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PubMed1991

The shaker and shaking-B genes specify elements in the processing of gustatory information in Drosophila melanogaster.

Mutations that affect the physiological properties of neurones or the development of neuronal circuits are likely to have profound effects on sensory and motor pathways. We have examined the effects of mutations in two loci--the Shaker complex and shaking-B-on the taste pathway of Drosophila melanogaster Meigen at the behavioural and electrophysiological levels. The Shaker locus encodes a variety of A-type potassium channels that are likely to be tissue- and stage-specific. Flies containing the different Shaker alleles examined exhibit a variety of defects in their gustatory responses to sucrose, NaCl and KCl. The firing patterns of the labellar chemosensory neurones in response to these stimuli are normal. This suggests that the channels encoded by the Shaker locus are probably not involved in taste transduction, but affect central gustatory circuits. The shaking-B locus affects neuronal connectivity, though its molecular nature is unknown. Mutants at this locus show increased thresholds for detection of sucrose and fructose and lack the attraction response to 0.1 mol l-1 sodium chloride that is exhibited by the wild-type fly.

Action Potentials↗
PubMed1977

Hana Kai II: a 17-day dry saturation dive at 18.6 ATA. VII: Auditory, visual, and gustatory sensations.

Five divers were tested for alterations in auditory, visual, and gustatory functioning during a 17-day saturation exposure to He-O2 at 18.6 ATA. No evidence of permanent hearing loss was disclosed. Critical flicker fusion was not affected, but peripheral visual thresholds were significantly increased during the first two weeks at 18.6 ATA; this was interpreted to be evidence of severe psychological and physiological stress. Foveal vision was unaffected across testings. Magnitude estimation techniques disclosed changes in taste sensitivity, with sweet sensitivity increasing over time and sour sensitivity declining over the course of the dive. Subjects were more sensitive to bitter stimuli at maximum pressure than at sea level, and less sensitive to salt at maximum pressure. The results indicate that appreciable alterations in sensory functioning can occur during saturation exposures, although the sense modalities were differentially affected by such environmental stressors as pressure, psycho-social stress, fatigue, and perceptual deprivation.

Adult↗
PubMed2003

Discovery and structure determination of a novel Maillard-derived sweetness enhancer by application of the comparative taste dilution analysis (cTDA).

Application of a novel screening procedure, the comparative taste dilution analysis (cTDA), on the non-solvent-extractable reaction products formed in a thermally processed aqueous solution of glucose and l-alanine led to the discovery of the presence of a sweetness-enhancing Maillard reaction product. Isolation, followed by LC-MS and 1D- and 2D-NMR measurements, and synthesis led to its unequivocal identification as N-(1-carboxyethyl)-6-(hydroxymethyl)pyridinium-3-ol inner salt. This so-called alapyridaine, although being tasteless itself, is the first nonvolatile, sweetness-enhancing Maillard reaction product reported in the literature. Depending on the pH value, the detection thresholds of sweet sugars, amino acids, and aspartame, respectively, were found to be significantly decreased when alapyridaine was present; for example, the threshold of glucose decreased by a factor of 16 in an equimolar mixture of glucose and alapyridaine. Studies on the influence of the stereochemistry on taste-enhancing activity revealed that the (+)-(S)-alapyridaine is the physiologically active enantiomer, whereas the (-)-(R)-enantiomer did not affect sweetness perception at all. Thermal processing of aqueous solutions of alapyridaine at 80 degrees C demonstrated a high thermal and hydrolytic stability of that sweetness enhancer; for example, more than 90 or 80% of alapyridaine was recovered when heated for 5 h at pH 7.0, 5.0, or 3.0, respectively.

Alanine↗
PubMed1992

Preferred salt levels and salt taste acuity in human subjects after ingestion of untasted salt.

We have examined whether salt loading alters the salt preference or salt taste acuity of nine human subjects on continuous low salt diet. Subjects were randomly assigned to either untasted salt tablets (120 mmol/day) or placebo over a 2-week period at the end of which salt preference and salt recognition thresholds were measured. Subjects then received the alternate substance for another 2 weeks and the measurements were repeated. While urinary Na+ and Cl- were significantly increased while on salt tablets, urinary volume, K+, urea and creatinine concentrations, blood pressure, body weight, salivary and plasma electrolyte concentrations were unchanged. Plasma renin and aldosterone levels were reduced while on salt tablets but not significantly. Salt tablets caused a significant increase in sodium recognition threshold but a significant decrease in salt addition to unsalted tomato juice and in ideal salt level assessed by presalted (150 mmol/l) tomato juice. Thus, an increase in untasted dietary salt may reduce salt preference in human subjects, a finding opposite to that with an increased, tasted salt intake over a similar period.

Adult↗
PubMed1999

Effect of protease inhibitors on the sense of taste.

The purpose of this study was to investigate the taste properties of protease inhibitors which are essential components of drug regimes used to treat human immunodeficiency virus (HIV) infection. In this study, the taste properties of four protease inhibitors (indinavir, ritonavir, saquinavir, and nelfinavir) were investigated in unmedicated HIV-infected patients and healthy controls. Three of the four protease inhibitors (indinavir, ritonavir, and saquinavir) were found to be predominantly bitter (with additional qualities of medicinal, metallic, astringent, sour, and burning). Nelfinavir was found to be relatively tasteless. HIV-infected and uninfected control subjects detected protease inhibitors at similar concentrations, but HIV-infected subjects perceived suprathreshold concentrations as more bitter than controls. Detection thresholds ranged from 0.0061 mM for saquinavir in HIV-infected patients to 0.0702 mM for ritonavir in uninfected control subjects. Suprathreshold studies indicated that protease inhibitors modified the taste perception of a variety of other taste compounds. These results are consistent with clinical findings that protease inhibitors produce taste complaints that can impact patient compliance.

Adult↗
PubMed1978

The taste reactivity test. I. Mimetic responses to gustatory stimuli in neurologically normal rats.

One or two bottle preference tests, i.e., relative fluid consumption, constitute the primary methodology for determining acceptance or rejection of tastes in animals other than humans. These tests require organisms to initiate and maintain drinking behavior, and, therefore, can not be applied to preparations which do not eat or drink spontaneously. The taste reactivity test, a new method for assessing responses to gustatory stimuli, circumvents this shortcoming. A 50 microliter taste stimulus is injected directly into the oral cavity of a freely moving rat and the immediate response videotaped for frame by frame analysis. Each of the sapid stimuli used (4 concentrations of sucrose, NaCl, HCl, and quinine HCl) generated a stereotyped response derived from a lexicon of 4 mimetic (movements of lingual, masticatory, and facial musculature) and 5 body response components. Responses to taste stimuli were highly consistent within and between rats. For example, sapid sucrose, NaCl and HCl stimuli elicited a response sequence beginning with low amplitude, rhythmic mouth movements, followed by rhythmic tongue protrusions, and then lateral tongue movements. No body movements accompanied these mimetic responses. In contrast, quinine in concentrations at and above 3 X 10(-5) M (1/2 log step above the absolute behavioral threshold for quinine) elicited a response pattern beginning with gaping and proceeding through as many as 5 body responses. These normative data for the intact rat can be directly compared to the taste reactivity of neurally ablated preparations which do not spontaneously feed or drink. Such comparisons can be utlized in determining the neural substrates necessary for the execution and regulation of ingestive behavior.

Animals↗
PubMed1975

Multiple sensitivity to chemical stimuli in single human taste papillae.

The sensitivities of 15 human fungiform papillae were tested using a 5-alternative forced-choice procedure. Subjects were aked to recognize which of the following stimuli was presented to a papilla on each of 250 trials: 5.0 M NaCl, 0.5 N citric acid, 1.0 M quinine hydrochloride, and distilled H2O. Solution droplets were delivered to individual papillae from 0.5 mm diameter platinum wire loops. Based on each subject's responses to distilled H2O, corrections were made for individual response biases. Of the papillae tested, 33 percent responded to all four compounds, 33 percent to three, none to only two, 20 percent to only one, and 13 percent to none of the chemical stimuli. These results are contradictory to earlier work, in which it was suggested that taste quality is encoded by chemically specific papillae, but are consistent with the electrophysiological data suggesting multiple sensitivity of mammalian gustatory receptor cells and first-order neurons. The data suggested that the narrow range of sensitivity reported by von Békésy [2] was determined by the reciprocal relationship between the size of the stimulated area and the concentration necessary to elicit a threshold sensation.

Adolescent↗
PubMed2005

Kinetics and mechanisms of formation of bromophenols during drinking water chlorination: assessment of taste and odor development.

Halophenols are often reported as off-flavor causing compounds responsible for medicinal taste and odor episodes in drinking water. To better understand and minimize the formation of 2-bromophenol and 2,6-dibromophenol which have low odor threshold concentrations (OTCs, 30 and 0.5 ng/L, respectively) a kinetic data base for the chlorination and bromination of phenols was established by combination of kinetic measurements and data from literature. Second-order rate constants for the reactions of chloro- and bromophenols with chlorine and bromine were determined over a wide pH range. The second-order rate constants for bromination of phenols are about three orders of magnitude higher than for chlorination. A quantitative structure activity relationship (QSAR) showed a good comparability of second-order rate constants from this study with those published previously for different phenol derivatives. The quantification of product distribution of the formed halophenols demonstrated that chlorine or bromine attack in ortho position is favored with respect to the para position. A kinetic model was formulated allowing us to investigate the influence of chlorine dose and some water quality parameters such as the concentration of phenol, ammonia, bromide and the pH on the product distribution of halophenols. The kinetic model can be applied to optimize drinking water chlorination with respect to phenol-born taste and odor problems. In general, high chlorine doses lead to low concentrations of intermediate odorous chlorophenols and bromophenols. An increase in the ammonia or phenol concentration leads to a higher consumption of HOCl and therefore greater final concentration of intermediate bromophenols. The presence of higher bromide than phenol concentration also facilitates the rapid bromination pathway which leads to further bromination of 2,6-dibromophenol to higher brominated phenols. Laboratory-scale experiments on taste and odor formation due to the chlorination of phenol- and bromide-containing waters have confirmed the trend of the model calculations.

Bromine↗
PubMed1983

Trihalogenated benzamides--a new class of artificial sweeteners.

2,4,6-tribromo-3-carboxyalkyl-benzamides and -carboxyalkoxy-benzamides are intensely sweet. With a recognition threshold value of about 1 mumol/l the 3-carboxyethyl compound is one of the sweetest compounds known. The intensity of the sweet taste depends upon the nature of the carboxyalkyl/carboxylalkoxy group. In respect to the acute toxicity to mice the compounds are similar to the sodium salt of saccharin and sodium cyclamate. The compounds are easily obtainable in good yield.

Animals↗
PubMed1982

Electrophysiological analysis of conditioned taste aversion in rats.

The memory mechanisms of conditioned taste aversion (CTA) were examined using electrophysiological methods. Presentation of the aversive taste to CTA trained animals inhibited unit activity in gustatory cortex, amygdala and ventromedial hypothalamus and caused delayed excitation of neurons in lateral hypothalamus. Lick-triggered rewarding stimulation of medial forebrain bundle substituted the taste CS in CTA experiments. The same stimulation triggered by nose-poking failed to be associated with subsequent poisoning. Importance of specific brain areas for CTA retrieval was assessed by the effect of lick-triggered stimulation of the examined site on gustatory discrimination. The disruption threshold was lowest in amygdala and lateral hypothalamus. Stimulation of other brain structures did not interfere with gustatory discrimination at current intensities subthreshold for disruption of licking. Unilateral electrical stimulation of vestibular nuclei following ingestion of saccharin elicited marked aversion to this taste.

Animals↗
PubMed1997

Analysis of odour and taste problems in high-density polyethene.

The compounds that cause off-flavours in plastics, have been recognized mainly as carbonyl compounds (aldehydes, ketones and esters). They occur in low concentrations, and due to their low-threshold odour concentrations, their typical odours were identified. Most of these off-flavour compounds are volatile. Chemical analysis of smelling compounds requires a very sensitive method with a high-resolution capability. The analysis of volatile organic compounds (VOCs) in high density polyethene (HD-PE) granules and waters in which the granules have been shaken for 4 h, were carried out by gas chromatography-mass spectrometry-sniffing system (GC-MS-SNIFF) and by gas chromatography-fourier transform infrared spectroscopy-sniffing system (GC-FTIR-SNIFF). A purge-and-trap technique was used to introduce the VOCs from samples into the gas chromatograph. Leaching waters of HD-PE granules were also evaluated by panel. This panel agreed upon six descriptive attributes for odour: sweet, chemical, stale, dusty, foul and floor-cloth. The attributes for taste were: sweet, metallic, stony, pungent, dusty, plastic, foul, stink bug and candle grease.

Chromatography, Gas↗
PubMed1991

Differential temperature dependence of taste nerve responses to various taste stimuli in dogs and rats.

The temperature dependence of the canine and rat chorda tympani nerve responses to various taste stimuli was examined. The temperature dependence greatly varied with species of stimuli. In the dog, the tonic responses to fructose, sucrose, acetic acid, and guanosine 5'-monophosphate (GMP) and the response induced by the synergism between monosodium glutamate (MSG) and GMP showed peaks at approximately 30 degrees C, whereas those to NaCl, NH4Cl, and MSG showed peaks between 10 and 20 degrees C. In the rat, the tonic response to NH4Cl increased with an increase in temperature up to 45 degrees C, whereas the responses to other stimuli examined showed peaks at approximately 30 degrees C. The responses to glycine, sucrose, and quinine showed sharp temperature dependence, and the responses to acids (HCl and acetic acid) and salts (NaCl and KCl) showed relatively flat dependence. The effects of the temperature change on dose-response curves for fructose, NH4Cl, and GMP were examined using dogs. The temperature change did not practically affect the thresholds for these stimuli and affected the magnitude of the responses to higher concentrations of stimuli. The origins of the temperature dependence were discussed in terms of taste receptor mechanisms.

Acetates↗
PubMed2005

Production and sensory characterization of a bitter peptide from beta-casein.

Peptide beta-casein fragment 193-209 (beta-CN f193-209) was isolated and purified for detailed sensory analysis in different matrices. The purity of the peptide was >98%. The mass of the peptide was 1882.51 Da, which coincided with the expected mass of beta-CN f193-209. N-Terminal analysis confirmed that the peptide started at residue 193 on the published sequence of beta-casein. Detection thresholds were 0.03, 0.06, and 0.63% (w/w) for water, milk, and cheese, respectively. Descriptive sensory analysis confirmed that the peptide exhibited a bitter taste, which increased with increasing concentrations, with minimal other flavors or tastes detected. The beta-CN f193-209 can contribute to bitterness in cheeses.

Animals↗
PubMed2002

A new specific ageusia: some humans cannot taste L-glutamate.

A new specific ageusia was found in human subjects for monosodium L-glutamate (MSG). Four tests were successively applied to discriminate non-tasters and hypotasters from tasters. (i) NaCl and MSG thresholds, and (ii) suprathreshold sensitivity were evaluated using the up-and-down procedure. Only 73% of 109 subjects common to both tests demonstrated a sensitivity for MSG significantly higher than their sensitivity to NaCl, and hence a specific sensitivity to L-glutamate. The remaining 27% who showed no significant difference in sensitivity to MSG and NaCl solutions were considered as putative hypotasters. (iii) Perception profiles (time-intensity) for MSG and NaCl were tested in 58 subjects and appeared significantly different in 47 tasters (81%). This technique helped in identifying among putative hypotasters of tests 1 and 2 a few tasters who perceived equal intensity for isoconcentration of NaCl and MSG but who could discriminate isomolar solutions on other cues. Thus, 19% of subjects, for whom no significant differences were found between MSG and NaCl time-intensity profiles, remained in the hypotaster group. (iv) A discrimination task including 24 triangular presentations per subject of NaCl and MSG 29 mM applied to the eight most severe hypotasters showed that two subjects at least (two of 58; 3.5%) could not discriminate between both stimuli. Moreover, these subjects probably perceived identical sensations for MSG and NaCl solutions. The six other hypotasters (10.3%) could discriminate both stimuli at the limit of significance. None of these eight subjects were able to identify the typical umami taste in 29 mM MSG.

Adolescent↗
PubMed1995

[The psychophysics of sweet taste. 6. Context effects by use of multiple stimuli sequences].

For the determination of differentiation probabilities in a multiple experimental design the range of stimuli is a significant source of disturbance. In order to determine their efficiency, sequences with 5 equidistant gradated concentrations of sucrose were used, which were compared with a basic concentration. The probability for each gradation was carried out with help of 2-AFC-technique (60 pairs each). 5 gradations at 3 basic concentrations with fixed, average balance were examined in a factorized experimental design. The frequency of the correct judgments is linearily dependent on the sequence of stimuli. In the experimental space the slope of this relationships decreases with increasing gradation hyperbolically (range-effects). The level of the basic stimuli is in this view without any greater importance. When determining the difference thresholds these context effects are to be considered.

Adult↗