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PubMed2001

Long-term follow-up results of electrogustometry and subjective taste disorder after middle ear surgery.

OBJECTIVES: The present study compares the long-term follow-up results of electrogustometry with patient reports of taste dysfunction after middle ear surgery. STUDY DESIGN: Retrospective review of 371 patients who underwent middle ear surgery. METHODS: Patients were divided into the following groups depending on the degree of manipulation or surgical damage to the chorda tympani nerves: the no-touch group (group 1 [n = 109]); the touch group (group 2 [n = 149]); and the severed nerve group (group 3 [n = 113]). Electrogustometry was periodically performed over the course of several years. RESULTS: The incidences of postoperative subjective taste disorder in groups 1, 2, and 3 were 2.8%, 25.5%, and 38.9%, respectively. Although the subjective taste disorder usually recovered within 1 to 2 years after surgery in all groups, it persisted for more than 2 years in 2.7% of the touch group and 5.3% of the severed nerve group. Concerning postoperative electrogustometric results, in the no-touch group, 8.3% of patients showed threshold elevation on electrogustometry, but the elevated thresholds completely recovered in all cases. In the touch group, 45% of patients exhibited elevated electrogustometric thresholds on their first postoperative test, including 32.9% who subsequently had complete electrogustometric recovery, 10.1% who subsequently had incomplete recovery, and 2% who failed to recover during the follow-up period. In the severed nerve group, none of the patients was responsive to the electrical stimulus on the first postoperative test, including 8.8% of patients who subsequently exhibited complete electrogustometric recovery, 32.7% who later had incomplete electrogustometric recovery, and 58.4% who never recovered any electrogustometric responsiveness. Nerve repair in the severed nerve group produced better recovery, as measured electrically. CONCLUSIONS: The incidence of postoperative subjective taste disorder was low, although inconsistent with the high incidence of threshold elevation on electrogustometry, especially in the severed nerve group. Preservation or repair of the chorda tympani nerve is recommended in order to maintain or recover gustatory function.

Adult↗
PubMed2000

Plant secondary metabolites as mammalian feeding deterrents: separating the effects of the taste of salicin from its post-ingestive consequences in the common brushtail possum (Trichosurus vulpecula).

The effect of the phenolic glycoside, salicin, on food intake of the common brushtail possum (Trichosurus vulpecula) was studied in a series of feeding experiments. Increasing the concentration of salicin in a diet of fruits and cereals led to significant reductions of food intake in the short term (6 days). After prolonged (20 days) exposure to salicin, food intake (19 g kg(-0.75) day(-1)) was still reduced relative to controls (31 g kg(-0.75) day(-1)) but not reduced to the same extent as in the short-term experiments. Nonetheless, over these 20 days, common brushtail possums regulated their intake of salicin so as not to exceed a threshold limit of 1.9 +/- 0.1 g kg(-0.75) day(-1). Manipulative experiments sought to determine whether this threshold intake was in response to pre-ingestive factors (taste) or the post-ingestive consequences of ingesting salicin. Dietary salicin (0.17-5.0% DM) had no significant effect on nitrogen balance or urea metabolism and injection of a specific serotonin receptor antagonist, ondansetron, did not lead to increases in salicin intake as has been found for some other plant secondary metabolites. Similarly, administration of 1.3 g salicin by gavage had no significant effect on the subsequent intake of salicin compared to controls that were gavaged with water. We concluded that pre-ingestive factors were responsible for common brushtail possums limiting their intake of salicin-rich diets rather than any measurable post-ingestive consequence of feeding.

Animal Nutritional Physiological Phenomena↗
PubMed1986

Responses of cerebellar cortex to electrical stimulation of the glossopharyngeal nerve in the frog.

In the frog cerebellar cortex, electrical stimulation of the glossopharyngeal (IXth) nerve induced negative field potentials with a peak latency of 57 ms whose distribution was bilateral with ipsilateral predominance. The site where the maximum negativity was induced by IXth nerve stimulation was histologically located within the molecular layer near the Purkinje cell layer. In extracellular recording, electrical stimulation of the IXth nerve induced complex and/or simple spike discharges of Purkinje cells. Such evoked potentials and unitary spikes in the cerebellum were attributed to the excitation of the IXth nerve afferents of higher threshold which are mainly composed of fibers sensitive to taste stimulation. These results suggest that gustatory information projects to the cerebellum, as well as those of other kinds of senses, such as touch, visual and auditory sensation.

Animals↗
PubMed1976

Electrical responses to frog taste cells to chemical stimuli.

1. Cells inside a fungiform papilla of the frog tongue were impaled with a glass capillary micro-electrode filled with 3 M-KCl. Cells considered to be taste cells showed a resting potential of about -35 mV and an input resistance of 17 Momega on the average. 2. Application of chemical stimuli such as salts, acids and quinine produced a sustained depolarization in a taste cell, the magnitude of depolarization being dependent on the stimulus concentration. Water and weak NaCl solution yielded a hyperpolarization. The thresholds for depolarization as well as the concentration-response relationships for various chemical stimuli in taste cells are in approximate agreement with those determined from the glossopharyngeal nerve responses. 3. The magnitude of depolarization produced by 0-1 M-NaCl and 0-03 M-CaCl2 was dependent on the membrane potential level and reduced linearly with a rise in the latter. However, depolarizations generated by 0-001 M-HDl and 0-02 M quinine changed little in magnitude by a membrane potential change over a wide range. 4. During depolarizations induced by NaCl and KCl a marked reduction in the input resistance of a cell was observed, the amount of the reduction depending on the stimulus concentration. The reduction was also produced by CaCl2 and HCl, but it is small compared with those by NaCl and KCl. Quinine produced an increase in the resistance associated with a depolarization. Water and weak NaCl solution produced an increase in the resistance associated with hyperpolarization. 5. The receptive mechanisms for various kinds of chemical stimuli are discussed in relation to changes in the membrane potential and the membrane conductance of taste cells.

Animals↗
PubMed2000

Capability of respirator wearers to detect aerosolized qualitative fit test agents (sweetener and Bitrex) with known fixed leaks.

This study was designed to evaluate and compare the ability of respirator wearers to detect qualitative respirator fit test agents (saccharin and Bitrex) when the respirators were modified to include fixed size leaks. In recent years the number of persons who require fit testing has increased, partly in response to the needs of health care workers with potential exposure to infectious bio-aerosols. Many health care providers have chosen qualitative respirator fit testing using saccharin and/or Bitrex for a variety of reasons, including (but not limited to) low initial equipment cost. Respirators were modified to include a mid-line sampling probe between the nose and mouth for quantitative fit testing with a TSI PortaCount. A second modification included the introduction of a shortened 14-gauge intravenous catheter at the bridge of the nose. The fixed leak was designed to produce fit factors < 100 when unplugged, with an average fit factor of 67 among 26 respirator wearers. A complete fit test was not performed, because one purpose of this study was to determine the ability of respirator wearers to detect a known fixed leak during a single normal breathing exercise, without introducing unknown and potentially variable size leaks. Sensitivity threshold screening included a placebo and requirement to correctly characterize the taste of the agent used. Quantitative fit factors without leaks ranged from 96 to > 20,000 and 22 to 160 with the leak present. Twenty four of 26 subjects had fit factors < 100 (92%) when fixed leaks were induced. All subjects correctly detected Bitrex with fixed leaks (sensitivity = 100%). Nine of 26 subjects (35%) were unable to detect saccharin in the presence of a known fixed leak even though the average fit factor for these subjects was 77. When the two subjects with fit factors > 100 were excluded, only 16 of 24 respirator wearers were able to detect saccharin with fixed leaks (sensitivity = 67%). There were several important aspects of our study design worth noting, including the introduction of a placebo during sensitivity threshold testing, limiting the subject response time to a single maneuver, using a higher concentration of Bitrex than commercially available, and requiring the subjects to correctly characterize the taste of the qualitative test agent. In conclusion, leak detection was correctly identified with Bitrex, but not saccharin.

Adolescent↗
PubMed1991

Gustatory neural coding in the monkey cortex: stimulus intensity.

1. We analyzed the activity of single neurons in gustatory cortex of alert cynomolgus monkeys in response to a range of stimulus intensities. Chemicals were deionized water, fruit juice, and several concentrations of the four prototypical taste stimuli: 10(-3)-1.0 M glucose, 10(-3)-1.0 M NaCl, 10(-4)-3 x 10(-2) M HCl, and 10(-5)-3 x 10(-3) M quinine HCl. 2. Taste-evoked responses could be recorded from a cortical gustatory area that measured 2.5 mm in its anteroposterior extent, 6.0 mm dorsoventrally, and 3.0 mm mediolaterally. Taste-responsive cells constituted 62 (3.7%) of the 1,661 neurons tested. Nongustatory cells gave responses associated with mouth movement (10.1%), somatosensory stimulation (2.2%), and approach or anticipation (0.9%). 3. Intensity-response functions were determined across 62 gustatory neurons. Neural thresholds for each stimulus quality conformed well to human psychophysical thresholds. Mean discharge rate was a direct function of stimulus concentration for glucose, NaCl, and quinine HCl. The most effective of the basic stimuli was glucose. 4. Power function exponents were calculated from the responses of neural subgroups most responsive to each basic stimulus. Those for glucose, NaCl, and quinine were within the range of psychophysically derived values. Thus the perceived intensity of each basic quality is presumably based on the activity of the appropriate neural subgroup rather than on the mean activity of all taste cells. 5. The mean breadth-of-tuning (entropy) coefficient for 62 gustatory neurons was 0.65 (range, 0.00-0.98). 6. There was no clear evidence of chemotopic organization in the gustatory cortex. 7. An analysis of taste quality indicated that sweet stimuli evoked patterns of activity that were clearly distinct from those of the nonsweet chemicals. Among the latter group, NaCl was differentiable from HCl and quinine HCl, whose patterns were closely related. 8. The response characteristics of cortical taste cells imply gustatory thresholds and intensity-response functions for the nonhuman primate that conform well to those reported in psychophysical studies of humans, reinforcing the value of this neural model for human taste intensity perception.

Action Potentials↗
PubMed1994

High sensitivity of the turtle olfactory system to nonvolatile substances: comparison of response properties with those in gustatory systems.

The olfactory responses of the aquatic turtles, Geocylemys reevesii whose nostrils are closed underwater to nonvolatile substances were measured by recording the olfactory bulbar responses. Various salts, acids and bitter substances elicited large responses, while sugars and amino acids did not elicit the responses. The thresholds for the salts were much lower than those of corresponding salts in the rat gustatory system. The responses to the salts were partially suppressed by amiloride. Various acids induced large responses and the magnitudes greatly depended on the anion species. The thresholds for the bitter substances were much lower than those of corresponding substances in the taste systems. Similar to the responses in taste systems, both electrostatic and hydrophobic interactions contribute to the binding of the substances to the receptor membranes. Similar to the taste systems, the response to quinine hydrochloride showed a sharp temperature dependence having a peak around 25 degrees C, while the responses to odorants did not show such peak. The present results suggest that the olfactory system has similar abilities to respond to salts, acids and bitter substances to those in gustatory systems and that the high sensitivity of the olfactory system to chemical stimuli is not only attributable to the second messenger amplification system, but also to the basic property of the receptor membrane independent of the amplification system.

Acids↗
PubMed1975

Effects of obesity and set point on taste responsiveness and ingestion in humans.

Two experiments investigated the relationships among degree of obesity, nearness to set point for adipose tissue mass, and responsiveness to taste. In Experiment 1, subjects rated milkshakes varying in sweetness intensity. Overweight and normal weight subjects did not have significantly different detection thresholds or preference ratings. However, overweight subjects worked longer than normals to obtain their most preferred substance. Experiment 2 varied the ease of tasting the milkshake. Preference and food intake of moderately overweight subjects were significantly more influenced by tastes that they found positive and negative than was the preference of normal weight or obese subjects. The ease of ingesting the taste substance also significantly influenced preference and food intake of the moderately obese only. Nearness to set point, operationally defined as weight stability for 2 years, had no significant effects.

Adipose Tissue↗
PubMed2005

PLCbeta2-independent behavioral avoidance of prototypical bitter-tasting ligands.

Using a brief-access taste assay, we show in the present report that although phospholipase C beta2 knockout (PLCbeta2 KO) mice are unresponsive to low- and midrange concentrations of quinine and denatonium, they do significantly avoid licking higher concentrations of these aversive compounds. PLCbeta2 KO mice displayed no concentration-dependent licking of the prototypical sweetener sucrose but were similar to wild-type mice in their responses to citric acid and NaCl, notwithstanding some interesting exceptions. Although these findings confirm an essential role for PLCbeta2 in taste responsiveness to sucrose and to low- to midrange concentrations of quinine and denatonium in mice as previously reported, they importantly suggest that higher concentrations of the latter two compounds, which are bitter to humans, can engage a PLCbeta2-independent taste transduction pathway.

Animals↗
PubMed2004

Validation of a stimulation protocol suited to the investigation of odor-taste interactions with fMRI.

A protocol suited to the investigations of odor-taste interactions in a functional magnetic resonance imaging (fMRI) scanner is described and results that confirm the validity of that protocol are presented. Stimuli were dissolved in water and presented to the mouth of the participant through plastic syringes and plastic tubes as 50 microl every 3 s for 18 s. Participants were lying on the back to simulate the conditions in a fMRI scanner and gave pleasantness and intensity ratings in response to each stimulus using a Labeled Magnitude Scale (LMS). Stimuli were three concentrations of two tastants (i.e., sucrose and NaCl) and two odorants [i.e., ethyl butyrate (fruity) and citral (citrus)] and all possible odor-taste mixtures. Results showed that additivity of intensity in odor-taste mixtures was linear and did not depend on the pleasantness of the mixture. This study showed the feasibility of acquiring reliable psychophysical data with a stimulation device compatible with the fMRI environment and provided the foundation for the interpretation of future fMRI investigations of odor-taste interactions in flavor.

Acyclic Monoterpenes↗
PubMed1987

Action potentials in epithelial taste receptor cells induced by mucosal calcium.

Chemosensory cells in the taste bud of the tongue of Necturus generate action potentials in response to electrical stimulation through a microelectrode, as recently described by Roper (Science, 220: 1311-1312, 1983). We report that the epithelial receptor cells also respond to 10 mM CaCl2, applied to the mucosal surface, with a depolarization which elicits action potentials when a threshold of -50 mV is reached. Since CaCl2 is one of the taste stimuli in amphibia, the firing of action potentials by chemoreceptor cells may be part of the signal chain in gustatory reception of Ca ions.

Action Potentials↗
PubMed1986

Taste and salivary function.

Human taste perception was remarkably unimpaired in eight individuals with severe, chronic failure of all major and minor salivary gland function. Subjective reports of taste experience and objective measures of suprathreshold sensitivity were within normal limits for the overwhelming majority of these individuals. Impairments of threshold sensitivity for at least one quality was common, but normal thresholds for all four qualities were observed in one individual. These data demonstrated that the functional integrity of the taste system is not dependent upon the presence of normal saliva in the mouth. Thus, the suggestion that a salivary factor is responsible for the maintenance of taste receptor end organs can be rejected and attention directed toward other mechanisms, not dependent on saliva, that might account for the unusual resistance of these cells to environmental insult.

Adult↗
PubMed1997

Flavor characteristics of glutathione in raw and cooked foodstuffs.

The flavor of glutathione (gamma-L-glutamyl-L-cysteinylglycine, GSH) was examined by several sensory evaluations. The measurement of a point of subjective equality (PSE) showed that the peptide increases the flavor characteristics but did not affect the intensity of basic tastes, such as sweetness, saltiness, sourness, and umami. However, the threshold value of GSH decreased significantly in an umami solution containing 0.05% each of monosodium glutamate (MSG) and disodium inosinate (IMP). This suggests that GSH interacts with the umami substance and has a certain effect on the flavor. GSH had a characteristic kokumi flavor, such as continuity, mouthfulness, and thickness in the umami solution as well as in a model beef extract constructed from analyzed components at a concentration of 0.02% w/v. Some foodstuffs, including meat, were found to contain GSH above its threshold value, which implicates the contribution of GSH to the flavor. The thermal degradation study suggested that a part of GSH have changed into its disulfide, pyroglutamic acid (PCA), and cyclocysteinylglycine in cooked foodstuffs.

Cooking↗
PubMed2006

Individual differences in oral thermosensation.

Although oral thermosensation is critical to the perception of food and drinks, little information is available on the organization of individual differences in these abilities. We examined the relationship between measures of cooling and warming on the tongue and lip and the association of these measures to taste sensitivity in a sample of 76 healthy subjects. Thermal abilities were assessed with a computer-controlled, 1.5 cm2 peltier plate that was placed on the anterior dorsal surface of the tongue or the lower lip. Thermal testing consisted of both cooling and warming threshold detection, and intensity ratings of warm and cool suprathreshold temperatures. Intensity ratings of different temperatures were highly correlated, especially for temperatures in the same class. Similarly, warming and cooling thresholds were highly correlated. In contrast, thermal detection abilities were largely dissociable from suprathreshold intensity ratings, especially in the cooling direction. Suprathreshold ratings of cooling on the tongue were also modestly associated with ratings of the taste intensity of 6-n-propylthiouracil (PROP). However, a similar association was observed for the lower lip, indicating that the effect does not reflect an isolated characteristic of lingual physiology. Unexpectedly, two subjects with no history of oral trauma demonstrated abnormally deficient (4 S.D. below the mean) cool threshold detection abilities for the tongue, suggesting that there may exist subjects in the population who have profoundly poor lingual temperature processing.

Adult↗
PubMed1989

[Determining the threshold level for sensibility responses to galvanic potentials in the oral cavity].

The presence of different alloys in the oral cavity may produce potential differences of up to 900 mV. In the majority of the patients this phenomenon presents no problems. Occasionally, however, disturbing sensations, such as "metallic taste", "twinging or stabbing" and "minute electric shock" are reported. In finding out on the threshold level for discomforting sensations due to galvanic potentials in different probands, a special battery operated device was developed. Using a pair of electrodes connected to metallic restorations in the mouth, this device enabled the application and adjustment of direct current voltage and a superimposed pulse spectrum to evoke sensible reactions. The trials were conducted with 102 probands. The mean value for the threshold of sensation was above 1000 mV. In solitary cases, however, the threshold level was as low as 250 mV. This method may be used as a diagnostic aid to the objective assessment of complaints due to galvanic effects in the oral cavity and for the selection of a suitable metal in sensitive patients.

Dental Alloys↗