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PubMed2005

Differential covariation in taste responsiveness to bitter stimuli in rats.

Variation exists in the sensitivity of individual rodents and humans to different bitter tastants. An absence of uniform correlation in responsiveness to different bitter substances across individuals within a species suggests heterogeneity in the mechanisms underlying stimulus processing within this taste modality. Here, we examined taste responsiveness of individual rats to three bitter compounds (quinine hydrochloride, denatonium benzoate, and cycloheximide) in short-term lick tests to determine the magnitude of covariation among responses to these stimuli and infer commonalities in their receptor and neural mechanisms. Rats were tested with a given pair of bitter stimuli during three sessions comprising randomized trial blocks of six concentrations of each stimulus + deionized water. Psychophysical functions were generated for individual rats for respective stimulus pairs, and concentrations of each stimulus that produced equivalent lick suppression relative to water were correlated across animals. Behavioral taste responsiveness to quinine hydrochloride strongly covaried with responsiveness to denatonium benzoate (r = +0.82). Lick responsiveness to quinine was less robustly correlated with that to cycloheximide (r = +0.44), and denatonium and cycloheximide responses failed to correlate. These results imply substantial overlap in the bitter taste coding mechanisms for quinine and denatonium but some degree of independence in the mechanisms responsible for gustatory processing of cycloheximide. More generally, these data reinforce the notion that bitter taste processing is not a homogeneous event.

Animals↗
PubMed2001

Long-term zinc deficiency decreases taste sensitivity in rats.

The effects of zinc deficiency on taste sensitivity were examined in rats by recording the electrophysiological responses of the chorda tympani (CT) nerve and by use of a preference test. Male 4-wk-old Sprague-Dawley rats were given free access to a diet containing 2.2 (zinc-deficient), 4.1 (low zinc) or 33.7 (zinc-sufficient) mg zinc/kg diet. A fourth group was pair-fed the zinc-sufficient diet (with respect to the zinc-deficient rats). A two-bottle preference test using 0.15 mol/L NaCl and water revealed that NaCl preference was greater in the zinc-deficient and low zinc groups than in the control groups (zinc-sufficient and pair-fed) after 4 d of feeding. In the case of quinine hydrochloride solution (0.01 mmol/L), the preference was greater in zinc-deficient rats than in the other groups after 9 d, and the low zinc rats never showed a preference. Electrophysiological recording indicated that in the zinc-deficient rats, the CT nerve response to 0.20 mol/L NaCl was significantly less than that in the control rats after 21 d of feeding. In the low zinc rats, this response was significantly less than in the control rats after 35 d. The responses to quinine hydrochloride (0.02 mol/L), L-glutamic acid, HCl (0.01 mol/L) and NH(4)Cl (0.25 mol/L) in the zinc-deficient rats were not significantly reduced until d 42. These findings suggest that long-term zinc deficiency decreases taste sensitivity at the level of the CT nerve and that the change in NaCl preference due to zinc deficiency occurs before any change in NaCl taste sensitivity.

Animal Nutritional Physiological Phenomena↗
PubMed1980

Cellular localization of peptides in neural structures.

By means of the immunohistochemical technique of Coons and collaborators, numerous peptide-containing neurons have been observed in the brain, spinal cord and periphery. These neurons may contain peptides such as substance P, vasoactive intestinal polypeptide (VIP), enkephalin or somatostatin. Some systems are very extensive. For example, immunoreactive substance P has been observed in more than 30 cell groups in the central nervous system, in primary sensory neurons, in sensory neurons in the vagus nerve and in taste buds, and in intestinal neurons. Thus, one and the same peptide can be utilized at many different levels in the nervous system. Several examples are now known where a regulatory peptide occurs together with a classical transmitter, such as a catecholamine, in the same neuron, which suggests the possibility that a neuron can release more than one transmitter substance. Of particular interest is the occurrence of VIP in presumed cholinergic neurons innervating exocrine glands in the cat, and the coexistence of a cholecystokinin (CCK)-like peptide in dopamine neurons projecting mainly to limbic areas. In the former system VIP seems to be responsible mainly for vasodilation, whereas acetylcholine mainly causes secretion. Furthermore, combined infusion of both substances in very low doses results in a marked potentiation of the secretory and vasodilatory responses. Thus, we have an example where two putative transmitters, released from the same nerve endings, seem to cooperate to activate a physiological response (secretion). With regard to the central CCK/dopamine neurons the type of interaction between the two coexisting transmitter candidates is at present unclear. It is suggested that elucidation of different types of coexistence phenomena may advance our understanding of chemical transmission at synapses under normal and pathological conditions, and may lead to new approaches to the treatment of some nervous disorders.

Adrenocorticotropic Hormone↗
PubMed2000

The pit organs of elasmobranchs: a review.

Elasmobranchs have hundreds of tiny sensory organs, called pit organs, scattered over the skin surface. The pit organs were noted in many early studies of the lateral line, but their exact nature has long remained a mystery. Although pit organs were known to be innervated by the lateral line nerves, and light micrographs suggested that they were free neuromasts, speculation that they may be external taste buds or chemoreceptors has persisted until recently. Electron micrographs have now revealed that the pit organs are indeed free neuromasts. Their functional and behavioural role(s), however, are yet to be investigated.

Animals↗
PubMed1977

The Merkel cell system and a comparison between it and the neurosecretory or APUD cell system.

The Merkel cell, a neural crest migrant to the skin, possesses a characteristic intranuclear rodlet, cytoplasmic membrane-bound granules, and horn projections and is usually associated with nerve terminations. It is also associated with all types of known organizations of sensory nerve endings in the skin and possesses characteristic enzyme reactions in relation to the ending. The Merkel cell is found in the skin and the oral mucous membranes, and similar cells are observed in the taste buds and pulmonary tissue. A comparison between the Merkel cell and the APUD cell system of polypeptide hormone and amine-producing cells reveals many structural and chemical similarities.

Animals↗
PubMed2005

Electrophysiological and behavioural characterization of gustatory responses to antennal 'bitter' taste in honeybees.

We combined behavioural and electrophysiological experiments to study whether bitter taste is perceived at the antennal level in honeybees, Apis mellifera. Our behavioural studies showed that neither quinine nor salicin delivered at one antenna at different concentrations induced a retraction of the proboscis once it was extended in response to 1 M sucrose solution delivered to the opposite antenna. Bees that extended massively their proboscis to 1 M sucrose responded only partially when stimulated with a mixture of 1 M sucrose and 100 mM quinine. The mixture of 1 m sucrose and 100 mM salicin had no such suppressive effect. No behavioural suppression was found for mixtures of salt solution and either bitter substance. Electrophysiological recordings of taste sensillae at the antennal tip revealed sensillae that responded specifically either to sucrose or salt solutions, but none responded to the bitter substances quinine and salicin at the different concentrations tested. The electrophysiological responses of sensillae to 15 mM sucrose solution were inhibited by a mixture of 15 mM sucrose and 0.1 mM quinine, but not by a mixture of 15 mM sucrose and 0.1 mM salicin. The responses of sensillae to 50 mM NaCl were reduced by a mixture of 50 mm NaCl and 1 mM quinine but not by a mixture of 50 mM NaCl and 1 mM salicin. We concluded that no receptor cells for the bitter substances tested, exist at the level of the antennal tip of the honeybee and that antennal bitter taste is not represented as a separate perceptual quality.

Action Potentials↗
PubMed2006

Taste deficits related to dental deafferentation: an electrogustometric study in humans.

Dental treatments, the prevalence of which increases with age, can cause orofacial somatosensory deficits. In order to examine whether they may also affect taste sensitivity, electrogustometric thresholds were measured at 9 loci on the tongue surface in 391 healthy non-smoking, non-medicated subjects. Results showed that the greater the number of deafferented teeth, the higher the thresholds. Irrespective of age, subjects with more than 7 deafferented teeth exhibited significantly higher thresholds than subjects with fewer than 7 deafferented teeth. Conversely, across age groups, no statistical difference was observed among subjects with no, or few, deafferented teeth. Hence, a taste deficit, which was not correlated to aging, was observed. An association was noticed between the location of taste deficits and the location of deafferented teeth. Higher thresholds at anterior sites, with no possible traumatic injury relationship, suggested that neurophysiological convergence between dental somatosensory and taste pathways - possibly in the nucleus tractus solitarius - could be responsible for these relative decreases of taste sensitivity when dental afferences were lacking. Among trigeminal contributions, lingual nerve and inferior alveolar nerve may synergize taste.

Adult↗
PubMed1999

Bitter taste thresholds, numbers and diameters of circumvallate papillae and their relation with age in a Turkish population.

OBJECTIVES: This study analyses the relationship between the sense of bitter taste and age. The relationships between these and the numbers and diameters of Circumvallate Papillae (CP) are also analysed. SUBJECTS: Twenty-four elderly subjects (from 65 to 85 years) and 30 young subjects (from 17 to 25 years) were studied. METHOD: Bitter taste thresholds were determined by the three drop method with an ascending series of concentrations. The numbers and diameters of CP were observed by direct naked eye observation using a wooden tongue depressor, a gauge and a light source. RESULTS: The bitter taste acuity was significantly poorer in the older sample. There was no relationship between the bitter taste acuity and number of papillae but an inverse relationship was observed between the bitter taste acuity and diameters of papillae, thus lower acuity was associated with larger papillae. It was also observed that the diameters of papillae were inversely related to the numbers of CP. The distribution of numbers and diameters of CP were not significantly different between these samples with age.

Adolescent↗
PubMed1978

Other tastes, other worlds.

The idea of four primary tastes has influenced our concept of the gustatory world of all animals. It has also been the basis for constructing theories of gustatory neural integration. Since natural chemical stimuli are complex mixtures to which responses are multineuronal, difficult questions about integration arise. Answers are usually framed in terms of "labeled line" or "across-fiber" hypotheses. Comparative studies of vertebrate and invertebrate taste reveal in all receptors universal basic parameters that bear on the controversy. Comparative studies also place in more accurate perspective diverse chemically related ecologies and behaviors.

Animals↗
PubMed1978

Taste responses in sheep medulla: changes during development.

Response characteristics of taste neurons in the sheep solitary tract and nuclei alter during development. Solitary tract cells in younger fetuses respond to stimulation of the tongue with fewer salts and acids than do cells in older fetuses, lambs, and adults. Further, responses to specific salts and acids develop in a particular sequence, not randomly. These changes may relate to maturation of taste receptor sites.

Age Factors↗
PubMed2006

Taste receptors in the gastrointestinal tract III. Salty and sour taste: sensing of sodium and protons by the tongue.

Taste plays an essential role in food selection and consequently overall nutrition. Because salt taste is appetitive, humans ingest more salt than they need. Acids are the source of intrinsically aversive sour taste, but in mixtures with sweeteners they are consumed in large quantities. Recent results have provided fresh insights into transduction and sensory adaptation for the salty and sour taste modalities. The sodium-specific salt taste receptor is the epithelial sodium channel whereas a nonspecific salt taste receptor is a taste variant of the vanilloid receptor-1 nonselective cation channel, TRPV1. The proximate stimulus for sour taste is a decrease in the intracellular pH of a subset of acid-sensing taste cells, which serves as the input to separate transduction pathways for the phasic and tonic parts of the sour neural response. Adaptation to sour arises from the activation of the basolateral sodium-hydrogen exchanger isoform-1 by an increase in intracellular calcium that sustains the tonic phase of the sour taste response.

Animals↗
PubMed1987

Amiloride-sensitive sodium channels and expression of sodium appetite in rats.

Lingual application of amiloride hydrochloride blocks a sodium transport system in the mammalian gustatory system. Effects of exposure to amiloride on subsequent licking for 3% NaCl by rats were found to differ as a function of the animal's sodium balance. Licking for 3% NaCl was significantly increased in sodium-replete rats and significantly decreased in sodium-deplete rats by amiloride pretreatment. In fact, expression of sodium appetite was virtually eliminated by pretreatment with amiloride. This suggests that the recognition of sodium solutions in animals with a sodium deficit is dependent on amiloride-sensitive sodium transport at the taste bud.

Amiloride↗
PubMed1999

Hensin, the polarity reversal protein, is encoded by DMBT1, a gene frequently deleted in malignant gliomas.

The band 3 anion exchanger is located in the apical membrane of a beta-intercalated clonal cell line, whereas the vacuolar H(+)-ATPase is present in the basolateral membrane. When these cells were seeded at confluent density, they converted to an alpha-phenotype, localizing each of these proteins to the opposite cell membrane domain. The reversal of polarity is induced by hensin, a 230-kDa extracellular matrix protein. Rabbit kidney hensin is a multidomain protein composed of eight SRCR ("scavenger receptor, cysteine rich"), two CUB ("C1r/C1s Uegf Bmp1"), and one ZP ("zona pellucida") domain. Other proteins known to have these domains include CRP-ductin, a cDNA expressed at high levels in mouse intestine (8 SRCR, 5 CUB, 1 ZP), ebnerin, a protein cloned from a rat taste bud library (4 SRCR, 3 CUB, 1 ZP), and DMBT1, a sequence in human chromosome 10q25-26 frequently deleted in malignant gliomas (9 SRCR, 2 CUB, 1 ZP). Rabbit and mouse hensin genomic clones contained a new SRCR that was not found in hensin cDNA but was homologous to the first SRCR domain in DMBT1. Furthermore, the 3'-untranslated regions and the signal peptide of hensin were homologous to those of DMBT1. Mouse genomic hensin was localized to chromosome 7 band F4, which is syntenic to human 10q25-26. These data suggest that hensin and DMBT1 are alternatively spliced forms of the same gene. The analysis of mouse hensin bacterial artificial chromosome (BAC) genomic clone by sequencing and Southern hybridization revealed that the gene also likely encodes CRP-ductin. A new antibody against the mouse SRCR1 domain recognized a protein in the mouse and rabbit brain but not in the immortalized cell line or kidney, whereas an antibody to SRCR6 and SRCR7 domains which are present in all the transcripts, recognized proteins in intestine, kidney, and brain from several species. The most likely interpretation of these data is that one gene produces at least three transcripts, namely, hensin, DMBT1, and CRP-ductin. Hensin may participate in determining the polarized phenotype of other epithelia and brain cells.

Agglutinins↗
PubMed1993

Responses of single hamster parabrachial neurons to binary taste mixtures: mutual suppression between sucrose and QHCl.

1. Although taste experience typically arises from a mixture of gustatory stimuli, nearly all previous neurophysiological studies of the mammalian central gustatory system have focused on responses to single chemical stimuli. To begin to systematically examine CNS responses to taste mixtures, we recorded the extracellular activity of single third-order neurons in the hamster PbN to anterior tongue stimulation with binary mixtures of sucrose and QHCl. In experiment 1, neurons were tested with four concentrations of sucrose (0.001, 0.01, and 1.0 M) presented alone and mixed with 0.1 M QHCl. In experiment 2, neurons were tested with four concentrations of QHCl (0.00032, 0.0032, 0.032, and 0.1 M) presented alone and mixed with 1.0 M sucrose. 2. The response to each binary mixture was compared with the response to the more effective component (MEC) presented alone, and those that differed by more than a selected criterion (based on response variability) were identified. Of all mixture responses, 37% (59/158) involved mixture suppression (mixture response < MEC response), only 4% (6/158) were greater than the MEC, and 59% (94/158) were classified as not different than the response to the MEC. Most neurons that displayed mixture suppression did so at several mixture concentrations. 3. Sucrose suppression (mixture response < sucrose response) was prevalent among neurons most responsive to sucrose and for the mixtures that contained the stronger sucrose concentrations. Among neurons that displayed sucrose suppression, the magnitude of suppression was significantly correlated with sucrose response magnitude but not with QHCl response magnitude. These and other factors suggest that a neuron's capacity to display sucrose suppression to sucrose+QHCl mixtures is related to its sucrose sensitivity. 4. QHCl suppression (mixture response < QHCl response) was less prevalent than sucrose suppression, and the neurons that displayed QHCl suppression were almost exclusively a subset of those that displayed sucrose suppression to the same or different mixtures. This finding and the observation that one-third of all mixture responses involved mutual suppression (response to the mixture less than that to either component alone), suggest an association between the factors underlying sucrose suppression and QHCl suppression. 5. The across-neuron patterns (ANPs) of taste responses, which are thought to represent taste quality, were compared for mixtures and components. In general, the ANP for each mixture was similar to (significantly correlated with) the ANP of the more stimulatory component. However, for the mixture that evoked the greatest sucrose suppression, the mixture ANP was more similar to the ANP of the less stimulatory component.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1993

Enduring alterations in neurophysiological taste responses after early dietary sodium deprivation.

1. Neurophysiological taste responses from neurons in the nucleus of the solitary tract (NST) were studied in four groups of rats during chemical stimulation of the tongue with sodium and non-sodium salts, citric acid, and sucrose. The four groups of rats consisted of those fed a NaCl-deficient diet (0.03% NaCl) from day 3 postconception to at least day 50 postnatal (deprived rats), rats initially fed the NaCl-deficient diet during development and then placed on a NaCl-replete diet at adulthood for > or = 5 wk (control-deprived rats), and rats always fed the NaCl-replete diet (control rats). 2. Compared with controls, dietary NaCl deprivation instituted early in development resulted in highly attenuated average response frequencies to sodium salts (as much as 50%) but not to nonsodium salts and nonsalt stimuli. Concomitantly, most NST neurons in deprived rats responded "best" to NH4Cl and few responded best to NaCl. This is in contrast to that observed in controls, where the same proportion of neurons responded best to NaCl and best to NH4Cl. 3. Taste responses in recovered rats exhibited a hyperresponsiveness to many sodium salts compared with controls. That is, sodium salts elicited average response frequencies significantly greater (as much as 100%) than that obtained in controls. The proportions of neurons responding best to NaCl or to NH4Cl were opposite to that in deprived rats. In recovered rats, the proportion of neurons that responded best to NaCl was much greater than that which responded best to NH4Cl. 4. Rats deprived of dietary NaCl only as adults responded like controls. Therefore the environmental manipulations must occur during early periods of development. 5. These findings show that early dietary manipulations of sodium and subsequent replacement of dietary sodium have neurophysiological effects relatively selective for sodium-elicited taste responses. Furthermore, because recordings in recovered rats were obtained > or = 5 wk after feeding the NaCl-replete diet, it appears as though early NaCl deprivation permanently alters the functional organization of the NTS. Although it is likely that alterations in peripheral neural activity play a role in the functional development of NTS neurons responsive to taste stimuli, other non-activity-related factors may also be important.

Age Factors↗
PubMed1993

Voltage dependence of the rat chorda tympani response to Na+ salts: implications for the functional organization of taste receptor cells.

1. Voltage-clamp and current-clamp data were obtained from a circumscribed region of the anterior rat lingual epithelium while simultaneously monitoring the afferent, stimulus-evoked, neural response from the same receptive field. 2. Chorda tympani (CT) responses at constant Na(+)-salt concentration were enhanced by submucosa negative voltage clamp and suppressed by positive voltage clamp. The complete CT response profile, including the time course of adaptation, was not uniquely determined by NaCl concentration alone. The response could be reproduced at different NaCl concentrations by applying a compensating voltage. 3. The form of the concentration and voltage dependence of the CT response indicates that the complete stimulus energy is the Na+ electrochemical potential difference across receptor cell apical membranes, and not Na+ concentration alone. This is the underlying principal behind the equivalence of chemical and electric taste for Na+ salts. 4. CT responses to sodium gluconate (25 and 200 mM) and 25 mM NaCl produced amiloride-insensitive components (AIC) of low magnitude. NaCl at 200 mM produced a significantly larger AIC. The AIC was voltage-clamp independent. The relative magnitude of the AIC was positively correlated with the transepithelial conductance of each salt. This suggests that the large AIC for 200 mM NaCl results from its relatively high permeability through the paracellular pathway. 5. Analysis of the CT response under voltage clamp revealed two anion effects on Na(+)-salt taste, both of which act through the paracellular shunt. 1) Anions modify the transepithelial potential (TP) across tight junctions and thereby modulate the cell receptor potential. This anion effect can be eliminated by voltage clamping the TP. 2) Sufficiently mobile anions facilitate electroneutral diffusion of Na+ salts through tight junctions. This effect is observed especially when Cl- is the anion and when the stimulus concentration favors NaCl influx, allowing Na+ to stimulate receptor cells from the submucosal side. Because the submucosal intercellular spaces are nearly isopotential regions, this effect is insensitive to voltage clamp of the TP. The large AIC associated with this anion effect is due to the low permeability of amiloride.

Afferent Pathways↗