The influence of nasal airflow on respiratory and olfactory epithelial distribution in felids.

The surface area of the maxilloturbinals and fronto-ethmoturbinals is commonly used as an osteological proxy for the respiratory and the olfactory epithelium, respectively. However, this assumption does not fully account for animals with short snouts in which these two turbinal structures significantly overlap, potentially placing fronto-ethmoturbinals in the path of respiratory airflow. In these species, it is possible that anterior fronto-ethmoturbinals are covered with non-sensory (respiratory) epithelium instead of olfactory epithelium. In this study, we analyzed the distribution of olfactory and non-sensory, respiratory epithelia on the turbinals of two domestic cats (Felis catus) and a bobcat (Lynx rufus). We also conducted a computational fluid dynamics simulation of nasal airflow in the bobcat to explore the relationship between epithelial distribution and airflow patterns. The results showed that a substantial amount of respiratory airflow passes over the anterior fronto-ethmoturbinals, and that contrary to what has been observed in caniform carnivorans, much of the anterior ethmoturbinals are covered by non-sensory epithelium. This confirms that in short-snouted felids, portions of the fronto-ethmoturbinals have been recruited for respiration, and that estimates of olfactory epithelial coverage based purely on fronto-ethmoturbinal surface area will be exaggerated. The correlation between the shape of the anterior fronto-ethmoturbinals and the direction of respiratory airflow suggests that in short-snouted species, CT data alone are useful in assessing airflow patterns and epithelium distribution on the turbinals.

The Effect of Ethnicity on Human Axillary Odorant Production.

Previous findings from our laboratory highlighted marked ethnic differences in volatile organic compounds (VOCs) from cerumen among individuals of Caucasian, East Asian, and African-American descent, based, in part, on genetic differences in a gene that codes for a transport protein, which is a member of the ATP-binding cassette transporter, sub-family C, member 11 (ABCC11). In the current work, we hypothesized that axillary odorants produced by East Asians would differ markedly from those obtained from individuals of European or African descent based on the pattern of ethnic diversity that exists in ABCC11. Using gas chromatography/mass spectrometry (GC/MS) we examined differences in axillary odorant VOCs among 30 individuals of African-American, Caucasian, and East Asian descent with respect to their ABCC11 genotype. While no qualitative differences in the type of axillary odorants were observed across ethnic groups, we found that characteristic axillary odorants varied quantitatively with respect to ethnic origin. We propose that ABCC11 is not solely responsible for predicting the relative amounts of volatiles found in axillary secretions and that other biochemical pathways must be involved.

Ethnic/racial and genetic influences on cerumen odorant profiles.

This report describes the volatile organic compounds (VOCs) associated with human cerumen (earwax) and the effects of ethnicity/race and variation on the ATP-binding cassette, sub-family C, member 11 gene (ABCC11). A single nucleotide polymorphism (SNP) in ABCC11 affects the cerumen VOC profiles of individuals from African, Caucasian, and Asian descent. Employing gas chromatography/mass spectrometry (GC/MS) we have identified the nature and relative abundance of cerumen VOCs from 32 male donors. Our results show that cerumen contains a complex mixture of VOCs and that the amounts of these compounds vary across individuals as well as across ethnic/racial groups. In six of the seven compounds whose detected concentrations were found to be statistically different across groups, individuals of African descent (AfD) > Caucasian descent (CaD) > Asians descent (AsD). Our findings also reveal that ABCC11 genotype alone does not predict the type and relative levels of volatiles found in human cerumen, and suggest that other biochemical pathways must be involved. Examination of the composition and diversity of external auditory canal microbiota in a small subset of our subject population revealed that the ear microbiota may not be directly correlated with either ethnic group membership or ABCC11 genotype.

Personal receptor repertoires: olfaction as a model.

BACKGROUND: Information on nucleotide diversity along completely sequenced human genomes has increased tremendously over the last few years. This makes it possible to reassess the diversity status of distinct receptor proteins in different human individuals. To this end, we focused on the complete inventory of human olfactory receptor coding regions as a model for personal receptor repertoires. RESULTS: By performing data-mining from public and private sources we scored genetic variations in 413 intact OR loci, for which one or more individuals had an intact open reading frame. Using 1000 Genomes Project haplotypes, we identified a total of 4069 full-length polypeptide variants encoded by these OR loci, average of ~10 per locus, constituting a lower limit for the effective human OR repertoire. Each individual is found to harbor as many as 600 OR allelic variants, ~50% higher than the locus count. Because OR neuronal expression is allelically excluded, this has direct effect on smell perception diversity of the species. We further identified 244 OR segregating pseudogenes (SPGs), loci showing both intact and pseudogene forms in the population, twenty-six of which are annotatively "resurrected" from a pseudogene status in the reference genome. Using a custom SNP microarray we validated 150 SPGs in a cohort of 468 individuals, with every individual genome averaging 36 disrupted sequence variations, 15 in homozygote form. Finally, we generated a multi-source compendium of 63 OR loci harboring deletion Copy Number Variations (CNVs). Our combined data suggest that 271 of the 413 intact OR loci (66%) are affected by nonfunctional SNPs/indels and/or CNVs. CONCLUSIONS: These results portray a case of unusually high genetic diversity, and suggest that individual humans have a highly personalized inventory of functional olfactory receptors, a conclusion that might apply to other receptor multigene families.

Stimulus selection for intranasal sensory isolation: eugenol is an irritant.

Both the olfactory and the trigeminal systems are able to respond to intranasal presentations of chemical vapor. Accordingly, when the nose detects a volatile chemical, it is often unclear whether we smell it, feel it, or both. The distinction may often be unimportant in our everyday perception of fragrances or aromas, but it can matter in experiments that purport to isolate olfactory processes or study the interaction between olfaction and chemesthesis. Researchers turn to a small pool of compounds that are believed to be "pure olfactory" stimuli with little or no trigeminal impact. The current report reexamines one such commonly used compound, namely eugenol, a flavor and fragrance ingredient that has anesthetic properties under some conditions. Using a standard method involving many trials during an experimental session (Experiment 1), subjects were unable to reliably lateralize eugenol, consistent with claims that this compound is detected primarily through olfaction. However, with more limited exposure (Experiments 2 and 3), subjects were able to lateralize eugenol. We speculate that anesthetic properties of eugenol could blunt its trigeminal impact in some paradigms. Regardless, the current experiments suggest that eugenol can in fact stimulate the trigeminal nerve but in a complex concentration-dependent manner. Implications and strategies for selection of model odorants are discussed.

A genome-wide study on the perception of the odorants androstenone and galaxolide.

Twin pairs and their siblings rated the intensity of the odorants amyl acetate, androstenone, eugenol, Galaxolide, mercaptans, and rose (N = 1573). Heritability was established for ratings of androstenone (h (2) = 0.30) and Galaxolide (h(2) = 0.34) but not for the other odorants. Genome-wide association analysis using 2.3 million single nucleotide polymorphisms indicated that the most significant association was between androstenone and a region without known olfactory receptor genes (rs10966900, P = 1.2 × 10(-7)). A previously reported association between the olfactory receptor OR7D4 and the androstenone was not detected until we specifically typed this gene (P = 1.1 × 10(-4)). We also tested these 2 associations in a second independent sample of subjects and replicated the results either fully (OR7D4, P = 0.00002) or partially (rs10966900, P = 0.010; N = 266). These findings suggest that 1) the perceived intensity of some but not all odorants is a heritable trait, 2) use of a current genome-wide marker panel did not detect a known olfactory genotype-phenotype association, and 3) person-to-person differences in androstenone perception are influenced by OR7D4 genotype and perhaps by variants of other genes.

Genetic analysis of chemosensory traits in human twins.

We explored genetic influences on the perception of taste and smell stimuli. Adult twins rated the chemosensory aspects of water, sucrose, sodium chloride, citric acid, ethanol, quinine hydrochloride, phenylthiocarbamide (PTC), potassium chloride, calcium chloride, cinnamon, androstenone, Galaxolide™, cilantro, and basil. For most traits, individual differences were stable over time and some traits were heritable (h(2) from 0.41 to 0.71). Subjects were genotyped for 44 single nucleotide polymorphisms within and near genes related to taste and smell. The results of these association analyses confirmed previous genotype-phenotype results for PTC, quinine, and androstenone. New associations were detected for ratings of basil and a bitter taste receptor gene, TAS2R60, and between cilantro and variants in three genes (TRPA1, GNAT3, and TAS2R50). The flavor of ethanol was related to variation within an olfactory receptor gene (OR7D4) and a gene encoding a subunit of the epithelial sodium channel (SCNN1D). Our study demonstrates that person-to-person differences in the taste and smell perception of simple foods and drinks are partially accounted for by genetic variation within chemosensory pathways.

The effect of menthol vapor on nasal sensitivity to chemical irritation.

INTRODUCTION: Among other effects, menthol added to cigarettes may modulate sensory response to cigarette smoke either by masking "harshness" or contributing to a desirable "impact." However, harshness and impact have been imprecisely defined and assessed using subjective measures. Thus, the current experiments used an objective measure of sensitivity to chemical irritation in the nose to test the hypothesis that menthol vapor modulates sensitivity to chemical irritation in the airways. METHODS: Nasal irritation thresholds were measured for 2 model compounds (acetic acid and allyl isothiocyanate) using nasal lateralization. In this technique, participants simultaneously sniff clean air in one nostril and chemical vapor in the other and attempt to identify the stimulated nostril. People cannot lateralize based on smell alone but can do so when chemicals are strong enough to feel. In one condition, participants were pretreated by sniffing menthol vapor. In a control condition, participants were pretreated by sniffing an odorless blank (within-subjects design). RESULTS: Pretreatment with menthol vapor decreased sensitivity to nasal irritation from acetic acid (participants required higher concentrations to lateralize) but increased sensitivity to allyl isothiocyanate (lower concentrations were required). CONCLUSIONS: The current experiments provide objective evidence that menthol vapor can modulate sensitivity to chemical irritation in the upper airways in humans. Cigarette smoke is a complex mixture of chemicals and particulates, and further work will be needed to determine exactly how menthol modulates smoking sensation. A better understanding could lead to treatments tailored to help menthol smokers quit by replacing the sensation of mentholated cigarettes.

Dynamics of nasal irritation from pulsed homologous alcohols.

Relatively, few studies have focused on how nasal irritation changes over time. To simulate the rhythm of natural respiration, subjects received 3-s pulses of volatile organic compounds interspersed with 3-s pulses of clean air. Each trial, subjects received 9 pulses of a chemical vapor over about 1 min. Subjects rated nasal irritation from each pulse using magnitude estimation. Within a trial, compound and concentration were fixed. Compound (ethanol, n-butanol, or n-hexanol) and concentration (4 levels for each compound) varied across trials. For all stimuli, rated irritation decreased over time (adaptation). Plots of log-rated intensity versus elapsed time were approximately linear (intensity decreased by a fixed ratio per unit time). Interestingly, the slopes of intensity versus time functions differed very little: Regardless of concentration and compound, rated irritation decreased by about 32% over the 9 pulses. The basic mechanism of short-term adaptation may be the same for the 3 alcohols studied. Regardless, these data suggest that very simple models might be able to describe some aspects of perceptual dynamics quite well.

Temporal integration in nasal lateralization of homologous propionates.

For nasal irritation from volatile chemicals, a version of Haber's rule (k = C(n)T) can model the trade-off between concentration (C) and duration of exposure (T) to achieve a fixed sensory impact, e.g. threshold-level irritation or a fixed suprathreshold intensity. The term k is a constant. The exponent, n, represents how well the system integrates over time. An exponent of 1 indicates complete temporal integration: an x-fold increase in stimulus duration exactly compensates for cutting the concentration 1/x. An exponent greater than 1 indicates incomplete temporal integration: more than an x-fold increase in duration is needed. In a previous study of homologous alcohols, n varied systematically with number of methylene units: integration became more complete as the length of the carbon chain increased. To explore the generality of this finding, we tested homologous esters that differ in the number of methylene units: n-ethyl propionate, n-propyl propionate, and n-butyl propionate. Nasal lateralization was used to measure irritation thresholds. Human subjects received a fixed concentration of a single compound within each experimental session. Stimulus duration was varied to find the briefest stimulus that caused lateralizable irritation. Concentration and compound varied across sessions. Consistent with results with n-alcohols, integration became more complete as the number of methylene units increased. Lipid solubility varies with chain length; hence, solubility in the nasal mucosa may play a role in the dynamics of irritation. Further, preliminary analyses suggest that, for data pooled across both chemical series, n varies systematically with molecular parameters related to solubility and diffusion.

Temporal integration in nasal lateralization of homologous alcohols.

Through temporal integration, sensory systems accumulate stimulus energy, e.g., photons, acoustic energy, or molecules, over time to detect weaker signals than they otherwise could. Past studies found imperfect temporal integration in detection of nasal irritation: To maintain a fixed level of detection, one must increase stimulus duration by more than twofold to compensate for cutting concentration in half. Despite this generality, integration varied widely among compounds, from nearly perfect, i.e., an increase in duration of slightly more than twofold could compensate for cutting concentration in half, to highly imperfect. How do such differences relate to molecular parameters? Perhaps molecules that more readily dissolve into the lipid-rich perireceptor environment will accumulate, and therefore integrate, better over time. To test this hypothesis, studies compared temporal integration for three compounds that differ systematically in lipid solubility: n-ethanol, n-butanol, and n-hexanol. Subjects were healthy, adult humans. Nasal lateralization was used to measure irritation threshold. Subjects received a fixed concentration of a single compound within each experimental session, and stimulus duration was varied to find the briefest stimulus subjects could reliably lateralize. Concentration and compound varied across sessions. Consistent with the hypothesis, integration did become closer to perfect as lipid solubility increased. That just one molecular parameter can help predict degree of integration suggests that a structure-activity approach to understanding temporal integration shows promise.

Comparative Morphology and Histology of the Nasal Fossa in Four Mammals: Gray Squirrel, Bobcat, Coyote, and White-Tailed Deer.

Although the anatomy of the nasal fossa is broadly similar among terrestrial mammals, differences are evident in the intricacies of nasal turbinal architecture, which varies from simple scroll-like to complex branching forms, and in the extent of nonsensory and olfactory epithelium covering the turbinals. In this study, detailed morphological and immunohistochemical examinations and quantitative measurements of the turbinals and epithelial lining of the nasal fossa were conducted in an array of species that include the gray squirrel, bobcat, coyote, and white-tailed deer. Results show that much more of the nose is lined with olfactory epithelium in the smallest species (gray squirrel) than in the larger species. In two species with similar body masses, bobcat and coyote, the foreshortened felid snout influences turbinal size and results in a decrease of olfactory epithelium on the ethmoturbinals relative to the longer canine snout. Ethmoturbinal surface area exceeds that of the maxilloturbinals in all four sampled animals, except the white-tailed deer, in which the two are similar in size. Combining our results with published data from a broader array of mammalian noses, it is apparent that olfactory epithelial surface area is influenced by body mass, but is also affected by aspects of life history, such as diet and habitat, as well as skull morphology, itself a product of multiple compromises between various functions, such as feeding, vision, and cognition. The results of this study warrant further examination of other mammalian noses to broaden our evolutionary understanding of nasal fossa anatomy. Anat Rec, 299:840-852, 2016. © 2016 Wiley Periodicals, Inc.

Temporal integration of nasal irritation from ammonia at threshold and supra-threshold levels.

Two experiments examined integration of perceived irritation over short-term (approximately 100-4000 ms) delivery of ammonia into the nasal cavity of human subjects. Experiment 1 examined trade-offs between time and concentration at threshold level by means of nasal lateralization, a common measure of irritation threshold. Within experimental sessions, the duration of a fixed-concentration stimulus varied to determine the shortest, detectable pulse. Subjects could lateralize increasingly weaker concentrations with longer stimulus presentations. Experiment 2 examined an analogous trade-off for supra-threshold irritation. Subjects rated irritation from presentations of ammonia that varied both in concentration and in duration. Rated intensity for a given concentration increased with stimulus duration. Hence integration occurred at both threshold and supra-threshold levels. However, more than a twofold increase in duration was required to compensate for a twofold decrease in concentration to maintain threshold lateralization or a fixed level of perceived intensity. These results suggest that an imperfect mass-integrator model may be able to describe short-term integration of nasal irritation from ammonia at both the threshold and supra-threshold levels.

Facts, fallacies, fears, and frustrations with human pheromones.

Among primates in general, pheromones are of variable importance to social communication. Data on humans have generated the greatest controversy regarding the existence of pheromonal communication. In this review, the likelihood of pheromonal communication in humans is assessed with a discussion of chemical compounds produced by the axilla that may function as pheromones; the likelihood that the vomeronasal organ (VNO), a putative pheromone receptor organ in many other mammals, is functional in humans; and the possible ways pheromones operate in humans. In the human axilla, the interactions between the cutaneous microflora and axillary secretions render this region analogous to scent glands found in other primates. Both the chemistry of axillary secretions and their effects on conspecifics in humans appear to be analogous to other mammalian pheromone systems. Whichever chemical compounds serve a pheromonal function in humans, another unknown is the receptor. Although the VNO has been implicated in the reception of pheromones in many vertebrates, it is not the only pathway through which such information has access to the central nervous system; there is ample evidence to support the view that the olfactory epithelium can respond to pheromones. Furthermore, if a chemical activates receptors within the VNO, this does not necessarily mean that the compound is a pheromone. An important caveat for humans is that critical components typically found within the functioning VNO of other, nonprimate, mammals are lacking, suggesting that the human VNO does not function in the way that has been described for other mammals. In a broader perspective, pheromones can be classified as primers, signalers, modulators, and releasers. There is good evidence to support the presence of the former three in humans. Examples include affects on the menstrual cycle (primer effects); olfactory recognition of newborn by its mother (signaler); individuals may exude different odors based on mood (suggestive of modulator effects). However, there is no good evidence for releaser effects in adult humans. It is emphasized that no bioassay-guided study has led to the isolation of true human pheromones, a step that will elucidate specific functions to human chemical signals.

Differential responses to odorant analogs after recovery from nerve transection.

We previously found that exposure-induced increase in odor sensitivity involves, at least in part, the olfactory epithelium. We did this by exposing mice to 5 alpha-androst-16-en-3-one (androstenone) and measuring changes in the epithelium. Past research showed that sensitivity to androstenone also could be induced by exposing individuals to 4-(4',4'-dimethylcyclohexyl)-2-methylcyclohexanone (DMCMC), a structural and functional analog of androstenone. What remained unknown is whether structural and/or functional odorant analogs share peripheral components. In the current work, we used a well-established model to disconnect the olfactory epithelium from the olfactory bulbs (BNX) to disrupt mechanisms underlying olfactory coding (when the afferents reinnervate the bulb, they do not synapse in their original glomeruli), and to examine the effects of disruption and restoration on exposure-induced odor sensitivity. In this study, we determined whether analogs of androstenone, viz., 5 alpha-androstan-3-one (androstanone) and DMCMC, could induce sensitivity to androstenone after BNX. Results demonstrate that exposure to either androstanone or DMCMC can induce sensitivity to androstenone in control mice. Different results were observed in mice that had recovered from bilateral BNX. Exposure to androstanone for 10 days immediately after surgery increased sensitivity to androstenone; however, exposure to DMCMC did not. These results suggest that androstanone and DMCMC, although apparent perceptual analogs of androstenone, may be using different pathways of olfaction within the central nervous system (CNS).

Identification of volatile organic compounds in human cerumen.

We report here the initial examination of volatile organic compounds (VOCs) emanating from human earwax (cerumen). Recent studies link a single nucleotide polymorphism (SNP) in the adenosine triphosphate (ATP) binding cassette, sub-family C, member 11 gene (ABCC11) to the production of different types of axillary odorants and cerumen. ABCC11 encodes an ATP-driven efflux pump protein that plays an important function in ceruminous apocrine glands of the auditory canal and the secretion of axillary odor precursors. The type of cerumen and underarm odor produced by East Asians differ markedly from that produced by non-Asians. In this initial report we find that both groups emit many of the same VOCs but differ significantly in the amounts produced. The principal odorants are volatile organic C2-to-C6 acids. The physical appearance of cerumen from the two groups also matches previously reported ethnic differences, viz., cerumen from East Asians appears dry and white while that from non-Asians is typically wet and yellowish-brown.

Volatile biomarkers from human melanoma cells.

Dogs can identify, by olfaction, melanoma on the skin of patients or melanoma samples hidden on healthy subjects, suggesting that volatile organic compounds (VOCs) from melanoma differ from those of normal skin. Studies employing gas chromatography-mass spectrometry (GC-MS) and gas sensors reported that melanoma-related VOCs differed from VOCs from normal skin sources. However, the identities of the VOCs that discriminate melanoma from normal skin were either unknown or likely derived from exogenous sources. We employed solid-phase micro-extraction, GC-MS and single-stranded DNA-coated nanotube (DNACNT) sensors to examine VOCs from melanoma and normal melanocytes. GC-MS revealed dozens of VOCs, but further analyses focused on compounds most likely of endogenous origin. Several compounds differed between cancer and normal cells, e.g., isoamyl alcohol was higher in melanoma cells than in normal melanocytes but isovaleric acid was lower in melanoma cells. These two compounds share the same precursor, viz., leucine. Melanoma cells produce dimethyldi- and trisulfide, compounds not detected in VOCs from normal melanocytes. Furthermore, analyses of the total volatile metabolome from both melanoma cells and normal melanocytes by DNACNT sensors, coupled with the GC-MS results, demonstrate clear differences between these cell systems. Consequently, monitoring of melanoma VOCs has potential as a useful screening methodology.

Dynamics of nasal chemesthesis.

Dynamics, or how stimulation occurs over time, influences the somatosensory impact of volatile chemicals. Within an experimental session, sensation waxes with steady presentation over seconds to minutes, may reach a plateau, and then may fade. Long-term occupational exposure can desensitize the trigeminal system. Short- and long-term dynamics might be mediated by different mechanisms. For brief intranasal exposures (i.e., up to about 10 seconds), studies have systematically manipulated both time (duration of exposure) and concentration to maintain a fixed perceived intensity or a fixed level of detection. A simple mass integration model describes the trade-off between concentration and time quite well: a fixed-ratio increase in duration compensates for a fixed-ratio decrease in concentration. However, for most compounds, more than a two-fold increase in duration are required to compensate for cutting concentration in half. For example, for ethanol, an increase in duration of about six-fold are required. For such compounds that display highly imperfect integration, a fixed number of molecules might have a much greater sensory impact when presented over 0.2 seconds than over 0.5 seconds. Nasal chemesthesis may be temporally sluggish compared to olfaction, but fine-grained dynamics still matter. Time-intensity ratings of nasal irritation from dynamic stimuli also support this conclusion. Although integration is generally imperfect, compounds vary widely in how far they fall short of perfect time-concentration trading. Current studies use a structure-activity approach to determine how molecular parameters correlate with how well a compound integrates over time.

Temporal integration in nasal lateralization of ethanol.

Two experiments examined the trade-off between concentration and stimulus duration in nasal lateralization of n-ethyl alcohol. In nasal lateralization, a common measure of irritation threshold, subjects receive chemical vapor in one nostril and clean air in the other. Subjects try to determine which nostril received the chemical. Within experimental runs, subjects received fixed concentrations (1650-5000 ppm) of ethanol, and duration was varied to find the shortest, lateralizable stimulus. In Experiment 1, a small group of subjects was tested intensively to obtain stable individual data. In Experiment 2, a larger group was studied using more rapid methods. In both cases, subjects could lateralize increasingly weaker concentrations with longer stimulus presentations. Hence integration occurred. However, more than a twofold increase in duration was required to compensate for a twofold decrease in concentration to maintain threshold lateralization. These results suggest that an imperfect, mass-integrator model can describe short-term integration of nasal lateralization of ethanol.

Preference for human body odors is influenced by gender and sexual orientation.

Human body odor may contribute to selection of partners. If so, sexual orientation may influence preference for and perhaps production of human body odors. In a test of these hypotheses, heterosexual and homosexual males and females made two-alternative forced-choice preference judgments for body odors obtained from other heterosexual and homosexual males and females. Subjects chose between odors from (a) heterosexual males and gay males, (b) heterosexual males and heterosexual females, (c) heterosexual females and lesbians, and (d) gay males and lesbians. Results indicate that differences in body odor are detected and responded to on the basis of, in part, an individual's gender and sexual orientation. Possible mechanisms underlying these findings are discussed.