Chemical Senses - recent issues

Nearest Neural Neighbors: Moth Sex Pheromone Receptors HR11 and HR13

Baker, T. C. — 2009-06-12

In moth sex pheromone olfaction systems, there is a stereotypical cocompartmentalization of two or sometimes three olfactory receptor neurons (ORNs) within single trichoid sensilla on which pheromone-sensitive odorant receptors (ORs) are differentially expressed. In this issue of Chemical Senses, Krieger et al. show through elegant double and triple in situ hybridization studies that in the moth, Heliothis virescens, a pheromone component–related OR (HR11) is expressed on an ORN that is reliably cocompartmentalized in the same sensillum as another OR (HR13) whose ligand is known to be (Z)-11-hexadecenal, the H. virescens major pheromone component. Although the ligand for HR11 is not yet known, mapping this OR to this particular ORN represents a key advance in piecing together the puzzle of H. virescens sex pheromone olfaction.

HR11 and HR13 Receptor-Expressing Neurons Are Housed Together in Pheromone-Responsive Sensilla Trichodea of Male Heliothis virescens

Krieger, J., Gondesen, I., Forstner, M., Gohl, T., Dewer, Y., Breer, H. — 2009-06-12

The highly specific recognition of female-released sex pheromones in insects by sensory neurons of the male antenna requires specific receptors. Recently, a small family of related candidate pheromone receptors has been identified for a few moth species. In this study, the candidate pheromone receptor HR11 from Heliothis virescens has been characterized. HR11 was found to be expressed in numerous cells located in short and long sensilla trichodea on the male antenna. The HR11 cells are stereotypically arranged in a paired pattern together with HR13 cells, which respond to the major component of the sex pheromone blend. Triple in situ hybridization approaches revealed that each pair of an HR11 cell and an HR13 cell was ensheathed by supporting cells, which express pheromone-binding proteins, thus constituting a structural unit. The paired pattern of HR11/HR13 cells is reminiscent of the pattern described for BmOR-1- and BmOR-3-expressing cells in the antenna of Bombyx mori, which respond to bombykol and bombykal, respectively. These results suggest that the ligand for HR11 may be related to the HR13 ligand and furthermore imply that an arrangement of cells expressing related receptor types in the same sensillum may be a general principle in moth pheromone detection systems.

Potential Chemosignals Associated with Male Identity in the Amphisbaenian Blanus cinereus

Lopez, P., Martin, J. — 2009-06-12

Pheromone-based chemosensory sex discrimination occurs in many reptiles, but the specific chemosignals responsible for this discrimination have been rarely identified. Chemoreception is especially important for amphisbaenians, a group of fossorial, almost blind, reptiles. We analyzed the role of semiochemicals produced by precloacal glands in intraspecific communication and chemosensory sex recognition of the amphisbaenian Blanus cinereus. We expected that sexual discrimination in amphisbaenians would be based on those chemicals that show intersexual differences in precloacal secretions, with squalene being the chemical that shows the greatest difference in relative abundance between sexes. Tongue-flick assays and behavioral responses to the scent of conspecifics confirmed that amphisbaenians are capable of detecting and discriminating between scent of conspecific males and females by using chemosensory cues alone. Differential responses of amphisbaenians to chemical compounds that are naturally found in precloacal secretions indicated that males can readily discriminate between different chemicals. Squalene, in particular, elicited in male amphisbaenians’ chemosensory and aggressive responses that were similar to those elicited by precloacal secretions. This result suggests that squalene alone allows male discrimination by male amphisbaenians. Furthermore, squalene might also signal dominance status or aggressiveness of a male amphisbaenian because higher concentrations of squalene elicited higher levels of aggression by males.

Orosensory Responsiveness to and Preference for Hydroxide-Containing Salts in Mice

St. John, S. J., Boughter, J. D. — 2009-06-12

Historically, taste researchers have considered the possibility that the gustatory system detects basic compounds, such as those containing the hydroxide ion, but evidence for an "alkaline taste" has not been strong. We found that, in 48 h, 2-bottle preference tests, C3HeB/FeJ (C3) mice showed a preference for Ca(OH)₂, whereas SWR/J (SW) mice showed avoidance. Strain differences were also apparent to NaOH but not CaCl₂. Follow-up studies showed that the strain difference for Ca(OH)₂ was stable over time (Experiment 2) but that C3 and SW mice did not differ in their responses to Ca(OH)₂ or NaOH in brief-access tests, where both mice avoided high concentrations of these compounds (Experiment 3). In order to assess the perceived quality of Ca(OH)₂, mice were tested in 2 taste aversion generalization experiments (Experiments 4 and 5). Aversions to Ca(OH)₂ generalized to NaOH but not CaCl₂ in both strains, suggesting that the generalization was based on the hydroxide ion. Both strains also generalized aversions to quinine, suggesting the possibility that the hydroxide ion has a bitter taste quality to these mice, despite the preference shown by C3 mice to middle concentrations in long-term tests.

Swallowing Is Differentially Influenced by Retronasal Compared with Orthonasal Stimulation in Combination with Gustatory Stimuli

Welge-Lussen, A., Ebnother, M., Wolfensberger, M., Hummel, T. — 2009-06-12

Identical stimuli are processed differently when presented ortho- or retronasally. In contrast to orthonasal olfaction, retronasal odorant perception is strongly associated with flavor and food intake, which is usually followed by swallowing. Along with other stimuli, gustatory stimuli are known to influence the swallowing reflex. It was therefore the aim of present study to examine whether retronasal olfaction, in combination with simultaneous gustatory stimuli, influences swallowing in a manner different from that of orthonasal olfaction. Fifty normosmic and normogeusic subjects took part in the study. A sweet taste (glucose, delivered via an intraoral taste dispenser) was presented simultaneously with vanillin, a food-like odor, either ortho- or retronasally at random using a computer-controlled olfactometer. Ultrasound imaging of the mouth floor was recorded on videotape to continuously monitor swallowing activity. After retronasal stimulation, swallowing occurred significantly faster (7.49 vs. 9.42 s; P < 0.001) and also took place more frequently compared with swallowing after orthonasal stimulation (1.38 times vs. 1.14 times; P < 0.001). These results show that a food-like odorant presented retronasally in combination with a congruent taste stimulus can influence swallowing. Whether these results can be assigned to other, unfamiliar, unpleasant nonfood-like odors has yet to be determined.

Identification and Expression Pattern of Putative Odorant-Binding Proteins and Chemosensory Proteins in Antennae of the Microplitis mediator (Hymenoptera: Braconidae)

Zhang, S., Zhang, Y.-J., Su, H.-H., Gao, X.-W., Guo, Y.-Y. — 2009-06-12

The parasitoids of Cotton Bollworm Microplitis mediator (Hymenoptera: Braconidae) find their hosts through the odor released by stressed plants. In this study, preliminary characterization and isolation of cDNAs from male M. mediator antennal libraries identified 8 putative odorant-binding proteins (OBPs). Real-time polymerase chain reaction method was used to study the expression pattern of these isolated genes. Their gene expression profiles under a wide range of conditions indicated that only 4 OBP genes in M. mediator were antenna specific. The remaining 4 genes are either expressed ubiquitously or strictly regulated in specialized tissues or during different developmental stages. Some OBP genes were gender specific. These findings support that OBPs play dynamic roles during development of M. mediator and are likely to be involved in broader physiological functions.

The Role of the Human Hippocampus in Odor-Place Associative Memory

Goodrich-Hunsaker, N. J., Gilbert, P. E., Hopkins, R. O. — 2009-06-12

Hippocampal lesions in rodents impair both object–place and odor–place associative memory. Subjects with hippocampal damage have impaired associative memory such as object–place memory. Whereas studies have investigated some types of associative memory, no investigation has specifically examined odor–place associative memory in subjects with well-defined amnesia. It is unknown whether amnesic subjects with hippocampal damage would be impaired on an odor–place associative task. We investigated the effect of hippocampal damage in amnesic subjects with hippocampal atrophy on odor–place associative memory and recognition memory tasks. Amnesic and healthy comparison subjects matched for age and education were tested on an odor–place associative task, an odor recognition task, and a place recognition task. The odor–place associative task required subjects to associate 6 odors with 6 spatial locations on a board. The recognition tasks required subjects to identify the 6 odors and the 6 locations that were presented during the associative task. Amnesic subjects were impaired for odor–place memory and place recognition, but not odor recognition compared with comparison subjects. These results suggest that the human hippocampus is necessary for odor–place associative memory and spatial recognition memory. These data provide support for the idea that odor–place associative memory is mediated by the hippocampus in both humans and rodents, suggesting an evolutionary continuity in cognitive function assigned to the hippocampus.

Comparison between Odor Thresholds for Phenyl Ethyl Alcohol and Butanol

Croy, I., Lange, K., Krone, F., Negoias, S., Seo, H.-S., Hummel, T. — 2009-06-12

Aim of the study was to compare results of odor threshold test using different numbers of dilution steps, separately for butanol and phenyl ethyl alcohol (PEA). Methods: A total of 116 subjects participated (29 patients with olfactory dysfunction and 87 normosmic subjects). The olfactory threshold for butanol and PEA was examined with 8 (wide step method) and 16 (narrow step method) dilutions. With a delay of about 1 week, all 4 tests were repeated. Results: Test time was shortened by approximately 2 min (25%) for patients when using the wide step method. Butanol and PEA thresholds were not significantly different; in addition, a significant correlation was found between thresholds for the 2 odors (r = 0.60, P < 0.001). Threshold test with both odorants as well as with wide or narrow step method provided satisfying reproducibility (test–retest reliability: r = 0.80–0.84, P < 0.001). Patients with olfactory dysfunction could be clearly separated from normosmic subjects using all 4 different tests. Discussion: The results indicate that threshold testing with PEA is an alternative to butanol. The wide step method provided similar results as the narrow step method but required less time.

Human Pheromone Detection by the Vomeronasal Organ: Unnecessary for Mate Selection?

Mast, T. G., Samuelsen, C. L. — 2009-06-12

Recently, Foltan and Sedy proposed a hypothesis stating that the adult human VNO is integral to the prevention of inappropriate mate selection. In this commentary, we address the authors’ assumption that humans have a functional VNO, that pheromones are detected exclusively by the VNO, and that human pheromones are responsible for negative stimuli during mate selection. After examining the published literature on human vomeronasal function, we argue that their hypothesis is critically flawed. We offer a brief review of the adult human VNO in support of our argument.

Editorial

2009-05-14

Morphological and Physiological Characteristics of the Serotonin-Immunoreactive Neuron in the Antennal Lobe of the Male Oriental Tobacco Budworm, Helicoverpa assulta

Zhao, X. C., Berg, B. G. — 2009-05-14

We have characterized, by intracellular recording and staining combined with immunocytochemistry, a serotonin-immunoreactive neuron in the central olfactory pathway of the male moth Helicoverpa assulta. The neuron joins the unique category of so-called SI antennal-lobe neurons, previously described in several insect species. In similarity with that originally discovered in the sphinx moth Manduca sexta, the neuron identified here has a large soma located posteriorly in the lateral cell cluster of the antennal lobe and an unbranched neurite projecting into the ipsilateral protocerebrum via the inner antennocerebral tract. After bypassing the central body, the axon crosses the midline and extends through the corresponding antennocerebral tract to the contralateral antennal lobe where it innervates the entire assembly of glomeruli including the male-specific macroglomerular complex. The neuron arborizes into several fine branches in bilateral protocerebral regions anterior to the calyces of the mushroom bodies, particularly on the contralateral side. The physiology of the neuron revealed 2 distinctly different spiking amplitudes, 1 small showing a relatively high spontaneous activity and 1 large showing low activity. The small-amplitude spikes displayed increased frequency when pheromones and plant odors were blown over the antenna. The large-amplitude spikes, which had an unusually long duration, showed no observable responses.

Human Salt Taste and the Lingual Surface Potential Correlate

Feldman, G. M., Heck, G. L., Smith, N. L. — 2009-05-14

We have demonstrated in humans that Na⁺ evokes changes in the lingual surface potential (LSP) using a custom chamber. To assess whether a relationship exists between the Na⁺-evoked changes in the LSP and the intensity of salt taste, we measured the LSP and the intensity of salt taste simultaneously in 7 subjects using test solutions (50, 100, 300, and 1000 mM NaCl) presented in random order. The evoked LSPs and intensity scores correlated with one another well (r² = 0.992, P < 0.01). We then screened 14 subjects for their ability to discriminate between 100 and 300 mM NaCl using the chamber. Three subjects were consistently capable of distinguishing the salt concentrations. In these 3 subjects, an inhibitor of the epithelial sodium channel, amiloride (10 µM), blocked the ability to distinguish salt concentrations and affected the LSP. These data suggest that the LSP may be a component of the signal transduction system involved in human salt taste. In adept salt tasters, an amiloride-sensitive mechanism appears to have a role in distinguishing salt concentrations.

Odorant Receptors from the Light brown Apple Moth (Epiphyas postvittana) Recognize Important Volatile Compounds Produced by Plants

2009-05-14

Moths recognize a wide range of volatile compounds, which they use to locate mates, food sources, and oviposition sites. These compounds are recognized by odorant receptors (OR) located within the dendritic membrane of sensory neurons that extend into the lymph of sensilla, covering the surface of insect antennae. We have identified 3 genes encoding ORs from the tortricid moth, Epiphyas postvittana, a pest of horticulture. Like Drosophila melanogaster ORs, they contain 7 transmembrane helices with an intracellular N-terminus, an orientation in the plasma membrane opposite to that of classical GPCRs. EpOR2 is orthologous to the coreceptor Or83b from D. melanogaster. EpOR1 and EpOR3 both recognize a range of terpenoids and benzoates produced by plants. Of the compounds tested, EpOR1 shows the best sensitivity to methyl salicylate [EC₅₀ = 1.8 x 10^–12 M], a common constituent of floral scents and an important signaling compound produced by plants when under attack from insects and pathogens. EpOR3 best recognizes the monoterpene citral to low concentrations [EC₅₀ = 1.1 x 10^–13 M]. Citral produces the largest amplitude electrophysiological responses in E. postvittana antennae and elicits repellent activity against ovipositing female moths. Orthologues of EpOR3 were found across 6 families within the Lepidoptera, suggesting that the ability to recognize citral may underpin an important behavior.

Retro-Nasal Aroma Release Depends on Both Subject and Product Differences: A Link to Food Intake Regulation?

Ruijschop, R. M.A.J., Burgering, M. J.M., Jacobs, M. A., Boelrijk, A. E.M. — 2009-05-14

It is hypothesized that differences in the extent of retro-nasal aroma release during consumption may be 1 of the reasons that people vary in their satiation characteristics. Using real-time atmospheric pressure chemical ionization mass spectrometry (APcI-MS), in vivo retro-nasal aroma release was determined for 30 subjects consuming 9 different food products, varying in physical structure (i.e., [semi]liquid and solid food products). Additionally, for a subset of the subjects ad libitum food intake was measured. Retro-nasal aroma release intensity and profile morphology appeared to be subject specific and relatively independent of the type of food product subjects consumed. A subject who was observed as having a relatively high retro-nasal aroma release intensity for a (semi)liquid food product also appeared to have a relatively high retro-nasal aroma release intensity for a solid food product. However, for all subjects, there were absolute differences between food products in the extent of retro-nasal aroma release comparing (semi)liquid and solid food products. This implies that the extent of retro-nasal aroma release is a valid physiological feature that characterizes any individual. Interestingly, a negative trend was observed between extent of retro-nasal aroma release and amount of ad libitum food intake (P = 0.07). This may have implications for the regulation of food intake.

Post-oral and Perioral Stimulations during Nursing Enhance Appetitive Olfactory Memory in Neonatal Rabbits

Serra, J., Ferreira, G., Mirabito, L., Levy, F., Nowak, R. — 2009-05-14

Nursing–suckling interactions facilitate olfactory learning in newborns as long as suckling and the olfactory stimulus temporally overlap. We tested the hypothesis that olfactory preferences would develop even with a long delay between odor presentation and nursing. Thyme was presented to 2-day-old rabbit pups by placing an odorized plate 2 cm above their nest box. Duration and time of nursing were controlled and occurred before, during, or after odor presentation. Controls were not nursed. When exposed to the odor for 15 min, control pups preferred thyme to a novel odor in a 2-choice test immediately after exposure but not 3 and 22 h later. When pups were nursed immediately before thyme exposure or during exposure, they preferred the familiar odorant until 22 h later. Identically, when nursing occurred 30 min before odor exposure, a preference for thyme was maintained up to 22 h. This was not observed when nursing occurred 60 min before odor presentation. We concluded that enhancement of olfactory memory occurs in neonates during nursing but also after post-oral stimulation by postprandial internal state.

Oral Thresholds and Suprathreshold Intensity Ratings for Free Fatty Acids on 3 Tongue Sites in Humans: Implications for Transduction Mechanisms

Mattes, R. D. — 2009-05-14

Multiple putative free fatty acid (FFA) transduction mechanisms have been identified in the oral cavity. They reportedly differ in their distribution on the tongue and each has a unique range of ligand specificities. This suggests that there should be regional differences in sensory responses to varying FFAs. This was assessed through spatial testing with caproic (C), lauric (L), and stearic (S) FFAs among 35 healthy adults. Stimuli were applied to the fungiform (FU), foliate (FO), and circumvallate (CV) papillae with a cotton-tipped applicator. Oral detection thresholds were measured by an ascending, 3-alternative, forced-choice, sip and spit procedure. Intensity ratings were obtained on the general labeled magnitude scale. Nongustatory cues were minimized by testing with the nares blocked, eyes covered, and by masking tactile cues with the addition of gum acacia and mineral oil to the stimuli vehicle. Thresholds were obtained from nearly all individuals at each site, and the concentration was similar across the 3 FFAs. Absolute intensity ratings differed significantly with C > L > S overall and at the CV and FO papillae. At the FU papillae, the L and S ratings were comparable. Ratings were highest at the FU followed by the CV and then the FO papillae. Slopes of the concentration–intensity rating functions were higher for L compared with C and S at the CV papillae as well as both L and C compared with S at the FO papillae. However, overall, slopes were comparable across sites. These findings strengthen evidence for oral FFA perception in humans by replicating threshold sensitivity findings and documenting monotonic scaling ability for these stimuli. Further, they challenge current views on transduction as sensory responsiveness was observed at tongue sites not predicted to support FFA detection.

An Odor Stimulator Controlling Odor Temporal Pattern Applicable in Insect Olfaction Study

Okada, K., Sakuma, M. — 2009-05-14

The olfactory system of an insect brain codes for information about odorant quality and quantity using the temporal pattern of neural activity as well as neurons' firing. Although an accurate odor temporal pattern is indispensable for investigations of olfactory systems, it is difficult to control in conventional odor stimulators. To overcome this problem, we fabricated an odor stimulator that can control the odor temporal pattern. The stimulator has 3 major parts: an "odor conditioner," with odor-laden air prepared with known concentrations of odorants; a Pitot tube; and a small wind tunnel of laminar flow. Using this stimulator, we realized not only timing control of the odor stimulation with millisecond order but also constant odor concentrations or intensity of stimulation, with error of 2.4% in replicated trials.

Test-Retest Reliability of the San Diego Odor Identification Test and Comparison with the Brief Smell Identification Test

2009-05-14

This study described the San Diego Odor Identification Test (SDOIT) reliability and compared the SDOIT and the Brief Smell Identification Test (B-SIT). Ninety participants aged 50–70 years completed this 2-visit olfaction study. During visit 1, the SDOIT and B-SIT were administered according to standard protocols. Three weeks later, participants returned to retake the SDOIT. The SDOIT score was the total number of odorants correctly identified out of 8 odorants presented, and olfactory impairment was defined as correctly identifying less than 6 odorants. The B-SIT score was the total number of odorants correctly identified out of 12 odorants presented, and participants correctly identifying less than 9 odorants were categorized as abnormal. The SDOIT reliability was high (concordance correlation coefficient = 0.85, 95% confidence interval [CI] = 0.79–0.91). The same score was obtained on retest for 73% of participants, whereas 18% improved, and 9% declined. Test–retest agreement was 96% for the SDOIT; 4% improved from impaired at visit 1 to unimpaired at visit 2. Overall, SDOIT impairment classification and B-SIT abnormal classification agreed in 96% of participants ( = 0.81, 95% CI = 0.63–0.99). In conclusion, the SDOIT showed good test–retest reliability. Agreement for impaired/abnormal olfaction was demonstrated for the SDOIT and the B-SIT.

Water Taste Transduction Pathway Is Calcium Dependent in Drosophila

Meunier, N., Marion-Poll, F., Lucas, P. — 2009-05-14

In mammals, detection of osmolarity by the gustatory system was overlooked until recently. In insects, specific taste receptor neurons detect hypoosmotic stimuli and are commonly called "W" (water) cells. W cells are easy to access in vivo and represent a good model to study the transduction of hypoosmotic stimuli. Using pharmacological and genetic approaches in Drosophila, we show that tarsal W cell firing activity depends on the concentration of external calcium bathing the dendrite. This dependence was confirmed by the strong inhibition of W cell responses to hypoosmotic stimuli by lanthanum (IC₅₀ = 8 nM), an ion known to inhibit calcium-permeable channels. Downstream, the transduction pathway likely involves calmodulin because calmodulin antagonists such as W-7 (IC₅₀ = 2 µM) and fluphenazine (IC₅₀ = 30 µM) prevented the activation of the W cell by hypoosmotic stimuli. A protein kinase C (PKC) may also be involved as W cell responses were blocked by PKC inhibitors, chelerythrine (IC₅₀ = 20 µM) and staurosporine (IC₅₀ = 30 µM). It was also reduced when expressing an inhibitory pseudosubstrate of PKC in gustatory receptor neurons. In the rat, the transduction pathway underlying low osmolarity detection involves aquaporin and swelling-activated ion channels. Our study suggests that the transduction pathway of hypoosmotic stimuli in insects differs from mammals.

Olfactory Cilia: Linking Sensory Cilia Function and Human Disease

Jenkins, P. M., McEwen, D. P., Martens, J. R. — 2009-05-14

The olfactory system gives us an awareness of our immediate environment by allowing us to detect airborne stimuli. The components necessary for detection of these odorants are compartmentalized in the cilia of olfactory sensory neurons. Cilia are microtubule-based organelles, which can be found projecting from the surface of almost any mammalian cell, and are critical for proper olfactory function. Mislocalization of ciliary proteins and/or the loss of cilia cause impaired olfactory function, which is now recognized as a clinical manifestation of a broad class of human diseases, termed ciliopathies. Future work investigating the mechanisms of olfactory cilia function will provide us important new information regarding the pathogenesis of human sensory perception diseases.

A High-Throughput Method to Measure NaCl and Acid Taste Thresholds in Mice

Ishiwatari, Y., Bachmanov, A. A. — 2009-04-22

To develop a technique suitable for measuring NaCl taste thresholds in genetic studies, we conducted a series of experiments with outbred CD-1 mice using conditioned taste aversion (CTA) and two-bottle preference tests. In Experiment 1, we compared conditioning procedures involving either oral self-administration of LiCl or pairing NaCl intake with LiCl injections and found that thresholds were the lowest after LiCl self-administration. In Experiment 2, we compared different procedures (30-min and 48-h tests) for testing conditioned mice and found that the 48-h test is more sensitive. In Experiment 3, we examined the effects of varying strength of conditioned (NaCl or LiCl taste intensity) and unconditioned (LiCl toxicity) stimuli and concluded that 75–150 mM LiCl or its mixtures with NaCl are the optimal stimuli for conditioning by oral self-administration. In Experiment 4, we examined whether this technique is applicable for measuring taste thresholds for other taste stimuli. Results of these experiments show that conditioning by oral self-administration of LiCl solutions or its mixtures with other taste stimuli followed by 48-h two-bottle tests of concentration series of a conditioned stimulus is an efficient and sensitive method to measure taste thresholds. Thresholds measured with this technique were 2 mM for NaCl and 1 mM for citric acid. This approach is suitable for simultaneous testing of large numbers of animals, which is required for genetic studies. These data demonstrate that mice, like several other species, generalize CTA from LiCl to NaCl, suggesting that they perceive taste of NaCl and LiCl as qualitatively similar, and they also can generalize CTA of a binary mixture of taste stimuli to mixture components.

Saliva Characteristics and Individual Sensitivity to Phenolic Astringent Stimuli

Dinnella, C., Recchia, A., Fia, G., Bertuccioli, M., Monteleone, E. — 2009-04-22

Astringency sensation is due to interactions between salivary proteins and phenols and is based on an increased-friction mechanism. Modifications to the profile of salivary proteins and their concentration could affect tannin/protein reactions and hence the intensity of perceived astringency. Salivary characteristics of 65 subjects were compared after abstention from phenol-containing food and immediately after ingestion of tannic acid. The effect of stimulation on saliva characteristics was expressed in terms of D value, computed as the arithmetic difference between values found in saliva samples from the 2 conditions. Based on D values, subjects were clustered in two groups. Cluster 1 (Cl1, 53 cases) was characterized by low D values thus indicating that the basal saliva condition was quickly restored in these subjects. Cluster 2 (Cl2) was composed of 12 subjects whose basal salivary condition was not quickly restored, particularly in terms of salivary protein concentration and profile and saliva haze-forming capacity. Sensory data showed that subjects capable of maintaining constant saliva characteristics were less sensitive to astringent stimuli than subjects in which the same stimulations induced significant saliva modifications. The results suggest that a large proportion of the population are able to maintain their salivary protein concentration and simultaneously intercept and inactivate dietary tannins.

A Candidate Pheromone Receptor and Two Odorant Receptors of the Hawkmoth Manduca sexta

Patch, H. M., Velarde, R. A., Walden, K. K.O., Robertson, H. M. — 2009-04-22

In this study, we cloned and characterized three Manduca sexta odorant receptors (ORs). One receptor is a putative pheromone receptor expressed exclusively in a cell associated with male-specific type-I trichoid sensilla. We describe the results of real-time PCR (RT-PCR) and quantitative real-time PCR (qRT-PCR) experiments that show MsextaOR1 is expressed only in male antennae. In situ hybridization labels a single cell associated with type-1 trichoid sensilla, which houses two neurons that have been previously determined to respond to the major components of the pheromone blend. The second receptor, MsextaOR2, was discovered using degenerate primers designed to conserved motifs of a unique group ORs that share as much as 88% identity. Comparison of RT-PCR, qRT-PCR, and in situ hybridization results with those of ORs in the Drosophila melanogaster Or83b subfamily shows a strong sequence and expression pattern similarity. The third receptor, MsextaOR3, was found by 5'-end sequencing of a normalized and subtracted cDNA library from male M. sexta antennae. RT-PCR and qRT-PCR show that this receptor is expressed only in male and female antennae. These are the first ORs, including a putative pheromone receptor, to be described from M. sexta.

Modulation in Reproductive Tissue Redox Profile in Sexually Receptive Female Rats after Short-Term Exposure to Male Chemical Cues

2009-04-22

It is well known that antioxidants play an important role in sperm fertility, but there is no data on the literature regarding the effect of male chemical cues in the antioxidant defenses of the female reproductive tract. Here, we evaluated oxidative parameters in ovaries and uterus of virgin female rats isolated from contact to males and exposed only to male-soiled bedding (MSB). Four-month-old Wistar (regular 4-day cyclic) virgin female rats were utilized from proestrus to estrus phase of the reproductive cycle for experimental exposure. In an isolated room, female rats were exposed for 90 min to MSB. For biochemical assays, female rats were killed by decapitation at 30, 90, 180, and 240 min after the end of exposure, and the ovaries and uterus were removed for further analysis. Antioxidant enzyme activities (superoxide dismutase, catalase, and glutathione peroxidase), the nonenzymatic antioxidant potential (total radical-trapping antioxidant parameter), and the oxidative damage parameters (thiobarbituric acid–reactive species and carbonyl content) were analyzed. We observed an increase in the nonenzymatic antioxidant potential and diminished free radical oxidative damage in uterine tissue, 30 and 90 min after exposure. Furthermore, in ovaries, enzymatic defenses were modulated distinctly along the 240 min after exposure. MSB exposure modulates the antioxidant profile in ovaries and uterus of receptive female rats. It is possible that the modifications in the oxidative profile of the female genital tract may have important implications in the process of fertilization.

Effects of Taste Solutions, Carbonation, and Cold Stimulus on the Power Frequency Content of Swallowing Submental Surface Electromyography

Miura, Y., Morita, Y., Koizumi, H., Shingai, T. — 2009-04-22

This study explored the effects of 5 taste solutions (citric acid, sucrose, sodium chloride, caffeine, and sodium glutamate) versus water on the power frequency content of swallowing submental surface electromyography (sEMG). Healthy subjects were presented with 5 ml of each of 5 tastants and water. Data were collected in 3 trials of the 5 tastants and water by using submental sEMG, which was then subjected to spectral analysis. Sour and salt taste solutions increased the spectrum-integrated values of the total power components. The spectrum-integrated values of low-frequency power (below 10 Hz) in the salt taste trial significantly increased, whereas those of high-frequency power (above 10 Hz) in the sour taste trial tended to increase. Neither pleasantness nor intensity of taste was related to these changes. This study also explored the effects of carbonation and cold stimulus on the power frequency content of continuous swallowing sEMG for 60-ml solutions. Carbonation significantly increased the spectrum-integrated value of the total power components by significantly increasing the high-frequency content. Cold stimulus significantly decreased the low-frequency content. In summary, this study reveals that taste, carbonation, and cold stimulus have qualitatively different influences on the power frequency content of swallowing sEMG.

Sensory Characterization of the Irritant Properties of Oleocanthal, a Natural Anti-Inflammatory Agent in Extra Virgin Olive Oils

Cicerale, S., Breslin, P. A.S., Beauchamp, G. K., Keast, R. S.J. — 2009-04-22

Oleocanthal is an olive oil phenolic possessing anti-inflammatory activity. Anecdotal evidence suggests that oleocanthal elicits a stinging sensation felt only at the back of the throat (oropharynx). Due to this compound possessing potentially health-benefiting properties, investigation into the sensory aspects of oleocanthal is warranted to aid in future research. The important link between the perceptual aspects of oleocanthal and health benefits is the notion that variation in sensitivity to oleocanthal irritation may relate to potential differences in sensitivity to the pharmacologic action of this compound. The current study assessed the unique irritant attributes of oleocanthal including its location of irritation, temporal profile, and individual differences in the perceived irritation. We show that the irritation elicited by oleocanthal was localized to the oropharynx (P < 0.001) with little or no irritation in the anterior oral cavity. Peak irritation was perceived 15 s postexposure and lasted over 180 s. Oleocanthal irritation was more variable among individuals compared with the irritation elicited by CO₂ and the sweetness of sucrose. There was no correlation between intensity ratings of oleocanthal and CO₂ and oleocanthal and sucrose (r = –0.15, n = 50, P = 0.92 and r = 0.17, n = 84, P = 0.12, respectively), suggesting that independent mechanisms underlie the irritation of CO₂ and oleocanthal. The unusual spatial localization and independence of acid (CO₂) sensations suggest that distinct nociceptors for oleocanthal are located in the oropharyngeal region of the oral cavity.

Temporal Contrast of Salt Delivery in Mouth Increases Salt Perception

Busch, J. L.H.C., Tournier, C., Knoop, J. E., Kooyman, G., Smit, G. — 2009-04-22

The impact of salt delivery in mouth on salt perception was investigated. It was hypothesized that fast concentration changes in the delivery to the receptor can reduce sensory adaptation, leading to an increased taste perception. Saltiness ratings were scored by a panel over time during various stimulation conditions involving relative changes in NaCl concentration of 20% and 38%. Changes in salt delivery profile had similar effect on saltiness perception when delivered either by a sipwise method or by a gustometer. The impact of concentration variations and frequency of concentration changes was further investigated with the gustometer method. Five second boosts and 2 s pulses were delivered during 3 sequential 10-s intervals, whereas the delivered total salt content was the same for all conditions. Two second pulses were found to increase saltiness perception, but only when the pulses were delivered during the first seconds of stimulation. Results suggest that the frequency, timing, and concentration differences of salt stimuli can affect saltiness. Specifically, a short and intense stimulus can increase salt perception, possibly through a reduction of adaptation.

Role of Plasma Membrane Calcium ATPases in Calcium Clearance from Olfactory Sensory Neurons

Saidu, S. P., Weeraratne, S.D., Valentine, M., Delay, R., Van Houten, J. L. — 2009-04-22

Odorants cause Ca²⁺ to rise in olfactory sensory neurons (OSNs) first within the ciliary compartment, then in the dendritic knob, and finally in the cell body. Ca²⁺ not only excites but also produces negative feedback on the transduction pathway. To relieve this Ca²⁺-dependent adaptation, Ca²⁺ must be cleared from the cilia and dendritic knob by mechanisms that are not well understood. This work focuses on the roles of plasma membrane calcium pumps (PMCAs) through the use of inhibitors and mice missing 1 of the 4 PMCA isoforms (PMCA2). We demonstrate a significant contribution of PMCAs in addition to contributions of the Na⁺/Ca²⁺ exchanger and endoplasmic reticulum (ER) calcium pump to the rate of calcium clearance after OSN stimulation. PMCAs in neurons can shape the Ca²⁺ signal. We discuss the contributions of the specific PMCA isoforms to the shape of the Ca²⁺ transient that controls signaling and adaptation in OSNs.

Chemical Senses announces new Editor-in-Chief

2009-04-22