Olfactory sensitivity to conspecific bile fluid and skin mucus in the European eel Anguilla anguilla (L.)

The present study assessed the olfactory potency of conspecific bile fluid and skin mucus in the European eel Anguilla anguilla by the electro-olfactogram. Immature males showed high olfactory sensitivity to conspecific bile, giving large amplitude responses in a concentration-dependent manner with estimated thresholds of detection of <1:10⁷ ( n = 6). Mucus also proved to contain highly potent odorants with thresholds of detection of c . 1:10⁶ ( n = 6). Crude solid-phase extraction of bile fluid (C-18 and C-2/ENV+ cartridges) showed that the majority of olfactory activity in bile fluid was contained in the eluate of C-18 cartridges ( n = 6). There were quantitative differences, however, between the sexes; female bile fluid had a higher proportion of activity in this fraction. Similar solid-phase extraction of mucus showed that it contains a higher proportion of odorants in the C-18 filtrate than bile fluid. Mucus from mature eels, however, had a higher proportion of olfactory activity in the eluate than immature fish ( n = 6). Cross-adaptation experiments suggest that there are qualitative differences in the odorants contained in bile and mucus depending on both the sex and state of sexual maturation of the donor ( n = 6). These results are consistent with a role for chemical communication in the reproduction of the European eel and suggest that both bile and mucus are potential sources of the odorants involved.     

Numerical modeling of odorant uptake in the rat nasal cavity

An anatomically accurate 3-dimensional numerical model of the right rat nasal cavity was developed and used to compute low, medium, and high flow rate inspiratory and expiratory mucosal odorant uptake (imposed patterning) for 3 odorants with different mucus solubilities. The computed surface mass flux distributions were compared with anatomic receptor gene expression zones identified in the literature. In general, simulations predicted that odorants that were highly soluble in mucus were absorbed dorsally and medially, corresponding roughly to receptors from one of the gene expression zones. Insoluble odorants tended to be absorbed more peripherally in the rat olfactory region corresponding to the other 2 zones. These findings also agreed in general with the electroolfactogram measurements and the voltage-sensitive dye measurements reported in the literature. This numerical approach is the first to predict detailed odorant flux information across the olfactory mucosa in the rat nasal cavity during inspiratory and expiratory flow and to relate it to anatomic olfactory receptor location, physiological function, and biochemical experiment. This numerical technique can allow us to separate the contributions of imposed and inherent patterning mechanisms on the rat olfactory mucosa.     

Dynamics of odorant binding to thin aqueous films of rat-OBP3

Uptake, retention and release of 5 selected odorants (benzaldehyde, 2-methylpyrazine, 2-isobutyl-3-methoxypyrazine, 2-isobutylthiazole, and 2,4,5-trimethylthiazole) by recombinant rat odor-binding protein 3 (rat-OBP3) were measured in a model system under nonequilibrium conditions. Gaseous odorants were introduced into a 100 mm section of a polar deactivated capillary in which aqueous rat-OBP3 films were formed to mimic the olfactory epithelium (OE), and the change in the gas-phase concentration of the outflow gas was monitored in real time using atmospheric pressure chemical ionization-mass spectrometry (APCI-MS). The 5 odorants were chosen because they exhibited a broad range of dissociation constants with rat-OBP3 and because they were amenable to detection by on-line APCI-MS. All 5 odorants were quantitatively bound by rat-OBP3, which resulted in an effective concentration of the odorants in the aqueous layer (about 50?000-fold). Odorant release from the rat-OBP3-odorant complex into the gas phase showed that odorant release was governed by the dissociation constant of the complex and the flow rate of odorant-free air. When 2 odorants were introduced into the system, odorant uptake and release were influenced by the method of introduction and their relative affinities for the protein. Because rat-OBP3 exhibits typical odorant-binding characteristics, the results not only provide fundamental information on the kinetics of odorant mass transfer induced by the presence of OBPs in the olfactory mucus layer but also support the possibility that vertebrate OBPs may facilitate the accumulation of odorants in the OE.     

Evidence of an odorant-binding protein in the human olfactory mucus: location,structural characterization,and odorant-binding properties

Odorant-binding proteins (OBPs) are small abundant extracellular proteins belonging to the lipocalin superfamily. They are thought to participate in perireceptor events of odor detection by carrying, deactivating, and/or selecting odorant molecules. Putative human OBP genes (hOBP) have recently been described [Lacazette et al. (2000) Hum. Mol. Genet. 9, 289-301], but the presence of the corresponding proteins remained to be established in the human olfactory mucus. This paper reports the first evidence of such expression in the mucus covering the olfactory cleft, where the sensory olfactory epithelium is located. On the contrary, hOBPs were not observed in the nasal mucus covering the septum and the lower turbinate. To demonstrate the odorant binding activity of these proteins, a corresponding recombinant protein variant, hOBP(IIa)(alpha), was secreted by the yeast Pichia pastoris and thoroughly characterized. It appears as a monomer with one disulfide bond located between C59 and C151, a conservative feature of all other vertebrate OBPs. By measuring the displacement of several fluorescent probes, we show that hOBP(IIa)(alpha) is able to bind numerous odorants of diverse chemical structures, with a higher affinity for aldehydes and large fatty acids. A computed 3D model of hOBP(IIa)(alpha) is proposed and reveals that two lysyl residues of the binding pocket may account for the increased affinity for aldehydes. The relatively limited specificity of hOBP(IIa)(alpha) suggests that other human OBPs are expected to take into account the large diversity of odorant molecules.     

Amino acid odorants stimulate microvillar sensory neurons

The olfactory epithelium (OE) of zebrafish is populated with ciliated and microvillar olfactory sensory neurons (OSNs). Whether distinct classes of odorants specifically activate either of these unique populations of OSNs is unknown. Previously we demonstrated that zebrafish OSNs could be labeled in an activity-dependent fashion by amino acid but not bile acid odorants. To determine which sensory neuron type was stimulated by amino acid odorants, we labeled OSNs using the ion channel permeant probe agmatine (AGB) and analyzed its distribution with conventional light- and electron-microscope immunocytochemical techniques. Approximately 7% of the sensory epithelium was labeled by AGB exposure alone. Following stimulation with one of the eight amino acids tested, the proportion of labeled epithelium increased from 9% for histidine to 19% for alanine; amino acid stimulated increases in labeling of 2-12% over control labeling. Only histidine failed to stimulate a significant increase in the proportion of labeled OSNs compared to control preparations. Most amino acid sensitive OSNs were located superficially in the epithelium and immuno-electron microscopy demonstrated that the labeled OSNs were predominantly microvillar. Large numbers of nanogold particles (20-60 per 1.5 microm(2)) were associated with microvillar olfactory sensory neurons (MSNs), while few such particles (<15 per 1.5 microm(2)) were observed over ciliated olfactory sensory neurons (CSNs), supporting cells (SCs) and areas without tissue, such as the lumen above the OE. Collectively, these findings indicate that microvillar sensory neurons are capable of detecting amino acid odorants.     

Specificity of odorant-binding proteins: a factor influencing the sensitivity of olfactory receptor-based biosensors

Odorant-binding proteins (OBPs) primarily function in the transport of hydrophobic odorants. In this study, OBPs originating from rat and pig were cloned into a mammalian expression vector, pcDNA3, and expressed in HEK-293 cells, and their specificity for odorants and olfactory receptors was examined. Results suggest that OBPs have a high affinity for the olfactory receptors when both the OBP and receptor originate from the same species. The rat OBPs were bound not only to the rat olfactory receptor I7 but also to the odorant specific to I7. The solubility of the odorant was increased by both OBP2 and OBP3, which originate from rat, but with different efficiencies. These results demonstrate that OBPs specifically interact with odorants as well as olfactory receptors, and these interactions can influence the sensitivity of olfactory receptor-based biosensors.     

A Gas chromatographic (GLPC) model for the sense of smell. Variation of olfactory sensitivity with conditions of stimulation

Computer simulation of an olfactory detector has been developed using a chemical kinetic scheme originally proposed by McNab and Koshland for bacterial chemotaxis. This model describes response as a function of two opposed reactions, both of which are activated by odorant. One reaction turns on response, while its opponent shuts it off. Net response to various stimulus profiles is compared to psychophysical experiments, with particular attention paid to simulating magnitude estimation and odor adaptation results. Effects of the access route to this detector are evaluated. Transport of odorant molecules is treated as having two sequential steps: step (i), airborne odorant is carried parallel to a retentive layer (mucus) into the detector region; step (ii), molecules diffuse through the retentive layer to the detector. Step (i) is represented as analogous to GLPC on an open tubular column. Each step has a characteristic time constant, which is proportional to (distance)²/diffusion coefficient. Response to highly volatile odorants tends to be limited by step (ii), while odorants of low volatility approach the step (i) limit. Sensitivity at both limits is attenuated by increasing the thickness of the retentive layer, but sensitivity at the step (i) limit is also affected by changes in air passageway and airflow characteristics. This picture can be used to explain variations in women's sensitivity to odorants of low volatility with the menstrual cycle, while their detection of volatile odorants fluctuates to a much lesser extent.     

Sniffing and spatiotemporal coding in olfaction

The act of sniffing increases the air velocity and changes the duration of airflow in the nose. It is not yet clear how these changes interact with the intrinsic timing within the olfactory bulb, but this is a matter of current research activity. An action of sniffing in generating a high velocity that alters the sorption of odorants onto the lining of the nasal cavity is expected from the established work on odorant properties and sorption in the frog nose. Recent work indicates that the receptor properties in the olfactory epithelium and olfactory bulb are correlated with the receptor gene expression zones. The responses in both the epithelium and the olfactory bulb are predictable to a considerable extent by the hydrophobicity of odorants. Furthermore, receptor expression in both rodent and salamander nose interacts with the shapes of the nasal cavity to place the receptor sensitivity to odorants in optimal places according to the aerodynamic properties of the nose.     

Olfactory functioning and callosotomy: a report of two cases

Two callosotomy patients with presumably intact anterior commissures were evaluated on a battery of olfactory tasks including sensitivity, discrimination, memory, identification, cross-modality matching, bilateral summation (dirhinic vs. monorhinic thresholds), and localization of odorants. One case was evaluated both pre- and post-surgery. He showed marked decrements after surgery in odor memory and in matching across modalities. After surgery, both patients were better able to name odorants presented to the left nostril than the right nostril. The patient who was asked to remember odorants that could be readily labeled was better able to remember those odorants presented to the left nostril. The findings that both cases performed equally well whether olfactory and tactile information was projected to the same hemisphere or a different one, that some bilateral summation was evident, and that the cases were unable to localize odorants suggests that the remaining neuronal pathways allow for some communication between hemispheres.     

Relationship between the differential adsorption of odorants by the olfactory mucus and their perception in mixtures

It was proposed recently that the differential adsorption ofodorants by the olfactory mucus may constitute the first stepin the processing of odor mixtures [Laing, D.G. (1988) Ann.NY Acad. Sci., 510, 61–66]. In the present study psychophysicalprocedures were used to determine if there was a relationshipbetween differential adsorption by the olfactory mucus and theperception of odorants of different polarity in binary mixtures.With the eight odor pairs studied, differential adsorption andthe polarity of an odorant were not predictors of how well anodorant would be perceived in a mixture or how it would suppressor enhance the perception of other odorants.     

The effect of concanavalin A on the rat electro-olfactogram at various odorant concentrations.

We have studied the effect of concanavalin A (Con A) on the rat electro-olfactogram response to several odorants. Each odorant was applied over a range of concentrations. For hydrophobic odorants whose response was affected by Con A, the diminution in response was maximal at odorant concentrations of about 1 microM in the olfactory mucus. The (odour) concentration-dependence of the change is compatible with the idea that Con A inactivates one or more types of olfactory receptor that normally bind odorants with dissociation constants of the order of 100 nM. With hydrophilic odorants we had to apply concentrations very much higher than this to elicit any response from the system. At these high concentrations we could observe Con A-induced diminutions in response.     

Odor recognition and second messenger signaling in olfactory receptor neurons

The detection of volatile odorants is supposed to begin with their interaction with soluble binding proteins which shuttle the hydrophobic ligands through the aqueous mucus layer towards specific odorant receptors in the ciliary membrane of olfactory neurons. A large family of receptors for odorants has been identified recently; individual receptor types are expressed in subsets of cells distributed in distinct zones of the olfactory epithelium. Ligand-receptor interaction triggers a rapid multistep reaction cascade, ultimately leading to an electrical response of the receptor neuron. Olfactory signaling is terminated by phosphorylation of receptors via a negative feedback reaction catalyzed by two types of kinases.     

Physical Variables in the Olfactory Stimulation Process

Electrical recording from small twigs of nerve in a tortoise showed that olfactory, vomeronasal, and trigeminal receptors in the nose are responsive to various odorants. No one kind of receptor was most sensitive to all odorants. For controlled stimulation, odorant was caused to appear in a stream of gas already flowing through the nose. Of the parameters definable at the naris, temperature, relative humidity, and nature of inert gas had little effect on olfactory responses to amyl acetate, whereas odorant species, odorant concentration, and volume flow rate effectively determined the responses of all nasal chemoreceptors. An intrinsic variable of accessibility to the receptors, particularly olfactory, was demonstrated. Flow dependence of chemoreceptor responses is thought to reflect the necessity for delivery of odorant molecules to receptor sites. Since the olfactory receptors are relatively exposed, plateauing of the response with flow rate for slightly soluble odorants suggests an approach to concentration equilibrium in the overlying mucus with that in the air entering the naris. Accordingly, data for responses to amyl acetate were fitted with Beidler's (1954) taste equation for two kinds of sites being active. The requirement for finite aqueous solubility, if true, suggests substitution of aqueous solutions for gaseous solutions. A suitable medium was found and results conformed to expectations. Olfactory receptors were insensitive to variation of ionic strength, pH, and osmotic pressure.     

Sparse incomplete representations: a potential role of olfactory granule cells

Mitral/tufted cells of the olfactory bulb receive odorant information from receptor neurons and transmit this information to the cortex. Studies in awake behaving animals have found that sustained responses of mitral cells to odorants are rare, suggesting sparse combinatorial representation of the odorants. Careful alignment of mitral cell firing with the phase of the respiration cycle revealed brief transient activity in the larger population of mitral cells, which respond to odorants during a small fraction of the respiration cycle. Responses of these cells are therefore temporally sparse. Here, we propose a mathematical model for the olfactory bulb network that can reproduce both combinatorially and temporally sparse mitral cell codes. We argue that sparse codes emerge as a result of the balance between mitral cells' excitatory inputs and inhibition provided by the granule cells. Our model suggests functional significance for the dendrodendritic synapses mediating interactions between mitral and granule cells.     

雌性根田鼠对血液气味的行为识别

大量研究表明尿液在动物的嗅觉通讯中具有重要作用,血液是尿液的根本来源,但对其嗅觉通讯功能的研究较少.因此以雌性根田鼠Microtus oeconomus为研究对象,在行为选择箱中观察其对4种气味源的行为响应模式以判断能否识别不同血液气味.气味源分别为雌性根田鼠血液、雄性根田鼠血液、雄性Wistar大鼠血液和蒸馏水对照.结果表明:雌性根田鼠能够识别血液气味,且通过血液气味进行种间识别,但不能进行性别识别.