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PubMed1995

Decline of taste sensitivity in protein deficient adult rats.

The influence of dietary protein levels on taste sensitivity was studied in adult rats. Low protein diets of 0.0, 2.5, or 5.0% purified egg protein (PEP) were fed to animals for 28 days. Two bottle choice preference tests between aqueous solutions of either 2, 9, 17, or 86 mM sodium chloride and deionized water were conducted in an ascending order on days 14, 16, 18, and 20. Urine samples were collected for zinc and creatinine analysis. Blood samples were also collected for measuring serum zinc and creatinine concentrations. Scanning electron microscopy was performed to observe rats' tongue epithelia. Protein free diet group showed significantly lower taste sensitivity and renal reabsorption rate than other protein containing diet groups, while serum zinc and creatinine concentrations, and creatinine clearance were not affected by dietary protein level. Degeneration of filiform papillae and imperforation of taste pore of fungiform papillae were observed in protein free diet group. This experiment implies at least 2.5% dietary protein is required to manifest normal taste function in the adult.

Age Factors↗
PubMed1994

Consummatory feeding behavior to amino acids in intact and anosmic channel catfish Ictalurus punctatus.

The entire sequence of feeding behavior patterns exhibited by intact and anosmic channel catfish to food extracts was also released by single amino acids. L-arginine (> 10(-6) M), L-alanine (> 10(-6) M), and L-proline (> 10(-4) M) were each highly effective at releasing consummatory behavior patterns, such as turning, increasing pumping of water across the gill arches, and biting-snapping. Swallowing required solid objects, whereas rhythmic movement of the hyoid was released by > 10(-2) M L-arginine alone. For the biting-snapping behavior, the number of bites depended upon both the number of eddies containing the amino acid above the behavioral threshold concentration and the amino acid applied. Multiple eddies of > 10(-3) M L-proline and L-alanine provoked up to 25 bites per test; however, the most effective stimulus for releasing biting-snapping behavior at low concentrations was L-arginine (behavioral threshold 3 x 10(-7) M). In comparison to 10(-4) M L-alanine and L-arginine, other amino acids were less effective stimuli.

Amino Acids↗
PubMed1994

Flavor preferences conditioned by intragastric infusions of dilute polycose solutions.

Prior studies have obtained strong conditioned preferences (> 90%) for flavors paired with intragastric (IG) infusions of Polycose (hydrolyzed starch) over different flavors paired with IG water infusions. These experiments used concentrated Polycose solutions (16-32%; 0.6-1.2 kcal/ml) that contributed 50% or more of the animals' daily caloric intake. The present experiment sought to determine if calorically dilute solutions would also support preference conditioning. Adult female rats with gastric cannulas were trained with a cue solution (the CS+) paired with Polycose infusions. On alternate days a different cue solution (the CS-) was paired with IG water infusions. The CSs were unsweetened or saccharin-sweetened citric acid and sucrose octaacetate solutions that were available 22 h/day; chow was freely available. Separate groups were infused with Polycose at concentrations of 0.5%, 1%, 2%, and 4% (0.019-0.152 kcal/ml). The three higher concentrations conditioned flavor preferences of up to 89%. The infused Polycose represented only 1-14% of the animals' daily caloric intake and did not reliably reduce chow consumption. These findings demonstrate the sensitivity of the viscerosensory feedback system mediating flavor conditioning.

Animals↗
PubMed1994

Adaptation of sweeteners in water and in tannic acid solutions.

Repeated exposure to a tastant often leads to a decrease in magnitude of the perceived intensity; this phenomenon is termed adaptation. The purpose of this study was to determine the degree of adaptation of the sweet response for a variety of sweeteners in water and in the presence of two levels of tannic acid. Sweetness intensity ratings were given by a trained panel for 14 sweeteners: three sugars (fructose, glucose, sucrose), two polyhydric alcohols (mannitol, sorbitol), two terpenoid glycosides (rebaudioside-A, stevioside), two dipeptide derivatives (alitame, aspartame), one sulfamate (sodium cyclamate), one protein (thaumatin), two N-sulfonyl amides (acesulfame-K, sodium saccharin), and one dihydrochalcone (neohesperidin dihydrochalcone). Panelists were given four isointense concentrations of each sweetener by itself and in the presence of two concentrations of tannic acid. Each sweetener concentration was tasted and rated four consecutive times with a 30 s interval between each taste and a 2 min interval between each concentration. Within a taste session, a series of concentrations of a given sweetener was presented in ascending order of magnitude. Adaptation was calculated as the decrease in intensity from the first to the fourth sample. The greatest adaptation in water solutions was found for acesulfame-K, Na saccharin, rebaudioside-A, and stevioside. This was followed by the dipeptide sweeteners, alitame and aspartame. The least adaptation occurred with the sugars, polyhydric alcohols, and neohesperidin dihydrochalcone. Adaptation was greater in tannic acid solutions than in water for six sweeteners. Adaptation of sweet taste may result from the desensitization of sweetener receptors analogous to the homologous desensitization found in the beta adrenergic system.

Adult↗
PubMed1994

Genetics of bitter perception in mice.

Inbred and congenic strains exhibited several patterns of relative sensitivity to bitter tastants in 48-h, two-bottle preference tests. With segregation analyses of descendents of crosses between contrasting strains, these patterns suggested at least three genetic loci influencing bitter perception. The extensively characterized Soa (sucrose octaacetate) locus underlies one pattern. Variation at this locus had pleiotropic effects on avoidance of other acetylated sugars, plus such structurally dissimilar bitter tastants as brucine, denatonium benzoate, and quinine sulfate. Unlike SOA, however, sensitivity to quinine sulfate was polygenically determined, and produced a second characteristic pattern. At least one, possibly several, additional unlinked loci contributed to quinine differences. Phenylthiocarbamide (PTC) aversion differences exemplified a third pattern. Segregation consistent with monogenic control of PTC aversion has been reported, and within segregating populations PTC aversion did not covary with SOA or quinine sulfate avoidance. Variants of the three major patterns may be useful for analysis of specific mechanisms. While both showed the SOA pattern, strychnine differences were markedly smaller than brucine (dimethoxystrychnine) differences. Likewise, a hop extract containing primarily iso-alpha acids (e.g., isohumulone) produced an SOA-like pattern, while an extract with nonisomerized alpha-acids (e.g., humulone) did not.

Animals↗
PubMed1994

Glossopharyngeal denervation alters responses to nutrients and toxic substances.

Functional roles of the glossopharyngeal (GL) nerve on food and fluid intake were studied by examining effects of the GL denervation on two biologically different activities induced by specific diets using mice and rats. First, we examined whether GL section alters the acceptability of a bitter tasting essential amino acid, L-lysine (Lys), by Lys-deficiency in mice. The aversion threshold for Lys, normally about 3 uM in mice, increased to about 300 uM when mice were fed the Lys-deficient diet for 10 days. This increase of the Lys aversion threshold (increase of acceptability for Lys) by Lys-deficiency was also evident in mice with the chorda tympani denervation but was not observed in mice with the GL denervation. Next, we examined whether GL section alters the induction of a salivary protein, cystatin S (a cysteine proteinase inhibitor), by a diet containing papain (a cysteine proteinase) in rats. GL denervation largely inhibited the induction of cystatin S in the rat submandibular glands by papain. These results collectively suggest that chemosensory information conveyed by the GL nerve plays important roles on recognition of both nutrient and toxic compounds in the diet and induction of biological responses that protect the animal from both nutritional deficiency and exogenous toxic compounds.

Animals↗
PubMed1994

Bitter taste in single chorda tympani taste fibers from chimpanzee.

We have found earlier that chimpanzee chorda tympani taste fibers fall into groups that conform with the human taste qualities. This study focuses on bitter taste and its relation to sweet taste. Eight fibers were classified as bitter fibers according to their responses to 31 stimuli. The stimuli included the bitter compounds quinine, denatonium benzoate and caffeine. The results indicate a clear dichotomy between the bitter and sweet fibers. Sweet fibers never responded to the bitter compounds. However, in addition to their responses to the above compounds, some of the bitter fibers were stimulated by other compounds. Most prominent were responses to NaCl-amiloride mixture, KCl and xylitol. In most cases the cause could be assumed to be a bitter taste in the compound. These results suggest that the bitter and sweet tastes are conveyed in specific and separate groups of nerve fibers in the chimpanzee. Because of the closeness between chimpanzee and human, this finding has implications on the question of taste coding in human and the concept of taste qualities.

Animals↗
PubMed1994

Representation of hedonics and quality of taste stimuli in the parabrachial nucleus of the rat.

The distribution of evoked expression of the proto-oncogene c-fos was immunohistochemically examined in the parabrachial nucleus (PBN) of water-deprived rats after free ingestion of palatable liquids, after intra-oral infusion of aversive taste solutions including various bitter substances, and after an intraperitoneal injection of LiCl. C-fos immunoreactive neurons (c-fos neurons) were densely packed in the external lateral subnucleus (els), external medial subnucleus (ems), dorsal lateral subnucleus (dls), central lateral subnucleus (cls), and the central medial subnucleus (cms) depending on the kind of stimulation. The rostral part of the els may be related to general visceral inputs; the caudal part of the els, negative hedonics or aversive behavior; the dls, positive hedonics or ingestive behaviour. Both the ems and the els may be related to taste information for bitter tasting compounds and HCl; the cls, for sucrose and saccharin; and the cms, for NaCl.

Animals↗
PubMed1994

Chemoreception and perception of the bitterness of isohumulones.

Psychophysical experiments were conducted to determine whether isohumulones share a common receptor mechanism with other bitter compounds, and whether parotid saliva flow affects perception of their bitterness. Findings from a study of inter-individual differences in sensitivity to 23 sweet and/or bitter compounds among 25 subjects using the time-intensity (TI) method suggest that isohumulone and tetrahydroisohumulone may share a common receptor mechanism with other bitter compounds except those with the thiourea moiety. Isohumulone and tetrahydroisohumulone displayed a unique dome-shaped TI profile. The bitterness of the two compounds took longer to develop, but it lasted as long as for other bitter stimuli. In a study of the relation between perception of bitterness in beer and parotid saliva flow in 20 young adults, no significant difference was found among the mean saliva flows triggered by 0, 15 and 30 mg/L of isohumulones added to beer, and no significant correlation was found between saliva flow and maximum intensity or total duration of bitterness.

Adolescent↗
PubMed1995

Effect of anesthesia of the chorda tympani nerve on taste perception in humans.

Individuals who have sustained considerable damage to parts of the taste system often fail to experience changes in everyday taste experience. The two halves of the tongue are independently innervated: the chorda tympani (branch of the facial or VIIth cranial nerve) innervating the anterior two-thirds and the glossopharyngeal (IXth cranial nerve) innervating the posterior one-third. Anesthesia of the chorda tympani nerve on one side produced increased taste intensities for some stimuli on the area innervated by the glossopharyngeal nerve on the other side. Because this effect occurs across the midline and taste projects ipsilaterally, the effect must occur in the central nervous system (CNS). This supports Halpern and Nelson's release-of-inhibition hypothesis that the area to which the chorda tympani projects in the CNS must normally inhibit that of the glossopharyngeal nerve. Anesthesia of the chorda tympani abolishes that inhibition and leads to perception of increased taste intensities from areas innervated by the glossopharyngeal nerve.

Afferent Pathways↗
PubMed1986

Constraints imposed on taste physiology by human taste reaction time data.

The speed with which an organism responds to stimulus events is reaction time (RT): the minimum time interval between stimulus arrival at a receptor organ, and an overt response by the organism. This time interval specifies maximum duration of all processes necessary for the RT sequence. Responses to any change in taste have RT less than 1 sec for suprathreshold concentrations. Therefore, constituent events at taste receptors, in the central nervous system (CNS), and at the response organ, must have sufficient durations less than 1 sec (Constraint 1). Taste stimulus durations of 50 msec, and therefore taste receptor events of approximately 50 msec, are sufficient for these responses (Constraint 2), as well as for taste quality identification responses (Constraint 3). Taste receptor latencies, neural conduction times, and RT response organ events are even briefer. Thus, 60% to 90% of human taste RT is CNS events. Taste receptor events remain crucial, but CNS processing is important, and apparently time limiting, in all human taste judgments.

Afferent Pathways↗
PubMed1994

Chemosensory transduction in eukaryotic microorganisms: trends for neuroscience?

It might appear curious to read about yeast, slime molds and protozoa in a journal dedicated to neuroscience. However, despite their distinct lack of synapses, eukaryotic microorganisms hold a wealth of information relevant to the signal-transduction pathways that underly activity in neuronal receptor cells, particularly those subserving the chemical senses. Microorganisms are sensitive to chemical stimuli from their environment and thus have similarities to receptor neurons of the olfactory system and the taste bud. Here, we introduce receptors, second messengers and effectors responsible for chemosensory signal transduction in yeast mating, sea-urchin spermatozoan chemotaxis, slime-mold aggregation and development, and ciliate chemoresponses.

Animals↗
PubMed1983

Binding of [14C]inosine to gustatory tissues of the turbot, Scophthalmus maximus.

Reversible specific binding of [14C]inosine has been demonstrated in turbot (Scophthalmus maximus) buccal tissues rich in taste buds. A highly significant correlation was found for a series of nucleosides and nucleotides between their feeding stimulant activity and their ability to displace bound [14C]inosine. It is concluded that the binding of inosine is the first step in the gustatory process.

Animals↗
PubMed1985

Monoclonal antibody 2C5: a marker for a subpopulation of small neurones in rat dorsal root ganglia.

Monoclonal antibody 2C5 labels a subset of dorsal root ganglion neurones in the rat. The cell sizes of these neurones fall within the range for the small dark cell population and the antibody labels between a half and two-thirds of the neurones in this size range. A subpopulation of small neurones was also labelled in the trigeminal and vagal ganglia. Other sites of immunoreactivity in the central nervous system are the region of the substantia gelatinosa of the spinal cord, fibres in Lissauer's tract, the tractus solitarius and the tuberculum olfactorium. These sites are consistent with the antigen being expressed by the central processes of primary afferent neurones. It is suggested that the size distributions of 2C5-positive dorsal root ganglion neurones and the pattern of 2C5 immunoreactivity within the spinal cord indicate that the labelled cells may be neurones with peripheral C fibers. Outside the nervous system the antigen is expressed in a number of specific cell types within a variety of organs. These include some pancreatic acinar cells, parietal cells of the gastric mucosa, some cells in taste buds, Leydig cells of the testis, scattered cells in lymph nodes and lung alveoli, some renal tubules, the epithelial lining of the fallopian tube, the epithelium covering the ovary and certain cells in the basal layer of the epidermis.

Animals↗
PubMed1982

Gustatory functions of the nucleus tractus solitarius in the rabbit.

Multiunit analysis revealed a rostral region of NTS containing cells responsive to taste stimulation of rostral tongue. Using representative stimuli for the 4 basic types of taste, maximal incidence and magnitude of response was found to NaCl, followed by HCl, sucrose and QHCl. Further analysis of temporal patterns of response to the tastants revealed differences among stimuli in latency and time course. A principal components analysis indicated that time course, apart from magnitude of response, could contribute to neural differentiation of tastants. Information was also derived on neural intensity functions for these basic types of tastants. Additional observations with sodium saccharin revealed minimal neuronal responsivity despite reported evidence of behavioral preference for this tastant by rabbits.

Animals↗
PubMed2004

Observation of tongue papillae by video microscopy and contact endoscopy to investigate their correlation with taste function.

OBJECTIVES: Contact endoscopy is a technique used to obtain detailed images of living epithelium in the fields of gynecology, rhinology and laryngology. Video microscopy is useful for observation of the surface of tongue papillae. In the present study, we attempted to apply the contact endoscopy technique together with video microscopy to observe tongue papillae, and to study the correlation between the condition of fungiform papillae and taste function. METHODS: Ten subjects (3 men, 7 women) were divided into two groups based on the results of a taste examination by electrogustometry. We compared the shape and blood vessels of the papillae between normal taste and taste disorder groups. RESULTS: In the normal taste group, round shaped papillae and clear blood vessels were observed with both microscopy and contact endoscopy. In the taste disorder group, flat and irregular papillae were observed with microscopy. Blood vessel flow of the papillae was observed to be poor with contact endoscopy. CONCLUSION: These findings suggested that the images of microscopy and contact endoscopy were related to taste function, and both techniques were useful for evaluating taste function.

Adult↗
PubMed2004

Ca2+/calmodulin-dependent protein kinase II in the rat cranial sensory ganglia.

Immunohistochemistry for Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) was performed on the rat cranial sensory ganglia. More than one half of neurons was immunoreactive for the enzyme in the trigeminal (60%), jugular (70%), petrosal (55%) and nodose ganglia (63%). These neurons were mainly small to medium-sized. The co-expression study demonstrated that one half of CaMKII-immunoreactive (ir) neurons was also immunoreactive for calcitonin gene-related peptide (CGRP) or the vanilloid receptor subtype 1 (VR1) in the trigeminal, jugular and petrosal ganglia. In the nodose ganglion, CaMKII-ir neurons were mostly devoid of CGRP-immunoreactivity (ir) (8.2%) whereas the co-expression with VR1-ir was common among such neurons (72%). In the facial skin, nasal mucosa and palate, the epithelium and taste bud were innervated by CaMKII-ir nerve fibers. In addition, the retrograde tracing study demonstrated that 39.6% and 44.8% of trigeminal neurons which were retrogradely traced with fluorogold from the facial skin and nasal mucosa exhibited CaMKII-ir. Forty-six percent of petrosal neurons which innervated the soft palate were immunoreactive for the enzyme.

Animals↗