Increasing the sensitivity of piezoelectric odour sensors based on molecularly imprinted polymers

The molecular imprinting technique has been used to create sensors with a predetermined selectivity for molecules in the gas phase. Based on previous results, piezoelectric quartz crystals were first coated with a layer of nylon, to provide increased sensitivity, and then a layer of a polymer imprinted with 2-methylisoborneol (MIB) was applied to endow the device with selectivity. The response of the 'imprinted' sensor was significantly higher than the response of the 'non-imprinted' sensor at MIB concentrations above 10 ppb. Our new sensor is thus 20 times more sensitive than our previous device. At concentrations greater than 10 ppb, the response of the 'non-imprinted' sensor to geosmin, another odorant often accompanying MIB, was significantly higher than the response of the 'imprinted' sensor. A number of other odorants were examined and, as in our previous work, the responses of the 'non-imprinted' sensors were found to be to greater than the responses of the 'imprinted' sensors.     

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.     

Similarity of ion dependence of odorant responses between lipid bilayer and olfactory system

In a previous paper (Nomura and Kurihara (1987) Biochemistry 26, 6135-6140), we demonstrated that the lipid bilayer membranes exhibit membrane potential changes in response to various odorants similarly to olfactory cells. The present study demonstrated that ion dependence of the responses of the lipid membranes to odorants is related to that in the carp olfactory system in the following point. (1) The responses to odorants diminished at low concentrations of salts and recovered upon addition of salts to stimulating solutions. (2) Divalent cations were effective in supporting the responses to odorants at much lower concentrations that monovalent cations. (3) Impermeable organic cations were effective in supporting the responses. The present results suggest that the initial process of generation of the receptor potential in olfactory cells resembles that in the lipid membranes.     

Olfactory sensitivity for sperm-attractant aromatic aldehydes: a comparative study in human subjects and spider monkeys

Using a three-alternative forced-choice ascending staircase procedure, we determined olfactory detection thresholds in 20 human subjects for seven aromatic aldehydes and compared them to those of four spider monkeys tested in parallel using an operant conditioning paradigm. With all seven odorants, both species detected concentrations <1 ppm, and with several odorants single individuals of both species even discriminated concentrations <1 ppb from the solvent. No generalizable species differences in olfactory sensitivity were found despite marked differences in neuroanatomical and genetic features. The across-odorant patterns of sensitivity correlated significantly between humans and spider monkeys, and both species were more sensitive to bourgeonal than to lilial, cyclamal, canthoxal, helional, lyral, and 3-phenylpropanal. No significant correlation between presence/absence of an oxygen-containing moiety attached to the benzene ring or presence/absence of an additional alkyl group next to the functional aldehyde group, and olfactory sensitivity was found in any of the species. However, the presence of a tertiary butyl group in para position (relative to the functional aldehyde group) combined with a lack of an additional alkyl group next to the functional aldehyde group may be responsible for the finding that both species were most sensitive to bourgeonal.     

Dual signal transduction mediated by a single type of olfactory receptor expressed in a heterologous system

Controversy exists over the relationship between the cAMP and IP3 pathways in vertebrate olfactory signal transduction, as this process is known to occur by either of the two pathways. Recent studies have shown that a single olfactory neuron responds to both cAMP- and IP3-producing odorants, suggesting the existence of an olfactory receptor protein that can recognize both ligands. In this study we found that the rat olfactory receptor I7, stably expressed in HEK-293 cells, triggers the cAMP pathway upon stimulation by a specific odorant (octanal) at concentrations lower than 10(-4) M; however, the receptor triggers both pathways at higher concentrations. This indicates that a single olfactory receptor, stimulated by a single pathway-inducing odorant, can evoke both pathways at high odorant concentrations. Using this heterologous system, both the dose-dependent response and receptor I7 specificity were analyzed. The dose-dependent Ca2+ response curve, which also includes the release of Ca2+ ions from internal stores at high odorant concentrations, was not monotonous, but had a local maximum and minimum with 10(-10) and 10(-7) M octanal, respectively, and reached a plateau at 10(-2) M octanal. The specificity of the I7 receptor was lower when exposed to higher concentrations of odorants.     

Intranasal Odorant Concentrations in Relation to Sniff Behavior

Knowledge on how odorants are transported through the nasal cavity to the olfactory epithelium is limited. One facet of this is how the sniffing behavior affects the abundance of odorants transferred to the olfactory cleft and in turn influences odor perception. A novel system that couples an online mass spectrometer with an odorant pulse delivery olfactometer was employed to characterize intranasal odorant concentrations of butane‐2,3‐dione (or butanedione, commonly known as diacetyl) at the interior naris and the olfactory cleft. Volunteers (n=12) were asked to perform different modes of sniffing in relation to the sniff intensity that were categorized as ‘normal’, ‘rapid’ and ‘forced’. The highest concentrations of butanedione at both positions in the nose were observed during normal sniffing, with the lowest concentrations correlating with periods of forced sniffs. This corresponded to the panelists' ratings that normal sniffing elicited the highest odor intensities. These feasibility assessments pave the way for more in‐depth analyses with a variety of odorants of different chemical classes at various intranasal positions, to investigate the passage and uptake of odorants within the nasal cavity.     

Olfactory Sensitivity for Six Predator Odorants in CD-1 Mice,Human Subjects,and Spider Monkeys

Using a conditioning paradigm, we assessed the olfactory sensitivity of six CD-1 mice (Mus musculus) for six sulfur-containing odorants known to be components of the odors of natural predators of the mouse. With all six odorants, the mice discriminated concentrations <0.1 ppm (parts per million) from the solvent, and with five of the six odorants the best-scoring animals were even able to detect concentrations <1 ppt (parts per trillion). Four female spider monkeys (Ateles geoffroyi) and twelve human subjects (Homo sapiens) tested in parallel were found to detect the same six odorants at concentrations <0.01 ppm, and with four of the six odorants the best-scoring animals and subjects even detected concentrations <10 ppt. With all three species, the threshold values obtained here are generally lower than (or in the lower range of) those reported for other chemical classes tested previously, suggesting that sulfur-containing odorants may play a special role in olfaction. Across-species comparisons showed that the mice were significantly more sensitive than the human subjects and the spider monkeys with four of the six predator odorants. However, the human subjects were significantly more sensitive than the mice with the remaining two odorants. Human subjects and spider monkeys significantly differed in their sensitivity with only two of the six odorants. These comparisons lend further support to the notion that the number of functional olfactory receptor genes or the relative or absolute size of the olfactory bulbs are poor predictors of a species’ olfactory sensitivity. Analysis of odor structure–activity relationships showed that in both mice and human subjects the type of alkyl rest attached to a thietane and the type of oxygen moiety attached to a thiol significantly affected olfactory sensitivity.     

Odorant-induced hyperpolarization and suppression of cAMP-activated current in newt olfactory receptor neurons

Although many studies have reported that odorants can elicit inhibitory responses as well as excitatory responses in vertebrate olfactory receptor neurons, the cellular mechanisms that underlie this inhibition are unclear. Here we examine the inhibitory effect of odorants on newt olfactory receptor neurons using whole cell patch clamp recording. At high concentrations, odorant stimulation decreased the membrane conductance and inhibited depolarization. Various odorants (anisole, isoamyl acetate, cineole, limonene and isovaleric acid) suppressed the depolarizing current in a dose-dependent manner. Furthermore, one odorant could suppress the depolarization caused by another odorant. The depolarization caused by isoamyl acetate was inhibited by anisole in cells that were excited by isoamyl acetate but not by anisole. Odorants were able to hyperpolarize cells that were depolarized by cAMP-induced conductance. Given that this inhibitory effect of odorants can affect excitation caused by other odorants, we suggest that it might play a role in coding odorants in olfactory receptor neurons.     

Sensitivity and transduction mechanisms of responses to general odorants in turtle vomeronasal system

(a) The responses of the vomeronasal organ to general odorants in the turtle, Geoclemys reevesii, were measured by recording the accessory olfactory bulbar responses. The threshold concentrations of the vomeronasal responses to various odorants were similar to those in main olfactory bulbar responses, indicating that vomeronasal cells lacking cilia and olfactory cells having many cilia have similar sensitivities to general odorants. (b) The vomeronasal epithelium was perfused with 100 mM NaCl solution and the salt-free solution and the effects of NaCl on the vomeronasal responses to various odorants were examined. There was no essential difference between the concentration-response curves for n-amyl acetate and menthone dissolved in 100 mM NaCl solution and those dissolved in the salt-free solution in the whole concentration range examined. The ratios of the magnitudes of vomeronasal responses in the salt-free solution to those in 100 mM NaCl solution were between 1.01 and 1.10 for seven odorants tested. (c) The magnitudes of responses to the odorants were unchanged by changes in NaCl concentrations. The replacement of Na+ with organic cations such as choline+, Bis-Tris propane2+, and N-acetyl-D-glucosamine+ did not affect the magnitudes of the responses to the odorants. The Na channel blocker amiloride also did not affect the responses. (d) The vomeronasal responses were practically unchanged by changes in CaCl2 concentration. The Ca channel blockers diltiazem and verapamil did not affect the responses. (e) The replacement of Cl- with SO4(2-) did not affect the magnitudes of the vomeronasal responses. (f) The present results suggest that ion transport across the apical membranes of vomeronasal receptor cells does not contribute to the responses to odorants in the turtle.     

Coffee aroma constituents and odorant metabolites in human urine

Excretion of odorants and their metabolites into human urine was investigated in urine samples obtained from 14 volunteers after consumption of common dosages of coffee with respect to blank urine samples prior to coffee consumption. Analyses were targeted both on common potent odor constituents of the coffee beverage, as characterized by aroma extract dilution analysis, as well as on volatile constituents of coffee occurring at elevated concentrations and thereby representing quantitatively dominating compounds in the coffee volatile fraction. Identification and quantification of the target substances was accomplished by two-dimensional high resolution gas chromatography mass spectrometry (2D-HR-GC-MS; heart-cut technique) in conjunction with stable isotope dilution assays. Quantification was made on free volatile or odoros marker substances in the urine and their glucuronidated derivatives. Data revealed that some odorants were present at considerably elevated concentrations after the ingestion of coffee. This was confirmed by the odor profiles of the respective urine samples during sensory analysis.     

Concentration and Membrane Fluidity Dependence of Odor Discrimination in the Turtle Olfactory System

In the present study, we examined the concentration dependenceof odor discrimination in turtle olfactory bulbar responsesusing the cross-adaptation technique. In the odorant pairs withdiverse molecular structures, the degree of discrimination wasunchanged or only slightly decreased with an increase in odorantconcentrations, suggesting that odorants are well discriminatedeven at high concentrations. In the odorant pairs with closelyrelated molecular structures, the degree of discrimination wasdecreased with an increase in odorant concentrations. An increasein the temperature of turtle olfactory epithelium also decreasedthe ability to discriminate these odorants. There was a goodcorrelation between changes in the odor discriminating abilityinduced by an increase in odor concentrations and those inducedby a temperature increase. The liposomes were made of lipidsextracted from the turtle olfactory epithelia and changes oftheir membrane fluidity induced by adsorption of odorants weremonitored with DPH. There was a good correlation between a decreasein odor discriminating ability and the membrane fluidity changesinduced by odorants. We suggest that decreases in odor discriminatingability induced either by an increase in odor concentrationor by a temperature increase are ultimately caused by changesin the membrane fluidity. Chem. Senses 22: 553–563, 1997.     

Odor discrimination of ‘cAMP-’ and ‘IP3-increasing’ odorants at high temperature and at high NaCl concentration in turtle olfactory system

The ability of the turtle olfactory system to discriminate between various cAMP- and IP₃-increasing odorants at high temperature and at high NaCl concentration in the olfactory bulb was examined by the cross-adaptation technique. The degrees of discrimination in high [Na⁺] solution were similar to those in normal Ringer's solution, suggesting that selectivities of receptors coupled with cAMP- and IP₃-dependent pathways are similar to those coupled with both cAMP- and IP₃-independent pathways. The mean values of the degree of discrimination among the IP₃-increasing odorants were higher than those among the cAMP-increasing odorants at high temperature and at high [Na⁺] concentration. The degrees of discrimination among the IP₃-increasing odorants at 40°C were greater than those at 25°C, while those among the cAMP-increasing odorants at 40°C were similar to those at 25°C, suggesting that the features of the receptors of cAMP-increasing odorants are different from those which respond to IP₃-increasing odorants.     

The effect of five organophosphorus insecticides on survival and temperature tolerance in the copepod, Macrocyclops albidus (Copepoda: Cyclopidae)

Macrocyclops albidus were exposed for 24 hours to ABATE®, fenthion, malathion, methyl parathion, and chlorpyrifos at concentrations of 1, 5, 10, 25, and 50 parts per billion (ppb). Exposure to chlorpyrifos resulted in the greatest mortality to M. albidus; concentrations of 25 and 50 ppb caused 100% mortality. The thermal tolerance was lowered significantly by all chemicals at concentrations from 1 to 50 ppb.     

Larval development of hermit crab Clibanarius longitarsus: Synergistic effect of heavy metals

The levels of heavy metals copper and zinc were found to be high in the Vellar estuary. Therefore their effects on the larval development of the abundant hermit crab Clibanarius longitarsus were studied individually and in combination from hatching till moulting to glaucothoe stage in the laboratory using freshly hatched Artemia nauplii as food. The 96 h LC50 values found with 100 larvae each kept in 10 different concentrations of copper and zinc (350, 300, 250, 200, 150, 100, 50, 25, 10 and 5 ppb) were 50 ppb for copper and 90 ppb for zinc. Based on these 96 h LC50 values, three sublethal concentrations were chosen for the metals copper and zinc at 50%, 25% and 10% levels of the LC50 values. With increase in concentration of the test medium, the survival rate decreased and the time required for the completion of each zoeal stage increased. Copper was found to be more toxic than zinc as the survival rate in copper concentrations was lower than those in zinc concentrations. The survival rate in the mixed concentrations of metals was lower than in individual concentrations.     

Subthreshold olfactory stimulation can enhance sweetness

The impact of olfactory perception on sweetness was explored in a model solution using odorants at subthreshold concentrations. First, the impact of 6 odorants, previously described in the literature as congruent with sweetness, was investigated at suprathreshold level in a sucrose solution. Ethyl butyrate and maltol were selected as they had the highest and the lowest sweetness-enhancing properties, respectively. Second, the impact on sweetness of the 2 odorants was investigated at subthreshold concentrations. A system delivering a continuous liquid flow at the same sucrose level, but with varying odorant concentrations, was used. At a subthreshold level, ethyl butyrate but not maltol significantly enhanced the sweetness of the sucrose solution. This study highlights that olfactory perception induced by odorants at a subthreshold level can significantly modulate taste perception. Finally, contrary to results observed with ethyl butyrate at suprathreshold levels, at subthreshold levels, the intensity of sweetness enhancement was not proportional to ethyl butyrate concentration.     

Effects of ozone on cell organelles of alfalfa (Medicago sativa L.) seedlings

Seedlings of alfalfa (Medicago sativa L.) were exposed to different concentrations of atmospheric ozone (20–30 (control), 40–60, 65–80, and 85–120 ppb) in four distinct areas in the Riyadh region, so as to decide how ozone affected some of the seedling cellular organelles. Results acquired utilizing transmission electron microscopy demonstrated certifiable impacts to exist on the cell organelles in the tissues of both the leaf mesophyll and stem cortex; contrasted with control plants, the chloroplasts seemed enlarged, irregular, different sizes, decomposed, and possibly dissolved, while the plastoglobules seemed deformed, more widely spaced, and enlarged, also the vacuoles contained no clear non-living components. Moreover, some parts of the cytoplasmic membranes were ruptured, with only a few vesicles created at all concentrations, particularly in plants exposed to concentrations of 65–80 and 85–120 ppb, while no effects were noted in these organelles in control plants or plants exposed to 40–60 ppb. High concentrations (85–120 ppb) led to enlarged, irregularly shaped nuclei and chromatin intensification; however, no clear effects of ozone were noted on the shapes of chloroplast starch grains or the mitochondria in leaf mesophyll and cortex cells in the stem. The high ozone concentrations can cause negative effects on the growth of alfalfa seedlings, leading to imbalances in their vital functions and acceleration of aging, thus potentially decreasing the total plant yield. The discoveries hence propose that alfalfa plants should not be planted near polluted areas, and that they can be utilized as bioindicators of air pollution by ozone.     

Liposomes as a model for olfactory cells: changes in membrane potential in response to various odorants

Various odorants were found to depolarize azolectin liposomes. The results obtained are as follows. (1) Changes in the membrane potential of azolectin liposomes in response to various odorants were monitored by measuring changes in the fluorescence intensity of 3,3'-dipropylthiocarbocyanine iodide [disS-C3(5)]. Ten odorants examined increased the fluorescence intensity of the liposome-dye suspensions in a dose-dependent manner, which indicates that odorants depolarize the liposomes. Concentrations of odorants that depolarized the liposomes greatly varied among the odorants. There existed a good correlation between the minimum concentrations of odorants to depolarize the liposomes and the thresholds of respective odorants in the frog or porcine olfactory responses. (2) Addition of sphingomyelin (SM) to azolectin led to a large enhancement of depolarizations by nonanol, citral, and n-amyl acetate. The results indicate that lipid composition of liposomes is one of the factors that control the sensitivity to odorants. (3) Odorants changed the membrane fluidity of the liposomes, which was monitored by changes in the fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH). The membrane fluidity was changed in concentration ranges of odorants similar to those where the membrane potential changes occurred, which suggests that changes in the membrane fluidity are related to generation of the membrane potential changes. (4) Changes in the membrane potential in response to odorants were electrically measured with the planar lipid bilayer made of an azolectin-SM (2:1 w/w) mixture. It was shown that odorants (nonanol, citral, and n-amyl acetate) depolarized the planar lipid bilayer.(ABSTRACT TRUNCATED AT 250 WORDS)     

An Epidemiologic Study of Arsenic-Related Skin Disorders and Skin Cancer and the Consumption of Arsenic-Contaminated Well Waters in Huhhot,Inner Mongolia,China

Well-use histories were obtained and dermatological examinations were conducted for 3,179 of the 3,228 (98.5%) residents of 3 villages in Inner Mongolia with well water arsenic levels as high as 2,000 ppb (ug/L). Eight persons were found to have skin cancer, 172 had hyperkeratoses, 121 had dyspigmentation, 94 had both hyperkeratoses and dyspigmentation, and, strikingly, none had Blackfoot disease. All 8 subjects with skin cancer also had both hyperkeratoses and dyspigmentation. Arsenic levels were measured for 184 wells and individual well-use histories were obtained. Arsenic exposure histories were summarized as both highest arsenic concentration (highest exposure level for at least 1-year duration) and cumulative arsenic exposure (ppb-years). Sixty-nine percent of the participants had highest arsenic concentrations below 100 ppb; 71% had cumulative arsenic exposures below 2,000 ppb-years. Exposure-response analyses included frequency-weighted, simple linear regression, and most-likely estimate (hockey-stick) models. Skin cancer cases were only found for those with a highest arsenic concentration greater than 150 ppb, and those with exposure less than 150 ppb had a statistically significant deficit. A frequency-weighted model showed a threshold at 150 ppb, and a hockey-stick model showed a threshold at 122 ppb. Considerations of duration, age, latency, and misclassification did not appear to markedly affect the analysis. The non-malignant skin findings showed thresholds of 40–50 ppb in the hockey-stick models. Application of these analytic models to the data from other epidemiological studies of arsenic ingestion and malignant and non-malignant skin disorders can be used to examine patterns of arsenic carcinogenicity.     

The effects of sublethal concentrations of five organophosphorus insecticides on temperature tolerance, reflexes, and orientation in Gambusia affinis affinis (Pisces: Poeciliidae)

Gambusia affinis were exposed to the insecticides ABATE®, fenthion, chlorpyrifos, methyl parathion, and malathion for 24 h at concentrations of 1, 5, and 10 ppb and for 48 h at 5 ppb. The thermal tolerance was lowered significantly for male and female G. affinis by the toxicants methyl parathion and chlorpyrifos at 5 and 10 ppb with 24 h exposure. Activity was restricted with fish exposed to methyl parathion and chlorpyrifos at concentrations of 10 ppb for 24 h and at 5 ppb for 48 h.