Showing papers in "Chemical Senses in 2007"

Taste-Signaling Proteins Are Coexpressed in Solitary Intestinal Epithelial Cells

Abstract: The taste system, made up of taste receptor cells clustered in taste buds at the surface of the tongue and the soft palate, plays a key role in the decision to ingest or reject food and thereby is essential in protecting organisms against harmful toxins and in selecting the most appropriate nutrients. To determine if a similar chemosensory system exists in the gastrointestinal tract, we used immunohistochemistry and real-time polymerase chain reaction (PCR) to investigate which taste-signaling molecules are expressed in the intestinal mucosa. The PCR data showed that T1r1, T1r2, T1r3, a-gustducin, phospholipase Cb2 (PLCb2), and Trpm5 are expressed in the stomach, small intestine, and colon of mice and humans, with the exception of T1r2, which was not detected in the mouse and human stomach or in the mouse colon. Using transgenic mice expressing enhanced green fluorescent protein under the control of the Trpm5 promoter, we found colocalization of Trpm5 and a-gustducin in tufted cells at the surface epithelium of the colon, but these cells did not express T1r3 or PLCb2. In the duodenal glands, 43%, 33%, and 38% of Trpm5expressing cells also express PLCb2, T1r3, or a-gustducin, respectively. The duodenal gland cells that coexpress PLCb2 and Trpm5 morphologically resemble enteroendocrine cells. We found a large degree of colocalization of Trpm5, a-gustducin, T1r1, and T1r3 in tufted cells of the duodenal villi, but these cells rarely expressed PLCb2. The data suggest that these duodenal cells are possibly involved in sensing amino acids.

The Drosophila larva as a model for studying chemosensation and chemosensory learning: a review

Abstract: Understanding the relationship between brain and behavior is the fundamental challenge in neuroscience. We focus on chemosensation and chemosensory learning in larval Drosophila and review what is known about its molecular and cellular bases. Detailed analyses suggest that the larval olfactory system, albeit much reduced in cell number, shares the basic architecture, both in terms of receptor gene expression and neuronal circuitry, of its adult counterpart as well as of mammals. With respect to the gustatory system, less is known in particular with respect to processing of gustatory information in the central nervous system, leaving generalizations premature. On the behavioral level, a learning paradigm for the association of odors with food reinforcement has been introduced. Capitalizing on the knowledge of the chemosensory pathways, we review the first steps to reveal the genetic and cellular bases of olfactory learning in larval Drosophila. We argue that the simplicity of the larval chemosensory system, combined with the experimental accessibility of Drosophila on the genetic, electrophysiological, cellular, and behavioral level, makes this system suitable for an integrated understanding of chemosensation and chemosensory learning.

Evidence for Human Orosensory (Taste?) Sensitivity to Free Fatty Acids

Abstract: Accumulating evidence suggests dietary fatty acids (FAs) may be sensed in the oral cavity. However, the effective cues have not been characterized. In particular, influences from other sensory cues have hampered identification of an independent gustatory contribution. Experiment 1 examined techniques to minimize the formation of FA oxidation products and improve the homogeneity of water/lipid emulsions to be used as stimuli in Experiment 2, a psychophysical study to determine FA detection thresholds in humans. Through sonication of chilled samples held in polypropylene labware and the addition of 0.01% ethylenediaminetetraacetic acid, calcium disodium salt, homogenous emulsions of unoxidized linoleic and oleic FAs were obtained. Spectrophotometric analysis revealed no oxidation product formation over a 24-h period. Coupled with these techniques, a masking approach was used to minimize other sensory cues imparted from linoleic, oleic, and stearic FAs. Concentration ranges from 0.00028% to 5% (w/v) were prepared in mixtures with 5% mineral oil (w/v) and 5% gum acacia (w/v) to mask lubricity and viscosity effects, respectively. Testing was conducted under red light with nares blocked to eliminate visual and olfactory cues. Oral rinses with 20 ppm capsaicin were administered to desensitize participants to selected irritation effects prior to remeasuring linoleic acid detection thresholds. To determine if the effective stimulus was an oxidation product, oxidized linoleic acid was included among the test stimuli. Detection thresholds were obtained using a 3-alternative, forced-choice ascendingconcentration presentation procedure. The mean detection threshold for linoleic acid pre-desensitization was 0.034 ± 0.008%, for linoleic acid post-desensitization was 0.032 ± 0.007%, for oleic 0.022 ± 0.003%, for stearic 0.032 ± 0.005%, and oxidized linoleic 0.025 ± 0.005%. The results suggest that linoleic, oleic, stearic, and oxidized linoleic acids are detectable in the oral cavity of humans with minimal input from the olfactory, capsaicin, and viscosity-assessing tactile systems.

Revisiting sugar-fat mixtures: sweetness and creaminess vary with phenotypic markers of oral sensation

Abstract: Genetic variation in oral sensation presumably influences ingestive behaviors through sensations arising from foods and beverages. Here, we investigated the influence of taste phenotype [6-n-propylthiouracil (PROP) bitterness, fungiform papillae (FP) density] on sweet and creamy sensations from sugar/fat mixtures. Seventy-nine subjects (43 males) reported the sweetness and creaminess of water or milk (skim, whole, heavy cream) varying in sucrose (0-20% w/v) on the general Labeled Magnitude Scale. Sweetness grew with sucrose concentration and when shifting from water to milk mixtures--the growth was greatest for those tasting PROP as most bitter. At higher sucrose levels, increasing fat blunted the PROP-sweet relationship, whereas at lower levels, the relationship was effectively eliminated. Perceived sweetness of the mixture exceeded that predicted from the sum of components at low sucrose concentrations (especially for those tasting PROP most bitter) but fell below predicted at high concentrations, irrespective of fat level. Creaminess increased greatly with fat level and somewhat with sucrose. Those tasting PROP most bitter perceived greater creaminess in the heavy cream across all sucrose levels. Perceived creaminess was somewhat lower than predicted, irrespective of PROP bitterness. The FP density generally showed similar effects as PROP on sweetness and creaminess, (but to a lesser degree) and revealed potential taste-somatosensory interactions in weakly sweet stimuli. These data support that taste phenotype affects the nature of enhancement or suppression of sweetness and creaminess in liquid fat/sugar mixtures. Taste phenotype effects on sweetness and creaminess likely involve differential taste, retronasal olfactory, and somatosensory contributions to these perceptual experiences.

A complex relationship among chemical concentration, detection threshold, and suprathreshold intensity of bitter compounds.

Abstract: Detection thresholds and psychophysical curves were established for caffeine, quinine-HCl (QHCl), and propylthiouracil (PROP) in a sample of 33 subjects (28 female mean age 24 +/- 4). The mean detection threshold (+/-standard error) for caffeine, QHCl, and PROP was 1.2 +/- 0.12, 0.0083 +/- 0.001, and 0.088 +/- 0.07 mM, respectively. Pearson product-moment analysis revealed no significant correlations between detection thresholds of the compounds. Psychophysical curves were constructed for each bitter compound over 6 concentrations. There were significant correlations between incremental points of the individual psychophysical curves for QHCl and PROP. Regarding caffeine, there was a specific concentration (6 mM) below and above which the incremental steps in bitterness were correlated. Between compounds, analysis of psychophysical curves revealed no correlations with PROP, but there were significant correlations between the bitterness of caffeine and QHCl at higher concentrations on the psychophysical curve (P<0.05). Correlation analysis of detection threshold and suprathreshold intensity within a compound revealed a significant correlation between PROP threshold and suprathreshold intensity (r=0.46-0.4, P<0.05), a significant negative correlation for QHCl (r=-0.33 to -0.4, P<0.05), and no correlation for caffeine. The results suggest a complex relationship between chemical concentration, detection threshold, and suprathreshold intensity.

Trying to detect taste in a tasteless solution: modulation of early gustatory cortex by attention to taste.

Abstract: Selective attention is thought to be associated with enhanced processing in modality-specific cortex. We used functional magnetic resonance imaging to evaluate brain response during a taste detection task. We demonstrate that trying to detect the presence of taste in a tasteless solution results in enhanced activity in insula and overlying operculum. The same task does not recruit orbitofrontal cortex (OFC). Instead, the OFC responds preferentially during receipt of an unpredicted taste stimulus. These findings demonstrate functional specialization of taste cortex in which the insula and the overlying operculum are recruited during taste detection and selective attention to taste, and the OFC is recruited during receipt of an unpredicted taste stimulus.

Food Perception with Age and Its Relationship to Pleasantness

Abstract: Differences between elderly subjects (n = 46, 61-86 years) and young subjects (n = 36, 18-25 years) in food perception and food liking were investigated. Intensity and liking ratings were assessed for custard dessert, in which flavor enrichment, textural change, and irritant addition were incorporated as strategies to compensate for sensory losses with increasing age. The sensory acuity (taste, olfaction, irritation, chewing efficiency) of both young and elderly subjects was measured with the help of different sensitivity tests. The elderly perceived the custards differently from the young, mainly as less intense in flavor (cherry/vanilla) and less intense in creaminess/swallowing effort. Several of the observed interaction effects were different for the elderly and the young. The majority of these differences manifested as lower intensity slopes for the elderly. Losses in sensitivity to taste and to olfactory and trigeminal stimuli as well as a reduced chewing efficiency were observed on average for the elderly compared with the young. Furthermore, subgroups of the elderly were observed in which the compensatory strategies flavor enrichment, textural change, and irritant addition led to an increase in food liking. However, these subgroups did not differ in their sensory acuity. The present study does not support the assumption that age-associated changes in food perception-caused by losses in sensory acuity-inevitably reduce the food liking of the elderly.

Chemical Composition of Scent Marks in the Ringtailed Lemur (Lemur catta): Glandular Differences, Seasonal Variation, and Individual Signatures

Abstract: The apocrine and sebaceous scent glands of ringtailed lemurs (Lemur catta) appear to serve different social functions. In behavioral experiments, lemurs modulate their responses to scent marks based on the type of odorant, their own physiological state, the signaler's physiological state, and prior social experience. To examine variation in odorant chemistry relative to olfactory behavior, we used gas chromatography and mass spectrometry to analyze over 86 samples of glandular secretion collected over 2 years from 15 adult lemurs. Labial and scrotal secretions contained organic acids and esters, whereas male brachial secretions were composed almost entirely of squalene and cholesterol derivatives. Principal component and linear discriminant analyses revealed glandular, individual-specific, and seasonal variation in chemical profiles but no relationship to the signaler's social status. The chemical composition of the various secretions provides further clues about the function of the different glands: the higher molecular weight compounds in genital and brachial secretions may increase signal longevity and provide lasting information to conspecifics, consistent with a role in advertising resource ownership or reproductive state. Conversely, the lower molecular weight compounds of antebrachial secretions produce ephemeral signals used primarily in social dominance displays and require integration of multiple sensory modalities for effective signal transmission.

Maxillary Palps Are Broad Spectrum Odorant Detectors in Culex quinquefasciatus

Abstract: A single type of olfactory sensilla on maxillary palps in many species of mosquitoes houses a very sensitive olfactory receptor neuron (ORN) for carbon dioxide reception. We performed extensive single sensillum recordings from this peg sensillum in Culex quinquefasciatus and have characterized the response threshold and kinetics for CO2 reception, with a detection threshold less than the CO2 concentration in the atmosphere. This ORN responded in a tonic mode to lower concentrations of CO2, whereas higher concentrations generated a phasic-tonic mode of action potential firing. Sensillum potentials accurately represented the response magnitude and kinetics of carbon dioxide–elicited excitatory responses. Stimulation of these ORNs with human breath, a complex mixture of mosquito kairomones and up to 4.5% CO2, elicited excitatory responses that were reliably detected by CO2-sensitive ORNs. Another ORN housed in these sensilla responded to 1-octen-3-ol and to various plant-derived compounds, particularly floral and green leaf volatiles. This ORN showed remarkable sensitivity to the natural enantiomer, (R)-()-1-octen3-ol, rivaling pheromone-detecting ORNs in moths. Maximum neuronal response was elicited with a 10 ng dose. A biological, ecological role of maxillary palps in detection of plant- and nectar-related sources is proposed.

Twin study of the heritability of recognition thresholds for sour and salty taste.

Abstract: Seventy-four pairs of monozygotic (identical) twins and 35 pairs of dizygotic (fraternal) twins provided recognition thresholds (modified Harris–Kalmus test) for the sourness of citric acid and the saltiness of sodium chloride during the Twins Days Festival in Twinsburg, OH. Variance components (ACE) models were applied to the data: total variation = additive genetic (A) + common environment (C) + nonshared environment (E). The best-fit model of variation in recognition thresholds for sourness included an additive genetic factor, accounting for 53% of the variance, but no common environment component. This level of heritability, on par with that of sensitivity to the bitter compounds 6-n-propylthiouracil and phenylthiocarbamide, strongly suggests that genetic factors play a larger role than shared environment in determining individual differences in recognition thresholds for sourness. In contrast, the best-fit model for saltiness recognition included a common environment component, accounting for 22% of the variance in thresholds, but no additive component. This result suggests that environment plays a larger role than genetics in determining individual differences in recognition thresholds for saltiness.

Olfactory Cues Modulate Facial Attractiveness

Abstract: We report an experiment designed to investigate whether olfactory cues can influence people's judgments of facial attractiveness. Sixteen female participants judged the attractiveness of a series of male faces presented briefly on a computer monitor using a 9-point visual rating scale. While viewing each face, the participants were simultaneously presented with either clean air or else with 1 of 4 odorants (the odor was varied on a trial-by-trial basis) from a custom-built olfactometer. We included 2 pleasant odors (geranium and a male fragrance) and 2 unpleasant odors (rubber and body odor) as confirmed by pilot testing. The results showed that the participants rated the male faces as being significantly less attractive in the presence of an unpleasant odor than when the faces were presented together with a pleasant odor or with clean air (these conditions did not differ significantly). These results demonstrate the cross-modal influence that unpleasant odors can have on people's judgments of facial attractiveness. Interestingly, this pattern of results was unaffected by whether the odors were body relevant (the body odor and the male fragrance) or not (the rubber and geranium odors).

Expression of trace amine-associated receptors in the Grueneberg ganglion.

Abstract: The Grueneberg ganglion (GG) in the vestibule of the anterior nasal cavity is considered as an olfactory subcompartment based on expression of the olfactory marker protein (OMP) and axonal projection to the olfactory bulb. Searching for olfactory receptors present in the GG, it has been observed recently that V2r83, a member of the V2R class of olfactory receptors, is expressed in numerous cells in the GG of mice. However, no other olfactory receptors have been found to be present in a considerable number of GG neurons so far. Here, we report that GG neurons express trace amine-associated receptors (TAARs) that have most recently been described as a novel class of olfactory receptors. It was observed that several TAAR subtypes are expressed by defined subpopulations of GG neurons distinct from the V2r83-positive cells. Analyzing the time course of TAAR expression during pre- and postnatal development revealed that TAARs are expressed by a substantial portion of GG neurons in late embryonic and neonatal stages, whereas in juveniles and adults, the number of TAAR-positive cells in the GG was significantly decreased.

Perceptual processing strategy and exposure influence the perception of odor mixtures

Abstract: In flavor perception, both experience with the components of odor/taste mixtures and the cognitive strategy used to examine the interactions between the components influence the overall mixture perception. However, the effect of these factors on odor mixtures perception has never been studied. The present study aimed at evaluating whether 1) previous exposure to the odorants included in a mixture or 2) the synthetic or analytic strategy engaged during odorants mixture evaluation determines odor representation. Blending mixtures, in which subjects perceived a unique quality distinct from those of components, were chosen in order to induce a priori synthetic perception. In the first part, we checked whether the chosen mixtures presented blending properties for our subjects. In the second part, 3 groups of participants were either exposed to the odorants contributing to blending mixtures with a "pineapple" or a "red cordial" odor or nonexposed. In a following task, half of each group was assigned to a synthetic or an analytical task. The synthetic task consisted of rating how typical (i.e., representative) of the target odor name (pineapple or red cordial) were the mixtures and each of their components. The analytical task consisted of evaluating these stimuli on several scales labeled with the target odor name and odor descriptors of the components. Previous exposure to mixture components was found to decrease mixture typicality but only for the pineapple blending mixture. Likewise, subjects engaged in an analytical task rated both blending mixtures as less typical than did subjects engaged in a synthetic task. This study supports a conclusion that odor mixtures can be perceived either analytically or synthetically according to the cognitive strategy engaged.

Cerebral Activation to Intranasal Chemosensory Trigeminal Stimulation

Abstract: Although numerous functional magnetic resonance imaging (FMRI) studies have been performed on the processing of olfactory information, the intranasal trigeminal system so far has not received much attention. In the present study, we sought to delineate the neural correlates of trigeminal stimulation using carbon dioxide (CO2) presented to the left or right nostril. Fifteen righthanded men underwent FMRI using single runs of 3 conditions (CO2 in the right and the left nostrils and an olfactory stimulant—phenyl ethyl alcohol—in the right nostril). As expected, olfactory activations were located in the orbitofrontal cortex (OFC), amygdala, and rostral insula. For trigeminal stimulation, activations were found in ‘‘trigeminal’’ and ‘‘olfactory’’ regions including the pre- and postcentral gyrus, the cerebellum, the ventrolateral thalamus, the insula, the contralateral piriform cortex, and the OFC. Left compared with right side stimulations resulted in stronger cerebellar and brain stem activations; right versus left stimulation resulted in stronger activations of the superior temporal sulcus and OFC. These results suggest a trigeminal processing system that taps into similar cortical regions and yet is separate from that of the olfactory system. The overlapping pattern of cortical activation for trigeminal and olfactory stimuli is assumed to be due to the intimate connections in the processing of information from the 2 major intranasal chemosensory systems.

Subthreshold olfactory stimulation can enhance sweetness.

Abstract: The impact of olfactory perception on sweetness was explored in a model solution using odorants at subthreshold concentrations. First, the impact of 6 odorants, previously described in the literature as congruent with sweetness, was investigated at suprathreshold level in a sucrose solution. Ethyl butyrate and maltol were selected as they had the highest and the lowest sweetness-enhancing properties, respectively. Second, the impact on sweetness of the 2 odorants was investigated at subthreshold concentrations. A system delivering a continuous liquid flow at the same sucrose level, but with varying odorant concentrations, was used. At a subthreshold level, ethyl butyrate but not maltol significantly enhanced the sweetness of the sucrose solution. This study highlights that olfactory perception induced by odorants at a subthreshold level can significantly modulate taste perception. Finally, contrary to results observed with ethyl butyrate at suprathreshold levels, at subthreshold levels, the intensity of sweetness enhancement was not proportional to ethyl butyrate concentration.

Proteomic analysis of a membrane preparation from rat olfactory sensory cilia.

Abstract: The cilia of mammalian olfactory receptor neurons (ORNs) represent the sensory interface that is exposed to the air within the nasal cavity. The cilia are the site where odorants bind to specific receptors and initiate olfactory transduction that leads to excitation of the neuron. This process involves a multitude of ciliary proteins that mediate chemoelectrical transduction, amplification, and adaptation of the primary sensory signal. Many of these proteins were initially identified by their enzymatic activities using a membrane protein preparation from olfactory cilia. This so-called "calcium-shock" preparation is a versatile tool for the exploration of protein expression, enzyme kinetics, regulatory mechanisms, and ciliary development. To support such studies, we present a first proteomic analysis of this membrane preparation. We subjected the cilia preparation to liquid chromatography-electrospray ionisation (LC-ESI-MS/MS) tandem mass spectrometry and identified 268 proteins, of which 49% are membrane proteins. A detailed analysis of their cellular and subcellular localization showed that the cilia preparation obtained by calcium shock not only is highly enriched in ORN proteins but also contains a significant amount of nonciliary material. Although our proteomic study does not identify the entire set of ciliary and nonciliary proteins, it provides the first estimate of the purity of the calcium-shock preparation and provides valuable biochemical information for further research.

Emotional stimulation alters olfactory sensitivity and odor judgment.

Abstract: Emotions have a strong influence on the perception of visual and auditory stimuli. Only little is known about the relation between emotional stimulation and olfactory functions. The present study investigated the relationship between the presentation of affective pictures, olfactory functions, and sex. Olfactory performance was assessed in 32 subjects (16 male). Olfactory sensitivity was significantly reduced following unpleasant picture presentation for all subjects and following pleasant picture presentation for male subjects only. Pleasantness and intensity ratings of a neutral suprathreshold odor were related to the valence of the pictures: After unpleasant picture presentation, the odor was rated as less pleasant and more intense, whereas viewing positive pictures induced a significant increase in reported odor pleasantness. We conclude that inducing a negative emotional state reduces olfactory sensitivity. A relation to functional deviations within the primary olfactory cortices is discussed.

Increased Behavioral and Neuronal Sensitivity to Sex Pheromone after Brief Odor Experience in a Moth

Abstract: Plasticity in the response to stimuli related to food and oviposition cues is well documented in insects. However, responses to cues related to reproduction, for example, sex pheromones, are considered to be innate and thus not affected by experience. Here we show that brief preexposure to sex pheromones, without ensuing reward, lowers the threshold for behavioral response and augments the sensitivity in antennal lobe interneurons to pheromone compared with naive male moths. Thus, the sex pheromone system in insects can be modulated by experience. In addition, we show that the behavioral attraction to sex pheromone increases after preexposure in a time-dependent manner: a short-term effect, possibly a form of sensitization, and a long-term effect after more than 24 h. The behavioral long-term effect is paralleled by an increase in sensitivity of interneurons in the primary olfactory center, whereas the peripheral olfactory system does not change its sensitivity. We hypothesize that short-term sensitization to sex pheromone serves as a kind of alert system, whereas the long-term effect improves male performance when reproductively active females are present.

Putative Chemical Signals about Sex, Individuality, and Genetic Background in the Preputial Gland and Urine of the House Mouse (Mus musculus)

Abstract: To explore whether preputial gland secretions and/or urine from the house mouse (Mus musculus) can be used for coding information about sex, individuality, and/or the genetic background of strain [ICR/albino, Kunming (KM), and C57BL/6], we compared the volatile compositions of mouse preputial glands and urine using a combination of dichloromethane extraction and gas chromatography coupled with mass spectrometry (GC-MS). Of the 40 identified compounds in preputial gland secretions, 31 were esters, 2 sesquiterpens, and 7 alcohols. We failed to find any compound unique to a specific sex, individual, or strain. However, many low molecular weight compounds between the sexes, most compounds among individuals, and several compounds among the 3 strains varied significantly in relative ratios. These quantitative differences in preputial gland volatiles (analog coding) are likely to convey information about sex, individual, and the genetic background of mouse strain. We identified 2 new main and male-elevated compounds, 1-hexadecanol (Z=3.676, P=0.000, N=19 in ICR; Z=3.576, P=0.000, N=18) and 1-hexadecanol acetate (Z=3.429, P=0.000, N=19 in ICR; Z=3.225, P=0.001, N=18), which were eluted in GC chromatogram after the 2 sesquiterpens. They might also be potential male pheromones, in addition to the well-known E-beta-farnesene and E,E-alpha-farnesene. Additionally, a few compounds including 1-hexadecanol also varied with strains and might also code for genetic information. Of the 9 identified volatile compounds in male urine, (s)-2-sec-butyl-4,5-dihydrothiazole and R,R-3,4-dehydro-exo-brevicomin are known urine-originated male pheromones from previous studies. We also detected 6-hydroxy-6-methyl-3-heptanone, a male urinary pheromonal compound, which had not been directly detected by GC-MS previously. Chemical analysis shows that the genetically more closely related ICR and KM strains had a higher similarity in the volatile compositions of preputial glands and urine than that between ICR or KM and C57BL/6. R,R-3,4-dehydro-exo-brevicomin, in particular, was sensitive to genetic shifts and differed in relative abundance among the 3 strains, whereas (s)-2-sec-butyl-4,5-dihydrothiazole differed between ICR or Km and C57BL/6. Hence, these 2 compounds might code for information about their genetic background.

Verbal cues modulate hedonic perception of odors in 5-year-old children as well as in adults.

Abstract: The judgment of pleasantness/unpleasantness is the prominent reaction to the olfactory world. In human adults, the hedonic valence of odor perception is affected by various factors, among which is an individual’s lexical knowledge about smells. The present study examined whether such top-down effects of lexical knowledge on hedonic judgment of olfactory input are similar in children (5–6 years) and adults (20–25 years). In both groups, the lexical knowledge was found to influence the perception of the least emotional (or most neutral) odors: the pleasantness of the smells of banana and mint was enhanced when participants were given the corresponding odor label before olfactory sensation. These results lend support to the notion that, during childhood, smells are not only encoded perceptually but that verbal encoding also steers contextual effects that may be prominent factors in the early memorization and categorization of odors.

Odor and Irritation Thresholds for Ammonia: A Comparison between Static and Dynamic Olfactometry

Abstract: Odor and lateralization (irritation) thresholds (LTs) for ammonia vapor were measured using static and dynamic olfactometry. The purpose of the study was to explore the test-retest reliability and comparability of dynamic olfactometry methodology, generally used to determine odor thresholds following European Committee for Standardization guidelines in the context of odor regulations to outside emissions, with static olfactometry. Within a 2-week period, odor and LTs for ammonia were obtained twice for each method for 24 females. No significant differences between methods were found: mean odor detection thresholds (ODTs) were 2.6 parts per million (ppm) for either method (P = 0.96), and mean LTs were 31.7 and 60.9 ppm for the static and dynamic method, respectively (P = 0.07). Test-retest reliability was higher for the dynamic than for the static method (r = 0.61 vs. 0.14 for ODTs and r = 0.86 vs. 0.45 for LTs). The choice of optimal method for any application, however, depends not only on psychometric factors but also on practical factors such as physicochemical properties of the compound, availability of equipment and expertise, task efficiency, and costs.

Chemosensory Cross-Modal Stroop Effects: Congruent Odors Facilitate Taste Identification

Abstract: In order to explore the cross-modal cognitive associations between smell and taste, a chemosensory analogue of the Stroop task (Stroop 1935) was developed. Fourteen participants were presented with an odorant and a tastant and asked to identify the tastant as "sweet" or "sour" by pressing 1 of 2 buttons as quickly as possible. Participants were faster to name the taste when it was presented with an odor that was congruent (e.g., strawberry/sweet) than with an incongruent odor (e.g., strawberry/sour). These results support the concept of a high level of cognitive integration between the senses of smell and taste and illustrates occasions of interference between information arising from different sensory systems.

Individual Differences in Odor Imaging Ability Reflect Differences in Olfactory and Emotional Perception

Abstract: We asked whether the large variability in odor imaging ability is underlain by interindividual differences in the processing of smells and emotion. Olfactory imaging ability, anhedonia level, and odor perception were measured in 40 subjects, using the Vividness of Olfactory Imagery Questionnaire (VOIQ), the Physical Anhedonia Scale, and the European Test of Olfactory Capabilities. ‘‘Good’’ olfactory imagers, defined primarily on the basis of the VOIQ, rated pleasant smells as more familiar and had lower anhedonia scores than ‘‘bad’’ olfactory imagers. Based on self-reported measures, these results suggest that, like olfactory perception, the mental imagery of smells is related to emotion and that, beyond their differences in vividness, good and bad olfactory imagers differ in their experience of emotion and long-term memory of smells.

Measures of Human Olfactory Perception During Pregnancy

Abstract: Although considerable anecdotal evidence suggests that pregnancy affects olfactory sensitivity, scientific evidence is limited and inconclusive. Whereas hedonic ratings are affected by pregnancy, odor identification is not. The aim of the current study was to examine odor perception in women across pregnancy and in the postpartum period. One hundred nonsmoking women who were pregnant, postpartum, or had never been pregnant were tested on the University of Pennsylvania Smell Identification Test (UPSIT). Intensity ratings and scratch patterns were collected as potential indicators of sensitivity, and participants rated the odors' pleasantness. Participants also rated their own sense of smell. Mean UPSIT scores did not differ significantly across groups indicating no difference in odor identification. Trends in planned comparisons suggested that in the first trimester, odors were rated as more intense and less pleasant. In the first trimester, women scratched the odor strips significantly fewer times. Consistent with previous reports, 90% of pregnant women reported that specific odors smelled less pleasant and 60% reported that some odors smelled more pleasant. Although nearly two-thirds of pregnant women rated their olfactory sensitivity to be enhanced during pregnancy and overall pregnant women's self-rated olfactory sensitivity was higher than controls', self-ratings were not correlated with UPSIT scores nor odor intensity ratings. These results suggest that these and previous findings may reflect the fact that the effect of pregnancy on olfaction is small and inconsistent.

Inflammatory obstruction of the olfactory clefts and olfactory loss in humans: a new syndrome?

Abstract: The first step in the olfactory perception is the activation by odorants of sensory neurones in the olfactory epithelium. In humans, this sensory epithelium is located at 2 narrow passages, the olfactory clefts, at the upper part of the nasal cavities. Little is known about the physiology of these clefts. We examined, in 34 patients, the impact of obstructed clefts upon detection and postlearning identification of 5 odorants. The location and extension of the obstructions were assessed using endoscopy, CT scans, and MRI. The inflammatory obstruction was usually bilateral, extending anteroposteriorly, and confined to the clefts, with no sign of obstruction or any inflammatory disease in the rest of the nasal cavities and sinuses. When tested with 5 odorants, these patients showed greatly impaired olfaction compared with a group of 73 normosmic subjects. The majority of these 34 patients had sensory deficits equivalent to that found in another group of 41 congenital anosmic patients, where inspection with MRI indicated the lack of olfactory bulbs. This study demonstrates that the olfactory clefts, in human, function as an entity that is different from other regions of the nasal cavity and is the target for local inflammatory events that are apparently not responding to corticoid and antibiotic treatments.

Sex Selectivity of Mouse Ultrasonic Songs

Abstract: In many species, reproduction requires detecting, recognizing, and courting a potential mate. Progress through these stages is guided by cues involving a wide range of sensory systems. Here we explore the tasks of detection, recognition, and response in terms of the ultrasonic songs of male mice presented with odor cues contained in urine. We find that the quantity of singing, more so than specific features of the songs, varies depending upon the odor cue. For experienced male mice, responses to female odor cues depend only on the concentration of female cues and are independent of the presence of male cues. However, for naive mice, male cues appear to be synergistic for the response to female cues. We therefore find no direct behavioral evidence for a role of opponent neural processing, such as lateral inhibition, in distinguishing sex by olfactory cues. However, modeling demonstrates that lateral inhibition could be one possible mechanism to account for the switch from synergy to independence.

Seasonal variations in olfactory sensory neurons--fish sensitivity to sex pheromones explained?

Abstract: Olfactory sensory neurons of vertebrates regenerate throughout the life of the animal. In fishes, crypt cells are a type of olfactory sensory neurons thought to respond to sex pheromones. Here, we demonstrate that the number of crypt cells in the olfactory epithelium of the crucian carp varies dramatically throughout the year. During winter, few crypt cells are observed at any location within the sensory epithelium. In spring, the majority of crypt cells are located deep in the epithelium not yet exposed to the environment. However, during the summer spawning season, crypt cells are positioned at the epithelial surface. These findings may explain previous studies demonstrating a relationship between circulating androgen and olfactory sensitivity to sex pheromones.

A Quantitative Structure–Activity Analysis on the Relative Sensitivity of the Olfactory and the Nasal Trigeminal Chemosensory Systems

Abstract: We have applied a quantitative structure-activity relationship (QSAR) approach to analyze the chemical parameters that determine the relative sensitivity of olfaction and nasal chemesthesis to a common set of volatile organic compounds (VOCs). We used previously reported data on odor detection thresholds (ODTs) and nasal pungency thresholds (NPTs) from 64 VOCs belonging to 7 chemical series (acetate esters, carboxylic acids, alcohols, aliphatic aldehydes, alkylbenzenes, ketones, and terpenes). The analysis tested whether NPTs could be used to separate out "selective" chemosensory effects (i.e., those resting on the transfer of VOCs from the gas phase to the receptor phase) from "specific" chemosensory effects in ODTs. Previous work showed that selective effects overwhelmingly dominate chemesthetic potency whereas both selective and specific effects control olfactory potency. We conclude that it is indeed possible to use NPTs to separate out selective from specific effects in ODTs. Among the series studied, aldehydes and acids, except for formic acid, show clear specific effects in their olfactory potency. Furthermore, for VOCs whose odor potency rests mainly on selective effects, we have developed a QSAR equation that can predict their ODTs based on their NPTs.

The olfactory pathway of decapod crustaceans--an invertebrate model for life-long neurogenesis.

Abstract: The first part of this review includes a short description of the cellular and morphological organization of the olfactory pathway of decapod crustaceans, followed by an overview of adult neurogenesis in this pathway focusing on the olfactory lobe (OL), the first synaptic relay in the brain. Adult neurogenesis in the central olfactory pathway has the following characteristics. 1) It is present in all the diverse species of decapod crustaceans so far studied. 2) In all these species, projection neurons (PNs), which have multiglomerular dendritic arborizations, are generated. 3) Neurons are generated by one round of symmetrical cell divisions of a small population of immediate precursor cells that are located in small proliferation zones at the inner margin of the respective soma clusters. 4) The immediate precursor cells in each soma cluster appear to be generated by repeated cell divisions of one or few neuronal stem cells that are located outside of the proliferation zone. 5) These neuronal stem cells are enclosed in a highly structured clump of small glial-like cells, which likely establishes a specific microenvironment and thus can be regarded as a stem cell niche. 6) Diverse internal and external factors, such as presence of olfactory afferents, age, season of the year, and living under constant and deprived conditions modulate the generation and/or survival of new neurons. In the second part of this review, I address the question why in decapod crustaceans adult neurogenesis persists in the visual and olfactory pathways of the brain but is lacking in all other mechanosensory-chemosensory pathways. Due to the indeterminate growth of most adult decapod crustaceans, new sensory neurons of all modalities (olfaction and chemo-, mechano-, and photoreception) are continuously added during adulthood and provide an ever-increasing sensory input to all primary sensory neuropils of the central nervous system. From these facts, I conclude that adult neurogenesis in the brain cannot simply be a mechanism to accommodate increasing sensory input and propose instead that it is causally linked to the specific "topographic logic" of information processing implemented in the sensory neuropils serving different modalities. For the presumptive odotopic type of information processing in the OL, new multiglomerular PNs allow interconnection of novel combinations of spatially unrelated input channels (glomeruli), whose simultaneous activation by specific odorants is the basis of odor coding. Thus, adult neurogenesis could provide a unique way to increase the resolution of odorant quality coding and allow adaptation of the olfactory system of these long-lived animals to ever-changing odor environments.

Removal of the Vomeronasal Organ Blocks the Stress-Induced Hyperthermia Response to Alarm Pheromone in Male Rats

Abstract: Previously, we reported that male Wistar rats release alarm pheromone from their perianal region, which aggravates stressinduced hyperthermia (SIH) in pheromone-recipient rats. The subsequent discovery that this pheromone could be trapped in water enabled us to expose recipients to the pheromone in their home cages. Despite its apparent influence on autonomic and behavioral functions, we still had no clear evidence as to whether the alarm pheromone was perceived by the main olfactory system (MOS) or by the vomeronasal system. In this study, we investigated this question by exposing 3 types of recipients to alarm pheromone in their home cages: intact males (Intact), vomeronasal organ–excised males (VNX), and sham-operated males (Sham). The Intact and Sham recipients showed aggravated SIH in response to alarm pheromone, whereas the VNX recipients did not. In addition, the results of the habituation/dishabituation test and soybean agglutinin binding to the accessory olfactory bulb verified the complete ablation of the vomeronasal organ (VNO) with a functional MOS in the pheromone recipients. These results strongly suggest that male rats perceive alarm pheromone with the VNO.