

Effects of electrical stimulation of the glossopharyngeal nerve on cells in the nucleus of the solitary tract of the rat.

Electrophysiological responses to electrical stimulation of the lingual branch of the glossopharyngeal (GP) nerve (which innervates taste buds on the caudal 1/3 of the tongue) were recorded from single cells in the rostral nucleus of the solitary tract (NTS) of anesthetized rats. Electrical stimulation was delivered as single pulses (n=55), paired-pulses (n=15) and tetanic trains (n=11). NTS cells with GP-evoked responses were also tested for responsivity to taste stimuli (0.1 M NaCl, 0.5 M sucrose, 0.01 M HCl and 0.01 M quinine HCl). Fifty-five neurons were studied: 49 cells showed GP-evoked (mean latency+/-SEM=18.0+/-1.32 ms); seven of these were taste-responsive. Spontaneous rate of these cells was low (mean+/-SEM=1.4+/-0.3 spikes per second; median=0.21 spikes per second) and many cells showed no spontaneous activity. Paired-pulse stimulation of the GP nerve in 13 rats produced both paired-pulse suppression (n=11) and paired-pulse enhancement (n=4); tetanic stimulation (25 Hz, 1.0 s) produced sustained (>20 s) increases or decreases in firing rate in 7 of 11 cells tested. Histological data suggested that GP-evoked responses recorded in the most rostral NTS were likely the result of polysynaptic connections. Cells with GP-evoked responses formed a heterogeneous group in terms of their response properties and differed from cells with evoked responses to chorda tympani (CT; which innervates taste buds on the rostral 1/3 of the tongue) nerve stimulation. These differences may reflect the respective functional specializations of the GP and CT nerves.

Action Potentials↗
PubMed1997

Effects of nicotine on tongue development in the CD-1 mouse.

Fetuses of pregnant CD-1 mice, exposed to 0.1% nicotine sulfate at a dose of 1.67 mg/kg body weight from the 6th through the 15th gestational days were compared with control fetuses to assess the effects of nicotine on tongue development. Mothers were sacrificed on the 18th gestational day. The heads of a total of 130 nicotine-treated and 348 control fetuses were embedded in paraffin and sectioned in the frontal plane. 9.6% of the nicotine-treated fetuses had palatal clefts and their tongue development was much retarded compared to the controls. The tongues of the clefted fetuses were misshaped, reduced in size, had no filiform or fungiform papillae, and their myotubes were just in the process of formation. The circumvallate papilla of these fetuses were present but neither taste buds nor glands of von Ebner had as yet developed. Tongue development of nicotine-treated, non-clefted fetuses were closer to those of the controls. The anlagen of their filiform and fungiform papillae were developing, their myotubes were longer and better arranged, their circumvallate papilla was present but without taste buds, and their glands of von Ebner were not developed. It is suggested that nicotine interferes with both palatal and mesenchymal components of tongue development.

Animals↗
PubMed2000

Distribution and innervation of lateral line organs in the channel catfish.

The lateral line system of the channel catfish is formed by mechanoreceptive neuromasts located within five pairs of cephalic and one pair of trunk canals, as well as superficial lines of neuromasts, termed accessory and/or pit lines. Five pairs of pit lines occur on the head, and three pairs of superficial lines occur on the trunk. In addition to these mechanoreceptors, which are found in most teleost fishes, catfish also possess a total of over 4000 electroreceptive ampullary organs scattered over the entire body. The lateral line receptors are innervated by five pairs of lateral line nerves whose rami are secondarily associated with facial and trigeminal fibers that innervate taste buds and the dermis of the skin, respectively. The neuromasts of the trunk canal and the ramules of the posterior lateral line nerve that innervate them seem to be organized in a segmental pattern. The same is true for the intervertebral ramules of the recurrent facial ramus, which innervate the external taste buds on the trunk. The fibers of the gustatory and lateral line systems may use the neural crest, the developing spinal nerves, or both, to establish this segmental pattern. In this context, it may not be surprising that there is an intimate relationship among each of the sensory systems in the trunk.

Animals↗
PubMed2002

Gross and microscopic observations on the lingual structure of the Florida Manatee Trichechus manatus latirostris.

The tongue of the Florida manatee (Trichechus manatus latirostris) was studied macroscopically, light and electron microscopically. The tongue was slender, muscular and firmly fixed in the oral cavity; only the cranial tip was free and mobile. Numerous filiform papillae were distributed over the dorsal surface of the rostral tongue. Multiple raised, round fungiform-like papillae were distributed over most of the dorsum. Typical fungiform papillae were restricted to the lateral margins of the tongue. Foliate papillae, presenting as multi-fossulate openings, were noted on the caudolateral margins. Open pits were located on the dorsocaudal surface and lateral walls. Microscopic examination showed that most of the lingual dorsum was covered with a thick stratified squamous epithelium. Open pits led to well-developed mucous salivary glands. Glands within the foliate papillae were mostly mucous, although some seromucous glands were present. Taste buds were restricted to the epithelium of the foliate papillae. Throughout the tongue, striated muscle was abundant below the epithelium. Blood vessels, lymph channels and nerve fibres were freely distributed throughout the intermuscular stroma. Nerve fibres reacted positively with neurone specific enolase (NSE) antibody throughout the tongue, including nerve bundles, glands and taste buds. Clear to translucent vacuoles were found juxtaposed to nuclei in the stratum spinosum in the foliate papillae epithelium.

Animals↗