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In the high-latitude shelf waters of Antarctica, fishes in the perciform suborder Notothenioidei dominate the fish fauna and constitute an adaptive radiation and a species flock. The 25 species of notothenioid plunderfishes, comprising four genera of the family Artedidraconidae, contribute substantially to fish species diversity on the high Antarctic shelf. A mental barbel is an autapomorphy for the family. Dolloidraco longedorsalis is the most abundant artedidraconid at depths over 400 m in these waters. In this article we present the anatomy and histology of the brain and special sense organs of Dolloidraco and compare it to the brains of other artedidraconids, closely related harpagiferids, and more generally to other notothenioids. We provide a detailed drawing of the brain and cranial nerves. The brain of Dolloidraco is simple, without external hypertrophy of sensory or motor regions, but contains several unusual features associated with the ventricular system and CSF, including well-developed circumventricular organs, subependymal expansions, and subarachnoid cisterns; and a ventricle in the corpus cerebellum. The brain of Dolloidraco also contains a lobed chief sensory nucleus of the trigeminal nerve that is correlated across species with barbel length. The eyes are large and contain a small choroid rete, a structure previously thought to be absent from members of this family. We document the histology of the duplex retina, olfactory apparatus, cutaneous taste buds, and barbel musculature and innervation. We discuss the role of pedomorphy in producing simplified brain morphologies. We consider the possibility that Dolloidraco is a somatosensory specialist-an unusual feature among vertebrates-and decide that this is unlikely., (Copyright 2003 Wiley-Liss, Inc.)

Basic anatomophysiological evidence underlying sense of taste, main causes of taste disorders, guides for practitioners how to detect these disorders and differentiate them with physicians of allied specialities, make prognosis and design policy of the disease treatment are reviewed.

We have studied by immunocytochemistry, the taste discs of the frog, Rana esculenta, with the aim of providing morphological and neurochemical data on the nitrergic system and of assessing the eventual presence of intrinsic neurons associated with the gustatory organs. In taste discs, antibodies against neuronal nitric oxide synthase (nNOS) revealed a positive immunoreaction in the taste receptor cell bodies and processes. The basal cells were also stained. All the fungiform papillae contained intragemmal nerve fibers showing nNOS immunoreactivity; these fiber were mainly located in the basal plexus. Immunoreactive nerve fibers were also visible at the periphery of the papilla-contacting ciliate cells, which form a ring around the taste disc. In conclusion, the findings obtained in this study suggest that the occurrence of nNOS-immunoreactivity in basal cells, taste cells and nerves might reflect a role for nitric oxide in taste mechanisms of Amphibia. The results may also sustain the physiological implication of NO as a molecule involved in the local target function of maintaining the taste bud mucosal integrity and in regulating the blood flow to the epithelium.

Goatfish use a pair of large chin barbels to probe the sea bottom to detect buried prey. The barbels are studded with taste buds but little else is known about the neural organization of this system. We found that the taste buds of the barbel are innervated in a strict orthogonal fashion. The barbel is innervated by a main nerve trunk running in the core of the barbel. A longitudinal nerve bundle originates from the main trunk and, after running a short distance distally, divides into two circumferential nerve bundles (CNB) extending respectively, medially and laterally around the barbel. Approximately 15 CNBs innervate each 1 mm length of barbel. At each transverse level, the CNB innervates two clusters of taste buds, each containing 14 end-organs. The primary taste centre in the brain is similarly extraordinary. The sensory inputs from the barbel terminate in a derived dorsal facial lobe, which has a highly convoluted surface forming a multitude of tubercles. Electrophysiological mapping experiments show that the entire barbel is somatotopically represented in a recurved elongate tubular fashion within the dorsal facial lobe.

The identification of two families of receptors, T1Rs and T2Rs, for sweet and bitter taste stimuli has opened the door to understanding some of the basic mechanisms underlying taste transduction in mammals. Studies of the functions of these receptors and their patterns of expression provide important information regarding the detection of structurally diverse taste compounds and the manner in which different taste qualities are encoded in the mouth.

We conducted a study to investigate whether taste buds are present on the human adult uvula. Our impetus was to determine whether surgical procedures that involve removal of the uvula can affect taste perception. Five human uvulae were removed via a modified carbon dioxide laser-assisted uvulopalatoplasty in an outpatient office setting. The uvulae were serially sectioned and stained with a solution specific for membrane-bound calcium-modulated adenosine triphosphatase, a high concentration of which is found in taste receptors. Examination of the stained sections under light microscopy failed to show that any taste receptors were present in any of the uvulae. This finding suggests that the taste disturbances noted after surgical procedures involving removal of the uvula are not attributable to a loss of taste receptors.

is well established that, on the anterior tongue, thresholds for chemical tastants are inversely related to the number of fungiform papillae. However, it is not known whether this is the case for thresholds to electrical currents presented to the lingual surface. In this study, electrical thresholds for 16 subjects were determined at four left-side anterior lingual locations: tongue tip (TT), a region 1.7 cm posterior to the tip, a region 3.4 cm posterior to the TT, and a region 1.7 cm from the tip along the lateral margin. Two electrode sizes were employed (12.5 and 50 mm2), and stimulus duration was held constant at 0.5 s. The number of fungiform papillae was determined using videomicroscopy. Analogous to what is seen with chemical stimulation, an inverse relationship was present between the mean electrical thresholds, expressed in terms of current density, and the number of papillae within the stimulated regions. The TT --which has the highest density of fungiform papillae -- was found to be more sensitive than the other tongue regions evaluated. Also paralleling chemical thresholds, the mean electrical threshold values were lower (i.e., sensitivity was higher) at a given tongue locus for the 50-mm2 than for the 12.5-mm2 stimulus area. Overall, this study demonstrates that thresholds for electrical stimulation vary across discrete regions of the anterior tongue and are specifically related to the number of fungiform papillae within the stimulated regions. These observations provide additional support for the hypothesis that lingual sensations induced by low levels of electrical current are mediated by the taste system.

It is well established that, on the anterior tongue, thresholds for chemical tastants are inversely related to the number of fungiform papillae. However, it is not known whether this is the case for thresholds for electrical currents presented to the lingual surface. In this study, electrical thresholds for 16 subjects were determined at four left-side anterior lingual locations: tongue tip (TT), a region 1.7 cm posterior to the TT, a region 3.4 cm posterior to the TT, and a region 1.7 cm from the TT along the lateral margin. Two electrode sizes (12.5 mm2 and 50 mm2) were employed for the anodal current, and stimulus duration was held constant at 0.5 s. The number of fungiform papillae was determined using videomicroscopy. Analogous to what is seen with chemical stimulation, an inverse relationship was present between the mean electrical thresholds, expressed in terms of current density, and the number of papillae within the stimulated regions. The TT-which has the highest density of fungiform papillae--was found to be more sensitive than the other tongue regions evaluated. Also paralleling chemical thresholds, the mean electrical threshold values were lower (i.e., sensitivity was higher) at a given tongue locus for the 50-mm2 than for the 12.5-mm2 stimulus area. Overall, this study demonstrates that thresholds for electrical stimulation vary across discrete regions of the anterior tongue and are specifically related to the number of fungiform papillae within the stimulated regions. These observations provide additional support for the hypothesis that lingual sensations induced by low levels of electrical current are mediated by the taste system.

Brain regions, cranial nerves, and sense organs in Muraenolepis microps, an Antarctic gadiform fish, were examined to determine which features could be attributed to a gadiform ancestry and which to habitation of Antarctic waters. We found that the central nervous system and sense organs are well developed, showing neither substantial regression nor hypertrophy. A detailed drawing of the brain and cranial nerves is provided. The rostral position of the olfactory bulbs and telencephalic size and lobation are common for the order. The optic tectum and corpus cerebelli are smaller than in most other gadiforms. The shape of the corpus cerebelli is not distinctive among gadiforms. The lateral line region is moderately well-developed, but not hypertrophied to the extent seen in deep-sea gadiforms. As is the case in gadids possessing barbels and elongated pelvic rays, Muraenolepis has well-developed facial lobes, although these are smaller and more laterally positioned. The vagal lobes are deeply placed in the rhombencephalon and project into the fourth ventricle. The brain of Muraenolepis resembles that of a phyletically derived gadoid, especially a phycid, more than it resembles the brain of a phyletically basal macrourid. Two histological features of the diencephalon of Muraenolepis appear to be unique among gadiforms: a well-organized thalamic central medial nucleus and subependymal expansions. Muraenolepis has a pure rod retina like many deep-sea species but lacks the superimposed layers of rod outer segments. The histology of the nonvisual sense organs, especially the olfactory and external taste systems, are well-developed in Muraenolepis but not hypertrophied. We relate our findings to what is known about neural morphology in other gadiforms and in phyletically distant notothenioids and liparids that are sympatric with Muraenolepis on the Antarctic shelf. The only feature that reflects an Antarctic existence is the diencephalic subependymal expansions, which within notothenioids mirror the habitation of cold waters and have been found in every Antarctic species examined to date. Although the waters of the Antarctic shelf are cold, dark, and deep, brain and sense organ morphology in Muraenolepis are remarkably free of extreme specialization., (Copyright 2001 Wiley-Liss, Inc.)

The morphology of dorsal lingual papillae of the Bactrian camel (Camelus bactrianus) was studied by using light and scanning electron microscopy. Filiform and lenticular papillae were considered as mechanical papillae but fungiform and vallate papillae were considered as gustatory papillae. Filiform papillae were distributed mostly in the anterior two-thirds region of the tongue. Each filiform papilla consisted of one primary papilla and a few smaller secondary papillae. Lenticular papillae were distributed on the torus linguae. The larger papillae were arranged in two parallel lines medially whereas the smaller papillae were laterally located. Most of the fungiform papillae were found on the lateral margins of the anterior two-thirds of the tongue. These papillae were small and round. Intra-epithelial taste buds were located on the dorsal surface of each papilla. The vallate papillae were arranged in two rows on each rim of the torus linguae. Each round- and flat-shaped vallate papilla was surrounded by a prominent gustatory groove and an annular pad. A few taste buds were observed in the lateral epithelium of the papillae. The keratinization of the covering stratified squamous epithelium of the mechanical lingual papillae was relatively thicker than those of the gustatory papillae. The lingual papillae of the Bactrian camel exhibited some different characteristics from other domestic ruminants. These morphological characteristics of the tongue of the Bactrian camel might have evolved to assist the camel in prehension and manipulating of the inorganic stiff plants that grow in its environment and therefore might relate to the feed and feeding habits of the animal.

Four areas of the brain which receive primary projections from chemical senses ([1] olfactory bulb, [2] gustatory area including facial and vagal lobes), the eye ([3] optic tectum), and mechanosensory, and-hair-cell based systems i.e. the lateral line, vestibular and auditory systems ([4] trigeminal and octavolateral regions) have been studied and relative size differences used to make deductions on the sensory preferences of 35 fish species living on or near the bottom of the deep sea. Furthermore the relative volumes of the telencephalon and the corpus cerebelli were determined. Two evaluation modes were applied: (1) the relative mean of each system was calculated and species with above-average areas identified; (2) a cluster analysis established multivariate correlations among the sensory systems. The diversity of sensory brain areas in this population of fish suggests that the benthic and epibenthic environment of the abyss presents a rich sensory environment. Vision seems to be the single most important sense suggesting the presence of relevant bioluminescent stimuli. However, in combination the chemical senses, smell and taste, surpass the visual system; most prominent among them is olfaction. The trigeminal/octavolateral area indicating the role of lateral line input and possibly audition is also well represented, but only in association with other sensory modalities. A large volume telencephalon was often observed in combination with a prominent olfactory system, whereas cerebella of unusually large sizes occurred in species with above-average visual, hair-cell based, but also olfactory systems, confirming their role as multimodal sensorimotor coordination centers. In several species the predictions derived from the volumetric brain analyses were confirmed by earlier observations of stomach content and data obtained by baited cameras., (Copyright 2001 S. Karger AG, Basel)

The taste buds of the fungiform papillae, circumvallate papilla, foliate papillae, soft palate and epiglottis of the rat oral cavity were examined by lectin histochemistry to elucidate the relationships between expression of glycoconjugates and innervation. Seven out of 21 lectins showed moderate to intense staining in at least more than one taste bud. They were succinylated wheat germ agglutinin (s-WGA). Dolichos biflorus agglutinin (DBA), Bandeiraea simplicifolia lectin-I (BSL-I), Ricinus communis agglutinin-I (RCA-I), peanut agglutinin (PNA), Ulex europaeus agglutinin-I (UEA-I) and Phaseolus vulgaris agglutinin-L (PHA-L). UEA-I and BSL-I showed moderate to intense staining in all of the taste buds examined. They strongly stained the taste buds of the epiglottis, which are innervated by the cranial nerve X. UEA-I intensely stained the taste buds of the fungiform papillae and soft palate, both of which are innervated by the cranial nerve VII. The taste buds of circumvallate papilla and foliate papillae were innervated by the cranial nerve IX and strongly stained by BSL-I. Thus, UEA-I and BSL-I binding glycoconjugates, probably alpha-linked fucose and alpha-D-galactose, respectively, might be specific for taste buds. Although the expression of these glycoconjugates would be related to the innervation of the cranial nerve X, the differential expression of alpha-linked fucose and alpha-D-galactose might be related to the innervation of the cranial nerve VII and IX, respectively.

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.

We tested the hypothesis that fat perception (sensitivity to and preferences for fat) may be linked to 6-n-propylthiouracil (PROP) taster status as a result of differences in trigeminal innervation of the oral cavity. In addition, we examined the relationship between taster status and sensitivity to other taste attributes, as well as tactile and olfactory sensitivities. Subjects (40 nontasters, 67 medium tasters, and 40 supertasters of PROP) rated samples (potato chips, chocolate drink, mashed potatoes, and vanilla pudding) varying in fat and flavor concentrations for the intensity of fattiness, saltiness, and sweetness, first without and then with nose clips, and for liking. Tactile sensitivity of the tongue was assessed according to responses to stimulation with Von Frey filaments (2.36, 2.44). Olfactory thresholds were determined for two odors (diacetyl and phenylethyl methyl ethyl carbinol). In general, taster status was not related to the perceptions of fat, saltiness, and sweetness. Subjects were able to accurately assess the fat content of the samples. Increasing the flavor levels in the potato chips and mashed potatoes enhanced the perception of fattiness for these systems. Supertasters were more sensitive to stimulation on the median of the tongue with the no. 2.36 Von Frey filament, and the olfactory thresholds for diacetyl were lower for PROP tasters and supertasters than for nontasters.

Alteration in the number of taste buds on the soft palate (SP), fungiform (FF), foliate (FL) and circumvallate (CV) papillae in the common marmoset at different postnatal ages was examined histologically. After paraffin embedding, complete serial sections at 10 microm thickness were made and stained by HE. Digitized images for each section were examined carefully. The number of FF taste buds at day 1 was 334. While only 20% of all the taste buds at birth possessed a taste pore, 39% of 174 SP taste buds at day 1 possessed a taste pore. The number of taste buds with pores at day 1 was small for the center CV (19 of 59), one side CV (7 of 25), and one side FL (2 of 16). These results suggest that the functional maturation of SP taste buds may precede maturation in other areas of the tongue. The total number of taste buds increased with increasing age, reached a maximum at 2 months of age: FF, 1069; SP, 609; CV-center, 530; CV-side, 390; FL, 201, and decreased thereafter. Almost all taste buds possessed a taste pore after 2 months of age. The decrease in the number of taste buds in the oral cavity with increase in age may change taste sensitivity.

The external taste buds of bony fishes are differentiated and grouped throughout the body epithelium, concentrating in the buccopharyngeal cavity or in certain external organs such as the lips, barbels or fins. The family Mullidae (goatfishes) is characterized by having barbels covered with taste buds (TBs). However, It is not known how the TBs are distributed and how their characteristics vary along the barbels. To obtain answers to these questions, the morphological variability in taste bud density (deltaTB), pore area (A(P)) and taste bud area (A(TB)) was studied in Mullus barbatus (L., 1758) (red mullet) and M. surmuletus (L., 1758) (striped red mullet), for fish ranging in size from 58 to 227 and from 56 to 287 mm in total length (L(T)), respectively. Assuming that larger fish are older, in both species the pore area (A(P)) and taste bud area (A(TB)) increased with ontogenic development. Also, in both species clear differences were observed along the barbel. The delta(TB) increased from the basal area to the apical area, whereas both the A(P) and A(TB) had an inverse pattern., (Copyright 2001 S. Karger AG, Basel)

The sense of taste lies at the interface between the external and internal milieux, at the point at which the animal must decide which chemicals from the environment to incorporate into itself. Accordingly, taste is organized along a neural dimension of nutrients versus toxins, which corresponds to a behavioral dimension of acceptance versus rejection, and to a hedonic dimension of appetitive versus aversive qualities. Reflexive responses, cognitive analyses, and hedonic reactions appear to be managed at different levels of the nervous system. At the first central relay, the nucleus of the solitary tract, somatic reflexes for acceptance or rejection, and autonomic reflexes anticipating digestion are orchestrated. At the second, the parabrachial nucleus of the rodent, associative mechanisms important to the development of conditioned aversions and sodium appetite are manifested. In the thalamic taste relay, gustatory memories associated with non-visceral events may be formed. Primary taste cortex appears to be the site for a cognitive evaluation of gustatory quality and intensity. Finally, a hedonic assessment of the chemical may be made in secondary taste cortex and in the ventral forebrain sites to which it projects. With this assessment comes integration of the gustatory signal with those from other senses, perhaps to create a perception of flavor. Therefore, a sequence that begins with an analysis of the molecular structure of a chemical in the mouth serves to incorporate that gustatory component into an appreciation of flavor, and to participate in the control of motivational processes that guide dietary selection.

The present report examined the morphology of fungiform papillae in adult rats that received bilateral chorda tympani transection at 10 days of age. Tongue tissue was examined using surface-structure analysis. Counts were made of fungiform papillae with a pore, fungiform papillae with no pore and fungiform papillae with a keratinized conical surface; a feature referred to as "filiform-like. " Neonatal chorda tympani nerve transection resulted not only in a loss of taste buds but also in a permanent loss in numbers of fungiform papillae. Compared with an average of 152 fungiform papillae in sham-operated control rats, there was an average of only 54 fungiform papillae after neonatal chorda tympani transection. Nearly 80% of these fungiform papillae in neonatal chorda tympani transected rats were filiform-like. No filiform-like papillae were noted in sham-operated rats. These results suggest that the chorda tympani nerve is necessary during an early postnatal period of development to maintain normal fungiform papillae morphology.

In this study, the origins of sensory neurons from the tongue that ascend in the hypoglossal nerve were identified and described in the leopard frog, Rana pipiens. Previous studies have shown that these afferents are used to coordinate the timing of jaw and tongue muscles, and are important in the motor control of feeding. These sensory neurons innervate the tongue bilaterally and appear to originate in the dorsal fungiform papillae of the tongue epithelium.

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.

We suggest that the description of the reciprocal relationships between the circumvallate papilla (CP) and von Ebner glands (VEGs) reported in most textbooks of anatomy must be rewritten. In the past, the VEG was described as a gland ancillary to the taste buds, mainly involved in the washing of the vallum around the CP or in perireceptorial events. Recent data obtained in our laboratory or reported in the literature indicate that both these structures form a single functional unity which could be called circumvallata papilla/von Ebner gland (CP/VEG) complex. The CP/VEG complex seems to represent an important enzyme- and pheromone-producing system composed of a sensitive (taste buds) and an effectory (VEG) branch linked by feedback mechanisms of control. In our hypothesis, the taste buds located in the distal portion of the VEG ductal system can be considered similar to the chemoreceptory cells located in other portions of the digestive apparatus such as pancreatic and bile ducts. Therefore, the CP/VEG complex represents a rare example of chemoreceptor-secretory organ.

Dietary sodium restriction has profound effects on the development of peripheral taste function and central taste system anatomy. This study examined whether early dietary sodium restriction also affects innervation of taste buds. The number of geniculate ganglion cells that innervate single fungiform taste buds were quantified for the midregion of the tongue in two groups of rats: those fed either a low-sodium diet and those fed a sodium replete diet (control rats) from early prenatal development through adulthood. The same mean number of ganglion cells in developmentally sodium-restricted and control adult rats innervated taste buds on the midregion of the tongue. However, the characteristic relationship of the larger the taste bud, the more neurons that innervate it did not develop in sodium-restricted rats. The failure to form such a relationship in experimental rats was likely due to a substantially smaller mean taste bud volume than controls and probably not to changes in innervation. Further experiments demonstrated that the altered association between number of innervating neurons and taste bud size in restricted rats was reversible. Feeding developmentally sodium-restricted rats a sodium replete diet at adulthood resulted in an increase in taste bud size. Accordingly, the high correlation between taste bud volume and innervation was established in sodium-replete rats. Findings from the current study reveal that early dietary manipulations influence neuron-target interactions; however, the effects of dietary sodium restriction on peripheral gustatory anatomy can be completely restored, even in adult animals.

Lingual taste buds form within taste papillae, which are specialized structures that develop in a characteristic spatial and temporal pattern. To investigate the signaling events responsible for patterning and morphogenesis of taste papillae, the authors examined the time course and distribution of expression of several related developmental signaling genes as well as the time course of innervation of taste papillae in mouse embryos from embryonic day 12 (E12) to E18. Lingual expression of the signaling molecule Sonic hedgehog (Shh), its receptor Patched (Ptc), and the Shh-activated transcription factor Gli1 were assayed by using in situ hybridization. Shh is expressed broadly in the lingual epithelium at E12 but becomes progressively restricted to developing circumvallate and fungiform papillary epithelia. Shh is expressed specifically within the central cells of the papillary epithelium starting at E13.5 and persisting through E18. Ptc and Gli1 expression follow a pattern similar to that of Shh. Compared with Shh, Ptc is expressed in larger regions surrounding the central papillary cells and also in the mesenchyme underlying Shh-expressing epithelium. Innervation of taste papillae was examined by using the panneuronal antibody to ubiquitin carboxyl terminal hydrolase (protein gene product 9.5). Nerves reach the basal lamina of developing taste papillae at E14 to densely innervate the papillary epithelium by E16. Thus, the pattern of Shh expression within developing taste papillae is established prior to innervation, ruling out neuronal induction of papillae. The results suggest that the Shh signaling pathway may be involved in: 1) establishing papillary boundaries in taste papilla morphogenesis, 2) papillary epithelial-mesenchymal interactions, and/or 3) specifying the location or development of taste buds within taste papillae.

The main purpose of this study was to determine the relationship between the number of circumvallate papillae and the bitter taste threshold with age. The study group consisted of 10 women (age range, 60-80) and 14 men (age range, 60-85) and the control group of 15 young women (age range, 18-25) and 15 young men (age range, 17-20); the total number of subjects was 54. The number of circumvallate papillae was counted by direct observation with the naked eye; bitter taste thresholds were evaluated by the three drop forced-choice method with an ascending series, using quinine sulfate dehydrate as the bitter agent. We observed that while the number of circumvallate papillae did not increase with age, the bitter taste threshold changed significantly with age.

Studies of feeding behavior in the largemouth bass, Micropterus salmoides, revealed that live goldfish or artificial food balls are ingested in three discrete steps: inhalation of the food into the oral cavity, passage through the pharyngeal cavity, and swallowing. Food balls with or without a feeding stimulant were inhaled with equal frequency; thus, vision was clearly the major sense affecting inhalation. However, food balls with defined concentrations of a feeding stimulant were swallowed in a dose-dependent manner, whereas food balls without a feeding stimulant were promptly expelled. Thus, gustation played a major role in stimulating swallowing. Videotaped observations of feeding behavior suggested that both food processing and gustation occur in the pharynx and take place before the swallowing of either goldfish or food balls. The well-developed pharyngeal jaws of largemouth bass consist of six major pads of caniform teeth in the upper pharynx and two pads in the lower pharynx. Scanning electron microscopy showed that taste buds were abundant around most of these pharyngeal teeth. Histological sections prepared from all pharyngeal pads revealed that both elevated and flattened taste buds occur with the teeth. The morphology of these taste buds was typical of that described in other teleosts. Neuronal profiles, visualized with an HNK-1 monoclonal antibody, were observed entering each taste bud. The antibody also selectively stained a group of one to four putative sensory cells in each taste bud and the distal processes of these cells in the receptor area. The co-localization of teeth and taste buds on the pharyngeal jaws indicates that food processing and gustation both occur there, and that together these processes determine whether a potential food item is swallowed.

Individuals who are sensitive to the bitter compound 6-n-propylthiouracil (PROP) are also more sensitive to selected bitter and sweet substances, to sharp foods and to the trigeminal irritant capsaicin. PROP tasters have a greater density of fungiform papillae, and it is speculated that they also have more trigeminal innervation. Since oral texture perception is also mediated, in part, by trigeminal fibers, it has been proposed that individual differences in fat perception might also be linked to PROP taster status and taste bud density. This work tests the hypothesis that individuals who are PROP tasters: (i) have a higher density of fungiform papillae; (ii) are more sensitive to capsaicin; and (iii) have increased ability to discriminate differences in fat content in salad dressing. Hedonic ratings for the salad dressing were also collected and related to the perceptual judgments. Individual subjects were classified as PROP nontasters, medium tasters or supertasters (n = 25/group) by comparing their psychophysical function for PROP to that of NaCl. Papillae densities (papillae/cm2) were significantly different among the three taster groups (p < 0.0001), and were highest among the supertasters. Both medium tasters and supertasters perceived more oral burn from capsaicin than did nontasters at concentrations of 50, 70 and 100 ppm (p < 0.0001). Medium tasters and supertasters could also discriminate differences in fat content between 40% fat and 10% fat salad dressings (p < 0.005), but the nontasters could not. Although medium and supertasters showed no preference for either dressing, the nontasters preferred the 40% fat sample. The reasons for these latter findings are unclear at present. These data support the hypothesis that fat perception and preference can be linked to genetic and anatomical differences between individuals.

Taste buds are the anatomical structures that mediate the sense of taste. They comprise taste cells and nerve fibers within specialized epithelial structures. Taste cells are traditionally described by histologic methods as basal, dark, intermediate, and light cells, with the nerve fibers surrounding and infiltrating the taste buds. By means of immunohistochemical methods, taste cells and gustatory nerve fibers can be classified in functional groups based on the expression of various cell adhesion molecules and other proteins. When taste buds become damaged, the loss of the ability to taste results. This loss is not uncommon and can impact health and quality of life. Patients who receive radiation therapy for head and neck cancer often experience taste loss, which leads to compromised nutritional intake and a worse outcome than patients who do not experience taste loss. The mode of radiation damage to taste cells and nerve fibers has been investigated using cell adhesion molecules, synaptic vesicle proteins, and other cell markers. The light and intermediate cells are preferentially affected by ionizing radiation, whereas the nerve fibers remain structurally intact. Experimental studies of radiation-induced taste loss are performed via a unique animal/human model.

Vertebrates possess four distinct chemosensory systems distinguishable on the basis of structure, innervation and utilization: olfaction, taste, solitary chemoreceptor cells (SCC) and the common chemical sense (free nerve endings). Of these, taste and the SCC sense rely on secondary receptor cells situated in the epidermis and synapsing on sensory nerve fibers innervating them near their base. The SCC sense occurs in anamniote aquatic craniates, including hagfish, and may be used for feeding or predator avoidance. The sense of taste occurs only in vertebrates and is always utilized for feeding. The SCC system achieves a high degree of specialization in two teleosts: sea robins (Prionotus) and rocklings (Ciliata). In sea robins, SCCs are abundant on the three anterior fin rays of the pectoral fin which are free of fin webbing and are used in active exploration of the substrate. Behavioral and physiological studies show that this SCC system responds to feeding cues and drives feeding behavior. It is connected centrally like a somatosensory system. In contrast, the specialized SCC system of rocklings occurs on the anterior dorsal fin which actively samples the surrounding water. This system responds to mucus substances and may serve as a predator detector. The SCC system in rocklings is connected centrally like a gustatory system. Taste buds contain multiple receptor cell types, including a serotonergic Merkel-like cell. Taste receptor cells respond to nutritionally relevant substances. Due to similarities between SCCs and one type of taste receptor cell, the suggestion is made that taste buds may be compound sensory organs that include some cells related to SCCs and others related to cutaneous Merkel cells. The lack of taste buds in hagfish and their presence in all vertebrates may indicate that the phylogenetic development of taste buds coincided with the elaboration of head structures at the craniate-vertebrate transition.

Background: Taste buds on the pig tongue have been neither studied in detail nor quantified. We have counted the numbers of fungiform and vallate papillae, estimated their taste bud densities, and computed numbers of taste buds per volume of papilla on porcine tongue. Pig was chosen for this work because it is an omnivorous animal, and is one of the better models for study of nutrition-related problems in omnivorous human beings., Methods: Tongues from three adult pigs were obtained from the local abattoir, fixed in 10% neutral buffered formalin, and mapped for the fungiform and vallate papillae. Serial 15 microns sections were prepared from blocks containing the papillae, and were stained by H & E. Density and volume of the taste buds were estimated using a Bioquant system., Results: Eight hundred fifty and 826 fungiform papillae were observed on tongue I and II, respectively; numerically vallate papillae were 1, 2, and 2 for tongue I, II and III, respectively. Number of taste buds per fungiform papilla was considerably less on the dorsal surface of the tongue (3.88/papilla) than on the lateral side (22.11/papilla). Vallate papillae contained significantly more taste buds, a mean of 732.67 per papilla (t = 14.27; df = 6; P = < 0.05), than in the fungiform papillae. Density of the buds per volume of fungiform papilla was notably less on the dorsum (13.69) than on the lateral border (30.08). The density of vallate papillae taste buds per volume of the papilla was significantly greater than the lateral and dorsal papillae taste bud density (t = 4.28; df = 6; P < or = 0.05)., Conclusions: The present results are relevant to studies on variations of taste sensitivity among regions of the tongue.

The occurrence, distribution and innervation of guinea pig vallate papillae were investigated by means of indirect immunofluorescence and immunoperoxidase methods using antibodies against: a neuron-specific protein, protein gene product 9.5 (PGP 9.5); various neuropeptides including calcitonin gene-related peptide (CGRP), substance P (SP), vasoactive intestinal polypeptide (VIP) and galanin; a monoamine, serotonin (5-hydroxytryptamine; 5HT). Numerous PGP 9.5-immunoreactive nerve fibers were found to form plexuses in the lingual epithelium both intragemmally and extragemmally and to comprise dense bundles in the lamina propria just beneath the epithelium. Moderate numbers of PGP 9.5-immunoreactive cells were observed in the taste buds. These cells, typically spindle in shape, extended through the entire thickness of the taste bud. CGRP-immunoreactive nerve fibers were numerous in the subgemmal connective tissue and entered the epithelium to form intragemmal and extragemmal networks. A dense subgemmal SP-immunoreactive network in the vallate papilla can be linked to the presence of taste buds, even though SP-immunoreactive nerve fibers rarely occurred intragemmally. No taste cells immunoreactive for CGRP and for SP were observed. Immunoreactivity for VIP or galanin was not detected in nerve fibers and taste cells. In contrast, some taste cells and a few, fine networks of nerve fibers in the connective tissue were immunoreactive for 5HT; none of the intraepithelial fibers were 5HT-immunoreactive. We suggest that: 1) functionally, 5HT-containing cells and the CGRP-containing nerve fibers may be primarily involved in the neural transmission or its modulation of the taste sensation; and 2) VIP and galanin can be excluded from that group of substances which plays important roles in taste sensation.

A transmission-electron microscope study of the rat circumvallate taste bud revealed that occasionally one and the same gustatory or Type III cell received innervation associated with subsurface cisterns as the Type II cell did, in addition to the ordinary afferent synapse. The subsurface cistern a flattened, smooth-surfaced saccular membrane system, hugged the plasma membrane of the gustatory cell along the boundary against the nerve terminal. The nerve terminal attaching to the cell was occupied with mitochondria and synaptic type vesicles. As these structural features resemble those of efferent synapses in certain other sensory cells including the inner ear hair cells, the gustatory cells dually innervated as demonstrated in the present study are presumably involved not only in the afferent but also in the efferent projection of nerves.

The present study was made to investigate the ontogeny of protein gene-product 9.5 (PGP 9.5)-like immunoreactivity (-LI) in the developing mouse circumvallate papilla (CVP), and its distribution was compared to that of neuron-specific enolase (NSE) and calcitonin gene-related peptide (CGRP). In adult CVP, PGP 9.5-LI was observed in the subgemmal nerve plexus; some thin PGP 9.5-like immunoreactive (-IR) nerve fibers penetrated taste buds and apical epithelium. PGP 9.5-LI was also observed in the spindle-shaped cells in taste buds, and a small number of round- or oval-shaped ganglionic cells in the lamina propria. The distribution of NSE-LI was comparable to that of PGP 9.5-LI. CGRP-LI was observed in the nerve fibers only; distribution of CGRP-IR nerve fibers was similar to that of PGP 9.5-IR nerve fibers, although the number of CGRP-IR nerve fibers was smaller than that of PGP 9.5-IR nerve fibers. At least six developmental stages were defined with regard to the developmental changes in the distribution of PGP 9.5-LI from embryonic day (E) 12 to adulthood: Stage I (E12-13)-a dense nerve plexus of PGP 9.5-IR nerve fibers was detected in the lamina propria beneath the core of newly-formed papilla. Stage II (E14-16) - thin PGP 9.5-IR nerve fibers penetrated the apical epithelium, and a few round-shaped cells in the apical epithelium also displayed PGP 9.5-LI. Stage III (E17-18) - thin PGP 9.5-IR nerve fibers penetrated the inner lateral epithelium of the trench. Stage IV [Postnatal day (P) 0-3] - many PGP 9.5-IR nerve fibers penetrated the outer lateral epithelium of the trench; later in this stage, taste buds appeared. Stage V (P5-10) - a small number of PGP 9.5-IR cells in the taste buds appeared, and their number increased gradually. Stage VI (P14-adult) - the number of PGP 9.5-IR taste cells increased and reached the adult level, while the number of PGP 9.5-IR nerve fibers decreased. The development of NSE-LI was similar to that of PGP 9.5-LI. CGRP-IR nerve fibers were detected at E12 in the lamina propria, and the development of the intraepithelial CGRP-IR nerve fibers was similar to that of PGP 9.5-IR nerve fibers. The present results indicate that invasion by nerve fibers of the epithelium of lingual papillae occurs in a complex manner, and that these nerve fibers may participate in the formation of the taste buds.

Light microscopic data on the innervation of taste buds in the soft palate of the rat obtained by methylene blue (MB) supravital staining are presented here for the first time. The taste pore including subpopulations of taste bud cells and nerve fibers were stained. Intragemmal nerve fibers were detected ascending up to the taste pore; this suggests the possibility of additional paracellular pathways in taste transduction directly via nerve fibers. Moreover, relatively large bulbous or laminar enlargements of the intragemmal nerve fibers were found. The branches of these nerve fibers, showing minute spiny protuberances, appeared to anastomose. Some perigemmal nerve fibers were also seen in close apposition to the taste pore. The basal plexus in the vicinity of the taste buds showed enlargements which resembled the Merkel's discs, but were significantly smaller. These structures did not occur in the subgemmal part of the basal plexus. Regarding the oxygen-dependency of the staining reaction, it was speculated that both MB and oxygen were attracted by iron-containing enzymes. Therefore, the strong affinities for MB shown by subpopulations of nerve fibers and taste bud cells were explained by their high requirements for oxygen. Furthermore due to its selectivity for intraepithelial nerve fibers and sensory cells, the method applied here is well-suited for routine use in light microscopy.

Despite the ancient origins and aberrant appearance of living jawless fishes, none of their features may be assumed to be primitive without comparisons among hagfishes, lampreys, and gnathostomes, and with the nearest relatives of all craniates, the cephalochordates. In this review, the sensory capabilities of lampreys and hagfishes will be compared, and the major features of early craniate sensory evolution will be infered using cladistic methodology and an accepted phylogeny of the hagfishes, lampreys and gnathostomes. Lampreys have well developed olfactory, visual and octavolateralis systems, each of which is known to play a role in lamprey life and behavior. Hagfishes have poorly developed visual and octavolateralis systems, but elaborate olfactory and chemosensory systems. Unfortunately, the natural behavior and lifestyle of hagfishes are poorly known, limiting our understanding of hagfish sensory biology. Both groups of living jawless fishes show mixtures of primitive and secondarily derived sensory features and have few shared derived sensory features that would indicate close relations between the two groups.

The distribution of laryngeal taste buds (TBs) and their neutral components in the cat were investigated by immunohistochemistry and electron microscopy. The antisera used in this study were against cytokeratin, protein gene product 9.5 (PGP9.5), neuron-specific enolase (NSE), S-100 protein, calbindin D, calcitonin gene-related peptide (CGRP), and substance P (SP). Taste bud cells were specifically immunoreactive to the antibodies of human cytokeratin subtypes 8 and 18 (CAM5.2). On observation with CAM5.2, TBs were seen distributed on the laryngeal surface of the epiglottis and spread caudally along the aryepiglottic folds, reaching peak density at the laryngeal side of the arytenoid tubercle. The PGP9.5 and NSE immunoreactivities were recognized in TB cells and nerve fibers, both within the TBs and in the subepithelial connective tissue. S-100 protein immunoreactivities were not found in any of the cells in the TBs but were found exclusively in the subepithelial neural elements. The calbindin-D, CGRP, and SP immunoreactivities were confined to a part of the neural elements that was very thin. Taste pores, taste villi, neuronal varicosity, and synapselike structures were observed by scanning and transmission electron microscopic study. From these results it is considered that the TBs act as a chemical receptor.

We investigated the positioning of the epiglottis in the pharyngo-laryngeal region and the distribution of taste buds on the epiglottis in the rat and house shrew, animals which have different feeding habits. In the fixed samples of both species, when the mouth was closed or slightly opened, the epiglottis was found to protrude into the nasopharyngeal hiatus above the soft palate. But it retracted from its position when the mouth was widely opened. In omnivorous rats (n = 6), the mean number (mean density +/- s.d.) of taste buds was 52 (12.6 +/- 2.2/mm2) on the laryngeal surface but only 4 (1.3 +/- 1.0/mm2) on the oral surface. The three-dimensional view was reconstructed from serial sections. The taste buds were distributed most densely close to the caudal base and became fewer toward the more rostral tip. In insectivorous house shrews (n = 2), 4 taste buds on average were found only on the laryngeal surface of the epiglottis. Epiglottal taste buds may work as chemosensory detectors to initiate the reflex reaction to protect the airway from oral substances during swallowing and drinking.

NaOH cell-maceration method was applied to the oral surface of the mouse hard palate to demonstrate the three-dimensional architecture of the connective tissue core (CTC) in the incisive portion. The CTC of the incisive papilla was inverted T-shaped, and was partially fused to that of the first antemolar ruga. Between the CTC of the incisive papilla and that of the first antemolar ruga, the incisive foramen opened in the shaped of crescent hiatus. Further, the round depressions, corresponding to the site of the taste buds, were situated exclusively in the anteromedial margin of the incisive foramen and in the oral aspect of the CTC of the incisive papilla close to the foramen. Such topographical relationship between the taste buds and the incisive foramen seems to be correlated to the discriminatory function of the taste buds. In the lateral sides of the incisive papilla, the connective tissue layer formed the conspicuous serrated ridges. It is suggested that the serrated ridges are interdigitated with the furrows in the basal surface of the epithelium, and act to prevent the epithelium from slipping during mastication.

Taste worlds of humans vary because of taste blindness to phenylthiocarbamide (PTC) and its chemical relative, 6-n-propylthiouracil (PROP). We review early PTC studies and apply modern statistical analyses to show that a higher frequency of women tasted PTC crystals, and were tasters (threshold classification). In our laboratory, scaling of PROP bitterness led to the identification of a subset of tasters (supertasters) who rate PROP as intensely bitter. Supertasters also perceive stronger tastes from a variety of bitter and sweet substances, and perceive more burn from oral irritants (alcohol and capsaicin). The density of taste receptors on the anterior tongue (fungiform papillae, taste buds) correlate significantly with perceived bitterness of PROP and support the supertaster concept. Psychophysical data from studies in our laboratory also show a sex effect; women are supertasters more frequently. The anatomical data also support the sex difference; women have more fungiform papillae and more taste buds. Future investigations of PTC/PROP tasting and food behaviors should include scaling to identify supertasters and separate sex effects.

The binding site of gurmarin, a peptide inhibiting the sweet-taste sensation, was studied in taste buds in rat circumvallate papillae by means of a histochemical technique. Frozen sections of tongues were incubated with gurmarin conjugated with biotin and thereafter examined with a light microscope. Positive reactivity for the peptide was localized to the taste hairs, the apical projections of taste bud cells. The reaction appeared in about 10% of the circumvallate taste buds examined. As electrophysiological studies indicate that gurmarin suppresses the sweet-taste sensation at the level of reception, the present study suggests that the receptor for sweet taste is located on the taste hairs, and, furthermore, is present only in a certain, limited number of the taste buds.

Background: The ability to detect chemical cues is highly developed in Scleroglossa, and particularly in anguid lizards. This ability was predicted because anguids possess a well-developed vomeronasal organ (VNO) (or Jacobson's organ) and rely largely on chemical cues in various behaviours as other active foragers. In this work, we have investigated the possible functional association between tongue flicking and the VNO in the lizard Anguis fragilis., Methods: The morphology of the tongue and the buccal cavity was investigated by light and scanning electron microscopy. The kinematics of tongue and jaw movements was studied by high speed cinematography., Results: The epithelial cells of the ventral aspect of the tongue tips show microstructures (microridges, microfacets, micropores) which are not present on other areas of the mouth. Beneath the tongue, the floor of the buccal cavity shows two concave-like elevations suggesting a structural analogy with the anterior processes described in snakes. The apex and the internal margin of these processes bear parallel oblique ridges. Taste buds occur anteriorly on the buccal floor and on the palate and are abundant on the internal side and on the edge on the anterior processes. The tongue showed three modes of tongue flicking: simple downward extension, single oscillation, and multiple oscillations. At each tongue flick, the ventral surface of the tips was observed contacting the substratum. Immediately after the tongue retraction, the buccal floor moved slightly upward. The observation of tongue flicking with the mouth open showed that the anterior processes moved upward when the tongue was retracted., Conclusions: These observations suggest that following: 1) during tongue flicking the ventral surface of the tongue tips invariably makes contact with the substratum; 2) the microstructures of the tongue tips and the ridges of the anterior processes might be helpful for collecting and receiving, respectively, chemicals during tongue flicking; 3) the anterior processes may be apposed on the roof of the mouth next to the ducts of VNOs when the buccal floor is fully elevated; 4) due to their localization, the taste buds could be equally stimulated by the molecules transferred during tongue flicking.

Taste bud cell turnover rate was examined in oral epithelium of the precocial chick, which at hatching contains the adult complement of taste buds. Forty newly hatched chicks received single or double pulse injections of tritiated thymidine (specific activity was 6.7 Curies/millimole; dosage was 0.5 microCuries/g body weight, intraperitoneally). Anterior mandibular epithelium was processed for light microscopic autoradiography at 2 and 16 hours, as well as 1, 2, 3, 4, 6, 8, 10, 12, 14, 16, 18, and 20 days after the initial pulse. In a coded and randomized procedure, the section (7 microns) through the bud's center was selected for counting > or = 6 silver grains over round-clear and gracile-dense gemmal cell nuclei. The mean number of labelled cells/bud varied significantly (P < or = 0.01) during the first four posthatch days, yielding the fastest gemmal cell turnover rates (3.4-4.4 days) yet reported in vertebrates. Average bud diameter also significantly changed during the first four posthatch days, and was reflected in shifts of the distribution of 40-69 microns and > or = 70 microns diameter buds. Both an increase in labelled bud cells and bud diameter during the first two posthatch days may reflect high proliferation rates in initially maturing buds. Subsequent decrease in bud diameter between 2 and 3 days postinjection may indicate splitting of large-diameter (> or = 70 microns) buds and/or normal bud cell death due to failure of sensory afferentation. Bud-splitting alone, however, cannot account for significant decreases in bud cell label which did not occur before 4-6 days postinjection.

When we eat or drink we perceive a sensation that is often described as taste. A better term for it would be flavour, because the experience is made up of different modalities of sensation. Amongst these modalities are those of smell, touch (texture), temperature, and, of course, the chemical sense of taste. In this paper only the sensations of oral chemoreception will be described. The distribution and the morphology of the chemoreceptors within the oral cavity, the mechanisms involved in the transduction of the signal and the central connections of the nerve fibres innervating the receptors will be discussed.

Calretinin-immunoreactivity (CR-ir) was examined in the rat oro-facial and pharyngeal tissues using an immunofluorescence method. CR-ir was distributed in the entire size range of trigeminal ganglion neurons. CR-ir was also observed in nerve fibers surrounding neuronal cell bodies in autonomic ganglia, and in nerve endings in the lip, tongue, incisal papilla, soft palate, pharynx and epiglottis. CR-immunoreactive nerve endings were all in close proximity to the epithelium, and classified into 2 types; simple (free nerve ending) and taste-bud-related types. In the salivary gland, positive nerve fibers were seen around large excretory ducts. The present study indicates that viscerosensory (probably including gustatory) nerve fibers innervating the oral and pharyngeal tissues contain CR, while somotosensory nerve fibers innervating the facial skin are devoid of CR.

Calcitonin gene-related peptide-like and neuron-specific enolase-like immunoreactivity (CGRP-IR and NSE-IR) were surveyed immunohistochemically in the fungi-form, foliate and circumvallate papillae in rats. A dense CGRP-IR network (subgemmal and extragemmal) in the taste papillae is linked to the presence of taste buds, even though CGRP-IR fibers are rarely present in the taste buds. Three typical fiber populations were detected with these two markers. (a) A population of coarse NSE-IR intragemmal fibers characterized by thick neural swellings, never expressing CGRP-immunoreactivity. (b) A population of thin varicose intragemmal NSE/CGRP-IR fibers. (c) A population of subgemmal and extragemmal NSE-/CGRP-IR fibers that partly penetrated the epithelium. The common distribution of CGRP-IR and NSE-IR fibers at the base of taste buds, their differential distribution and morphology within taste buds, added to their restricted nature (gustatory or somatosensory) suggest that a population of CGRP-IR fibers undergoes a target-induced inhibition of its CGRP phenotype while entering the taste buds. The combined use of NSE and CGRP allowed a better characterization of nerve fibers within and between all three types of taste papillae. NSE was also a very good marker for a subtype of taste bud cells in the foliate and in the circumvallate papillae, but no such cells could be observed in the fungiform papillae.

Immunoreactivity to neuron-specific enolase (NSE), a specific neuronal marker, and calcitonin gene-related peptide (CGRP) was localized in lingual taste papillae in the pigs. Sequential staining for NSE and CGRP by an elution technique allowed the identification of neuronal subpopulations. NSE-staining revealed a large neuronal network within the subepithelial layer of all taste papillae. NSE-positive fibers then penetrated the epithelium as isolated fibers, primarily in the foliate and circumvallate papillae, or as brush-shaped units formed by a multitude of fibers, especially in the fungiform papillae and in the apical epithelium of the circumvallate papilla. Taste buds of any type of taste papillae were found to express a dense subgemmal/intragemmal NSE-positive neuronal network. CGRP-positive nerve fibers were numerous in the subepithelial layer of all three types of taste papillae. In the foliate and circumvallate papillae, these fibers penetrated the epithelium to form extragemmal and intragemmal fibers, while in the fungiforms, they concentrated almost exclusively in the taste buds as intragemmal nerve fibers. Intragemmal NSE- and CGRP-positive fiber populations were not readily distinguishable by typical neural swellings as previously observed in the rat. The NSE-positive neuronal extragemmal brushes never expressed any CGRP-like immunoreactivity. Even more surprising, fungiform taste buds, whether richly innervated by or devoid of NSE-positive intragemmal fibers, always harboured numerous intragemmal CGRP-positive fibers. Consequently, NSE is not a general neuronal marker in porcine taste papillae. Our observations also suggest that subgemmal/intragemmal NSE-positive fibers are actively involved in synaptogenesis within taste buds. NSE-positive taste bud cells were found in all three types of taste papillae. CGRP-positive taste bud cells were never observed.

The chemosensory gustatory cells in taste buds form chemical synapses with intragemmal neurites. We investigated the ultrastructure of the guinea pig gustatory cells after stimulation with a mixture of monosodium L-glutamate and guanosine 5'-monophosphate. The gustatory cells responded to the stimulus. The dense-cored vesicles localized in the presynaptic regions discharged the contents into the synaptic cleft by means of exocytosis, which resulted in a marked decrease of their population. These findings strongly suggest that the transmitter or transmitters contained in the vesicles are released in response to the taste stimulation at the cell apex, to conduct the excitement of the cell to the nerves.

Several hundred taste buds develop and mature in the trench walls of the rat's vallate papilla during the first 3 months after birth. The objective of this investigation of taste bud development was to determine: (i) whether the vallate papilla has local growth zones where new taste buds form, (ii) whether new taste buds arise by the division of mature taste buds, (iii) how many days are required for a new taste bud to mature, and (iv) whether a taste pore forms as the taste bud reaches a critical volume. Camera lucida drawings were made of more than 4000 iron hematoxylin-stained, serially sectioned, vallate taste buds. The relative abundance of immature taste buds declined exponentially with age, from 18% of the mature taste buds at day 15 to 2% at day 90. At days 21, 33 and 45 most of the immature taste buds (those lacking a taste pore) were located in growth zones at the anterior and posterior extremes of the vallate trench. A mean of 10.5 days was required for the maturation of each cohort of immature taste buds present at days 15, 21, 33 and 45. Vallate taste buds were added de novo; fission of mature taste buds was rare. Taste buds varied widely in the taste bud volume at which a pore formed and in the final volume of the taste bud.