Search

Odorants activate sensory transduction in olfactory receptor neurons (ORNs) via a cAMP-signaling cascade, which results in the opening of nonselective, cyclic nucleotide-gated (CNG) channels. The consequent [Ca.sup.2+] influx through CNG channels activates Cl channels, which serve to amplify the transduction signal. We investigate here some general properties of this Ca-activated Cl channel in rat, as well as its functional interplay with the CNG channel, by using inside-out membrane patches excised from ORN dendritic knobs/cilia. At physiological concentrations of external divalent cations, the maximally activated Cl current was ~30 times as large as the CNG current. The Cl channels on an excised patch could be activated by [Ca.sup.2+] flux through the CNG channels opened by cAMP. The magnitude of the Cl current depended on the strength of Ca buffering in the bath solution, suggesting that the CNG and Cl channels were probably not organized as constituents of a local transducisome complex. Likewise, Cl channels and the Na/Ca exchanger, which extrudes [Ca.sup.2+], appear to be spatially segregated. Based on the theory of buffered [Ca.sup.2+] diffusion, we determined the [Ca.sup.2+] diffusion coefficient and calculated that the CNG and Cl channel densities on the membrane were ~8 and 62 [micro][m.sup.-2], respectively. These densities, together with the [Ca.sup.2+] diffusion coefficient, demonstrate that a given Cl channel is activated by [Ca.sup.2+] originating from multiple CNG channels, thus allowing low-noise amplification of the olfactory receptor current. KEY WORDS: olfaction * signal transduction * Ca diffusion * ion channel

It has long been believed that vertebrate olfactory signal transduction is mediated by independent multiple pathways (using cAMP and Ins[P.sub.3] as second messengers). However, the dual presence of parallel pathways in the olfactory receptor cell is still controversial, mainly because of the lack of information regarding the single-cell response induced by odorants that have been shown to produce Ins[P.sub.3] exclusively (but not cAMP) in the olfactory cilia. In this study, we recorded activities of transduction channels of single olfactory receptor cells to Ins[P.sub.3]-producing odorants. When the membrane potential was held at--54 mV, application of Ins[P.sub.3]-producing odorants to the ciliary region caused an inward current. The reversal potential was 0 [+ or -] 7 mV (mean [+ or -] SD, n = 10). Actually, Ins[P.sub.3]-producing odorants generated responses in a smaller fraction of cells (lilial, 3.4%; lyral, 1.7%) than the cAMP-producing odorant (cineole, 26%). But, fundamental properties of responses were surprisingly homologous; namely, spatial distribution of the sensitivity, waveforms, I-V relation, and reversal potential, dose dependence, time integration of stimulus period, adaptation, and recovery. By applying both types of odorants alternatively to the same cell, furthermore, we observed cells to exhibit symmetrical cross-adaptation. It seems likely that even with odorants with different modalities adaptation occurs completely depending on the amount of current flow. The data will also provide evidence showing that olfactory response generation and adaptation are regulated by a uniform mechanism for a wide variety of odorants. KEY WORDS: Ins[P.sub.3] * cAMP * olfactory receptor cell * signal transduction * adaptation

High-density sensor arrays were prepared with microbead vapor sensors to explore and compare the information coded in sensor response profiles following odor stimulus. The coded information in the sensor-odor response profiles, which is used for odor discrimination purposes, was extracted from the microsensor arrays via two different approaches. In the first approach, the responses from individual microsensors were separated (decoded array) and independently processed. In the second approach, response profiles from all microsensors within the entire array, i.e., the sensor ensemble, were combined to create one response per odor stimulus (nondecoded array). Although the amount of response data is markedly reduced in the second approach, the system shows comparable odor discrimination rates for the two signal extraction methods. The ensemble approach streamlines system resources without decreasing system performance. These signal compression approaches may simulate or parallel information coding in the mammalian olfactory system.

Olfaction is important in mammals and other animals for foraging, predator avoidance, and communication. However, very little is known about how the physical environment influences the activity of odorants. Many pesticides are organic molecules that appear to behave similarly to odorants of interest to rodent foragers. In this article, the literature on pesticide residues is used to construct a conceptual model of how odorants might behave under different environmental conditions. The primary focus of the model concerns how the environment might affect detection of buried seeds by rodents. The most important environmental variable influencing volatilizing of pesticides from soil is water content of soil. In dry soil, pesticides are adsorbed onto soil particles. However, when soil moisture increases above a monomolecular layer, pesticides desorb and vapor densities increase dramatically. These observations on changes in vapor density of pesticides as soil moisture changes are consistent with experimental data on olfaction in rodents. Other factors that influence pesticide volatilization include relative humidity, temperature, wind, soil characteristics (particle size, organic matter, and bulk density), and burial depth. Limited data suggest that these factors also influence the vapor density of odorants and, therefore, olfaction. The literature on pesticides allows us to make predictions about how animals detect odorants and then test those predictions experimentally. Key words: foraging behavior, granivory, odorants, olfaction, predator-prey relationships, rodents, scent marking, seed caching, seed water, weather

The psychological basis of odor quality is poorly understood. For pragmatic reasons, descriptions of odor quality generally rely on profiling odors in terms of what odorants they bring to mind. It is argued here that this reliance on profiling reflects a basic property of odor perception, namely that odor quality depends on the implicit memories that an odorant elicits. This is supported by evidence indicating that odor quality as well as one's ability to discriminate odors is affected by experience. Developmental studies and cross-cultural research also point to this conclusion. In this article, these findings are reviewed and a model that attempts to account for them is proposed. Finally, the model's consistency with both neurophysiological and neuropsychological data is examined.

The sense of smell is arguably our most primal faculty and also the least understood. Even our own olfactorily impaired species is capable of detecting [approximately equal to] 10,000 distinct scents [Buck, L. & Axel, R. (1991) Cell 65, 175-1871. To achieve that amazing diversity, mammals have [approximately equal to] 1,000 olfactory genes, which accounts for [approximately equal to] 3% of their entire genome [Mombaerts, P. (1999) Science 286, 707-711]. The olfactory receptors (ORs) are believed to be seven-helix transmembrane proteins, with an odorant-binding site on the periplasmic domain and a G protein-binding site on the cytoplasmic domain. Odorants first bind to an OR, which then undergoes some structural change that triggers the G protein activation and the following cascade of events leading to nerve cell activity. The structural details of ORs, however, remain to be determined. In this paper, we will describe a hypothesis in which metal ions play an important role for odorant recognition. We analyze the predicted structure and consensus sequence of the ORs and propose a metal-binding site in the loop between fourth and fifth helix (4-5 loop). We have prepared synthetically a pentapeptide that contains this putative binding site and find that it not only has high affinity for binding Cu(II) and Zn(II) ions, but that it also undergoes a dramatic transition to an [alpha]-helical structure upon metal ion binding. Based on these observations, we propose a 'shuttlecock' mechanism for the possible structural change in ORs upon odorant binding. This mechanism involves membrane penetration of the 4-5 loop after residue charge neutralization by metal ion binding. olfaction | G protein-coupled receptors | transmembrane protein

Olfaction is crucial to spotted hyenas (Crocuta crocuta), yet there are no controlled studies of their reactions to odors. In Experiment 1, the authors examined responses of captive hyenas to various environmental (prey, nonprey animal, and plant) odors. Subjects approached and sniffed all odors equally but preferentially licked prey odors, scent marked next to odors, and rolled in animal-based odors. In Experiment 2, the authors examined the function of rolling by applying odors to the pelts of captive hyenas. When hyenas wore carrion, they gained positive social attention (increased investigation and allogrooming) from pen mates, but when they wore camphor, the normal social greeting ceremony was curtailed. Thus, olfactory stimuli elicit specific responses, influence where behavior is directed, and can be used to affect social interaction.

The sensory brain areas of a sample of

Research indicates that lilac aldehydes are a primary factor in the attraction of silver Y moths to the orchid genus Platanthera bifolia. Studies were conducted in a flight tunnel using P. bifolia blossoms, single compounds and synthetic blends, and noting moth responses to each.

We demonstrate that Caenorhabditis elegans is able to form an association between the presence of the odorant benzaldehyde and the food content of its environment. When exposed to 100% benzaldehyde for 1 h in the absence of food the naive attractive response is reduced, and we have found that this olfactory adaptation is attenuated by the presence of food. Contrary to nonassociative (single stimulus) learning theory, this response is not a function of the total time of exposure to benzaldehyde but rather an associative function of the ability of benzaldehyde to predict a nutrient-deficient environment. Genetic and pharmacological evidence revealed that the effects of food in this learning paradigm are mediated by serotonergic signaling.

An olfactory conditioning paradigm tested whether newborn rats can acquire a conditioned aversion to olfactory events associated with their first postnatal meal 3-5 hr after birth. Exposure to lemon odor (conditioned stimulus [CS]) paired with intraoral infusions of 0.1% quinine (unconditioned stimulus) resulted in explicit conditioning. Responsiveness to a surrogate nipple providing water in the presence of the CS was significantly lower than the 3 control conditions. The conditioning dramatically suppressed responsiveness to a surrogate nipple providing milk, which normally is expressed voraciously in terms of sustained nipple attachment and milk intake. These findings suggest that as early as 3-5 hr after birth newborn rats are capable of aversive conditioning to odors in the context of suckling behavior.

The olfactory system has become an important model system for neurobiologicel function and sensory processing. In insects, odours play a vital role in all aspects of life. From the late 1950s until very recently, research into the structure and function of the insect olfactory system has often preceded similar investigations in vertebrates and has been important in the formulation of general principles.

The first step in processing olfactory information, before neural filtering, is the physical capture of odor molecules from the surrounding fluid. Many animals capture odors from turbulent water currents or wind using antennae that bear chemosensory hairs. We used planar laser-induced fluorescence to reveal how lobster olfactory antennules hydrodynamically alter the spatiotemporal patterns of concentration in turbulent odor plumes. As antennules flick, water penetrates their chemosensory hair array during the fast downstroke, carrying fine-scale patterns of concentration into the receptor area. This spatial pattern, blurred by flow along the antennule during the downstroke, is retained during the slower return stroke and is not shed until the next flick., Many animals use chemical cues in the water or air around them to detect mates, competitors, food, predators, and suitable habitats (1-3). Large-scale turbulent flow in the environment carries odorants [...]

Different sensory neurons and different neural pathways in the brain appear to be involved in the sensing of general odors and pheromones. This is critical because pheromones regulate behavior in many animals.

Porcine odorant binding protein (pOBP) is discussed relative to its conformational stability and binding properties. Results of thermodynamic study by high-sensitivity differential scanning calorimetry and isothermal titration calorimetry indicate that the mechanism of binding to pOBP of the odorants studied is not primarily a hydrophobic process related to any change in protein hydration. Likely it is driven by polar and van der Waals interactions.

Evidence suggests that odorants are important for forming attachments by domestic chicks but there is little evidence that nestlings remember odorants presented soon after they are hatched. A new study investigates whether early exposure to nonaversive odorants alters a chick's responses to natural odours, such as food, feathers and faeces of adult chicken. The study concludes that chicks learn about their olfactory environment during the latter part of incubation and in the early posthatching period.

Tamias minimus, or least chipmunks may mark a patch of seeds, a type of behavior which is unusual in rodents, and is more often found in otters, wolves, foxes and coyotes. Unprofitable patches tend to be marked, and this means that the chipmunk may be signalling that the patch is depleted. This could benefit chipmunks other than the market. Marking may help jog the memory of the marker and help it to seek food more efficiently. Slightly depleted patches may be marked if the seeds are not of a type preferred by the chipmunk.

Our objective was to develop a method for assessing the effects of olfaction on feed preference. Two multiparous lactating Holstein cows were offered a totally mixed ration consisting of corn silage, alfalfa haylage, and a ground corn and soybean meal-based concentrate mixture (25:25:50 on a DM basis) for their ad libitum consumption in four consecutive 2.5-h periods daily for 5 d. An apparatus was developed that allowed odorants to be distributed at a set rate over two feeding containers with limited possibility of odor carryover. Four odorants and a control (no odorant) were compared against each other. All possible comparisons were conducted on the left and right feeding sides to avoid potential lateral-preference effects. Rank values of 0 or .5 were assigned to each odorant based on the percentage of total feed consumed in a period. A test of overall equality based on the sums of squares of ranks was used to determine whether odors affected preference. The limited results indicated that inhalation of odorants did not affect preference. Rank values were doubled for several odorants when compared with others, which. suggested that the sample size limited experimental sensitivity. To attain reasonable power, we estimated that at least six cows were needed per study. Large effects of odorants on feed preference would have been required to reach statistical significance in this trial; however, the method provides a practical technique for testing the effects of olfaction on feed preference in cattle when the suggested number of cows is used. Key Words: Smell, Feeding Preferences, Holstein Cows

BACKGROUND: Olfactory dysfunction affects millions of people worldwide. This sensory impairment is associated with neurodegenerative disease and significantly decreased quality of life. Exposure to airborne pollutants has been implicated in olfactory decline, likely due to the anatomic susceptibility of the olfactory nerve to the environment. Historically, studies have focused on occupational exposures, but more recent studies have considered effects from exposure to ambient air pollutants. OBJECTIVES: To examine all relevant human data evaluating a link between ambient pollution exposure and olfaction and to review supporting animal data in order to examine potential mechanisms for pollution-associated olfactory loss. METHODS: We identified and reviewed relevant articles from 1950 to 2015 using PubMed and Web of Science and focusing on human epidemiologic and pathophysiologic studies. Animal studies were included only to support pertinent data on humans. We reviewed findings from these studies evaluating a relationship between environmental pollutant exposure and olfactory function. RESULTS: We identified and reviewed 17 articles, with 1 additional article added from a bibliography search, for a total of 18 human studies. There is evidence in human epidemiologic and pathologic studies that increased exposure to ambient air pollutants is associated with olfactory dysfunction. However, most studies have used proxies for pollution exposure in small samples of convenience. Human pathologic studies, with supporting animal work, have also shown that air pollution can contact the olfactory epithelium, translocate to the olfactory bulb, and migrate to the olfactory cortex. Pollutants can deposit at each location, causing direct damage and disruption of tissue morphology or inducing local inflammation and cellular stress responses. CONCLUSIONS: Ambient air pollution may impact human olfactory function. Additional studies are needed to examine air pollution-related olfactory impacts on the general population using measured pollution exposures and to link pollution exposure with olfactory dysfunction and related pathology. http://dx.doi.org/10.1289/EHP136, Introduction Olfactory dysfunction is a significant public health problem worldwide, with a prevalence estimated to be between 13.9% and 31.7% in older adults (~ 60-90 years of age) in the [...]

Although numerous studies have investigated the content of laboratory and home dream reports, surprisingly little is known about the prevalence of various sensory modes in dreams. 49 men and 115 women completed a battery of questionnaires and kept a home dream diary for two to three consecutive weeks. Retrospective responses to the questionnaire indicate that approximately 33% of men and 40% of women recalled having experienced sensations of smell or taste in their dreams. A total of 3372 dream reports were collected and scored for unambiguous references to auditory, olfactory, and gustatory experiences. Auditory experiences were reported in approximately 53 % of all dream reports. Olfactory and gustatory sensations occurred in approximately 1% of all dream reports. A significantly greater percentage of women than men reported one or more dreams containing references to olfactory sensations. The results lend support to previous studies which have shown that a variety of sensory experiences, although relatively rare, can occur in dreams.

The molecular mechanisms mediating chemosensory discrimination in insects are unknown. Using the enhancer trapping approach, we identified a new Drosophila mutant, lush, with odorant-specific defects in olfactory, behavior. lush mutant flies are abnormally attracted to high concentrations of ethanol, propanol, and butanol but have normal chemosensory responses to other odorants. We show that wild-type flies have an active olfactory avoidance mechanism to prevent attraction to concentrated alcohol, and this response is defective in lush mutants. This suggests that the defective olfactory behavior associated with the lush mutation may result from a specific defect in chemoavoidance. lush mutants have a 3-kb deletion that produces a null allele of a new member of the invertebrate odorant-binding protein family, LUSH. LUSH is normally expressed exclusively in a subset of trichoid chemosensory sensilla located on the ventral-lateral surface of the third antennal segment. LUSH is secreted from nonneuronal support cells into the sensillum lymph that bathes the olfactory neurons within these sensilla. Reintroduction of a cloned wild-type copy of lush into the mutant background completely restores wild-type olfactory behavior, demonstrating that this odorant-binding protein is required in a subset of sensilla for normal chemosensory behavior to a subset of odorants. These findings provide direct evidence that odorant-binding proteins are required for normal chemosensory behavior in Drosophila and may partially determine the chemical specificity of olfactory neurons in vivo.

Goldfish reproduction is coordinated by pheromones that are released by ovulating females and detected by males. Two highly potent pheromones, a dihydroxyprogesterone and a prostaglandin, previously have been identified, and their effects on goldfish behavior have been studied in depth. We have cloned goldfish olfactory epithelium cDNAs belonging to two multigene G-protein coupled receptor families as a step toward elucidating the molecular basis of pheromone recognition. One gene family (GFA) consists of homologs of putative odorant receptors ([approximately equal to]320 residues) found in the olfactory epithelium of other fish and mammals. The other family (GFB) consists of homologs of putative pheromone receptors found in the vomeronasal organ (VNO) of mammals and also in the nose of pufferfish. GFB receptors ([approximately equal to] 840 residues) are akin to the V2R family of VNO receptors, which possess a large extracellular N-terminal domain and are homologs of calcium-sensing and metabotropic glutamate receptors. In situ hybridization showed that the two families of goldfish receptors are differentially expressed in the olfactory epithelium. GFB mRNA is abundant in rather compact cells whose nuclei are near the apical surface. In contrast, GFA mRNA is found in elongated cells whose nuclei are positioned deeper in the epithelium. Our findings support the hypothesis that the separate olfactory organ and VNO of terrestrial vertebrates arose in evolution by the segregation of distinct classes of neurons that were differentially positioned in the olfactory epithelium of a precursor aquatic vertebrate.

Hamsters preferentially remember or value the top scent of a scent over-mark. What cues do they use to do this? Using habituation-discrimination techniques, we exposed male golden hamsters (Mesocricetus auratus) on 3 to 4 trials to genital over-marks from 2 females and then tested subjects for their familiarity with these 2 scents compared with that of a novel female's secretion. Preferential memory for 1 of the 2 individuals' scents did not occur if the 2 marks did not overlap or did not overlap but differed in age, but it did occur if a region of overlap existed or 1 mark apparently occluded another (but did not overlap it). Thus, hamsters use regions of overlap and the spatial configuration of scents to evaluate over-marks. These phenomena constitute evidence for previously unsuspected perceptual abilities, including olfactory scene analysis, which is analogous to visual and auditory scene analysis.

Infants are not passive recipients of flavored foods. Their responses to particular formulas change during infancy and their early experiences influence their first experience with solid food. Parents should offer variety of food to aid in preference development as well offering nutritional balance.

Response data were collected for a carbon black-polymer composite electronic nose array during exposure to homologous series of alkanes and alcohols. The mean response intensity of the electronic nose detectors and the response intensity of the most strongly driven set of electronic nose detectors were essentially constant for members of a chemically homologous odorant series when the concentration of each odorant in the gas phase was maintained at a constant fraction of the odorant's vapor pressure. A similar trend is observed in human odor detection threshold values for these same homologous series of odorants. Because the thermodynamic activity of an odorant at equilibrium in a sorbent phase is equal to the partial pressure of the odorant in the gas phase divided by the vapor pressure of the odorant and because the activity coefficients are similar within these homologous series of odorants for sorption of the vapors into specific polymer films, the data imply that the trends in detector response can be understood based on the thermodynamic tendency to establish a relatively constant concentration of sorbed odorant into each of the polymeric films of the electronic nose at a constant fraction of the odorant's vapor pressure. Similarly, the data are consistent with the hypothesis that the odor detection thresholds observed in human psychophysical experiments for the odorants studied herein are driven predominantly by the similarity in odorant concentrations sorbed into the olfactory epithelium at a constant fraction of the odorant's vapor pressure.

I. INTRODUCTION The morphology of olfactory receptor neurons (ORNs) was first described by Schultze (314, 315; reviewed in Ref. 366) 140 years ago. How ORNs function, however, has remained a [...]

The ability of yellow pine chipmunks (Tamias amoenus), deer mice (Peromyscus maniculatus), and other rodents to detect buried Jeffrey pine (Pinus jeffreyi) and antelope bitterbrush (Purshia tridentata) seeds using olfaction was investigated during dry and moist conditions at the Whittell Forest and Wildlife Area in Little Valley, Washoe County, Nevada, USA. Removal of cached seeds was monitored on two Jeffrey pine foraging grids (each with 100 caches of five seeds buried 5 mm deep) and on two bitterbrush foraging grids (each with 100 caches of 15 seeds buried at the same depth). Under dry conditions, soil typically contained Key words: granivory; olfaction; Peromyscus maniculatus; Pinus jeffreyi; Purshia tridentata; scatter hoarding; seed water; Tamias amoenus., INTRODUCTION Many rodents rely heavily on olfaction to find food items. Granivorous rodents use olfaction to find seeds scattered in or on the surface of the soil, to locate buried [...]

Research shows that the oscillatory synchronization of assemblies of projection neurons exist in honeybees to stimulate odour encoding behaviour. The Gamma-aminobutyric acid receptor antagonist picrotoxin prevents synchronization, making it impossible for odour discrimination to take place through fine sensory functionality. The inhibitory effects of picrotoxin are shown, together with honeybee neuronal responses.

D. Algom and W. S. Cain (1991b) found relative invariance in the pattern of judgments of perceptual and mental mixtures of banana and grass odors. Invariance held both for judgments of total intensity and for those of an individual constituent. For 2 tastes, H. N. J. Schifferstein (1997) found a pattern with both similarities to and differences from D. Algom and W. S. Cain's. A key difference lay in finding more symmetry of masking in mental mixtures than in perceptual mixtures. H. N. J. Schifferstein concluded from this alone that any similarity between the perceptual and mental arose from knowledge of 'mixture suppression.' The authors of this article do not refute the possibility; however, they reject the premise that a statistically reliable difference between the perceptual and the imaginal rules out imagery. The authors review relevant considerations and find no a priori reason to assume that what held for attributes in taste will hold for odors. An approach to resolve the issue is also suggested.

A study of olfactory learning in sheep has indicated that nitric oxide plays a significant role in the identification of odor. Within two hours after giving birth, sheep recognize the smell of their offspring. This is because nitric acid and another chemical are formed immediately after birth. The study found that once olfactory memory has been formed, the inhibition of nitric oxide and other related chemicals does not prevent its recall or the neuro-chemical release triggered by learned lamb smell.

University women who were either nonsmokers or who had smoked regularly for at least two years (ns = 7) attempted to discriminate a gustatory stimulus five days before and five days after their menses. The stimuli were presented 3 min. or 5 min. after the introduction of a target stimulus. A statistically significant interaction was found among history of smoking, menstrual phase, and latency for taste comparisons. However, when the shared variance between olfactory and gustatory accuracy was partialled out, the results for smokers suggested significant increases in gustatory thresholds relative to those of nonsmokers regardless of menstrual phase. Smokers also displayed significantly less ([eta.sup.2] = 25%) accuracy for olfactory discrimination than nonsmokers.

Rats' ability to discriminate between familiar conspecifics was investigated in a series of three experiments using a go/no-go discrimination procedure. Results of the first experiment revealed that rats are able to recognize conspecifics as individuals. The second experiment showed that rats had more difficulty in acquiring a reversed discrimination than a novel discrimination. Results of the last experiment indicated that rats can recognize individuals using only their olfactory signatures.

The role of olfaction on the homing ability of precocial or semi-precocial chicks of underground-nesting seabirds were analyzed in Hydrobates pelagicus or the British storm-petrel. Homing experiments with the British storm-petrel chicks indicated the absence of parent-offspring recognition after the end of brooding. However, British storm-petrel chicks exhibited olfactory homing abilities and are capable of nest recognition which were crucial for survival.

The adaptational mechanism in intact olfactory cells is investigated through the use of a combination of odorant stimulation and caged cAMP photolysis. Odorant- and cAMP-induced responses indicated that adaptation occurs entirely downstream of the cyclase. A modulation of the cAMP-gated channel by Ca2+ feedback is determined as the principal mechanism underlying odorant adaptation.