Taste Buds In Fungiform Papillae Research Articles

Cell non-autonomous requirement of p75 in the development of geniculate oral sensory neurons

During development of the peripheral taste system, oral sensory neurons of the geniculate ganglion project via the chorda tympani nerve to innervate taste buds in fungiform papillae. Germline deletion of the p75 neurotrophin receptor causes dramatic axon guidance and branching deficits, leading to a loss of geniculate neurons. To determine whether the developmental functions of p75 in geniculate neurons are cell autonomous, we deleted p75 specifically in Phox2b + oral sensory neurons (Phox2b-Cre; p75fx/fx) or in neural crest-derived cells (P0-Cre; p75fx/fx) and examined geniculate neuron development. In germline p75−/− mice half of all geniculate neurons were lost. The proportion of Phox2b + neurons, as compared to Phox2b-pinna-projecting neurons, was not altered, indicating that both populations were affected similarly. Chorda tympani nerve recordings demonstrated that p75−/− mice exhibit profound deficits in responses to taste and tactile stimuli. In contrast to p75−/− mice, there was no loss of geniculate neurons in either Phox2b-Cre; p75fx/fx or P0-Cre; p75fx/fx mice. Electrophysiological analyses demonstrated that Phox2b-Cre; p75fx/fx mice had normal taste and oral tactile responses. There was a modest but significant loss of fungiform taste buds in Phox2b-Cre; p75fx/fx mice, although there was not a loss of chemosensory innervation of the remaining fungiform taste buds. Overall, these data suggest that the developmental functions of p75 are largely cell non-autonomous and require p75 expression in other cell types of the chorda tympani circuit.

A STUDY TO DETECT THE SAFETY OF ELECTRONIC CIGARETTE ON THE TASTE BUDS OF ALBINO RATS TONGUE PAPILLAE

Background: Electronic cigarette is a substitute to traditional nicotine smoke invented since 2004. There is no enough data about its safety with its the widespread usage.Aim of the study: The present study was designed to verify the impact of E-liquid of electronic cigarette on taste buds of fungiform papillae in albino rats.Materials and methods: 22 young adult male albino rats were divided into 3 groups. Group I: (control group), injected i.p by normal saline daily. Group II: (E-cigarette group): animals were injected i.p by E-cigarette refill liquid (ECRL) containing 0.5 mg of nicotine/kg for 6 days then continue to be administered the same dose day after day for 4 weeks. Group III (E-cigarette + vitamin C treated group): animals had been i.p injected by (ECRL) containing 0.5 mg of nicotine/kg. One hour from i.p injection of the liquid, the animals were received vitamin C 300 mg/ kg through oro-gastric gavage for 6 days. Then animals were receive the regimen day after day till the end of 4 weeks. Rats of groups sacrificed 24 hs from last injection. After processing the tissue samples, they were stained using Haematoxylin & Eosin and Cytokeratin 7 & TNF α. The results were analyzed statistically using one way ANOVA test.Results: Evaluation of the sections revealed significant differences between all groups with marked improvement in group III. p value was less than 0.05.Conclusion: E-cigarette smoking has a harmful effect on taste buds of fungiform papilla histologically and immunohistochemically. Vitamin C has a protective effect on taste bud against E-cigarette refill liquid.

Expression of the candidate fat taste receptors in human fungiform papillae and the association with fat taste function.

Significant experimental evidence supports fat as a taste modality; however, the associated peripheral mechanisms are not well established. Several candidate taste receptors have been identified, but their expression pattern and potential functions in human fungiform papillae remain unknown. The aim of this study is to identify the fat taste candidate receptors and ion channels that were expressed in human fungiform taste buds and their association with oral sensory of fatty acids. For the expression analysis, quantitative RT-PCR (qRT-PCR) from RNA extracted from human fungiform papillae samples was used to determine the expression of candidate fatty acid receptors and ion channels. Western blotting analysis was used to confirm the presence of the proteins in fungiform papillae. Immunohistochemistry analysis was used to localise the expressed receptors or ion channels in the taste buds of fungiform papillae. The correlation study was analysed between the expression level of the expressed fat taste receptors or ion channels indicated by qRT-PCR and fat taste threshold, liking of fatty food and fat intake. As a result, qRT-PCR and western blotting indicated that mRNA and protein of CD36, FFAR4, FFAR2, GPR84 and delayed rectifying K+ channels are expressed in human fungiform taste buds. The expression level of CD36 was associated with the liking difference score (R -0·567, β=-0·04, P=0·04) between high-fat and low-fat food and FFAR2 was associated with total fat intake (ρ=-0·535, β=-0·01, P=0·003) and saturated fat intake (ρ=-0·641, β=-0·02, P=0·008).

Impact of chorda tympani nerve injury on cell survival, axon maintenance, and morphology of the chorda tympani nerve terminal field in the nucleus of the solitary tract

Chorda tympani nerve transection (CTX) has been useful to study the relationship between nerve and taste buds in fungiform papillae. This work demonstrated that the morphological integrity of taste buds depends on their innervation. Considerable research focused on the effects of CTX on peripheral gustatory structures, but much less research has focused on the central effects. Here, we explored how CTX affects ganglion cell survival, maintenance of injured peripheral axons, and the chorda tympani nerve terminal field organization in the nucleus of the solitary tract (NTS). After CTX in adult rats, the chorda tympani nerve was labeled with biotinylated dextran amine at 3, 7, 14, 30, and 60 days post-CTX to allow visualization of the terminal field associated with peripheral processes. There was a significant and persistent reduction of the labeled chorda tympani nerve terminal field volume and density in the NTS following CTX. Compared with controls, the volume of the labeled terminal field was not altered at 3 or 7 days post-CTX; however, it was significantly reduced by 44% and by 63% at 30 and 60 days post-CTX, respectively. Changes in the density of labeled terminal field in the NTS paralleled the terminal field volume results. The dramatic decrease in labeled terminal field size post-CTX cannot be explained by a loss of geniculate ganglion neurons or degeneration of central axons. Instead, the function and/or maintenance of the peripheral axonal process appear to be affected. These new results have implications for long-term functional and behavioral alterations.

Expression of sulfonylurea receptors in rat taste buds

To test the possibility that a fast-onset promoting agent repaglinide may initiate prandial insulin secretion through the mechanism of cephalic-phase insulin release, we explored the expression and distribution character of sulfonylurea receptors in rat taste buds. Twenty male Wistar rats aged 10 weeks old were killed after general anesthesia. The circumvallate papillae, fungiform papillae and pancreas tissues were separately collected. Immunohistochemical staining was used to detect the expression and distribution of sulfonylurea receptor 1 (SUR1) or sulfonylurea receptor 2 (SUR2) in rat taste buds. Reverse transcriptase polymerase chain reaction (RT-PCR) was used to analyze the expression of SUR1 or SUR2 mRNA. The pancreatic tissues from the same rat were used as positive control. This is the first study to report that SUR1 is uniquely expressed in the taste buds of fungiform papillae of each rat tongue, while the expression of SUR1 or SUR2 was not detected in the taste buds of circumvallate papillae. SUR1 is selectively expressed in rat taste buds, and its distribution pattern may be functionally relevant, suggesting that the rapid insulin secretion-promoting effect of repaglinide may be exerted through the cephalic-phase secretion pathway mediated by taste buds.

Morphological changes in the tongue as a consequence of manganese inhalation in a murine experimental model: Light and scanning electron microscopic analysis

Air pollution by suspended particles has become a worldwide health problem. The main sources of these particles are fossils and additives combustion. Mn enters the body through inhalation, but part of the particles accesses contact with tongue's posterior surface where lingual tonsils and lingual papillae are placed. We decided to explore in a mouse model, the impact that the deposit of inhaled Mn has on the tongue's surface. Atrophy of the lingual tonsil, filiform papillae, as well as the swelling of taste buds in fungiform papillae, were the predominant changes. Ferropenic anemia is associated with the changes described and could be related to the interference of Mn in iron metabolism and riboflavin absorption. More research should be done to explore the participation of suspended particles trapped in the oral cavity in toxicology of Mn or other inhaled pollutants.

Contact Endoscopic Comparison of Morphology of Human Fungiform Papillae of Healthy Subjects and Patients with Transected Chorda Tympani Nerve

The chorda tympani nerve (CTN) carries gustatory fibers from taste buds of fungiform papillae (fPap) of the anterior portion of the tongue. Accordingly, middle ear surgery with transection of the CTN may result in gustatory impairment. With use of contact endoscopy, the present study aimed to compare number and shape of fPap and subepithelial vessel formation in patients after CTN transection with that of healthy controls. The number of fPap per square centimeter was obtained in addition to measures of gustatory sensitivity using electrogustometry and intensity ratings of natural taste stimuli. Data from 32 healthy subjects (mean age 40 yr; 16 female, 16 male) were compared with those from 14 patients whose CTN had been cut and partly resected during middle ear surgery because of cholesteatoma (mean age 38 yr; 7 female, 7 male). Middle ear surgery was performed by two of the authors. In healthy subjects, a higher fPap density was found on the tongue's tip compared with its edge; younger subjects had higher densities than older subjects. No sex-related differences were observed. Patients with transected CTN exhibited a significant decrease of taste function as measured with both natural and electric stimuli. In patients, we found significantly fewer and flatter fPap on the side of the tongue where surgery had been performed in comparison with the contralateral side. In addition, fPap density at the ipsilateral side was significantly lower compared with fPap density on the respective side in healthy controls. As established through contact endoscopy, the number of fPap decreases in relation to deafferentation and also in relation to the subjects' age, both of which are accompanied by a decreased gustatory sensitivity.

Confocal microscopy of the Peripheral Gustatory System: Comparison between Healthy Subjects and Patients Suffering from Taste Disorders during Radiochemotherapy

Laser-scanning microscopy (LSM) was used to compare taste buds and epithelia of fungiform papillae of healthy subjects with those of patients suffering from taste disorders during/after radiochemotherapy (RCT). Aim of the study was to investigate effects responsible for taste loss at a microscopic level. Prospective study. Data from 12 healthy subjects (mean age 52.4, SD 9.5 years) were compared with those of 12 patients (mean age 54.7, SD 8.5 years) with head and neck cancer suffering from taste disorders during RCT. Four parameters from LSM were selected for analysis: 1) distance between the pore of the taste buds of fungiform papillae and the crest of the papillary vessels; 2) epithelial cells of each taste bud at 34 mum; 3), cell density, and 4) area of the taste pore at 4 mum. These data were correlated to measures of gustatory sensitivity obtained with both the validated "taste strips" test kit and electrogustometry. Patients complaining from taste disorders during RCT exhibited a significant decrease of taste function assessed with both natural and electric stimuli. In these patients, we found thicker epithelia and smaller areas of the taste pores compared with healthy subjects. In 30% of those patients, no taste pores were detectable; in deeper sections, however, normal taste buds were present. In conclusion, in RCT patients with taste disorders, LSM indicates changes of epithelia of fungiform papilla but no changes of the taste bud structure. Damage of the chorda tympani nerve by scattered rays, direct or indirect mucotoxic effects of chemotherapeutic agents, and covering of taste pores by epithelial cells are likely reasons for taste loss during RCT.

Gap Junctions among Taste Bud Cells in Mouse Fungiform Papillae

Introduction Mouse taste buds in fungiform papillae consist of ∼50 cells (TBCs; unpublished data), but only a few of them have synaptic contacts with taste nerves (Kinnamon et al., 1993; Seta and Toyoshima, 1995). Neither chemical nor electrical synapses/gap junctions have been confirmed in mammalian taste buds, though a subpopulation of TBCs expressed a variety of neurotransmitter receptors (Kumazawa et al., 2001; Hayato et al., 2002). Non-innervated TBCs thus have been assumed to be supportive. However, we considered their roles in taste transduction. We tested this hypothesis under in situ whole-cell patch clamp and optical recording conditions (Ohtubo et al., 2001). Patch clamp studies showed that a part of TBCs generated depolarizing or hyperpolarizing receptor potentials in response to taste substances. Optical recordings with a voltage-sensitive dye showed that such chemosensitive TBCs tended to form colonies by the polarity of their receptor potentials, suggesting the existence of any interactions among TBCs. In the present study, we show the diffusion of probe dyes from injected TBCs to their neighbors (dye-couplings), which evidences the existence of intercellular corridor between TBCs. These results suggest that there are TBC networks within mammalian taste buds, and that taste buds are miniature processing units rather than the aggregation of chemosensitive cells.

PROP (6-n-propylthiouracil) supertasters and the saltiness of NaCl.

Taste blindness to phenylthiocarbamide (PTC) and its chemical relative 6-n-propylthiouracil (PROP) was discovered in the 1930s. Family studies showed that those who could not taste PTC/PROP (nontasters) carried two recessive alleles. In recent years, we have classified tasters into two groups: medium (PROP is moderately bitter) and supertasters (PROP is intensely bitter). With our classification, approximately 25% of Americans are nontasters, 50%, medium tasters, and 25%, supertasters. Studies showed that supertasters form a cohesive group. Anatomical studies showed that supertasters have the most fungiform papillae. Psychophysical studies showed that supertasters perceive the most intense bitterness and sweetness from a variety of compounds, the most intense burn from oral irritants, and the most intense tactile sensations from viscous solutions. Oral burn and touch are presumably perceived to be the most intense to supertasters because taste buds in fungiform papillae are innervated by the trigeminal nerve (pain, touch) as well as the chorda tympani nerve (taste). The psychophysical scaling method used was magnitude matching with NaCl as the control modality. With this method, subjects rated the intensities of a series of NaCl and PROP solutions. The assumption that the taste of NaCl did not vary with PROP status allowed comparisons of the bitterness of PROP across subjects. Early magnitude matching studies, using sound as the control, had suggested that this assumption was reasonable. However, recent studies challenged that conclusion. Larger samples with more diverse populations, using sound as the control, showed that the taste of NaCl varied with PROP bitterness; supertasters perceived the strongest taste and nontasters, the weakest. Thus our earlier conclusions were conservative because differences between nontasters, medium tasters, and supertasters were concealed by using NaCl as a standard. Using magnitude matching with sound as the standard, or using the Green scale, which employs intensity labels, we found that the differences between PROP groups are larger. Note that the association between PROP status and salt taste is interesting in itself, since variability in salt taste may have important nutritional consequences.

Modulation of rat chorda tympani nerve activity by lingual nerve stimulation.

1. A subpopulation of lingual nerve (LN) fibers surround and/or terminate in taste buds in fungiform papillae. One possible function of these fibers is to modulate chorda tympani fiber (CT) or taste responses. To test this hypothesis, the rat LN was stimulated electrically at various voltages (to 20 V), and single- and multiunit CT responses to water-0.1 M NaCl cycles were recorded before, during, and after LN stimulation. 2. When a thermally controlled water-0.1 M NaCl stimulus cycle was applied onto the tongue's surface, the surface temperature remained constant, independent of the stimulation voltage. In the absence of a liquid stimulus, the tongue's surface temperature increased approximately 4 degrees C upon LN stimulation for voltages > or = 5 V. This temperature increase, caused by vasodilation by way of the axon reflex flare mechanism, was taken as evidence that LN stimulation induces peptide release. 3. Comparison of CT activity before LN stimulation with the activity either during or after stimulation revealed statistically significant changes in CT activity. During LN stimulation the CT activity decreased. After LN stimulation, the variability in amount of CT activity increased. 4. In rats treated postnatally with subcutaneous injections of capsaicin to reduce or eliminate polymodal nociceptors, LN stimulation did not produce increases in the tongue's surface temperature or changes in CT activity. 5. Changes in CT activity could be detected seconds after LN stimulation, suggesting that the intragemmal and/or perigemmal LN fibers modulate CT activity. 6. The physiological implications of this study suggest that CT responses to salt can be modulated by endogenous compounds (probably peptides), eating foods that activate LN responses (e.g., foods that are very acidic or contain capsaicin) may modulate taste responses, and peri- and intragemmal fibers should be considered an integral part of the taste receptor system.

Three-dimensional structure of the gustatory cell in the mouse fungiform taste buds: a computer-assisted reconstruction from serial ultrathin sections.

Taste buds in fungiform papillae of the mouse were examined with transmission electron microscopy and computer-assisted, three-dimensional reconstruction from serial ultrathin sections. In accord with observation by Murray (1971), four distinct cell types, type I, II, III and basal cells, were identified. Of these, only the type III cell made synaptic contacts with nerve terminals and contained both small, clear vesicles and dense-cored granules. The former vesicles were synaptic-type and accumulated in the cytoplasm just below the synaptic in membrane thickenings. This finding clearly indicates a sensory function for the type III cell. One to three type III cells were identified within a taste bud. The type III cell had at most eight synapses with nerve terminals. One nerve fiber making two synapses with the type III cell was occasionally observed in its terminal region.

鼓索・舌神経切除によるウサギ茸状乳頭の形態的変化に関する電子顕微鏡的研究

The epithelia of rabbit fungiform papillae and filiform papillae were studied by electron microscopy. Further, filiform changes observed in the dorsal epithelium of fungiform papillae after chorda-lingual neurectomy were studied by scanning electron microscopy ; the state of keratinization of the epithelium was observed by transmission electron microscopy ; and the findings were compared with those in the epithelium of normal filiform papillae. The surface of fungiform papillae was relatively smooth, and the dorsal epithelium was covered by a thin keratin layer with no keratohyalin granules. In filiform papillae, the nature of keratinization was quite different between the epithelial cell layers on the anterior and posterior aspects of the papillae. On the anterior aspect, epithelial cells contained many keratohyalin granules, were nucleated to the topmost layer, and formed a soft keratin layer, showing a strong tendency toward parakeratosis. On the posterior aspect, in contrast, the cytoplasm of epithelial cells was rich in ribosomes and tonofibrils, but few keratohyalin granules were noted. The superficial cells had no nuclei or cell organelles and showed true keratinization, forming a hard keratin layer. After chorda-lingual neurectomy, taste buds in fungiform papillae degenerated, and marked progression of keratinization was observed in the dorsal epithelium of many fungiform papillae 1 week after denervation. The keratin layer on the dorsal aspect of these papillae was thickened, and the papillae were characteristically pointed as in filiform papillae and curved toward the pharynx. These changes became more notable with time, and the fungiform papillae were difficult to distinguish from surrounding filiform papillae by scanning electron microscopy 6 months after denervation. In the dorsal epithelium of fungiform papillae showing marked changes, transmission electron microscopy showed a pseudokeratotic layer occasionally containing condensed nuclei in the anterior aspect of the papillae but a keratin layer without nuclei or cell organelles in the posterior aspect. The ultrastructural examination of markedly degenerated fungiform papillae revealed a dual keratinization pattern similar to that in the epithelium of filiform papillae. Keratohyalin granules were observed in fungiform papillae showing marked keratinization. The appearance of keratohyalin granules not observed in normal fungiform papillae showing only mild keratinization suggests that they play a role in keratinization of fungiform papillary epithelium.

Evidence for stimulus access to taste cells and nerves during development: An electron microscopic study

We have examined developing taste buds in fungiform papillae of rats from the 18th day of gestation (E18) to the 15th postnatal day (P15). Nerve processes were seen in the epithelium of E18 rats before taste buds were obvious. At E20, early taste buds were visible, but were embedded within the epithelium, i.e., their cells were shielded from the oral cavity by overlying squamous epithelium. At this stage, the epithelium on the lateral aspects of the fungiform papillae was keratinized, but that overlying the taste bud was not. Some taste bud cells at E20 contained synapse-like structures near their contacts with nerve processes. In postnatal animals, keratinized epithelial cells were seen overlying taste buds, but taste pores were not observed until P10. How, then, do stimuli reach the taste cells and elicit physiological and behavioral responses as reported by others? The keratinized epithelium overlying the buds was unlike that on the lateral aspect of the papilla in at least one significant way. Few lamellated bodies were present in intercellular spaces beneath the stratum corneum, whereas these were abundant in the corresponding location within epithelium on the slope of the papilla. Although some were present within the squamous epithelium overlying the bud, they apparently were not released into the intercellular space. These lipid-rich lamellated bodies are thought to represent the water barrier of the epithelium, i.e., the barrier which prevents aqueous solutions from passing through the epithelium. We determined that the keratinized epithelium overlying the taste bud was permeable to a tracer, lanthanum nitrate, whereas that on the lateral surface was not. Lanthanum was visualized around taste cells and around nerve profiles within and near the taste bud. We propose that the absence of an aqueous permeability barrier in the epithelium overlying taste buds likely explains the ability of tastants to reach the taste bud cells and nerves in the developmental period before pore formation.

味らいの化学的損傷に関する実験的研究 酸性化学物質による茸状乳頭味らいの傷害

Lesions of the taste buds are often seen in an injuried tongue, but the histopathology of these lesions are not obvious.So, the purpose of this study was to examine the microstructure of the taste buds of tongue injuried by acid chemical substances.Experimental methods: 6-week-old Wistar strain rats were used as experimental animals. In order to give a tongue injury these rats were generally anesthesized with nembutal, and 5%, 10%, and 20% diluted Hel aqueous solutions were applied to the anterior 1/3 part of the tongue dorsal center for 1 minute. After application for a given time, the injured tongues were removed, and possible lesions of the taste buds of fungiform papillae were examined by light and transmission electron microscopes.Experimental results: Despite the damage of the tongue by as low as 5% HC1 aqueous solution, the taste buds of fungiform papillae were surely injured. After application, the taste cells (1 4 type) showed an increased electron density, and light and/or dark cells could not clearly be demarcated. In addition, a degenerating tendency of these cell components and organizations was observed: namely pycnosis, swelling of mitochondria and loss of cristae, decreased endoplasmic reticulum, increased vacuoles in the nerve ending region and breaked microvilli in the taste pore, etc. With higher concentrations of HC1 aqueous solution (10% and 20%), there was a tendency of the taste buds to be damaged excessively. The cell components were degenerated and destroyed, suggesting a functional disturbance. The degree of injury by acid chemical substances in the type 3 cells and the nerve endings of the taste buds were greater then that in the surrounding epithelial cells.

Fixation and occurrence of dark and light cells in taste buds of fungiform papillae.

The fine structure of taste buds of the fungiform papillae of the Old World monkey Cynomolgus (Macaca fascicularis) was found to vary with the primary fixative solution used. Standard primary fixative solutions of glutaraldehyde as well as fixatives containing both formaldehyde and glutaraldehyde gave non-reproducible and usually poor results. Osmium tetroxide in distilled water gave reproducible fixation of acceptable quality. Further, when fixed in osmium tetroxide in distilled water, taste buds of the fungiform papillae did not show the dark and light cells well known from other studies. It is therefore suggested that the terms dark and light cells not be used as synonyms for receptor or support cells, since the appearance of taste bud cells is affected by fixation.

Quantitative anatomical study of taste buds in fungiform papillae of young and old Fischer rats.

To determine if differences in neural taste responses relate to taste bud loss in old age, taste buds were counted in fungiform papillae of Fischer 344 rats aged 4 to 6 months, 20 to 24 months, and 30 to 37 months. Papillae anterior to the intermolar eminence on one half of the tongue were examined in serial sections. Presence or absence of a taste bud was noted and taste bud diameter was measured. Average percentages of papillae that contained a taste bud in the three groups were 99.6, 99.3, and 94.7%. This is a significant age-related difference but actual number of taste buds lost in the oldest rats was small. Taste bud diameter did not differ with age and general anatomical characteristics of buds were similar in all groups. Thus, anatomical observations on taste bud maintenance in rats over a wide age range, coupled with neurophysiological data, demonstrate that the integrity of the peripheral gustatory system is not altered greatly in old age.

舌の化学的損傷に関する病理組織学的研究 低濃度酸，アルカリによる創傷治ゆについて

Tongue injuries are caused mechanically, thermically, chemically and radiologically, etc., but these lesions and healing processes seem to have been less studied.The authors examined tongue injuries by acid or alkali substances, and discussed some problems about the healing process.Experimental methods:Six-week-old Wistar strain male rats were used as experimental animals. HC1 was used as acid, while NaOH used as alkali. The concentration of each chemical used in this study was 10, 20 and 30% diluted aqueous solution with application time of 1 minute. These experimental animals were generally anesthesized with Nembutal and the afilter paper sufficiently soaked with HCl or NaOH was applied to the anterior 2/3 part of tongue dorsal surfae.Thirty day-research was made on tongue damage and recovery which were examined by light and scanning electron microscope.Experimental results:Macroscopically, no remarkable change occurred by HCl or NaOH, but light and scanning electron microscopic examinations revealed the tongue injured by increased drug concentration and considerably destroyed taste buds of fungiform papillae. One or two weeks after the tongue injury, these damaged areas showed healing of the filiform and fungiform papillary wounds, and 30 days after the injury they showed regeneration with an almost normal structure of the taste bud. In this case, however, though usually a fungiform papillary taste bud has a taste pore, some of the regenerated taste buds had several taste pores, a very intresting finding in terms of the regeneration mechanism.

Aging effects on anatomy and neurophysiology of taste and smell.

Taste and smell have a primary role in food ingestion. Therefore, to understand why eating habits alter in elderly people, age‐related differences in the chemical senses should be investigated. In early anatomical studies, substantial decreases in numbers of taste buds in old human and mouse circumvallate papillae were observed. However, recent investigations in humans, monkeys, and rats indicate that there is not a significant loss of taste buds in old age. Neurophysiological recordings from the chorda tympani nerve, innervating taste buds in fungiform papillae, demonstrate significant but small differences in response magnitudes for some chemicals in old rats. Greater age‐related differences have been observed in the olfactory sense. Numbers of receptor neurons in the rat olfactory epithelium initially increase in adults and then decline in old animals; this decline is reflected in subsequent changes in the olfactory bulb. However, numbers of synapses in the bulb per receptor neuron are increased in the oldest rats, suggesting some compensatory mechanism. Differences in degree of aging effects in taste and smell might relate to the nature of receptors: a modified epithelial cell in taste versus a neuron in smell. However, in both sensory systems, large numbers of receptors remain even in old age. Since taste bud cells and olfactory receptors turn over and are replaced throughout life, the peripheral taste and smell systems might be relatively resistant to aging effects.

Content of biogenic amines in taste buds of fungiform papillae in rats

Content of biogenic amines in taste buds of fungiform papillae in rats