Showing papers in "Chemical Senses in 2010"
TL;DR: The data suggest that the detection of the numerous bitter chemicals is related to the molecular receptive ranges of hTAS2Rs, and some receptors recognized only few agonists, others displayed moderate or extreme tuning broadness.
Abstract: Humans perceive thousands of compounds as bitter. In sharp contrast, only ;25 taste 2 receptors (TAS2R) bitter taste receptors have been identified, raising the question as to how the vast array of bitter compounds can be detected by such a limited number of sensors. To address this issue, we have challenged 25 human taste 2 receptors (hTAS2Rs) with 104 natural or synthetic bitter chemicals in a heterologous expression system. Thirteen cognate bitter compounds for 5 orphan receptors and 64 new compounds for previously identified receptors were discovered. Whereas some receptors recognized only few agonists, others displayed moderate or extreme tuning broadness. Thus, 3 hTAS2Rs together were able to detect ;50% of the substances used. Conversely, though 63 bitter substances activated only 1–3 receptors, 19 compounds stimulated up to 15 hTAS2Rs. Our data suggest that the detection of the numerous bitter chemicals is related to the molecular receptive ranges of hTAS2Rs.
870 citations
TL;DR: This article presents an initial effort at identifying and categorizing these functions, using 3 sources of information as a guide: 1) losses experienced by anosmic participants; 2) olfactory function in other mammals; and 3) capacity, namely, whether the human Olfactory system can support the suggested function and whether there is evidence that it does.
Abstract: Although referred to in passing in several places, there have been few attempts to specify the functions of the human olfactory system. This article presents an initial effort at identifying and categorizing these functions, using 3 sources of information as a guide: 1) losses experienced by anosmic participants; 2) olfactory function in other mammals; and 3) capacity, namely, whether the human olfactory system can support the suggested function and whether there is evidence that it does. Three major classes of function were identified, relating to Ingestion (Detection/identification prior to ingestion; Detection of expectancy violations; Appetite regulation; Breast orientation and feeding), Avoiding environmental hazards (Fear related; Disgust related), and Social communication (Reproductive [inbreeding avoidance, fitness detection in prospective mates]; Emotional contagion [fear contagion, stress buffering]). These suggested functions were then examined with respect to 1) issues of ecological validity in human olfactory research; 2) their impact on olfactory loss; and 3) their general and specific implications for the study of human olfaction.
474 citations
TL;DR: This is the first study on persisting structural changes in cortical GM volume after complete olfactory loss, and a comparison with results of an additionally executed functional MRI study on olfaction in healthy subjects was performed to evaluate the significance of the observed atrophy areas in cerebral Olfactory processing.
Abstract: Chronic olfactory disorders, including the complete loss of the sense of smell (anosmia), are common. Using voxel-based morphometry (VBM) in magnetic resonance imaging (MRI), structural changes in the cerebral gray matter (GM) of a group of patients with anosmia compared with a normosmic, healthy control group were evaluated. Patients with anosmia presented a significant decrease of GM volume mainly in the nucleus accumbens with adjacent subcallosal gyrus, in the medial prefrontal cortex (MPC) including the middle and anterior cingulate cortices, and in the dorsolateral prefrontal cortex (dlPFC). These areas are part of the limbic loop of the basal ganglia and except the dlPFC secondary olfactory areas. They also play an important role in many neurological diseases. Furthermore, volume decreases in smaller areas like the piriform cortex, insular cortex, orbitofrontal cortex, hippocampus, parahippocampal gyrus, supramarginal gyrus, and cerebellum could be seen. Longer disease duration was associated with a stronger atrophy in the described areas. No local increases in the GM volume could be observed. A comparison with results of an additionally executed functional MRI study on olfaction in healthy subjects was performed to evaluate the significance of the observed atrophy areas in cerebral olfactory processing. To our knowledge, this is the first study on persisting structural changes in cortical GM volume after complete olfactory loss.
129 citations
TL;DR: The similarity of the findings to those for other mammals and in primates that are more distantly related to humans suggests a broader role for odor in primate communication than is currently recognized.
Abstract: Primates are traditionally considered to be microsmatic, with decreased reliance on olfactory senses in comparison to other sensory modalities such as vision. This is particularly the case for Old World monkeys and apes (catarrhines). However, various lines of evidence suggest that chemical communication may be important in these species, including the presence of a sternal scent-gland in the mandrill. We investigated the volatile components of mandrill odor using gas chromatography-mass spectrometry. We identified a total of 97 volatile components in 88 swabs of the sternal gland secretion and 95 samples of sternal gland hair saturated with scent-gland secretion collected from 27 males and 18 females. We compared odor profiles with features of the signaler using principle components and discriminant function analyses and found that volatile profiles convey both variable (age, dominance rank in males) and fixed (sex, possibly individual identity) information about the signaler. The combination of an odor profile that signals sex, age, and rank with increased motivation to scent-mark and increased production of secretion in high-ranking males leads to a potent signal of the presence of a dominant, adult male with high testosterone levels. This may be particularly relevant in the dense Central African rain forest which mandrills inhabit. By contrast, we were unable to differentiate between either female cycle stage or female rank based on odor profiles, which accords with behavioral studies suggesting that odor signals are not as important in female mandrills as they are in males. The similarity of our findings to those for other mammals and in primates that are more distantly related to humans suggests a broader role for odor in primate communication than is currently recognized.
100 citations
TL;DR: It is shown here that Tmem16b expression is highly specific for the OE, in contrast to the closely related T Mem16a, which shows a broad expression pattern in secretory epithelial cells.
Abstract: Calcium-activated chloride channels (CaCCs) are involved in many physiological processes, including sensory signal transduction, but only little is known to date about their structure and function. We performed a proteome analysis of the olfactory epithelium (OE) membrane proteome and identified so far uncharacterized membrane proteins as candidate channels. One of the most abundant membrane proteins in olfactory sensory neurons (OSNs) was Tmem16b, a member of a recently identified family of CaCCs. In addition to former studies performed on Tmem16b, we show here that Tmem16b expression is highly specific for the OE, in contrast to the closely related Tmem16a, which shows a broad expression pattern in secretory epithelial cells. Native Tmem16b is localized in the cilia of the OSNs, which is in agreement with previous electrophysiological recordings.
96 citations
TL;DR: A new computational framework for merging odor response data sets from heterogeneous studies is developed, creating a consensus metadatabase, the database of odor responses (DoOR), and a functional atlas of all available odor responses in Drosophila melanogaster is obtained.
Abstract: We have developed a new computational framework for merging odor response data sets from heterogeneous studies, creating a consensus metadatabase, the database of odor responses (DoOR). As a result, we obtained a functional atlas of all available odor responses in Drosophila melanogaster. Both the program and the data set are freely accessible and downloadable on the Internet (http://neuro.uni-konstanz.de/DoOR). The procedure can be adapted to other species, thus creating a family of ‘‘olfactomes’’ in the near future. Drosophila melanogaster was chosen because of all species this one is closest to having the complete olfactome characterized, with the highest number of deorphanized receptors available. The database guarantees long-term stability (by offering time-stamped, downloadable versions), up-to-date accuracy (by including new data sets as soon as they are published), and portability (for other species). We hope that this comprehensive repository of odor response profiles will be useful to the olfactory community and to computational neuroscientists alike.
90 citations
TL;DR: Results from a detailed chemical examination of the uropygial secretions from 2 petrel species, Antarctic prions and blue petrels are presented, demonstrating that the secretions contain critical socioecological information such as species, gender, and individual identity.
Abstract: Avian chemosignaling remains relatively unexplored, but its potential importance in birds’ social behaviors is becoming recognized. Procellariiform seabirds provide particularly appropriate models for investigating these topics as they possess a well-developed olfactory system and unequalled associated capabilities. We present here results from a detailed chemical examination of the uropygial secretions (the main source of avian exogenous chemicals) from 2 petrel species, Antarctic prions and blue petrels. Using gas chromatography–mass spectrometry techniques and recently developed multivariate tools, we demonstrate that the secretions contain critical socioecological information such as species, gender, and individual identity. Importantly, these chemosignals correlate with some of the birds’ olfactory behaviors demonstrated in the field. The molecules found to be associated with social information were essentially large unsaturated compounds, suggesting that these may be precursors of, or correlates to the actual airborne signals. Although the species-specific chemosignal may be involved in interspecific competition at the breeding grounds, the role of the sexually specific chemosignal remains unclear. The existence of individually specific signals (i.e., chemical signatures) in these birds has important implications for processes such as individual recognition and genetically based mate choice already suspected for this group. Our results open promising avenues of research for the study of avian chemical communication.
87 citations
TL;DR: The hypothesis that sequence variations occurring in genes encoding taste signaling molecules can influence sweet taste perception in humans is evaluated and genetic association analysis revealed significant correlation of sucrose AUC scores with genetic variation occurring in the GNAT3 gene, which encodes the taste-specific G(alpha) protein subunit gustducin.
Abstract: Variation in taste perception of different chemical substances is a well-known phenomenon in both humans and animals. Recent advances in the understanding of sweet taste signaling have identified a number of proteins involved in this signal transduction. We evaluated the hypothesis that sequence variations occurring in genes encoding taste signaling molecules can influence sweet taste perception in humans. Our population consisted of unrelated individuals ( n= 160) of Caucasian, African– American, and Asian descent. Threshold and suprathreshold sensitivities of participants for sucrose were estimated using a sorting test and signal detection analysis that produced cumulative R-index area under the curve (AUC) scores. Genetic association analysis revealed significant correlation of sucrose AUC scores with genetic variation occurring in the GNAT3 gene (single point P= 10 3 to 10 4 ), which encodes the taste-specific Ga protein subunit gustducin. Subsequent sequencing identified additional GNAT3 variations having significant association with sucrose AUC scores. Collectively, GNAT3 polymorphisms explain 13% of the variation in sucrose perception. Our findings underscore the importance of common genetic variants influencing human taste perception.
82 citations
TL;DR: The behavioral data robustly suggested that the 3 alkanols synergistically created a female attractant odor or male pheromone in the budgerigar and that bird uropygial glands have broader implications in sexual behavior than previously known.
Abstract: The possible role of uropygial gland-secreted compounds in olfactory discrimination of sex or sex attractants in the budgerigar, Melopsittacus undulatus, was investigated using behavioral 2-choice tests and gas chromatography–mass spectrometry analysis. Our data showed that female budgerigars were capable of distinguishing males from females in a Y maze via body odor, indicating its sexual dimorphism. When we conducted a chemical assay of the uropygial preen gland secretions, we found 4 times more volatile octadecanol, nonadecanol, and eicosanol in ratios in males than in females, making them putative male pheromone candidates. Female birds also showed overt preferences for the odor of male preen gland secretions or the 3-alkanol blend equivalent preened onto the plumage of a male over that of female counterparts. Removal of any one alkanol was associated with a loss of attractiveness to the female. In another test device (a test cage) with visible male bird stimulus, females chose the male with the 3-alkanol blend of males over the other male with female preen gland secretion, whereas did not differentiate their responses between the males with either this blend or male preen gland secretions. The behavioral data robustly suggested that the 3 alkanols synergistically created a female attractant odor or male pheromone in the budgerigar and that bird uropygial glands have broader implications in sexual behavior than previously known. This is the first investigation with bioassay of components of the gland in a bird species.
82 citations
TL;DR: Results show that receptor oligomerization occurs between TAS2R bitter taste receptors; however, functional consequences of hetero-oligomerization were not obvious.
Abstract: A family of 25 G protein-coupled receptors, TAS2Rs, mediates bitter taste in humans. Many of the members of this family are coexpressed in a subpopulation of taste receptor cells on the tongue, thereby allowing the possibility of receptor-receptor interactions with potential influences on their function. In this study, we used several experimental approaches to investigate whether TAS2Rs can form oligomers and if this has an effect on receptor function. Coimmunoprecipitations clearly demonstrated that TAS2Rs can physically interact in HEK293T cells. Further bioluminescence resonance energy transfer analysis of all 325 possible binary combinations of TAS2Rs established that the vast majority of TAS2R pairs form oligomers, both homomers and heteromers. Subsequent screenings of coexpressed bitter receptors with 104 different tastants did not reveal any heteromer-specific agonists. Additional studies also showed no obvious influence of TAS2R hetero-oligomerization on plasma membrane localization or pharmacological properties of the receptors. Thus, our results show that receptor oligomerization occurs between TAS2R bitter taste receptors; however, functional consequences of hetero-oligomerization were not obvious.
81 citations
TL;DR: The brain representation of sweet and salty taste intensity are represented in the middle insula using functional magnetic resonance imaging, and Amygdala activation is only modulated by saltiness.
Abstract: The intensity of the taste of a food is affected mostly by the amount of sugars (mono- and disaccharides) or salt it contains. To season savory-tasting foods mainly table salt (NaCl) is used and to sweeten foods, sugars like sucrose are used. Foods with highly intense tastes are consumed in smaller amounts. The optimal taste intensity of a food is the intensity at which it is perceived as most pleasant. When taste intensity decreases or increases from optimal, the pleasantness of a food decreases. Here, we investigated the brain representation of sweet and salty taste intensity using functional magnetic resonance imaging. Fifteen subjects visited twice and tasted a range of 4 watery solutions (0-1 M) of either sucrose or NaCl in water. Middle insula activation increased with increasing concentration for both NaCl and sucrose. Despite similar subjective intensity ratings, anterior insula activation by NaCl increased more with concentration than that by sucrose. Amygdala activation increased with increasing NaCl concentration but not sucrose concentration. In conclusion, sweet and salty taste intensity are represented in the middle insula. Amygdala activation is only modulated by saltiness. Further research will need to extrapolate these results from simple solutions to real foods.
TL;DR: The relationships between genetic variation in TAS2R38, functional variation in the encoded receptor, and threshold taste responses to goitrin, PROP, and PTC in 50 subjects were examined to suggest that mutations in T as 2R38 play a role in shaping goitrina perception.
Abstract: The perceived bitterness of cruciferous vegetables such as broccoli varies from person to person, but the functional underpinnings of this variation are not known. Some evidence suggests that it arises, in part, from variation in ability to perceive goitrin (5-vinyloxazolidine-2-thione), a potent antithyroid compound found naturally in crucifers. Individuals vary in ability to perceive synthetic compounds similar to goitrin, such as 6-propyl-2-thiouracil (PROP) and phenylthiocarbamide (PTC), as the result of mutations in the TAS2R38 gene, which encodes a bitter taste receptor. This suggests that taste responses to goitrin itself may be mediated by TAS2R38. To test this hypothesis, we examined the relationships between genetic variation in TAS2R38, functional variation in the encoded receptor, and threshold taste responses to goitrin, PROP, and PTC in 50 subjects. We found that threshold responses to goitrin were associated with responses to both PROP ( P= 8.9 · 10 4 ; rs = 0.46) and PTC ( P= 7.5 · 10 4 ; rs = 0.46). However, functional assays revealed that goitrin elicits a weaker response from the sensitive (PAV) allele of TAS2R38 (EC50 = 65.0 lM) than do either PROP (EC50 = 2.1 lM) or PTC (EC50 = 1.1 lM) and no response at all from the insensitive (AVI) allele. Furthermore, goitrin responses were significantly associated with mutations in TAS2R38 ( P= 9.3 · 10 3 ), but the same mutations accounted for a smaller proportion of variance in goitrin response (r 2 = 0.16) than for PROP (r 2 = 0.50) and PTC (r 2 = 0.57). These findings suggest that mutations in TAS2R38 play a role in shaping goitrin perception, but the
TL;DR: The results support the inhibiting role of proteins with strong phenol-binding activity on astringency elicitation and individual physiological variations of parotid gland functionality might account for differences in sensitivity to astringent phenolic stimuli.
Abstract: The extent of the change in salivary protein characteristics after repeated stimulations was shown to be correlated to differences in perceived astringency. Salivary characteristics of 77 subjects were compared after masticatory (S1) and taste/masticatory (S2) stimulations. The variations (S2 minus S1) of protein concentration and saliva haze-forming capacity (HFC) were used to define 3 subject groups: low responding (LR, n = 20), medium responding (MR, n = 37), and high responding (HR, n = 20). Salivary protein concentration did not change in LR subjects; decreased a little, but significantly, in MR subjects; and strongly decreased in HR subjects. After S2, HFC increased in LR subjects, slightly decreased in MR subjects, and strongly decreased in HR subjects. Salivary protein electrophoresis patterns for HR and LR subjects were analyzed. No significant modifications of glycosylated proline-rich proteins (PRPs), PRPs, and amylases and a slight decrease in cystatins and histatins were found when S2 and S1 samples were compared in LR subjects, whereas HR subjects showed a strong decrease in all the above proteins after S2. Significant modifications of mucins were not found. Tannic acid (TA, 3 g/L) astringency ratings after S1 from HR subjects were significantly higher than those from the other 2 groups, whereas no differences were found comparing LR and MR ratings. The "carryover" effect due to 4 sequential exposures to TA samples (1.4 g/L) was observed in both HR and MR groups, whereas no significant astringency rating variation was found in the LR group. The results support the inhibiting role of proteins with strong phenol-binding activity on astringency elicitation. Individual physiological variations of parotid gland functionality might account for differences in sensitivity to astringent phenolic stimuli.
TL;DR: It is found that there is no significant reduction in taste responsiveness in Pkd1l3 mutant mice in behavioral or electrophysiological tests when compared with wild-type controls, and further studies are needed to elucidate the function of PKD1L3 in taste bud cells.
Abstract: Recent studies, both in vitro and in vivo, have suggested the involvement of the polycystic kidney disease-1 and -2 like genes, Pkd1l3 and Pkd2l1, in acid taste transduction. In mice, disruption of taste cells expressing PKD2L1 eliminates gustatory neural responses to acids. However, no previous data exist on taste responses in the absence of PKD1L3 or on behavioral responses in mice lacking either of these proteins. In order to assess the function of PKD1L3, we genetically engineered mice with a targeted mutation of the Pkd1l3 gene. We then examined taste responsiveness of mutant and wild-type mice using several different approaches. In separate groups of mice, we measured preference scores in 48-h 2-bottle tests, determined NaCl or citric acid taste thresholds using a conditioned taste aversion technique, and conducted electrophysiological recordings of activity in the chorda tympani and glossopharyngeal nerves. Multiple taste compounds representing all major taste qualities were used in the preference tests and nerve-recording experiments. We found no significant reduction in taste responsiveness in Pkd1l3 mutant mice in behavioral or electrophysiological tests when compared with wild-type controls. Therefore, further studies are needed to elucidate the function of PKD1L3 in taste bud cells.
TL;DR: It is suggested that specific as well as common plant odor cues play a role in L. botrana host recognition and that there is plasticity in attraction to partial blends.
Abstract: In herbivorous insects with more than 1 host plant, attraction to host odor could conceptually be mediated by common compounds, by specific compounds released by each plant or by combinations of common and specific compounds. We have compared the attraction of female grapevine moth, Lobesia botrana, with specific and common (shared) odors from 2 different plants: a wild host (Daphne gnidium) and a recently colonized host (Vitis vinifera). Odor blends eliciting female attraction to V. vinifera have previously been identified. In this study, olfactory cues from D. gnidium were identified by electroantennographic detection and chemical analysis. The attraction of mated females to synthetic odor blends was then tested in a wind tunnel bioassay. Female attraction was elicited by a blend of compounds released by both from D. gnidium and V. vinifera and by 2 blends with the compounds released specifically from each host. However, more complete odor blends of the 2 plants elicited stronger attraction. The common compounds in combination with the specific compounds of D. gnidium were the most attractive blend. This blend was tested with the common compounds presented both in the ratio emitted by D. gnidium and by V. vinifera, but there was no difference in female attraction. Our findings suggest that specific as well as common plant odor cues play a role in L. botrana host recognition and that there is plasticity in attraction to partial blends. The results are discussed in relation to mechanisms behind host odor recognition and the evolution of insect-plant associations.
TL;DR: Results support the existence of an integrated supramodal flavor system in the anterior ventral insula that preferentially communicates with the circuits guiding feeding when the flavor is potentially nutritive.
Abstract: Taste, which is almost always accompanied by other oral sensations, serves to identify potential nutrients and toxins. The present study was designed to determine the influence of sensory modality (chemesthetic vs. gustatory) and physiological significance (potentially nutritive vs. potentially harmful) on insular response to oral stimulation. Sixteen subjects underwent functional magnetic resonance imaging scanning while receiving 2 potentially nutritive solutions (sucrose and NaCl), 2 potentially harmful solutions (quinine and capsaicin, a chemesthetic stimulus), and a tasteless control solution. We identified a region of anterior ventral insula that responded to oral stimulation irrespective of modality or physiological significance. However, when subjects tasted a potentially nutritive stimulus, the connectivity between the insula and a feeding network including the hypothalamus, ventral pallidum, and striatum was greater than when tasting a potentially harmful stimulus. No differential connectivity was observed as a function of modality (gustatory vs. chemesthetic). These results support the existence of an integrated supramodal flavor system in the anterior ventral insula that preferentially communicates with the circuits guiding feeding when the flavor is potentially nutritive.
TL;DR: The results suggest that the olfactory system may provide a path to manipulate respiration in sleep, and not increase the frequency of arousals or wake but did influence respiration.
Abstract: To assess the feasibility of using odors as a potential mechanism for treating sleep apnea, we set out to test the hypothesis that odorants delivered during sleep would modify respiratory patterns without inducing arousal or wake in healthy sleepers. We used 2 mildly trigeminal odorants: the pleasant lavender and unpleasant vetiver oil and 2 pure olfactory odorants: the pleasant vanillin and unpleasant ammonium sulfide. During sleep, an olfactometer delivered a transient odorant every 9,12, or 15 min (randomized), providing 21–37 odorant presentations per night. Each of 36 participants was studied for 1 night and with 1 of the 4 different odorants tested. In addition to standard overnight polysomnography, we employed highly accurate measurements of nasal and oral respiration. Odorants did not increase the frequency of arousals or wake but did influence respiration. Specifically, all 4 odorants transiently decreased inhalation and increased exhalation for up to 6 breaths following odor onset. This effect persisted regardless of odorant valence or stage of sleep. These results suggest that the olfactory system may provide a path to manipulate respiration in sleep.
TL;DR: It is established that volatiles associated with illicit substances, many of which are of nonnatural origin, are also detected by Drosophila receptors.
Abstract: Insects can detect a large range of odors with a numerically simple olfactory system that delivers high sensitivity and accurate discrimination. Therefore, insect olfactory receptors hold great promise as biosensors for detection of volatile organic chemicals in a range of applications. The array of olfactory receptor neurons of Drosophila melanogaster is rapidly becoming the best-characterized natural nose. We have investigated the suitability of Drosophila receptors as detectors for volatiles with applications in law enforcement, emergency response, and security. We first characterized responses of the majority of olfactory neuron types to a set of diagnostic odorants. Being thus able to correctly identify neurons, we then screened for responses from 38 different types of neurons to 35 agents. We identified 13 neuron types with responses to 13 agents. As individual Drosophila receptor genes have been mapped to neuron types, we can infer which genes confer responsiveness to the neurons. The responses were confirmed for one receptor by expressing it in a nonresponsive neuron. The fly olfactory system is mainly adapted to detect volatiles from fermenting fruits. However, our findings establish that volatiles associated with illicit substances, many of which are of nonnatural origin, are also detected by Drosophila receptors.
TL;DR: The outcome suggests that subjects did not attend selectively to one flavor component or the other in the experimental condition and further supports the conclusion that (late) decisional or attentional strategies do not exert a large influence on the gustatory-olfactory flavor integration.
Abstract: It is easier to detect mixtures of gustatory and olfactory flavorants than to detect either component alone. But does the detection of mixtures exceed the level predicted by probability summation, assuming independent detection of each component? To answer this question, we measured simple response times (RTs) to detect brief pulses of one of 3 flavorants (sucrose [gustatory], citral [olfactory], sucrose–citral mixture) or water, presented into the mouth by a computer-operated, automated flow system. Subjects were instructed to press a button as soon as they detected any of the 3 nonwater stimuli. Responses to the mixtures were faster (RTs smaller) than predicted by a model of probability summation of independently detected signals, suggesting positive coactivation (integration) of gustation and retronasal olfaction in flavor perception. Evidence for integration appeared mainly in the fastest 60% of the responses, indicating that integration arises relatively early in flavor processing. Results were similar when the 3 possible flavorants, and water, were interleaved within the same session (experimental condition), and when each flavorant was interleaved with water only (control conditions). This outcome suggests that subjects did not attend selectively to one flavor component or the other in the experimental condition and further supports the conclusion that (late) decisional or attentional strategies do not exert a large influence on the gustatory–olfactory flavor integration.
TL;DR: The preference response of rodents to stevia sweeteners is notable in view of their minimal response to some other noncaloric sweeteners (aspartame and cyclamate); similar tests of sweet receptor T1R3 knockout mice and brief-access licking tests with normal mice suggested that the preferences were based on sweet taste rather than post-oral effects.
Abstract: Use of natural noncaloric sweeteners in commercial foods and beverages has expanded recently to include compounds from the plant Stevia rebaudiana. Little is known about the responses of rodents, the animal models for many studies of taste systems and food intake, to stevia sweeteners. In the present experiments, preferences of female Sprague-Dawley rats and C57BL/6J mice for different stevia products were compared with those for the artificial sweetener saccharin. The stevia component rebaudioside A has the most sweetness and least off-tastes to human raters. In ascending concentration tests (48-h sweetener vs. water), rats and mice preferred a high-rebaudioside, low-stevioside extract as strongly as saccharin, but the extract stimulated less overdrinking and was much less preferred to saccharin in direct choice tests. Relative to the extract, mice drank more pure rebaudioside A and showed stronger preferences but still less than those for saccharin. Mice also preferred a commercial mixture of rebaudioside A and erythritol (Truvia). Similar tests of sweet receptor T1R3 knockout mice and brief-access licking tests with normal mice suggested that the preferences were based on sweet taste rather than post-oral effects. The preference response of rodents to stevia sweeteners is notable in view of their minimal response to some other noncaloric sweeteners (aspartame and cyclamate).
TL;DR: Chemical ablation causes temporary reduction with swift regeneration of the OE occurring within a week, with the most significant reduction following Triton X-100 treatment corresponded to the region of supporting cells and mature olfactory sensory neurons.
Abstract: The effects of Triton X-100 on the olfactory epithelium (OE) of adult zebrafish were examined to study neuronal turnover in this model system. Fish were killed at various time points after detergent application and stained with hematoxylin and eosin to examine olfactory structures, immunocytochemistry to examine cell types, or DiI to examine connections to the olfactory bulb. A significant decrease in epithelial thickness of treated sides was observed 1-day posttreatment. Epithelium thickness recovered by 5 days. The most significant reduction in the OE following Triton X-100 treatment corresponded to the region of supporting cells and mature olfactory sensory neurons. Labeling for all neurons with anti-Hu and for the 3 sensory neuron subtypes of the zebrafish OE (ciliated, microvillous, and crypt neurons) diminished 1 day after lesion and returned by 5 days posttreatment. Retrograde labeling from the olfactory bulb showed that the majority of mature olfactory sensory neurons disappeared in 1 day and reappeared by 5 days after treatment. Anti-proliferating cell nuclear antigen was used to show mitotic activity, and after chemical lesion, there was an increase in proliferation in specific regions of the OE. Thus, chemical ablation causes temporary reduction with swift regeneration of the OE occurring within a week.
TL;DR: It is suggested that oleic acid in femoral secretions might be a reliable advertisement of a male's body condition, which females could use to select high-quality mates in conjunction with information provided by other chemicals.
Abstract: Pheromones of vertebrates are often a mixture of several chemicals with different properties and messages, and their production seems condition dependent. Thus, pheromones are a good, but little studied, example of multiple sexual signals. Femoral gland secretions of male rock lizards Iberolacerta cyreni contain steroids that may act as pheromones, but there are also many other lipids, such as oleic acid, whose allocation to secretions may be costly because it has to be diverted from body fat reserves. This suggests that oleic acid could also have some function in secretions. Chemical analyses showed that proportions of oleic acid in femoral secretions of males were positively related to body condition of males, suggesting that the oleic acid secreted may reflect the amount of body fat reserves of a male. Tongue-flick bioassays showed that females were able to detect by chemosensory cues alone differences in proportions of oleic acid in secretions of males. Scents of males with more oleic acid elicited stronger chemosensory responses by females. Further tests with chemical standards confirmed that females distinguished oleic acid, and changes in its concentration, from other chemicals that are naturally found in secretions of males. Moreover, choice trials of scent-marked substrates showed that females were more attracted to areas that were experimentally manipulated to increase the proportion of oleic acid in natural scent marks of males. We suggest that oleic acid in femoral secretions might be a reliable advertisement of a male's body condition, which females could use to select high-quality mates in conjunction with information provided by other chemicals. Alternatively, scent marks with more oleic acid might be simply more attractive to females if chemosensory responses of females to scent of males were originated by a preexisting sensory bias for food chemicals such as the oleic acid. Nevertheless, this sensory trap might have evolved into an honest signal because the elaboration of the signal seems differentially costly for males with different body conditions.
TL;DR: Both experimental settings demonstrated that the multicomponent strawberry aroma was able to enhance perceived satiation, which was perceived as being more complex, yet of similar aroma quality, intensity, and pleasantness compared with the single-component strawberry aroma.
Abstract: The acute effect of complexity in aroma composition on perceived satiation and food intake was investigated in 41 young, healthy, and normal weight subjects. Subjects consumed 2 different strawberry-aromatized sweetened yogurt products (i.e., test and placebo product) in either an olfactometer-aided or an ad libitum eating experimental design. The test product was aromatized with a multicomponent strawberry aroma, whereas the placebo product was aromatized with a single-component strawberry aroma. Compared to placebo, subjects felt significantly more satiated during aroma stimulation with the multicomponent strawberry aroma in the olfactometer-aided setting. Additionally, perceived satiation was significantly increased 10-15 min after consumption of the multicomponent strawberry-aromatized sweetened yogurt product in the ad libitum eating setting. There was no effect on the amount of strawberry-aromatized sweetened yogurt product consumed ad libitum. Apart from the differences in timing of the appetite-regulating effects, both experimental settings demonstrated that the multicomponent strawberry aroma, which was perceived as being more complex, yet of similar aroma quality, intensity, and pleasantness compared with the single-component strawberry aroma, was able to enhance perceived satiation. The methodology of the olfactometer-aided aroma stimulation proved to be representative of a real-life setting with regard to aroma exposure and satiation. Food products, which are perceived as being more complex, have been suggested to delay the development of sensory satiation as a result of implicitly cueing for variation. The present results may be explained by increased sensory stimulation, due to concurrent exposure to multiple aroma components cueing for sensorily similar strawberry perception.
TL;DR: This study reconfirmed the distribution of the 44 olfactory sensilla of the common bed bug and identified 3 different sensillum types located at the distal tip of C. lectularius antenna by external morphology mapping and correlated the morphological mapping with an electrophysiological characterization of the Olfactory receptor neurons housed in each specific sensilla.
Abstract: The common bed bug Cimex lectularius (Hemiptera; Cimicidae) is a temporary ectoparasite on humans that is currently reinvading the developed countries. Like other haematophagous arthropods, host seeking and orientation in C. lectularius is partially mediated by olfaction. In this study, we reconfirmed the distribution of the 44 olfactory sensilla and identified 3 different sensillum types located at the distal tip of C. lectularius antenna by external morphology mapping. Using a panel of relevant odorants previously reported to be bioactive in various haematophagous arthropods, we correlated the morphological mapping with an electrophysiological characterization of the olfactory receptor neurons housed in each specific sensillum. We found that all 9 grooved peg sensilla responded specifically in a dose-dependent manner to ammonia, whereas (E)-2-hexenal, (E)-2-octenal, dimethyl trisulfide, 6-methyl-5-hepten-2-one, alpha-pinene, indole, and ethyl butyrate evoked dose-dependent responses within the 6 smooth peg sensilla. Based on the pattern of response to the tested compounds, we were able to separate the 6 smooth peg sensilla of the bed bug into 3 distinct functional classes. We compare our results with previous electrophysiological recordings made with these compounds on other haematophagous arthropods.
TL;DR: The behavioral dose-response functions emerge at concentrations 2-5 orders of magnitude lower than those required for functions tracing the activation of specific human ORs by the same aldehydes in cell/molecular studies, after all functions were expressed as vapor concentrations.
Abstract: We have measured concentration detection (i.e., psychometric) functions to determine the odor detectability of homologous aliphatic aldehydes (propanal, butanal, hexanal, octanal, and nonanal) and helional. Subjects (16 < or = n < or = 18) used a 3-alternative forced-choice procedure against carbon-filtered air (blanks), under an ascending concentration approach. Generation, delivery, and control of each vapor were achieved via an 8-station vapor delivery device. Gas chromatography served to quantify the concentrations presented. Group and individual functions were modeled by a sigmoid (logistic) equation. Odor detection thresholds (ODTs) were defined as the concentration producing a detectability (P) halfway (P = 0.5) between chance (P = 0.0) and perfect detection (P = 1.0). ODTs decreased with carbon chain length: 2.0, 0.46, 0.33, and 0.17 ppb, respectively, from propanal to octanal, but the threshold increased for nonanal (0.53 ppb), revealing maximum sensitivity for the 8-carbon member. The strong olfactory receptor (OR) ligands octanal and helional (0.14 ppb) showed the lowest thresholds. ODTs fell at the lower end of previously reported values. Interindividual variability (ODT ratios) amounted to a factor ranging from 10 to 50, lower than typically reported, and was highest for octanal and hexanal. The behavioral dose-response functions emerge at concentrations 2-5 orders of magnitude lower than those required for functions tracing the activation of specific human ORs by the same aldehydes in cell/molecular studies, after all functions were expressed as vapor concentrations.
TL;DR: Data strongly indicate a linkage between ethanol-induced behavior and ethanol metabolism in adult fruit flies: Adh deficiency resulted in reduced preference to low ethanol concentrations and reduced aversion to high ones, despite recovery from ethanol being strongly impaired.
Abstract: Preference determines behavioral choices such as choosing among food sources and mates. One preference-affecting chemical is ethanol, which guides insects to fermenting fruits or leaves. Here, we show that adult Drosophila melanogaster prefer food containing up to 5% ethanol over food without ethanol and avoid food with high levels (23%) of ethanol. Although female and male flies behaved differently at ethanol-containing food sources, there was no sexual dimorphism in the preference for food containing modest ethanol levels. We also investigated whether Drosophila preference, sensitivity and tolerance to ethanol was related to the activity of alcohol dehydrogenase (Adh), the primary ethanol-metabolizing enzyme in D. melanogaster. Impaired Adh function reduced ethanol preference in both D. melanogaster and a related species, D. sechellia. Adh-impaired flies also displayed reduced aversion to high ethanol concentrations, increased sensitivity to the effects of ethanol on postural control, and negative tolerance/sensitization (i.e., a reduction of the increased resistance to ethanol's effects that normally occurs upon repeated exposure). These data strongly indicate a linkage between ethanol-induced behavior and ethanol metabolism in adult fruit flies: Adh deficiency resulted in reduced preference to low ethanol concentrations and reduced aversion to high ones, despite recovery from ethanol being strongly impaired.
TL;DR: It was found that Gs, Gi, Gq, and G(beta13F) subunits displayed generalized expression in the antennal tissue, including ORNs support cells and glial cells, and complete coexpression was found between Gi and GQ, which are mediators of the cyclic adenosine monophosphate and IP3 transduction cascades, respectively.
Abstract: In many species, olfactory transduction is triggered by odorant molecules that interact with olfactory receptors coupled to heterotrimeric G-proteins. The role of G-protein–linked transduction in the olfaction of Drosophila is currently under study. Here, we supply a thorough description of the expression in the olfactory receptor organs (antennae and maxillary palps) of all known Drosophila melanogaster genes that encode for G-proteins. Using RT-polymerase chain reaction, we analyzed 6 Ga (Gs, Gi, Gq, Go, Gf, and concertina), 3 Gb (Gb5, Gb13F, and Gb76C), and 2 Gc genes (Gc1 and Gc30A). We found that all Ga proteinencoding genes showed expression in both olfactory organs, but Gf mRNA was not detected in palps. Moreover, all the Gb and Gc genes are expressed in antennae and palps, except for Gb76C. To gain insight into the hypothesis of different G-protein subunits mediating differential signaling in olfactory receptor neurons (ORNs), we performed immunohistochemical studies to observe the expression of several Ga and Gb proteins. We found that Gs, Gi, Gq, and Gb13F subunits displayed generalized expression in the antennal tissue, including ORNs support cells and glial cells. Finally, complete coexpression was found between Gi and Gq, which are mediators of the cyclic adenosine monophosphate and IP3 transduction cascades, respectively.
TL;DR: Adding 17alpha-methyltestosterone to aquaria containing juveniles of 4 cyprinid species concluded that androgen-induced increase in olfactory responsiveness to pheromonal prostaglandins is common among the family Cyprinidae.
Abstract: In the tinfoil barb (Barbonymus schwanenfeldii; family Cyprinidae), we previously found that increased olfactory sensitivity to a female prostaglandin pheromone could induce sexual behavior display in juvenile fish treated with androgens. Here, we determined if this phenomenon is widespread among cyprinid fishes by adding 17a-methyltestosterone (MT) to aquaria containing juveniles of 4 cyprinid species (tinfoil barbs; redtail sharkminnows, Epalzeorhynchos bicolor; goldfish, Carassius auratus; zebrafish, Danio rerio) and then using electro-olfactogram (EOG) recordings and behavioral assays to determine if androgen treatment enhances pheromone detection and male sex behaviors. In all 4 cyprinids, MT treatment increased the magnitudes and sensitivities of EOG response to prostaglandins and, consistent with our initial study on tinfoil barbs, did not affect EOG responses to the free and conjugated steroid to which each species is most sensitive. In zebrafish, EOG responses to prostaglandins were similar in MT-treated juveniles and adult males, whereas responses of control (ethanol exposed) fish were similar to those of adult females. Finally, as previously observed in tinfoil barbs, MT treatment of juvenile redtail sharkminnows increased courtship behaviors (nuzzling and quivering) with a stimulus fish. We conclude that androgen-induced increase in olfactory responsiveness to pheromonal prostaglandins is common among the family Cyprinidae. This phenomenon will help us unravel the development of sexually dimorphic olfactory-mediated behavior.
TL;DR: A simple method for the large-scale detection of soluble proteins from the Drosophila antenna by chromatographic separation of tryptic peptides followed by tandem mass spectrometry with femtomole detection sensitivities is described.
Abstract: The olfactory system of Drosophila melanogaster is one of the best characterized chemosensory systems. Identification of proteins contained in the third antennal segment, the main olfactory organ, has previously relied primarily on immunohistochemistry, and although such studies and in situ hybridization studies are informative, they focus generally on one or few gene products at a time, and quantification is difficult. In addition, purification of native proteins from the antenna is challenging because it is small and encased in a hard cuticle. Here, we describe a simple method for the large-scale detection of soluble proteins from the Drosophila antenna by chromatographic separation of tryptic peptides followed by tandem mass spectrometry with femtomole detection sensitivities. Examination of the identities of these proteins indicates that they originate both from the extracellular perilymph and from the cytoplasm of disrupted cells. We identified enzymes involved with intermediary metabolism, proteins associated with regulation of gene expression, nucleic acid metabolism and protein metabolism, proteins associated with microtubular transport, 8 odorant-binding proteins, protective enzymes associated with antibacterial defense and defense against oxidative damage, cuticular proteins, and proteins of unknown function, which represented about one-third of all soluble proteins. The procedure described here opens the way for precise quantification of any target protein in the Drosophila antenna and should be readily applicable to antennae from other insects.
TL;DR: It is affirm that CCs are present from the first few posthatching (PH) days and cells with highly similar characteristics to those of CCs may correspond to immature CCs in which the crypt, the final feature of their morphological differentiation, has not yet formed.
Abstract: In acipenserids, crypt cells (CCs) have only been observed in juvenile specimens, and it has not been clarified whether they differentiate along with olfactory receptor neurons (ORNs) during the lecithotrophic stage or during later development stages. Furthermore, no detailed optical microscopy (OM) or electron microscopy study on the development of CCs has been published to date. In the present study, we used OM and electron microscopy to follow the development of CCs in Acipenser naccarii from hatching to the establishment of exogenous feeding. Based on these observations, we can affirm that CCs are present from the first few posthatching (PH) days. CCs appear with their nucleus close to the basal lamina of the epithelium and enveloped by supporting cells. In addition, from the beginning of day 2 PH, we observed cells with highly similar characteristics to those of CCs (absence of knob, abundant mitochondria and filamentous material in apical cytoplasm, numerous microtubules, and envelopment by supporting cells) but with cilia still remaining on their noninvaginated apical surface. We conclude that these cells may correspond to immature CCs in which the crypt, the final feature of their morphological differentiation, has not yet formed.