Experimental assessment of human olfactory thresholds in air for some thiols and alkanes

Human olfactory thresholds of four n-alkanes from C₁₂ to C₁₈and four n-thiols from C₄ to C₁₂ have been determined. Contraryto previous assumptions, the olfactory effectiveness of boththese substance series increases with the number of carbon atomsin an almost linear fashion. ¹Presented at the Second Congress of ECRO, Reading (UK), 22to 24 September, 1976.     

Mechanisms for mixture suppression in olfactory receptors of the spiny lobster

The mechanisms by which the output of olfactory receptor cellsis suppressed, as can happen, for example, when receptor cellsare activated by stimulus mixtures, are ill defined. We showthat subthreshold concentrations of some odorants suppress theresponses of antennular (olfactory) chemoreceptors of the spinylobster to stimulatory odorants in a manner indicative of competitiveinhibition. The effect of these suppressive odorants on theresponse of other receptor cells is inconsistent with this hypothesis,allowing that non-competitive mechanisms also contribute toperipheral mixture suppression in the olfactory pathway of thespiny lobster.     

Membrane potential and its electrode-recorded counterpart in an electrical model of an olfactory sensillum

Insect receptor neurons are surrounded with auxiliary cells and encased in a hair. Their electrical activity is usually recorded with an electrode located at the tip of the hair. Analytical expressions giving the membrane potential along the sensory dendrite and the tip-recorded potential are derived for a neuron in steady-state conditions. They formally close the gap between theoretical models and experimental measurements, when transduction mechanisms and active membrane properties are not taken into account. It is shown that the tip-recorded potential reflects correctly the relative variations of the dendritic membrane potential as a function of stimulus intensity over a large range of parameters. The geometric and electrical characteristics of the sensillum that need be known to compute the dendritic membrane potential from the tip-recorded potential are given.     

A comparison of taste thresholds for sweet and astringent-tasting compounds in great apes

Taste responses to fructose and tannic acid were compared between great apes using the 'two-bottle test' with tests of brief duration. The taste thresholds for fructose were [10-20] mM in Pongo pygmaeus, [40-50] mM in Pan troglodytes, and [70-80] mM in Gorilla gorilla. Inhibition thresholds for tannic acid were [2.9-3.5] mM in Pongo and [2.9-5.9] mM in Pan. Gorillas apparently significantly preferred tannins at low concentrations ([0.59-5.9] mM) but rejected concentrations above [8.8-14.7] mM. These results are discussed in relation to the effects of phylogenetic inertia and biological adaptation.     

Toxicity of a mixture of polychlorinated organic compounds towards an unacclimated methanogenic consortium

Summary The toxicity of a mixture of polychlorinated aliphatic compounds towards an unacclimated methanogenic consortium was assayed in carrier-free, continuously-stirred batch experiments. Results obtained indicate that a 50 % inhibition of methanogenesis occurs at 3.3 mg toxic mixture per litre mixed liquor and that at 100 mg toxic mixture per litre mixed liquor, the inhibition of methanogenesis is complete.     

Hyperpolarizing receptor potentials in lobster olfactory receptor cells: implications for transduction and mixture suppression

Physiological studies of olfactory receptor cells have focusedon excitatory responses, in part because the evidence for inhibitoryresponses from extracellular recordings, although long-standing,has been equivocal. Intracellular recording from the olfactorycells of two species of lobsters revealed that small but concentrationdependentand repeatable hyperpolarizing receptor potentials could beevoked by a mixture of L-arginine, L-cysteine and L-proline,as well as by histamine. Large, depolarizing receptor potentialswere evoked in the same cells by a complex odor mixture. Simultaneousapplication of depolarizing and hyperpolarizing stimuli reducedthe magnitude of the evoked depolarization. These results implythat multiple, opposing transduction mechanisms are presentin single lobster olfactory receptor cells and reveal a noncompetitivemechanism for peripheral mixture suppression.     

An odorant derivative as an antagonist for an olfactory receptor

Different odorants are recognized by different combinations of G protein-coupled olfactory receptors, and thereby, odor identity is determined by a combinatorial receptor code for each odorant. We recently demonstrated that odorants appeared to compete for receptor sites to act as an agonist or an antagonist. Therefore, in natural circumstances where we always perceive a mixture of various odorants, olfactory receptor antagonism between odorants may result in a receptor code for the mixture that cannot be predicted from the codes for its individual components. Here we show that stored isoeugenol has an antagonistic effect on a mouse olfactory receptor, mOR-EG. However, freshly purified isoeugenol did not have an inhibitory effect. Instead, an isoeugenol derivative produced during storage turned out to be a potent competitive antagonist of mOR-EG. Structural analysis revealed that this derivative is an oxidatively dimerized isoeugenol that naturally occurs by oxidative reaction. The current study indicates that as odorants age, they decompose or react with other odorants, which in turn affects responsiveness of an olfactory receptor(s).     

Assessment of reliability of microarray data and estimation of signal thresholds using mixture modeling

DNA microarray is an important tool for the study of gene activities but the resultant data consisting of thousands of points are error-prone. A serious limitation in microarray analysis is the unreliability of the data generated from low signal intensities. Such data may produce erroneous gene expression ratios and cause unnecessary validation or post-analysis follow-up tasks. In this study, we describe an approach based on normal mixture modeling for determining optimal signal intensity thresholds to identify reliable measurements of the microarray elements and subsequently eliminate false expression ratios. We used univariate and bivariate mixture modeling to segregate the microarray data into two classes, low signal intensity and reliable signal intensity populations, and applied Bayesian decision theory to find the optimal signal thresholds. The bivariate analysis approach was found to be more accurate than the univariate approach; both approaches were superior to a conventional method when validated against a reference set of biological data that consisted of true and false gene expression data. Elimination of unreliable signal intensities in microarray data should contribute to the quality of microarray data including reproducibility and reliability of gene expression ratios.     

Detection thresholds for phenyl ethyl alcohol using serial dilutions in different solvents

Detection thresholds are typically obtained by presenting a subject with serial dilutions of an odorant. Many factors, including the solvent used to dilute the odorant, can influence the measurement of detection thresholds. Differences have been reported in detection thresholds for phenyl ethyl alcohol (PEA) when different solvents are used. In this study we used gas chromatography (GC) to investigate further the effect of solvent on odor detection thresholds. We used a single ascending method and serial dilutions of PEA in four different solvents--liquid paraffin (LP), mineral oil (MO), propylene glycol (PG) and dipropylene glycol (DPG)--to determine the PEA thresholds for 31 adult subjects. For each solvent, we prepared eight serial log base 10 step dilutions (1-8), with corresponding liquid PEA concentrations of 6.3 x 10(1)-6.3 x 10(-6) (% v/v). We found that the threshold concentrations for PEA in LP (step 6.5) and PEA in MO (step 5.5) were significantly lower (P < 0.05) than for PEA in PG (step 4.0) and DPG (step 4.0) We then used GC to measure both the liquid and gas PEA concentrations for the dilution steps prepared with LP and PG. Although there were large threshold differences in the liquid concentrations of PEA in LP and PG, the headspace gas concentrations of PEA were the same. These results demonstrate the importance of determining the gas concentration of odorant stimuli when performing odor threshold measurements, in particular when comparing odor detection thresholds obtained using different solvents.     

A chaotic neural network mimicking an olfactory system and its application on image recognition

1 Introduction A biological neural system is complicated and ef-ficient. People have tried for years to simulate it to per-form complex signal processing functions. For example,the artificial neural network is a kind of model derivedfrom a biological neural system. Most artificial neuralnetworks simulate some important features such as thethreshold behaviour and plasticity of synapses. However,they are primary simulations and still much simpler incomparison with specific biological neural…     

海洋生态资本价值结构要素与评估指标体系

针对海洋生态系统的特点,构建了海洋生态资本价值的结构要素及其评估指标体系。海洋生态资本的价值是指海洋生态资本的存量价值及其产生的收益流价值,包括各类海洋生态资源的现存量价值及其组成海洋生态系统整体而产生的生态系统服务价值。其中,海洋生态资源的现存量价值由海洋生物资源存量价值和海洋生境资源存量价值构成。海洋生态系统服务价值包含海洋供给服务、海洋调节服务、海洋文化服务和海洋支持服务等4个子要素的价值。     

Interaction of ricin and its constituent polypeptides with dipalmitoylphosphatidylcholine vesicles

The interaction of ricin and of its constituent polypeptides, the A- and B-chain, with dipalmitoylphosphatidylcholine (DPPC) vesicles was investigated. The A- and B-chain were individually associated with DPPC vesicles, although the intact ricin was not associated. The maximum binding and association constants were evaluated to be 154 micrograms per mg of DPPC and Ka = 2.30 X 10(5) M-1 for the A-chain, and 87 micrograms per mg of DPPC and Ka = 14.5 X 10(5) M-1 for the B-chain, respectively. The A-chain could induce the phase transition release of carboxyfluorescein from DPPC vesicles to a greater extent than the B-chain, whereas the release induced by the intact ricin was negligible. The evidence indicated that the hydrophobic regions on the A-chain and on the B-chain were buried inside when the two chains constituted the intact ricin molecule through one interchain disulfide bond, and that the A-chain caused perturbation of the DPPC bilayer at the phase transition temperature with consequent leakage of carboxyfluorescein.     

Thermal stability of human plasma fibronectin and its constituent domains

Human plasma fibronectin undergoes thermal denaturation with a midpoint between 62 and 64 degrees C. The irreversible transition is characterized by an increase in the intensity and wavelength of intrinsic tryptophan fluorescence, by an increase in the ability to enhance the fluorescence of 1,8-anilinonaphthalene sulfonate, and by an increase in the fluorescence polarization of covalently attached fluorescein. Addition of molecules which bind to fibronectin with high affinity, e.g. gelatin or heparin, had no stabilizing effect. This was attributed to the presence of multiple domains, all of which must be stabilized to prevent denaturation and aggregation. Further support for this interpretation came from studies of six different proteolytic fragments of fibronectin which collectively span almost the entire molecule. Cell-binding fragments derived from the central regions of the chain were least stable, exhibiting behavior similar to that of the whole protein. Fragments derived from the C-terminal regions were more stable by 7-8 degrees C, and those derived from the N-terminal region showed no thermal transition by any of the fluorescence parameters up to 85 degrees C in some experiments. A fluorescein-labeled 60-kilodalton gelatin-binding fragment which had been heated to 70 degrees C produced an increase in polarization upon addition of gelatin with Kd = 1.3 X 10(-7) M, similar to that of an unheated control. The intrinsic fluorescence spectra of the fragments had maxima which decreased progressively from 335 nm at the N terminus to 313 nm at the C terminus. These observations further elaborate the multidomain structure of human plasma fibronectin and reveal significant differences between the tertiary structure and stabilities of the various domains.     

13C NMR or coenzyme A and its constituent moieties.

Natural abundance 13C nuclear magnetic resonance spectra, in D2O, were obtained for the following: pantoyl lactone, beta-alanine, cysteamine hydrochloride, cystamine dihydrochloride, calcium pantothenate, beta-aletheine oxalate, pantetheine, pantethine, pantetheine 4'-phosphate, oxypantetheine 4'-phosphate, desulfopantetheine 4'-phosphate, N-acetyl-aminodesthiopantetheine 4'-phosphate, adenosine 2',5'-diphosphate, adenosine 3',5'-diphosphate, and coenzyme A. A complete assignment of the 13C chemical shifts in the NMR spectrum of CoA is reported. Comparison of spectra indicates that CoA most likely exists in an extended conformation.     

敲低CTCF腺病毒表达载体的构建及效果检测

目的:获得敲低效果较好的CCCTC结合因子(CTCF)的RNA干扰腺病毒载体,以便于研究其在肿瘤发生发展中的作用。方法:从已发表文献中获得CTCF敲低靶序列,合成2对含有小发卡结构的寡核苷酸序列,将其进行退火磷酸化后,分别克隆到腺病毒包装载体上;将重组质粒转染人胚肾293A细胞,收获腺病毒;将收获的腺病毒分别感染人胚肾HEK293细胞和靶细胞人肺腺癌细胞A549,通过RT-PCR和Western印迹鉴定相关基因的表达变化。结果与结论:RT-PCR和Western印迹鉴定显示构建的表达CTCF短发夹RNA(shRNA)的腺病毒载体能够有效抑制CTCF转录和蛋白水平,为后续CTCF的生物学功能和机制研究奠定了基础。