Showing papers in "Chemical Senses in 2002"

Autonomic Nervous System Responses to Odours: the Role of Pleasantness and Arousal

Abstract: Perception of odours can provoke explicit reactions such as judgements of intensity or pleasantness, and implicit output such as skin conductance or heart rate variations. The main purpose of the present experiment was to ascertain: (i) the correlation between odour ratings (intensity, arousal, pleasantness and familiarity) and activation of the autonomic nervous system, and (ii) the inter-correlation between self-report ratings on intensity, arousal, pleasantness and familiarity dimensions in odour perception. Twelve healthy volunteers were tested in two separate sessions. Firstly, subjects were instructed to smell six odorants (isovaleric acid, thiophenol, pyridine, L-menthol, isoamyl acetate, and 1-8 cineole), while skin conductance and heart rate variations were being measured. During this phase, participants were not asked to give any judgement about the odorants. Secondly, subjects were instructed to rate the odorants on dimensions of intensity, pleasantness, arousal and familiarity (self-report ratings), by giving a mark between 1 (not at all intense, arousing, pleasant or familiar) and 9 (extremely intense, arousing, pleasant or familiar). Results indicated: (i) a pleasantness factor correlated with heart rate variations, (ii) an arousal factor correlated with skin conductance variations, and (iii) a strong correlation between the arousal and intensity dimensions. In conclusion, given that these correlations are also found in other studies using visual and auditory stimuli, these findings provide preliminary information suggesting that autonomic variations in response to olfactory stimuli are probably not modality specific, and may be organized along two main dimensions of pleasantness and arousal, at least for the parameters considered (i.e. heart rate and skin conductance).

The Effect of Viscosity on the Perception of Flavour

Abstract: A trained sensory panel assessed flavour and sweetness intensity in solutions containing varying concentrations of hydroxy propyl methylcellulose (HPMC), sugar and flavour volatile. The flavour and sweetness of the viscous solutions were rated using magnitude estimation with a controlled modulus. In addition, the concentration of volatile released on the breath was measured using MS Nose. For low concentrations of HPMC ( 0.6 g/100 g). The change in perceived intensity occurred at the point of random coil overlap (c(*)) for this hydrocolloid. The perceived sweetness of the solution showed a similar pattern with increasing HPMC concentration, although the inflection at c(*) was not so obvious. Despite the change in perceived flavour intensity, the actual concentration of volatile measured on the breath was not affected by the change in HPMC concentration. Low-order polynomial models were produced to describe perceived flavour intensity and sweetness in viscous solutions containing HPMC and potential explanations for the changes in perception are discussed.

Taste enhancements between various amino acids and IMP.

Abstract: It is well known that a strong synergistic interaction of umami occurs between L-alpha-amino acids with an acidic side chain, such as L-Glu or L-Asp, and 5'-mononucleotides, such as inosine 5'-monophosphate (IMP). We tested taste interactions between various L-alpha-amino acids and IMP by the psychophysical method and found that taste enhancement occurred when IMP was added to several sweet amino acids, such as L-Ala, L-Ser and Gly. The enhanced quality of taste was recognized as umami, and was not blocked by the sweetness inhibitor +/-2-(p-methoxyphenoxy)propanoic acid. The total taste intensities of various concentrations of the amino acid and IMP mixtures were measured using magnitude estimation. The results showed that the potentiation ratios were larger than 1 in the cases of L-Ala, L-Ser and Gly. However, the ratio was approximately 1 in the case of D-Ala, which had an enhanced taste of sweetness. Thus the umami taste enhancement of several sweet L-alpha-amino acids by IMP was synergistic rather than additive as that of acidic amino acids.

Demystifying Wine Expertise: Olfactory Threshold, Perceptual Skill and Semantic Memory in Expert and Novice Wine Judges

Abstract: We investigated recognition and identification of wine-relevant odours as a function of domain-specific expertise. Eleven wine experts and 11 wine novices participated in tasks measuring olfactory threshold, odour recognition, odour identification, and consistency of odour naming. Twenty-four wine-relevant odorants were sampled orthonasally by each participant in the semantic (identification; consistency of naming) and episodic (recognition) memory tasks. Results showed superior olfactory recognition by expert wine judges, despite their olfactory sensitivity and bias measures being similar to those of novices. Contrary to predictions based on reports of an association between odour memory and semantic processing, wine experts did not perform better than novices on the verbal memory tasks. Further, ability to recognize odours and ability to name odours were not positively correlated, although the novices’ data showed a trend in this direction. The results imply that the source of superior odour recognition in wine experts was not enhanced semantic memory and linguistic capabilities for wine-relevant odours. One interpretation of the data is that wine experts were less susceptible than wine novices to verbal overshadowing. When forced to identify the odorants, experts’ superior perceptual skills protected them from verbal interference, whereas novices’ generated verbal representations of the odours were emphasized at the expense of the odorant itself. This has implications for training in wine-evaluation skills.

A high-throughput screening procedure for identifying mice with aberrant taste and oromotor function.

Abstract: Little is known about how specific genes influence taste function in mammals. One of the most promising ways to fill this void is to screen the progeny of chemically mutagenized (or genetically altered) mice for aberrant taste phenotypes and then identify the mutated gene(s) that is associated with each taste anomaly. To exploit this approach, a high-throughput and robust screening procedure is needed. We have attempted to meet this demand by developing an automated procedure that assesses taste responsiveness of individual mice to palatable and unpalatable taste stimuli. We focused on three taste stimuli (quinine hydrochloride, QHCl; sodium chloride, NaCl; and sucrose) and one mouse strain (C57BL/6). We used a commercially available gustometer system that both monitors the licking responses of mice and controls the presentation of each taste stimulus during successive 5 s trials. We describe a screening procedure that (after 2 days of simple training) can generate a concentration-response curve for NaCl or sucrose during a single 30 min test session, and for QHCl over three 30 min test sessions. A normative database based on the responses of 98 mice subjected to our screening procedure is also presented. We envision that investigators could use this normative database to assess taste function in the progeny of mutagenized (or genetically altered) mice. Any mouse that deviates significantly-e.g. three standard deviations (SD)-from the mean of the normative database would be flagged as having a potentially interesting mutation. We also developed an additional second screen for identifying mice with oromotor abnormalities. This latter screen is necessary because oromotor problems could lead to false positives or negatives in the screen for taste function, but is also useful for researchers interested in genes influencing oromotor circuitry. Throughout the development of the screening protocol, we sought to balance two conflicting demands: the need to maximize the screen's sensitivity and minimize its duration. This screen represents a significant improvement over the common two-bottle preference test because it assesses taste function more specifically and in a fraction of the time.

Distortion of Olfactory Perception: Diagnosis and Treatment

Abstract: Clinically, olfaction can fail in any of three ways: (i) decreased sensitivity (hyposmia, anosmia) and two types of distortion (dysosmia); (ii) distorted quality of an odorant stimulation (troposmia); (iii) perceived odor when no odorant is present (phantosmia, hallucination). The distortions are usually much more upsetting to a person's quality of life than a simple loss. An ipsilatersal loss of olfactory sensitivity is often identified in the nostril with any type of olfactory distortion. The pathophysiology of a stimulated distortion (troposmia) is likely a decreased number of functioning olfactory primary neurons so that an incomplete characterization of the odorant is made. In phantosmia, two possible causations include an abnormal signal or inhibition from the primary olfactory neurons or peripheral olfactory or trigeminal signals that "trigger" a central process. The clinician's goal is to carefully define the problem (e.g. taste versus smell, real versus perceived, one versus two nostrils), to perform the appropriate examination and testing and to provide therapy if possible. Treatment includes assurance with no active therapy (because many of these will naturally resolve), topical medications, systemic medications, anesthesia to parts of the nose and, rarely, referral for surgical excision of olfactory neurons. Endoscopic transnasal operations have the advantage of treating phantosmia and sometimes allowing a return of olfactory ability after the operation.

Biopsies of Human Olfactory Epithelium

Abstract: It has been shown that olfactory epithelium can be safely biopsied from the living, intact human being. Observations of the ultrastructure of this epithelium shows changes that can then be correlated with the etiology and degree of olfactory loss, allowing a greater understanding of both normal transduction and of the pathology of dysfunction. Examples of the common forms of olfactory dysfunction are presented and discussed. Additionally, the technique will allow additional immunohistochemical and molecular study of the tissue, will increase the understanding of both normal and pathological function and should translate to new therapeutic regimens.

Intranasal volume and olfactory function.

Abstract: The aim of this exploratory study was to identify the volume intranasal segments as they relate to parameters of olfactory function. Fifty healthy male volunteers (age range 22-59 years, mean age 28.5 years) were included. Olfactory function was measured by lateralized phenyl ethyl alcohol odor thresholds and odor discrimination, and by bilateral odor identification. Magnetic resonance imaging of the nasal cavity was performed immediately following olfactometry. To correlate the results of olfactometry with intranasal volume, each nasal cavity was divided into 11 segments. Significant correlations were found between the odor thresholds and volumes of the anterior part of the lower and upper meatus of the right nasal cavity. These results reveal that two nasal segments are important for inter-individual differences of odor thresholds in healthy subjects: (i) the segment in the upper meatus below the cribriform plate and (ii) the anterior segment of the inferior meatus. The latter finding is of special interest for nasal surgery, which allows modification of this volume through resection of the inferior turbinate and/or septoplasty.

The Discovery of Umami

Abstract: Sweet, bitter, salty and sour are the four taste qualities upon which the human sense of taste is based. But is this really all? Is there room for more basic tastes on the human tongue? Well, there is. Strangely, though, while people tasted it daily, the fifth taste long remained unknown and unnamed. Its final discovery, made nearly a century ago, was due entirely to a single man, a chemistry professor at the Imperial University of Tokyo, Kikunae Ikeda. It was Ikeda’s insight and endurance alone which powered this early work. The tedious chemical isolation and identification of the new taste substance was done without the help from postdoctorates or students, as would be usual today, aided only by one technician. The investigation was based on an observation concerning the dominant taste of dashi, a Japanese soup base. The taste of dashi is mild but, according to Ikeda, clearly distinct from that of the four basic tastes. Ikeda proceeded to isolate the principal taste substance from a main ingredient of dashi, the seaweed Laminaria japonica. This was done with the procedures of classical chemistry, aqueous extraction, removal of large-scale contaminants (mannitol, NaCl, KCl) by crystallization, lead precipitation and numerous other steps of preparative chemistry. Finally, low-pressure evaporation resulted in the slow crystallization of a single substance with the mass formula C5H9NO4: glutamic acid. Its taste was named umami, a word derived from the Japanese adjective umai (delicious). It has taken root as a scientific term internationally. The scientific community received this discovery with moderate applause only. Many, especially in Englishspeaking countries, remained unconvinced. One hindrance for the accceptance may have been that the detailed publication of Ikeda’s work appeared in Japanese (Ikeda, 1909). Other hindrances were that umami taste is mild even at high concentrations of the tastants. Furthermore, high concentrations of glutamate, an anion, are necessarily accompanied by cations, the salty or sour taste of which confused the issue. Umami research proceeded on a larger scale especially since about 1980. The umami substances L-glutamate, inosine 5′-monophosphate (IMP) and guanosine 5′-monophosphate (of which the latter two enhance the glutamate taste) were defined, and taste responses to them were investigated in humans and animals. Animal models, however, were of limited use as the responses of different species, even of different strains of mice, were at variance. Today a search in PubMed (MedLine) for papers concerned with taste and containing the term ‘umami’ retrieved 86 references. (For comparison, ‘sweet taste’ retrieved 10 times more references published since 1980.) A search with the Google engine found >4000 web pages containing the phrase ‘umami’. Some of these pages were from restaurants advertising umami food. Others dealt with the misconception that glutamate contained in food might be harmful. But foremost among them were pages reprinting newspaper articles about the discovery of umami receptors. The discovery of umami receptors, taste receptors for L-glutamate, using methods of molecular biology is one of the recent highlights of taste research. In 2000, a modified glutamate receptor of the brain was found, the tastemGluR4. It is a G protein-coupled (metabotropic) receptor. The taste variety of mGluR4 has a truncated N-terminal to which L-glutamate still binds, albeit with reduced affinity. Presumably, therefore, the truncation adapted the receptor to the high glutamate concentration in food (Chaudhari et al., 2000). More recently, another umami receptor was discovered. Interestingly, this one is a heteromere built of the G protein-coupled receptors T1R1 and T1R3. In mice this heteromere responds to many amino acids contained in food, but in humans its response is preferentially to L-glutamate and is enhanced by IMP (Nelson et al., 2002).

Turbidity as a Measure of Salivary Protein Reactions with Astringent Substances

Abstract: Binding of tannins to proline-rich proteins has been proposed as an initial step in the development of astringent sensations. In beer and fruit juices, formation of tannin-protein complexes leads to the well-known effect of haze development or turbidity. Two experiments examined the development of turbidity in human saliva when mixed with tannins as a potential in vitro correlate of astringent sensations. In the first study, haze was measured in filtered human saliva mixed with a range of tannic acid concentrations known to produce supra-threshold psychophysical responses. The second study examined relationships among individual differences in haze development and the magnitude of astringency ratings. Mostly negative correlations were found, consistent with the notion that high levels of salivary proteins protect oral tissues from the drying effects of tannic acid.

DNA microarray analysis of the aging brain.

Abstract: To examine molecular events associated with brain aging and its retardation by caloric restriction (CR), we have employed high-density oligonucleotide arrays providing data on 6347 genes to define transcriptional patterns in two brain regions (cerebellum and neocortex). Male C57BL/6 mice were either fed normally or subjected to CR. To investigate aging, 5 month (young adult) and 30 month-old normally fed mice were compared. To study CR, 30 month-old control and CR mice were compared. In both brain regions, aging resulted in a gene expression profile suggestive of a marked inflammatory response, oxidative stress and reduced neuronal plasticity and neurotrophic support. In the brain, CR selectively attenuated the age-associated induction of genes encoding inflammatory and stress responses. In addition to providing an improved understanding of the aging process, the use of DNA microarrays generates panels of hundreds of transcriptional biomarkers of molecular aging, providing a new tool to measure biological age on a tissue-specific basis. These studies suggest that genomic approaches may be useful in understanding the molecular basis of the aging process in experimental animals.

Spatial Representation of Odours in the Antennal Lobe of the Moth Spodoptera littoralis (Lepidoptera: Noctuidae)

Abstract: Glomeruli within the antennal lobe (AL) of moths are convergence sites for a large number of olfactory receptor neurons (ORNs). The ORNs target single glomeruli. In the male-specific cluster of glomeruli, the macroglomerular complex (MGC), the input is chemotypic in that each glomerulus of the MGC receives information about a specific component of the conspecific female sex pheromone. Little is known about how neurons that detect other odorants arborize in and amongst glomeruli. The present study focuses on how sex pheromones and biologically relevant semiochemicals are represented in the ALs of both sexes of the moth Spodoptera littoralis. To assess this, we optically measured odour-evoked changes of calcium concentration in the ALs. Foci of calcium increase corresponded in size and shape with anatomical glomeruli. More than one glomerulus was normally activated by a specific non-pheromonal odorant and the same glomerulus was activated by several odorants. All odorants and pheromone components tested evoked unique patterns of glomerular activity that were highly reproducible at repeated stimulations within an individual. Odour-evoked patterns were similar between individuals for a given odorant, implicating a spatial olfactory code. In addition, we demonstrated that activity patterns evoked by host-plant related volatiles are similar between males and females.

A New Specific Ageusia: Some Humans Cannot Taste L-Glutamate

Abstract: 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.

Odor discrimination using insect electroantennogram responses from an insect antennal array

Abstract: Insects have a highly developed olfactory sensory system, mainly based in their antennae, for the detection and discrimination of volatile compounds in the environment. Electroantennogram (EAG) response profiles of five different insect species, Drosophila melanogaster, Heliothis virescens, Helicoverpa zea, Ostrinia nubilalis and Microplitis croceipes, showed different, species-specific EAG response spectra to 20 volatile compounds tested. The EAG response profiles were then reconstructed for each compound across the five insect species. Most of the compounds could be distinguished by comparing the response spectra. We then used a four-antenna array, called a Quadro-probe EAG, to see if we could discriminate among odorants based on the relative EAG amplitudes evoked when the probe was placed in plumes in a wind tunnel and in a field. Stable EAG responses could be simultaneously and independently recorded with four different insect antennae mounted on the Quadro-probe, and different volatile compounds could be distinguished in real time by comparing relative EAG responses with a combination of differently tuned insect antennae. Regardless of insect species or EAG amplitudes, antennae on the Quadro-probe maintained their responsiveness with higher than 1 peak/s of time resolution.

Bitter taste of saccharin and acesulfame-K.

Abstract: The relationships among suprathreshold taste responses to acesulfame-K, Na-saccharin and 6-n-propylthiouracil (PROP) were examined in two studies. In the first study, the labeled magnitude scale was used with the high anchor labeled as 'strongest imaginable oral sensation' and in the second study, it was labeled as 'strongest imaginable sensation of any kind'. Results from the two procedures were similar. Individual differences among 65 subjects were seen in bitter responses to acesulfame-K and saccharin. Bitter responses to acesulfame-K ands accharin were positively correlated, but showed no significant relationship with responses to PROP bitterness or with PROP taster groups. Saccharin and acesulfame-K may share a common mechanism for bitter taste reception and transduction, one that varies across individuals and is different from mechanisms mediating bitter responses to PROP. Changing the instructions of the labeled magnitude scale induced a context effect. Ratings of sweetness referenced to the 'strongest imaginable sensationof any kind' were lower than ratings referenced to just oral sensations.

The Signal Function of Thematically (In)congruent Ambient Scents in a Retail Environment

Abstract: An odor emitted by an object signals the presence of that object and may draw attention to it. Can odors that are not actually emitted by an object also function as a signal? We investigated whether the degree of thematic congruency between an ambient odor and a magazine affected magazine sales in a retail store. We selected two odors: a grass odor, congruent with soccer, animal/nature and gardening magazines; and a sunflower odor, congruent with personal care and women's magazines. In a field study in three bookstores, the ambient odors did not increase sales for thematically congruent magazines, nor did they decrease sales for incongruent magazines. Several explanations for these unexpected findings are discussed.

A Putative Pheromone Receptor Gene Is Expressed in Two Distinct Olfactory Organs in Goats

Abstract: Mammals possess two anatomically and functionally distinct olfactory systems. The olfactory epithelium (OE) detects volatile odorants, while the vomeronasal organ (VNO) detects pheromones that elicit innate reproductive and social behavior within a species. In rodent VNO, three multigene families that encode the putative pheromone receptors, V1Rs, V2Rs and V3Rs, have been expressed. We have identified the V1R homologue genes from goat genomic DNA (gV1R genes). Deduced amino acid sequences of gV1R genes show 40–50% and 20–25% identity to those of rat and mouse V1R and V3R genes, respectively, suggesting that the newly isolated goat receptor genes are members of the V1R gene family. One gene (gV1R1 gene) has an open reading frame that encodes a polypeptide of 309 amino acids. It is expressed not only in VNO but also in OE. In situ hybridization analysis revealed that gV1R1-expressing cells were localized in neuroepithelial layers of VNO and OE. These results suggest that the goat may detect pheromone molecules through two distinct olfactory organs.

Receptor Neuron Discrimination of the Germacrene D Enantiomers in the Moth Helicoverpa armigera

Abstract: Plants release complex mixtures of volatiles, including chiral constituents. In the search for the biologically relevant plant odorants, gas chromatography linked to electrophysiological recordings from single receptor neurons has been employed. In heliothine moths, including the females of the Eurasian cotton bollworm moth Helicoverpa armigera, a major type of receptor neurons is identified, showing high sensitivity and selectivity for the sesquiterpene germacrene D. In the present study, gas chromatography with a chiral column linked to single cell recordings were performed. It was found that all germacrene D neurons belonged to one type; all responded to both enantiomers, but (–)-germacrene D had ~10 times stronger effect than (+)-germacrene D. Parallel dose–response curves for the two enantiomers were obtained by direct stimulations. The enantiomeric composition of germacrene D, which differed in six plant species and in different individuals of one species, was determined on the basis of the neuron responses. The results, showing the presence of one neuron type for receiving the information about germacrene D in the various plants, suggests that the two enantiomers mediate the same kind of information to the moth, but with different intensity.

A brief-access test for bitter taste in mice.

Abstract: Inbred mouse strains vary in their response to bitter-tasting compounds as assessed by 48 h preference tests. These differences are generally assumed to result from altered gustatory function, although such long-term tests could easily reflect additional factors. We developed a brief-access taste test and tested the responses of two inbred strains, as well as C3. SW congenic mice, to the bitter stimulus sucrose octaacetate (SOA). Water-deprived trained mice were tested with five concentrations of SOA (0.00018-0.18 mM) and distilled water in a Davis MS- 160 apparatus. Trials were 5 s in duration and stimuli were presented randomly within blocks; each stimulus trial was preceded by a water rinse trial. Each concentration was presented twice in a session and mice were repeatedly tested across consecutive days. SOA-taster mice, including the SWR/J (SW) inbred and C3. SW congenic taster (T) mice, avoided licking SOA at concentrations >0.003 mM. In comparison, C3HeB/FeJ (C3) and C3. SW demitaster mice (D) licked all concentrations at the same rate as water. Concentration-response functions were similar across strains for both the brief-access test and a parallel 48 h preference test run on separate groups of mice. Furthermore, concentration-response functions were similar whether or not the brief-access test was preceded by a 4 day, single concentration pretest with SOA. The brief-access test is a suitable assay for bitter taste function in mice because it minimizes possible post-ingestive influences on taste.

Germacrene D increases attraction and oviposition by the tobacco budworm moth Heliothis virescens.

Abstract: The sesquiterpene germacrene D (GD) activates a major type of olfactory receptor neuron on the antennae of the heliothine moths. In Heliothis virescens females, 80% of the recordings have shown activity of one neuron type responding with high sensitivity and selectivity to GD. With the aim of determining the behavioural significance of this sesquiterpene, we have used a two-choice wind-tunnel to study the preference of mated H. virescens females for host plants with and without (-)-GD added. Tobacco plants containing dispensers with low release rate of (-)-GD had a greater attractiveness than tobacco plants without this substance. In addition, a significant increase of oviposition was found on the plants with (-)-GD.

Odorants of Different Chemical Classes Interact with Distinct Odorant Binding Protein Subtypes

Abstract: The ligand profile for three odorant binding proteins (OBPs) of the rat have been determined using a large number of odorous compounds from different chemical classes. To evaluate the binding spectra of distinct subtypes, all OBPs were produces in Escherichia coli as recombinant His-tagged fusion proteins. The individual binding properties of each OBP subtype were analysed using a large array of organic compounds, representing derivatives of aliphatic and aromatic compounds, as well as terpenes, pyrazines and thiazoles, in a competitive spectroscopic binding assay with various fluorescence chromophores as the specific interacting partner for the OBPs. Most of the compounds were identified to interact only with one OBP subtype. But interestingly, a small change, for example in the 2-methyl or 2-ethoxy side chain in the pyrazine and thiazole derivatives to a 2-isobutyl group, caused overlapping binding affinities to rat-OBP1 and rat-OBP3. However, the data strongly support the notion that each OBP subtype displays a characteristic ligand binding profile and interacts with a different subset of exogenous organic compounds in a micromolar range.

Gustatory evoked cortical activity in humans studied by simultaneous EEG and MEG recording.

Abstract: Evoked potentials are widely used in clinical medicine for objective evaluation of sensory disturbances. However, gustatory evoked potentials (GEPs) have not been extensively studied due to lack of agreement among investigators regarding the waveforms. In this study GEPs and gustatory magnetic fields (GEMfs) were simultaneously recorded from five subjects in response to 0.3 M NaCl in an attempt to establish GEP recording as an objective gustatometer. Each subject received a total of 240 stimulus presentations over six sessions. Three GEP components (P1, N1 and P2) were observed and correlated with their corresponding equivalent current dipoles (ECD1, ECD2 and ECD3, respectively). ECD1 was localized to area G in all subjects, P1 being the indicator of intact gustatory projection to area G. No significant GEP activity was detected during the time preceding P1, which suggests that there was no activity in cortical gyri other than that detected by magnetoencephalography. ECD2 and ECD3 were localized to various cortical structures, including the inferior insula and the superior temporal sulcus, indicating that N1 and P2 reflect higher order gustatory functions. The present results indicate that measurement of GEPs may be useful for objective evaluation of gustatory disturbance.

Taste Suppression Following Lingual Capsaicin Pre-treatment in Humans

Abstract: The effect of oral capsaicin on taste sensations in humans was reinvestigated with attention to methodological issues raised in previous studies, including the mode of presentation and temperature of the tastant stimulus, as well as the sensitizing and desensitizing properties of capsaicin. One-half of the dorsal anterior tongue was pre-treated with capsaicin, followed by bilateral tastant application (sucrose, NaCl, quinine, monosodium glutamate and citric acid). Subjects indicated on which side the taste intensity was greater in a two-alternative, forced-choice procedure and also rated taste intensity independently on each side of the tongue. Each of the five tastants was tested sequentially, with reapplication of capsaicin between trials in order to maintain a constant level of burn. Four experiments were conducted: (i) a high concentration (33 p.p.m.) (109 microM) capsaicin effect on taste intensity elicited by high tastant concentrations; (ii) a high concentration capsaicin effect on taste intensity elicited by low tastant concentrations; (iii) a low concentration (1.5 p.p.m.) (4.9 microM) capsaicin effect on taste intensity elicited by low tastant concentrations; and (iv) validation of the method for localizing taste by pre-treating one side of the tongue with Gymnema sylvestre, followed by bilateral application of sucrose. In the first experiment, a significant proportion of the subjects chose the non-treated side in the two-alternative, forced-choice procedure and assigned significantly higher ratings to that side for sucrose-induced sweetness, quinine-induced bitterness and glutamate-induced umami sensations. Salty and sour sensations were not different between sides. A 15 min break was imposed in order to allow the capsaicin burn to disappear and desensitization to set in, followed by reapplication of the tastant test solutions. There were no bilateral differences in the intensity of the sensations elicited by any of the five tastants. Similar results were obtained in experiments 2 and 3. In the fourth experiment, all 15 subjects tested chose the side not treated with Gymnema sylvestre as having a stronger sweet taste and assigned significantly higher ratings to that side, thereby validating the method for taste localization. These results indicate that oral capsaicin reduces certain but not all taste sensations and are discussed in terms of possible physiological and cognitive interactions.

Selection of Odorants for Memory Tests on the Basis of Familiarity, Perceived Complexity, Pleasantness, Similarity and Identification

Abstract: In a procedure for the selection of two equivalent sets of familiar and two equivalent sets of unfamiliar odours for use in odour memory studies, 24 naive subjects were first asked to rate the familiarity, perceived complexity and pleasantness of 54 a priori unfamiliar odours and 57 a priori familiar odours and to identify the latter. After selection of the 40 most familiar and the 40 least familiar odours, the subjects sorted each of these two sets into groups of similar odours. Their results were analysed by multidimensional scaling and cluster analysis and each set was divided into two recognition sets that had the same degree of similarity between target and distractor odours and that had similar values of familiarity, pleasantness, perceived complexity (familiar and unfamiliar sets) and identifiability (familiar sets). Finally, recognition tasks were performed in order to check the equivalence in memory performance of both the two familiar and the two unfamiliar recognition sets.

Amino Acid Odorants Stimulate Microvillar Sensory Neurons

Abstract: The olfactory epithelium (OE) of zebrafish is populated with ciliated and microvillar olfactory sensory neurons (OSNs). Whether distinct classes of odorants specifically activate either of these unique populations of OSNs is unknown. Previously we demonstrated that zebrafish OSNs could be labeled in an activity-dependent fashion by amino acid but not bile acid odorants. To determine which sensory neuron type was stimulated by amino acid odorants, we labeled OSNs using the ion channel permeant probe agmatine (AGB) and analyzed its distribution with conventional light- and electron-microscope immunocytochemical techniques. Approximately 7% of the sensory epithelium was labeled by AGB exposure alone. Following stimulation with one of the eight amino acids tested, the proportion of labeled epithelium increased from 9% for histidine to 19% for alanine; amino acid stimulated increases in labeling of 2–12% over control labeling. Only histidine failed to stimulate a significant increase in the proportion of labeled OSNs compared to control preparations. Most amino acid sensitive OSNs were located superficially in the epithelium and immuno-electron microscopy demonstrated that the labeled OSNs were predominately microvillar. Large numbers of nanogold particles (20–60 per 1.5 µm 2 ) were associated with microvillar olfactory sensory neurons (MSNs), while few such particles (<15 per 1.5 µm 2 ) were observed over ciliated olfactory sensory neurons (CSNs), supporting cells (SCs) and areas without tissue, such as the lumen above the OE. Collectively, these findings indicate that microvillar sensory neurons are capable of detecting amino acid odorants.

Ratings of different olfactory judgements in schizophrenia.

Abstract: We assessed the influence of schizophrenia on different olfactory tasks. Forty patients with schizophrenia (20 males and 20 females) and 40 control subjects (20 males and 20 females) were tested. The experiment included two sessions. Initially, 12 odorants were presented at a rate of one per minute. The subjects were asked to rate intensity, pleasantness, familiarity and edibility for each odour using linear rating scales. The odorants were then presented a second time and the subjects were asked to identify them. The results showed that the scores for pleasantness, familiarity, edibility and identification but not intensity were disturbed in patients when compared with control subjects. Furthermore, the familiarity judgement of male patients was more often deficient than that of female patients and they rated odorants as being inedible when the women judged them as neutral. Considered together, these data show that our olfactory test may be used in patients with schizophrenia for evidencing various dysfunctions specific to different types of olfactory processing that represent steps in the odour name identification process.

Gustatory projections from the nucleus of the solitary tract to the parabrachial nuclei in the hamster.

Abstract: Taste-responsive cells in the nucleus of the solitary tract (NST) either project to the parabrachial nuclei (PbN) of the pons, through which taste information is transmitted to forebrain gustatory nuclei, or give rise to axons terminating locally within the medulla.Numerous anatomical studies clearly demonstrate a substantial projection from the rostral NST, where most taste-responsive cells are found, to the PbN.In contrast, previous electrophysiological studies in the rat have shown that only a small proportion (21–45%) of taste-responsive NST cells are antidromically activated from the PbN, suggesting that less than half the cells recorded from the NST are actually involved in forebrain processing of gustatory information.In the present experiment we investigated the projections from the NST to the PbN electrophysiologically in urethane anesthetized hamsters. Responses of 101 single neurons in the rostral NST were recorded extracellularly following lingual stimulation with 32 mM NaCl, sucrose and quinine hydrochloride (QHCl) and 3.2 mM citric acid. The taste-responsive region of the PbN was identified electrophysiologically and stimulated with a concentric bipolar electrode to antidromically activate each NST cell.Of the 101 taste-responsive NST cells, 81 (80.2%) were antidromically activated from the ipsilateral PbN. The mean firing rates to taste stimulation and the spontaneous activity of these projection neurons were significantly greater than those of non-projecting cells.Every sucrose-best neuron in the sample projected to the PbN.The mean conduction velocity of the 23 QHCl-best neurons was significantly lower than that of the other 58 PbN projection neurons, suggesting that the most QHCl-responsive cells are a subset of smaller neurons.These data show that a large majority of NST cells responsive to taste stimulation of the anterior tongue project to the gustatory subdivisions of the PbN and that these cells have the most robust responses to gustatory stimulation.

Cross-adaptation and bitterness inhibition of L-Tryptophan, L-Phenylalanine and urea : further support for shared peripheral physiology

Abstract: A previous study investigating individuals' bitterness sensitivities found a close association among three compounds: L-tryptophan (L-trp), L-phenylalanine (L-phe) and urea (Delwiche et al., 2001, Percept. Psychophys. 63, 761-776). In the present experiment, psychophysical cross-adaptation and bitterness inhibition experiments were performed on these three compounds to determine whether the bitterness could be differentially affected by either technique. If the two experimental approaches failed to differentiate L-trp, L-phe and urea's bitterness, then we may infer they share peripheral physiological mechanisms involved in bitter taste. All compounds were intensity matched in each of 13 subjects, so the judgments of adaptation or bitterness inhibition would be based on equal initial magnitudes and, therefore, directly comparable. In the first experiment, cross-adaptation of bitterness between the amino acids was high (>80%) and reciprocal. Urea and quinine-HCl (control) did not cross-adapt with the amino acids symmetrically. In a second experiment, the sodium salts, NaCl and Na gluconate, did not differentially inhibit the bitterness of L-trp, L-phe and urea, but the control compound, MgSO4, was differentially affected. The bitter inhibition experiment supports the hypothesis that L-trp, L-phe and urea share peripheral bitter taste mechanisms, while the adaptation experiment revealed subtle differences between urea and the amino acids indicating that urea and the amino acids activate only partially overlapping bitter taste mechanisms.

Anti-inflammatory and Surgical Therapy of Olfactory Disorders Related to Sino-nasal Disease

Abstract: Olfactory loss may be caused by mechanical obstruction or inflammation of the olfactory epithelium due to allergic/non-allergic rhinitis and chronic sinusitis with or without polyps. Treatment of olfactory loss related to sino-nasal disease is possible. Apart from surgical approaches and/or treatment with antibiotics, both systemic and topical steroids are effectively used in the therapy of olfactory loss related to sino-nasal disease. In most cases improvement of olfactory function appears to relate to the anti-inflammatory actions of the steroids used. While some details of therapeutic effect and dose regimen are not clear, systemic steroids are often helpful even in patients without nasal obstruction due to polyps or obvious inflammatory changes.

The Alarm Reaction in Crucian Carp is Mediated by Olfactory Neurons with Long Dendrites

Abstract: In the present study, we applied a lipophilic tracer, Dil (1,1-dilinoleyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate), to the synaptic region of the medial olfactory bulb in formaldehyde-fixed preparations from the crucian carp. We observed staining both in the axons of secondary neurons leading to the brain and in the olfactory receptor neurons (ORNs) of the olfactory epithelium. In those preparations, where staining of the tract was restricted to axons of the medial part of the medial olfactory tract, the majority (86-98%) of the somata of the sensory neurons were found in the deep layers of olfactory epithelium. Since the medial bundle of the medial olfactory tract mediates alarm behaviour in the crucian carp, we conclude that the sensory neurons with long dendrites participate in the reception of alarm pheromones.