Odor Capture Research Articles

Aerosol Alteration of Behavioral Response to Pheromone in Bombyx mori.

Because of the complexity to study them, aerosols have been neglected in nearly all studies on olfaction, especially studies dealing with odor capture. However, aerosols are present in large quantities in the atmosphere and have the physico-chemical ability to interact with odor molecules, in particular the many pheromones with low volatility. We submitted male moths of Bombyx mori to bombykol puffs, the main fatty alcohol component of its sex pheromone, depending on whether the air is free of aerosols, charged with ambient concentration aerosols or supplemented with aqueous aerosols and recorded their arousal behavior. Aerosols and pheromone do interact consistently over all experiments and moths react better in low aerosol-concentration conditions. We propose four hypotheses for explaining this impediment, the two most likely resorting to competition between odor molecules and aerosols for the olfactory pores and postulate a reversal to a positive impact of aerosols on communication, depending on the particular physico-chemical properties of the multiphasic interaction. Studying the partitioning between gas and particulate phases in the transport and reception of odors is key for advancing the chemico-physical understanding of olfaction.

Active Sensing in Bees Through Antennal Movements Is Independent of Odor Molecule.

When sampling odors, many insects are moving their antennae in a complex but repeatable fashion. Previous studies with bees have tracked antennal movements in only two dimensions, with a low sampling rate and with relatively few odorants. A detailed characterization of the multimodal antennal movement patterns as function of olfactory stimuli is thus wanted. The aim of this study is to test for a relationship between the scanning movements and the properties of the odor molecule. We tracked several key locations on the antennae of bumblebees at high frequency and in three dimensions while stimulating the insect with puffs of 11 common odorants released in a low-speed continuous flow. Water and paraffin were used as negative controls. Movement analysis was done with the neural network Deeplabcut. Bees use a stereotypical oscillating motion of their antennae when smelling odors, similar across all bees, independently of the identity of the odors and hence their diffusivity and vapor pressure. The variability in the movement amplitude among odors is as large as between individuals. The main type of oscillation at low frequencies and large amplitude is triggered by the presence of an odor and is in line with previous work, as is the speed of movement. The second oscillation mode at higher frequencies and smaller amplitudes is constantly present. Antennae are quickly deployed when a stimulus is perceived, decorrelate their movement trajectories rapidly, and oscillate vertically with a large amplitude and laterally with a smaller one. The cone of airspace thus sampled was identified through the 3D understanding of the motion patterns. The amplitude and speed of antennal scanning movements seem to be function of the internal state of the animal, rather than determined by the odorant. Still, bees display an active olfactory sampling strategy. First, they deploy their antennae when perceiving an odor. Second, fast vertical scanning movements further increase the odorant capture rate. Finally, lateral movements might enhance the likelihood to locate the source of odor, similarly to the lateral scanning movement of insects at odor plume boundaries.

Sniffing out Stingray Noses: The Functional Morphology of Batoid Olfaction.

Batoid fishes (rays, skates, sawfishes, and guitarfishes) are macrosmatic, meaning they rely on their sense of smell as one of the primary senses for survival and reproduction. Olfaction is important for long-distance tracking and navigation, predator and prey recognition, and conspecific signaling. However, the mechanisms by which batoids harness odorants is unknown. Without a direct pump-like system, it is hypothesized that batoids irrigate their nostrils via one or a combination of the following: the motion pump, buccopharyngeal pump, pressure (ex. pitot-like mechanism), or a shearing force (ex. viscous entrainment). These mechanisms rely on the size, shape, and position of the nostrils with respect to the head and to each other. Batoids are united as a group by their dorsoventrally compressed body plans, with nostrils on the ventral side of their body. This position presents several challenges for odor capture and likely limits the effectivity of the motion pump. Batoid fishes display an expansive nasal morphology, with inlet nostrils ranging from thin, vertical slits to wide, horizontal ovals to protruding, tube-like funnels, and more. In this paper, a morphometric model is developed to quantify the vast diversity in batoid nose shapes, sizes, and positions on the head in an ecological and functional framework. Specifically, swimming mode, lifestyle, habitat, and diet are examined for correlations with observed nasal morphotypes. Morphometric measurements were taken on all 4 orders present in Batoidea to broadly encompass batoid nasal diversity (Rhinopristiformes 4/5 families; Rajiformes 2/4 families; Torpediniformes 4/4 families; Myliobatiformes 8/11 families). All batoid external nasal diversity was found to be categorized into 5 major morphological groups and were termed: flush nare [circle, comma, intermediate], open nare, and protruding nare. Several morphometric traits remained significant when accounting for shared ancestry, including the position and angle of the nostril on the head, the width of the inlet hole, and the spacing of the nostrils from each other. These measurements were found to be closely correlated and statistically significant with the swimming mode of the animal. This study provides the first crucial step in understanding batoid olfaction, by understanding the diversity of the morphology of the system. Because odor capture is a strictly hydrodynamic process, it may be that factors relating more directly to the fluid dynamics (i.e., swimming mode, velocity, Reynolds number) may be more important in shaping the evolution of the diversity of batoid noses than other ecological factors like habitat and diet.

Validation of a polymer odor capture-and-release (POCR) aid for training canines to detect triacetone triperoxide (TATP)

A major issue in canine training for the detection of hazardous materials is the limited availability of materials for handlers and trainers on a routine basis. This is particularly a challenge for homemade explosives such as triacetone triperoxide (TATP), which is friction and impact sensitive, making it hazardous to handle for all canine and bomb technician personnel. The polymer odor capture and release training aid (POCR) was designed as a solution to this challenge. The TATP POCR consists of a layer of absorptive polymer enclosed in a seamless metal container. In this configuration, the POCR provides a non-hazardous training aid that delivers odor at a known, reproducible rate. This study evaluated the TATP POCR both chemically and in canine testing to provide a validated training aid. Chemical analysis determined how much TATP was absorbed by the polymer in the POCR, and subsequently determined that the POCR had an odor concentration comparable to a 1 g laboratory-grade TATP training aid with a 13-hole lid. Finally, the dissipation rate of TATP from the POCR (7.8 m/min) was established up to 0.5 m.The chemical results were compared to the success in canine detection results. Three phases of canine testing were conducted: 1) Initial validation with an internal cohort of canines imprinted on the TATP POCR, 2) Pilot testing with operational explosives detection canines imprinted on the bulk TATP, and 3) External testing with operational explosives detection canines imprinted on either TATP POCR or bulk TATP. Across all phases, alerts to the respective testing odor in both controlled odor discrimination and operational search testing was above 80 %. For the internal cohort of canines that were trained on the TATP POCR, alerts to the TATP training aid were >90 % and false alerts were < 10 %, validating the training method and material. The combined results provide evidence that the TATP POCR may be used efficiently in initial or maintenance training as well as in retaining motivation and performance in operational settings. This is one of the first studies of its kind to thoroughly evaluate a canine training aid by presenting chemical analysis and supporting canine testing across internally-sourced and operational externally-sourced canine groups.

Oscillations for active sensing in olfaction: bioinspiration from insect antennal movements

Crustacean and insect antennal scanning movements have been postulated to increase odorant capture but the exact mechanisms as well as measures of efficiency are wanting. The aim of this work is to test the hypothesis that an increase in oscillation frequency of a simplified insect antenna model translates to an increase of odorant capture, and to quantify by how much and through which mechanism. We approximate the antennal movements of bumblebees, quantified in a previous study, by a vertical oscillatory movement of a cylinder in a homogeneous horizontal flow with odorants. We test our multiphysics flow and mass transfer numerical model with dedicated experiments using particle image velocimetry. A new entire translating experimental measurement setup containing an oil tank enables us to work at appropriate Strouhal and Reynolds numbers. Increasing antennal oscillating frequency does increase the odorant capture rate, up to 200%, proving this behavior being active sensing. This result holds however only up to a critical frequency. A decrease of efficiency characterizes higher frequencies, due to molecules depletion within oversampled regions, themselves defined by overlaying boundary layers. Despite decades of work on thermal and mass transfer studies on oscillating cylinders, no analogy with published cases was found. This is due to the unique flow regimes studied here, resulting from the combination of organ small size and low frequencies of oscillations. A theory for such flow regimes is thus to be developed, with applications to fundamental research on animal perception up to bioinspired olfaction.

Flexible air curtain optimization for isolating tobacco odor in large-scale space

Controlling the isolation of different tobacco odors in the tobacco workshop is of great significance to the air quality regulation in the workshop. For the isolation of odor, the existing literature mainly adopts the method of controlling the diffusion source with mechanical device, but this method is not suitable for the tobacco workshop where the diffusion source is widely distributed and complex. This paper proposed the alternative idea of flexible isolation of two types of storage cabinets using air curtains. Numerical simulations were performed to study the effects of the airflow collection device width (H), the inlet and extraction air velocities (vs and Vc) on the air curtain airflow path and collection, and the odor isolation efficiency. At small airflow collection device width, the air curtain airflow path was split into three sections leading to the two types of storage cabinets and inside the airflow collection device, respectively. As inlet air velocities increased and the extraction air velocities decreased, the pressure difference at the entrance of the airflow collection device dropped, the airflow turbulence effect intensified, in contrast to the coupling effect between the air curtain airflow and the extraction airflow. This expanded the vortex area, deteriorating the air curtain airflow collection efficiency. At high the inlet and extraction air velocities the thickness and range of the air curtain increased, improving the odor isolation efficiency. The optimal parameters provided the air curtain airflow collection efficiency of 99.01%, the odor isolation efficiency of 94.6%. This economical and simple scheme allows for efficient odor isolation and partial odor capture.

Surface Properties and Architectures of Male Moth Trichoid Sensilla Investigated Using Atomic Force Microscopy

The surfaces of trichoid sensilla on male moth antennae have been sculpted over evolutionary time to capture pheromone odorant molecules emitted by the females of their species and transport the molecules in milliseconds into the binding protein milieu of the sensillum lumen. The capture of pheromone molecules likely has been optimized by the topographies and spacings of the numerous ridges and pores on these sensilla. A monolayer of free lipids in the outer epicuticle covers the sensillar surfaces and must also be involved in optimal pheromone odorant capture and transport. Using electro-conductive atomic force microscopy probes, we found that electrical surface potentials of the pores, ridges and flat planar areas between ridges varied in consistent ways, suggesting that there is a heterogeneity in the distribution of surface lipid mixtures amongst these structures that could help facilitate the capture and transport of pheromone molecules down through the pores. We also performed experiments using peak force atomic force microscopy in which we heated the sensilla to determine whether there is a temperature-related change of state of some of the surface lipid exudates such as the prominent domes covering many of the pores. We found that these exudates were unaffected by heating and did not melt or change shape significantly under high heat. Additionally, we measured and compared the topographies of the trichoid sensilla of five species of moths, including the distributions, spacings, heights and diameters of ridges, pores and pore exudates.

Effects of polydimethylsiloxane (PDMS) on triacetone triperoxide (TATP) volatilization

The effect of the polymer polydimethylsiloxane (PDMS) on triacetone triperoxide (TATP) volatilization was explored. TATP vapor contained in PDMS, known as the TATP polymer odor capture and release training aid (POCR), can be used to train field vapor detection systems, such as canines. Thermogravimetric analysis (TGA) was used to define the vapor pressure and enthalpy of sublimation for TATP and to calculate values for comparison using the TATP POCR. The vapor pressure (at 25 °C) and enthalpy of sublimation for bulk TATP were 0.0474 torr and 84.8 kJ/mol, respectively. The vapor pressure (at 25 °C) of TATP within the POCR was lower, at 0.00897 torr. The enthalpy of volatilization for the TATP POCR was also lower at 25.7 kJ/mol, implying that while it took less energy for TATP to enter the gas phase from the PDMS, the tendency for it to do so was lower. These interactions between TATP and the PDMS can be used to explain the headspace concentrations above TATP and the TATP POCR at equilibrium, despite differences in quantity and surface area. Finally, the vapor pressure (0.0520 torr at 25 °C) and enthalpy of sublimation (84.9 kJ/mol) were determined for deuterated TATP, showing that deuterium does not significantly affect sublimation of TATP.

Real-time monitoring of TATP released from PDMS-based canine training aids versus bulk TATP using DART-MS

Direct analysis in real time-mass spectrometry (DART-MS) was used to explore the behavior of vapor released from triacetone triperoxide (TATP) versus an absorption-based canine training aid sometimes called a polydimethylsiloxane (PDMS) polymer odor capture and release (POCR) system. The results compare dissipation from the source to the instrument (in minutes), steady state signal intensity (i.e. approximate relative amounts), and dissipation of the odor after removing the source (also in minutes). Several parameters were tested: reproducibility between POCRs, TATP versus TATP with a lid (containing 13 drilled holes), distance from the detector, heights of the source, concealment, purposeful air disturbances, blanks, and containment systems.In general, the PDMS-based training aid behaved similarly to the TATP with a 13-hole lid, which is the aid most often used by the FBI’s National Canine Improvised Explosives Detection Program. Results shows that the PDMS-based training aids are reproducible and reliable at steady state as a vapor release system. As expected, signal was decreased given increased distance from the DART interface for all sample types, when using the odor-restricting lid with the 1 g TATP sample, when all samples were placed at height, and when using a cotton bag as a method of concealment. Despite having no direct correlation, these results support anecdotal canine evidence since canine handlers tend to report that their dogs have more difficulty finding training aids within those same parameters. Further, adding purposeful air disturbances had a larger effect on signal intensity for 1 g TATP than on the PDMS-based training aid. Finally, adding a masking odor at the DART interface decreased detection of TATP regardless of the vapor source, but did not fully diminish it. This too agrees with canine handler reports and previous research, where dogs may have a more difficult time locating odors in the presence of high background.This is the first report of its kind to use real-time detection to characterize vapor release and dissipation from a biosensor training aid in comparison to the corresponding true material it intends to replace. By using the three phases of odor release (saturation, steady state, and depletion), the study investigates the effects of several ambient parameters on TATP volatile detection from true material and the PDMS-based training aid.

Insect pectinate antennae maximize odor capture efficiency at intermediate flight speeds

Flying insects are known to orient themselves over large distances using minute amounts of odors. Some bear pectinate antennae of remarkable architecture thought to improve olfactory performance. The semiporous, multiscale nature of these antennae influences how odor molecules reach their surface. We focus here on the repeating structural building blocks of these antennae in Saturniid moths. This microstructure consists of one ramus or branch and its many hair-like sensilla, responsible for chemical detection. We experimentally determined leakiness, defined as the proportion of air going through the microstructure rather than flowing around it, by particle image velocimetry visualization of the flow around three-dimensional printed scaled-up mock-ups. The combination of these results with a model of mass transfer showed that most pheromone molecules are deflected around the microstructure at low flow velocities, keeping them out of reach. Capture is thus determined by leakiness. By contrast, at high velocities, molecular diffusion is too slow to be effective, and the molecules pass through the structure without being captured. The sensory structure displays maximal odor capture efficiency at intermediate flow speeds, as encountered by the animal during flight. These findings also provide a rationale for the previously described "olfactory lens," an increase in pheromone reception at the proximal end of the sensors. We posit that it is based on passive mass transfer rather than on physicochemical surface processes.

Two-temperature preparation method for PDMS-based canine training aids for explosives

Canine training aids based on vapor capture-and-release into a flexible polymer, polydimethylsiloxane (PDMS), have been used for in canine detection of explosives that have volatile or semi-volatile odorants. To enhance the rate of odor capture for less volatile targets, two temperatures are used for aid preparation. By using an elevated temperature for the target explosive, the amount of vapor is enhanced, increasing the production of the characteristic odor profile. The polymeric adsorbent is maintained at a cool temperature, favoring vapor capture. The success of this two-temperature approach is demonstrated for training aids targeting the low volatility explosive TNT using SPME (solid-phase microextraction) headspace analysis. In addition, the effect of using two temperatures on preparing training aids based on TNT and its more volatile impurities 2,4-DNT and 2,6-DNT are evaluated in canine trials. A thermal pretreatment to minimize the non-target odors in the PDMS polymer is presented.

What Can Computational Modeling Tell Us about the Diversity of Odor-Capture Structures in the Pancrustacea?

A major transition in the history of the Pancrustacea was the invasion of several lineages of these animals onto land. We investigated the functional performance of odor-capture organs, antennae with olfactory sensilla arrays, through the use of a computational model of advection and diffusion of odorants to olfactory sensilla while varying three parameters thought to be important to odor capture (Reynolds number, gap-width-to-sensillum-diameter ratio, and angle of the sensilla array with respect to oncoming flow). We also performed a sensitivity analysis on these parameters using uncertainty quantification to analyze their relative contributions to odor-capture performance. The results of this analysis indicate that odor capture in water and in air are fundamentally different. Odor capture in water and leakiness of the array are highly sensitive to Reynolds number and moderately sensitive to angle, whereas odor capture in air is highly sensitive to gap widths between sensilla and moderately sensitive to angle. Leakiness is not a good predictor of odor capture in air, likely due to the relative importance of diffusion to odor transport in air compared to water. We also used the sensitivity analysis to make predictions about morphological and kinematic diversity in extant groups of aquatic and terrestrial crustaceans. Aquatic crustaceans will likely exhibit denser arrays and induce flow within the arrays, whereas terrestrial crustaceans will rely on more sparse arrays with wider gaps and little-to-no animal-induced currents.

Fine Structure of Scorpion Pectines for Odor Capture

AbstractThe paper revealed the fine structure of the scorpion (Mesobuthus martensii) pectines and showed how the fine structure of the pecten influences odor flow. The first step of our investigation was to prove that scorpion pectines work as olfactory and this was done via experiments utilizing paraffin coverage. Subsequently, the location, morphology, section structure, and arrangement of the pectines were studied via stereomicroscopy and Scanning Electron Microscopy (SEM). The fine structure of pecten comprises a comb-like structure with 24–30 knife-like teeth and thousands of micron bowl-like pecten sensilla in staggered arrangement on the surface of the tooth. Computational Fluid Dynamics (CFD) was applied to predict odor flow around the pecten via the relevant Reynolds numbers. The comb-like structure amplified the odor flow velocity similar to an amplifier, transporting the odor flow of increased velocity to the micron pecten sensilla, improving transport efficiency of the odor flow. The staggered arrangement of the pecten sensilla generated a vortex, improving contact duration between pecten sensilla and odorant molecules. Thus, the pecten fine structure was likely acting as an effective comb with non-smooth teeth for the transport and capture of odorant molecules.

One-step synthesis of silicon carbide foams supported hierarchical porous sludge-derived activated carbon as efficient odor gas adsorbent

Hierarchical porous sludge-derived activated carbon coated on macroporous silicon carbide (SiC) foams substrate has been facilely fabricated via a simple one-step strategy by utilizing sludge as carbon source, and jointly using zinc chloride and hexadecanol as pore forming agents. The sludge-derived carbon has been confirmed to be hierarchical macro-meso-microporous structure based on detailed characterization by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectra and nitrogen adsorption-desorption measurement. The adsorption tests showed that the hierarchical porous sludge-derived activated carbon fabricated by one-step pore-forming (zinc chloride and hexadecanol microemulsion mixture) possesses excellent adsorption capacity (259.9mgg−1, breakthrough time reach 90min and saturation end-time up to 140min) of methyl mercaptan (CH3SH). The excellent adsorption performance can be attributed to the macroporous SiC foam skeleton and the mesopores channel formed by nonionic surfactant hexadecanol micelles, as well as the micropores activated by ZnCl2 as odor capture sites. The proposed pore-forming strategy paves an avenue for the sludge disposal and even the development of bio-derived materials.

Do terrestrial hermit crabs sniff? Air flow and odorant capture by flicking antennules.

Capture of odorant molecules by olfactory organs from the surrounding fluid is the first step of smelling. Sniffing intermittently moves fluid across sensory surfaces, increasing delivery rates of molecules to chemosensory receptors and providing discrete odour samples. Aquatic malacostracan crustaceans sniff by flicking olfactory antennules bearing arrays of chemosensory hairs (aesthetascs), capturing water in the arrays during downstroke and holding the sample during return stroke. Terrestrial malacostracans also flick antennules, but how their flicking affects odour capture from air is not understood. The terrestrial hermit crab, Coenobita rugosus, uses antennules bearing shingle-shaped aesthetascs to capture odours. We used particle image velocimetry to measure fine-scale fluid flow relative to a dynamically scaled physical model of a flicking antennule, and computational simulations to calculate diffusion to aesthetascs by odorant molecules carried in that flow. Air does not flow into the aesthetasc array during flick downstrokes or recovery strokes. Odorants are captured from air flowing around the outside of the array during flick downstrokes, when aesthetascs face upstream and molecule capture rates are 21% higher than for stationary antennules. Bursts of flicking followed by pauses deliver discrete odour samples to olfactory sensors, causing intermittency in odour capture by a different mechanism than aquatic crustaceans use.

Design and Implementation of Air Extraction using the Odor Capture Performance for the Containment of Odors

Design and Implementation of Air Extraction using <i>the Odor Capture Performance</i> for the Containment of Odors

Flexibility of crab chemosensory sensilla enables flicking antennules to sniff.

The first step in smelling is capture of odorant molecules from the surrounding fluid. We used lateral flagella of olfactory antennules of crabs Callinectes sapidus to study the physical process of odor capture by antennae bearing dense tufts of hair-like chemosensory sensilla (aesthetascs). Fluid flow around and through aesthetasc arrays on dynamically scaled models of lateral flagella of C. sapidus was measured by particle image velocimetry to determine how antennules sample the surrounding water when they flick. Models enabled separate evaluation of the effects of flicking speed, aesthetasc spacing, and antennule orientation. We found that crab antennules, like those of other malacostracan crustaceans, take a discrete water sample during each flick by having a rapid downstroke, during which water flows into the aesthetasc array, and a slow recovery stroke, when water is trapped in the array and odorants have time to diffuse to aesthetascs. However, unlike antennules of crustaceans with sparse aesthetasc arrays, crabs enhance sniffing via additional mechanisms: 1) Aesthetascs are flexible and splay as a result of the hydrodynamic drag during downstrokes, then clump together during return strokes; and 2) antennules flick with aesthetascs on the upstream side of the stalk during downstrokes, but are hidden downstream during return strokes. Aiming aesthetascs into ambient flow maintains sniffing. When gaps between aesthetascs are wide, changes in antennule speed are more effective at altering flow through the array than when gaps are narrow. Nonetheless, if crabs had fixed gap widths, their ability to take discrete samples of their odorant environment would be diminished.

Scaling of olfactory antennae of the terrestrial hermit crabs Coenobita rugosus and Coenobita perlatus during ontogeny.

Although many lineages of terrestrial crustaceans have poor olfactory capabilities, crabs in the family Coenobitidae, including the terrestrial hermit crabs in the genus Coenobita, are able to locate food and water using olfactory antennae (antennules) to capture odors from the surrounding air. Terrestrial hermit crabs begin their lives as small marine larvae and must find a suitable place to undergo metamorphosis into a juvenile form, which initiates their transition to land. Juveniles increase in size by more than an order of magnitude to reach adult size. Since odor capture is a process heavily dependent on the size and speed of the antennules and physical properties of the fluid, both the transition from water to air and the large increase in size during ontogeny could impact odor capture. In this study, we examine two species of terrestrial hermit crabs, Coenobita perlatus H. Milne-Edwards and Coenobita rugosus H. Milne-Edwards, to determine how the antennule morphometrics and kinematics of flicking change in comparison to body size during ontogeny, and how this scaling relationship could impact odor capture by using a simple model of mass transport in flow. Many features of the antennules, including the chemosensory sensilla, scaled allometrically with carapace width and increased slower than expected by isometry, resulting in relatively larger antennules on juvenile animals. Flicking speed scaled as expected with isometry. Our mass-transport model showed that allometric scaling of antennule morphometrics and kinematics leads to thinner boundary layers of attached fluid around the antennule during flicking and higher odorant capture rates as compared to antennules which scaled isometrically. There were no significant differences in morphometric or kinematic measurements between the two species.

The Sniff as a Unit of Olfactory Processing

Sniffing is a rhythmic motor process essential for the acquisition of olfactory information. Recent behavioral experiments show that using a single sniff rats can accurately discriminate between very similar odors and fail to improve their accuracy by taking multiple sniffs. This implies that each sniff has the potential to provide a complete snapshot of the local olfactory environment. The discrete and intermittent nature of sniffing has implications beyond the physical process of odor capture as it strongly shapes the flow of information into the olfactory system. We review electrophysiological studies-primarily from anesthetized rodents-demonstrating that olfactory neural responses are coupled to respiration. Hence, the "sniff cycle" might play a role in odor coding, by allowing the timing of spikes with respect to the phase of the respiration cycle to encode information about odor identity or concentration. We also discuss behavioral and physiological results indicating that sniffing can be dynamically coordinated with other rhythmic behaviors, such as whisking, as well as with rhythmic neural activity, such as hippocampal theta oscillations. Thus, the sniff cycle might also facilitate the coordination of the olfactory system with other brain areas. These converging lines of empirical data support the notion that each sniff is a unit of olfactory processing relevant for both neural coding and inter-areal coordination. Further electrophysiological recordings in behaving animals will be necessary to assess these proposals.

Ligand-binding properties and structural characterization of a novel rat odorant-binding protein variant.

After characterization of a novel odorant-binding protein (OBP) variant isolated from the rat nasal mucus, the corresponding cDNA was cloned by RT-PCR. Recombinant OBP-1F, the sequence of which is close to that of previously reported rat OBP-1, has been secreted by the yeast Pichia pastoris at a concentration of 80 mg.L-1 in a form identical to the natural protein as shown by MS, N-terminal sequencing and CD. We observed that, in contrast with porcine OBP-1, purified recombinant OBP-1F is a homodimer exhibiting two disulfide bonds (C44-C48 and C63-C155), a pairing close to that of hamster aphrodisin. OBP-1F interacts with fluorescent probe 1-aminoanthracene (1-AMA) with a dissociation constant of 0.6 +/- 0. 3 microM. Fluorescence experiments revealed that 1-AMA was displaced efficiently by molecules including usual solvents such as EtOH and dimethylsulfoxide. Owing to the large OBP-1F amounts expressed, we set up a novel biomimetic assay (volatile-odorant binding assay) to study the uptake of airborne odorants without radiolabelling and attempted to understand the odorant capture by OBP in the nasal mucus under natural conditions. The assay permitted observations on the binding of airborne odorants of different chemical structures and odors (2-isobutyl-3-methoxypyrazine, linalool, isoamyl acetate, 1-octanal, 1-octanol, dimethyl disulfide and methyl thiobutyrate). Uptake of airborne odorants in nearly physiological conditions strengthens the role of OBP as volatile hydrophobic odorant carriers in the mucus of the olfactory epithelium through the aqueous barrier towards the chemo-sensory cells.