Olfactory stimulation of blowflies by homologous alcohols

The response of the blowfly Phormia regina to stimulation by alcohols in the vapor phase has been investigated by means of an olfactometer which permitted quantitative control of stimulus concentration. The median rejection threshold was selected as a criterion of response. As was true in the case of contact chemoreception, the distribution of thresholds in the fly population is normal with respect to the logarithm of concentration. In terms of molar concentration the alcohols are rejected at logarithmically decreasing concentration as chain length is increased. Beyond decanol there is no further stimulation. When thresholds are expressed as pressures and plotted against saturated vapor pressures on logarithmic coordinates, the data fit a line the slope of which is not significantly different from 1; i.e., the thresholds vary directly with vapor pressure. Individual threshold values, however, deviate significantly from this line. and the deviation must be ascribed to other factors which have not as yet been identified. When thresholds are expressed as activities, all alcohols are equally stimulating. It appears that the limiting process of olfaction, at least in so far as the normal alcohols are concerned, may involve an equilibrium process. Conformity to this concept is most exact for intermediate members of the series.     

Taste sensitivity of the cotton leafworm, Spodoptera littoralis, to chemicals

Threshold values of acceptance and rejection for 16 sugars and 12 electrolytes were measured. Most pentoses, hexoses, di- and tri-saccharides are stimulating. Compounds with α-linkage are superior stimuli. Substitution in the sugar molecule causes an obvious change in its stimulating characteristic. The rejection thresholds of the larvae to electrolytes showed a higher stimulating effectiveness for either acids or hydroxides than for neutral inorganic salts. The cations in a uniform anion combination stimulated in an order which was mostly correlated to their ionic mobilities. The stimulating efficiency of aliphatic alcohols was found to increase with the increase of molecular weight. An inverse relation was found between the stimulating efficiency and the vapour pressure of the alcohols tested. The line describing the relation between the rejection thresholds and the chain length of alcohols showed an inflection near butanol with a molecular weight of 74.     

The limiting mechanism in tarsal chemoreception

Rejection thresholds of eight primary alcohols applied to the tarsal chemoreceptors of the blowfly Phormia regina Meigen and the ovipositor of Gryllus assimilis Fab. have been determined. Three different solvents for the alcohols have been used: water, ethylene glycol, and mineral oil. The comparative stimulating effectiveness of the alcohols assumes a different aspect with each different solvent. In oil the range of thresholds from methanol to octanol extends over less than one log unit as compared with the corresponding thresholds in water which extend over four log units. In glycol the thresholds extend over two and one half log units only. When water is employed as a solvent, the line which describes the relationship between threshold concentration and chain length of the compound exhibits a sharp break at or near butanol. No such discontinuity is evident when glycol or oil is employed as solvent. This is offered as evidence supporting the hypothesis that the limiting mechanism in tarsal chemoreception involves a two phase system whereby highly water-soluble compounds gain access to the receptor through an aqueous phase and the larger lipoid-soluble molecules chiefly through a lipoid phase. Additional facts which support this idea are gained from data which show that the inflection in the curve occurs at different points with different species of insects and is conspicuously absent in the case of man. When thresholds in aqueous solutions are converted from molar concentrations to activities, it is clear that the relation of equal physiological effect at equal thermodynamic activities does not apply here. The lower members of the series stimulate at progressively increasing activities up to pentanol and then at progressively decreasing activities. Furthermore, the ratio of water threshold to oil threshold exhibits no obvious agreement with the water/oil partition coefficients determined experimentally. These results indicate either that the limiting process of chemoreception in these insects does not depend upon the establishment of an equilibrium or that some kinetic effect is obscuring an underlying relationship which does so depend.     

An analysis of the relationship between solubility and stimulating effect in tarsal chemoreception

The rejection thresholds of the blowfly Phormia regina Meigen for a selected series of substituted aliphatic hydrocarbons have been determined and an analysis made of the effect on stimulation of increasing the number of like substitutions from one to two, of the interaction of different types of substituent, and of the position of the substituent in the molecule. The order of stimulating efficiency (reciprocal of rejection threshold) of the functional groups which have been studied is: Br > Cl ? CH₃ ? CHO > C=O > OH. There is a consistent decrease in stimulating effect following the introduction of a second hydroxyl group. The introduction of a second C=O has little effect. Introduction of a second halogen is generally followed by a decrease in threshold. Two different species of functional group, one of which tends to increase water solubility and the other to decrease it, tend to counter-balance each other. A single oxygen-containing functional group on the end of the molecule or two of these groups which are terminal reduce the stimulating effect less than when one or more of such groups are subterminal or located elsewhere within the molecule. Branching of the carbon chain decreases effectiveness. Sulfur and oxygen linkages also decrease effectiveness. In general, the length of the free alkyl group largely determines the stimulating effectiveness. Its power is modified to varying degrees by the nature of the attached polar groups. Of all chemical properties examined, solubility alone agrees consistently with the foregoing data. Threshold varies directly with the molar solubility of the compounds in water. The fact that the threshold values for individual compounds are frequently different from those which would be expected solely on the basis of the correlation between threshold and solubility in water suggests that other factors are also concerned in stimulation. These have not yet been identified.     

THE RELATIONSHIP BETWEEN CHEMICAL STRUCTURE AND THE RESPONSE OF BLOWFLIES TO TARSAL STIMULATION BY ALIPHATIC ACIDS

Using the technique of proboscis extension in antennectomized-labellectomized flies, the rejection thresholds of Phormia regina for 18 fatty acids and one mineral acid have been determined. The conclusions reached on the basis of these data may be summarized in the following terms: Tarsal stimulation by acids involves the summation of components from at least two sources. Of these the hydrogen ion is the most important. The other major factor is probably the anion rather than the undissociated acid. The stimulating power of the anions (or free acid molecules) increases with increasing chain length in both the mono- and dicarboxylic series, but the rate of increase decreases as the series is ascended. Acids containing 6 or more carbon atoms are not sufficiently soluble in 0.1 M sucrose to reach the threshold of rejection. Substitution of —H in the acyl grouping by —Cl, —OH, =O or —COOH, the presence of a C=C bond, or a shift from the trans- to the cis- configuration all diminish the effectiveness of the anion (or free acid). But since such alterations also augment the degree of dissociation and consequently the concentration of hydrogen ions, the net result is ordinarily a lowering of threshold in terms of the molar concentration required for rejection.     

The stimulating effect of glycols and their polymers on the tarsal receptors of blowflies

The rejection thresholds of Phormia regina Meigen for twenty-four glycols have been determined. A definite relationship between the concentration of the test material and the distribution of thresholds has been noted regularly in samples of flies selected at random from a population of known age which had been reared under standard conditions. The scattering of thresholds is normal with respect to the logarithm of concentration. Recalculation of the data of other workers reveals the same sort of relationship with other species of insects and the minnow Phoxinus. The underlying reason for the phenomenon is not known. The glycols in common with other series of homologous alipbatic compounds are rejected at logarithmically decreasing concentrations as the chain length is increased. In general the straight chain diols are more stimulating than the corresponding polyethylene and polypropylene glycols. This difference is related in some manner to the presence of ether linkages in the latter. Polypropylene glycols, with chains of three carbon atoms between the ether linkages are more stimulating than polyethylene glycols, where the spacing is -O-C-C-O-. Unipolymers are more stimulating than mixtures of homologues with the same average molecular weights. Polyethylene glycol 1540 is the largest molecule of measured molecular weight known to stimulate chemoreceptors. The introduction of a second terminal hydroxyl group into the straight hydrocarbon chain reduces the stimulating effect. Alcohols corresponding to the first three diols average about four times as stimulating as the latter while those corresponding to the higher diols average more than one hundred times as stimulating.     

Olfactory sensitivity and odor structure-activity relationships for aliphatic carboxylic acids in CD-1 mice

Using a conditioning paradigm, the olfactory sensitivity of CD-1 mice for a homologous series of aliphatic n-carboxylic acids (ethanoic acid to n-octanoic acid) and several of their isomeric forms was investigated. With all 14 odorants, the animals significantly discriminated concentrations as low as 0.03 ppm (parts per million) from the solvent, and with four odorants the best-scoring animals even detected concentrations as low as 3 ppt (parts per trillion). Analysis of odor structure-activity relationships showed that the correlation between olfactory detection thresholds of the mice for the unbranched carboxylic acids and carbon chain length can best be described as a U-shaped function with the lowest threshold values at n-butanoic acid. A significant positive correlation between olfactory detection thresholds and carbon chain length of the carboxylic acids with their branching next to the functional carboxyl group was found. In contrast, no such correlation was found for carboxylic acids with their branching at the distal end of the carbon chain relative to the functional carboxyl group. Finally, a significant correlation was found between olfactory detection thresholds and the position of the branching of the carboxylic acids. Across-species comparisons suggest that mice are more sensitive for short-chained (C(2) to C(4)) aliphatic n-carboxylic acids than other mammalian species, but not for longer-chained ones (C(5) to C(8)). Further comparisons suggest that odor structure-activity relationships are both substance class- and species-specific.     

Olfactory sensitivity for aliphatic aldehydes in squirrel monkeys and pigtail macaques

Using a conditioning paradigm, the olfactory sensitivity of three squirrel monkeys and three pigtail macaques for a homologous series of aliphatic aldehydes ( n-butanal to n-nonanal) was assessed. With only few exceptions, the animals of both species significantly discriminated concentrations below 1 ppm from the odorless solvent, and with n-butanal and n-hexanal individual pigtail macaques even demonstrated thresholds below 1 ppb. The results showed (1). both primate species to have a well-developed olfactory sensitivity for aliphatic aldehydes, (2). pigtail macaques to generally perform better than squirrel monkeys in detecting members of this class of odorants, and (3). no significant correlation between perceptibility in terms of olfactory detection thresholds and carbon chain length of the aliphatic aldehydes in both species tested. These findings lend further support to the growing body of evidence suggesting that between-species comparisons of the number of functional olfactory receptor genes or of neuroanatomical features are poor predictors of olfactory performance. Further, our findings suggest that olfaction may play an important and hitherto underestimated role in the regulation of behavior in the species tested.     

Olfactory discrimination ability of CD-1 mice for aliphatic aldehydes as a function of stimulus concentration

Using an operant conditioning paradigm, we tested the ability of CD-1 mice to discriminate between members of a homologous series of aliphatic aldehydes presented at four different concentrations. We found that the mice were clearly capable of discriminating between all odorant pairs when stimuli were presented at concentrations of 1, 0.01, and 0.001 ppm (corresponding to four, two, and one log unit above the highest individual detection threshold) with no significant difference in performance between these concentrations. In contrast, the animals generally failed to discriminate above chance level when stimuli were presented at 0.0001 ppm (corresponding to the highest individual detection threshold) although stimuli were clearly detectable. Further, we found a significant negative correlation between discrimination performance and structural similarity of odorants in terms of differences in carbon chain length. These findings suggest that an increase in stimulus concentration of only one log unit above detection threshold appears to be sufficient for recruitment of additional subpopulations of odorant receptors to allow for qualitative recognition of aliphatic aldehydes.     

A study of the parameters of electric stimulation on the dorsal hippocampus for the "after discharge", carried out with the aid of a current-operated telestimulator, in the rabbit supplied with permanent electrodes

Our purpose in this work has been to carry out experiment of electric stimulation of the dorsal hippocampus, by measuring exactly the quantity of stimulating current, expressed in mA, in order to ascertain the actual quantities of electric charges, expressed in microcoulombs and conveyed to the examined structure and able to cause "an after discharge". the optimum stimulation frequency involving supply of the lowest quantity of electric charges and such frequency is more or less equal to the frequency of discharge of the paroxysmal bioelectric activity (about 20 c/sec). The optimum length of the train of stimulation is very short, but non shorter than 1 sec; consequently the length of the train of stimuli of 2, 5 sec, corresponding to a current intensity inferior to 1 mA and to a sufficiently low quantity fo charges, is to be regarded as the optimum length. The optimum length of the single stimulus is very short too, but it cannot be too short, since, also in this case, the intensity of current necessary to reach the threshold for the "after discharge" would reach such values as to cause lesions in the stimulated structure; consequently the length of the single stimulus corresponding to 0, 4 msec is to be considered as to optimum length.     

REJECTION THRESHOLDS OF THE BLOWFLY FOR A SERIES OF ALIPHATIC ALCOHOLS

Series of concentrations of 15 aliphatic alcohols were presented in 0.1 M sucrose to the tarsi of antennectomized-labellectomized blowflies (Phormia regina Meigen). With the pri-n-alcohols the mean concentrations at rejection formed a Traube series. When the rejection thresholds for all the alcohols tested were compared with their boiling points, vapor pressures, molecular surface areas) molecular moments, water-cottonseed oil distribution coefficients, standard free energies, and activity coefficients, a very high degree of correlation was found in each case. It is concluded that the limiting process which was measured is concerned with the receptor cells rather than with some other element in the complex response. Stimulative power was evidently not dependent on osmotic pressure nor on rate of molecular diffusion in solution, and the correlation with vapor pressure was inverse. It is judged that surface energy relationships are concerned in stimulation, but the exact mechanism cannot be defined until more is known about the structure of the sensory surface and about the process of excitation. The physiological activity of the alcohols is related more closely to the ease with which they gain access to the cell than to their chemical interaction with cellular constituents.     

Olfactory discrimination of aliphatic odorants at 1 ppm: too easy for CD-1 mice to show odor structure–activity relationships?

Using an operant conditioning paradigm we tested the ability of CD-1 mice to discriminate between 25 odorants comprising members of five homologous series of aliphatic odorants (C4-C8) presented at a gas phase concentration of 1 ppm. We found (a) that all mice significantly discriminated between all 50 stimulus pairs that involved odorants sharing the same functional group, but differing in carbon chain length, as well as between all 50 stimulus pairs that involved odorants sharing the same carbon chain length but differing in functional group, (b) a significant negative correlation between discrimination performance and structural similarity of odorants in terms of differences in carbon chain length with the acetic esters and the 2-ketones, but not with the 1-alcohols, n-aldehydes, and n-carboxylic acids tested, and (c) that odorant pairs differing in functional group were significantly better discriminated than odorant pairs differing in carbon chain length. These findings demonstrate that CD-1 mice have excellent discrimination ability for structurally related aliphatic odorants, that correlations between discrimination performance and structural similarity of odorants are odorant class-specific rather than a general phenomenon, and that both carbon chain length and type of functional group play an important role for odor quality coding in mice.     

Validation of the hedonic threshold methodology in determining the hedonic rejection threshold

The hedonic thresholds methodology was recently proposed which allows for determination of two new sensorial thresholds, the compromised acceptance threshold and the hedonic rejection threshold (HRT). For a new methodology to be accepted by the scientific community, its ability to produce reliable results must be demonstrated. Thus, this study sought to validate this new methodology when used to calculate the HRT. In order to do so, the analytical performance indices of precision (repeatability, intermediate precision, and reproducibility), accuracy and robustness for the results for the HRT calculation were measured. The results of seven experiments demonstrated that the methodology possesses high repeatability, intermediate precision and robustness, and satisfactory accuracy and reproducibility. It was therefore concluded that the HRT determination methodology satisfactorily met the analytical performance criteria evaluated, therefore generating reliable results.

Practical applications

The hedonic thresholds methodology (HTM) has numerous applications, including the application of a more severe thermal treatment to obtain greater microbial or enzymatic inactivation, the determination of food shelf life based on its sensory acceptance, the reduction of specific, expensive ingredients in food formulations, reduction of ingredients that are harmful to health when consumed in excess (e.g., sucrose, sodium, and fat), determination of the maximum “defect” threshold that may be present in food and others. The HTM is a recently proposed methodology; therefore, the reliability of the values of the hedonic rejection threshold must be validated, calculated via the HTM. Reliability of the HRT results was confirmed when HTM validation was performed. Thus, the methodology can undoubtedly be applied for the intended purpose.     

Chain length selectivity during the polycondensation of siloxane-containing esters and alcohols by immobilized Candida antarctica lipase B

We have examined the chain length selectivity for a series of acyl donors by lipase B from Candida antarctica (CalB). CalB accepted aliphatic diesters of C4, C6 and C12 chain lengths equally. The introduction of a carbon–carbon double bond into the C4 esters dramatically lowered the rate constant associated with polymerization highlighting the role of geometry in catalysis; fumarate esters were polymerized at a reduced rate compared to the succinate esters, while the maleate esters were not polymerized above 5% over the course of 24 h. A disiloxane-containing diester impeded catalysis by CalB. We examined a series of vinyl siloxane esters and alcohols, and learned that the Z arrangement around the double bond stalled esterification by CalB completely. The distance between the ester carbonyl and the dimethylsiloxy group was shown to be an important factor in mediating catalysis. The rate constants were similar when the methylene spacer was 3, 4, or 5 units in length; beyond 6 methylene units, the rate constants increased. This has been tentatively attributed to the local reduction on the steric bulk when the larger siloxane moiety lies outside of the active site of the enzyme.     

Evoked-potential measurement of olfactory thresholds of laboratory mice (Mus musculus) to carboxylic acids

Evoked potentials recorded by implanted electrodes were usedto measure olfactory thresholds of unanesthetized laboratorymice (Mus musculus) to aliphatic carboxylic acids (formic acid,acetic acid, n-propionic acid, n-butyric acid, n-valeric acid,and n-caproic acid). The thresholds conformed to the typicalmammalian pattern, sensitivity to carboxylic acids increasingwith increasing chain length. The highest threshold was thatto formic acid, 7?10¹¹ molecules/cm³ of air; that to caproicacid was lowest, 1.1?10⁸ molecules/cm³.     

Redox state of glutathione and thioredoxin in differentiation and apoptosis

This study was organized by Professor Karl Folkers with the objective of finding derivatives of coenzyme Q which could be more effectively absorbed and would give better biomedical effects. In this series all the compounds are 2,3 dimethoxy, 5 methyl p benzoquinone with modified side chains in the 6 position. The modifications are primarily changes in chain length, unsaturation, methyl groups and addition of terminal phenyl groups. The test system evaluates the growth of serum deficient HL60, 3T3 and HeLa cells in the presence of coenzyme Q10 or coenzyme Q analogs. Short chain coenzyme Q homologues such as coenzyme Q2 give poor growth but compounds with saturated short aliphatic side chains from C10 to C18 produce good growth. Introduction of a single double bond at the 2' or 8' position in the aliphatic chain retains growth stimulation at low concentration but introduces inhibition at higher concentration. Introduction of a 3' methyl group in addition to the 2' enyl site in the side chain decreases the growth response and maintains inhibition. Addition of a terminal phenyl group to the side chain from C5 to C10 can produce analogs which give strong stimulation or strong inhibition of growth. The action of the analogs is in addition to the natural coenzyme Q in the cell and is not based on restoration of activity after depletion of normal coenzyme Q. The effects may be based on any of the sites in the cell where coenzyme Q functions. For example, coenzyme Q2 is known to decrease mitochondrial membrane potential whereas the analog with a 10C aliphatic side chain increases potential. Both of these compounds stimulate plasma membrane electron transport. Inhibition of apoptosis by coenzyme Q may also increase net cell proliferation and the 10C analog inhibits the permeability transition pore.     

用脑干电位的互相关函数客观估计听力阈值

将脑干诱发电位记录分为大小相等的两个子集均,求其互相关函数。互相关函数在原点附近的平均幅度作为估计听力阈值的参数,并通过实验得出表达该参数与阈上刺激强度关系的直线回归方程,从而求出听力阈值的估计公式。把三种阈上刺激强度下的参数值分别代入估计公式,平均结果作为听力阈值的估计。对8个有不同听力损失的病耳进行了估计,其结果与主观阈值平均相差4.6dB。     

Olfactory discrimination ability for homologous series of aliphatic alcohols and aldehydes.

We tested the ability of human subjects to distinguish between members of homologous series of aliphatic alcohols (ethanol to n-octanol) and aldehydes (n-butanal to n-decanal). In a forced-choice triangular test procedure 20 subjects per series were repeatedly presented with all 21 binary combinations of the seven stimuli and asked to identify the bottle containing the odd stimulus. We found (i) that as a group, the subjects performed significantly above chance level in all tasks but two with the alcohols and all tasks but four with the aldehydes, and thus were clearly able to discriminate between most of the odor pairs presented; (ii) marked interindividual differences in discrimination performance, ranging from subjects who were able to significantly distinguish between all 21 odor pairs of a series to subjects who failed to do so with the majority of tasks; and (iii) a significant negative correlation between discrimination performance and structural similarity of odorants in terms of differences in carbon chain length for both homologous series. This suggests that carbon chain length may be one of presumably several determinants of the interaction between stimulus molecule and receptor, and thus may be a molecular property affecting odor quality of aliphatic alcohols and aldehydes.     

Mechanisms of reflex bladder activation by pudendal afferents

Activation of pudendal afferents can evoke bladder contraction or relaxation dependent on the frequency of stimulation, but the mechanisms of reflex bladder excitation evoked by pudendal afferent stimulation are unknown. The objective of this study was to determine the contributions of sympathetic and parasympathetic mechanisms to bladder contractions evoked by stimulation of the dorsal nerve of the penis (DNP) in α-chloralose anesthetized adult male cats. Bladder contractions were evoked by DNP stimulation only above a bladder volume threshold equal to 73 ± 12% of the distension-evoked reflex contraction volume threshold. Bilateral hypogastric nerve transection (to eliminate sympathetic innervation of the bladder) or administration of propranolol (a β-adrenergic antagonist) decreased the stimulation-evoked and distension-evoked volume thresholds by -25% to -39%. Neither hypogastric nerve transection nor propranolol affected contraction magnitude, and robust bladder contractions were still evoked by stimulation at volume thresholds below the distension-evoked volume threshold. As well, inhibition of distention-evoked reflex bladder contractions by 10 Hz stimulation of the DNP was preserved following bilateral hypogastric nerve transection. Administration of phentolamine (an α-adrenergic antagonist) increased stimulation-evoked and distension-evoked volume thresholds by 18%, but again, robust contractions were still evoked by stimulation at volumes below the distension-evoked threshold. These results indicate that sympathetic mechanisms contribute to establishing the volume dependence of reflex contractions but are not critical to the excitatory pudendal to bladder reflex. A strong correlation between the magnitude of stimulation-evoked bladder contractions and bladder volume supports that convergence of pelvic afferents and pudendal afferents is responsible for bladder excitation evoked by pudendal afferents. Further, abolition of stimulation-evoked bladder contractions following administration of hexamethonium bromide confirmed that contractions were generated by pelvic efferent activation via the pelvic ganglion. These findings indicate that pudendal afferent stimulation evokes bladder contractions through convergence with pelvic afferents to increase pelvic efferent activity.     

Variation of acceptance thresholds in the blowfly by increasing sugar concentrations in the food

Summary Aduld blowflies,Phormia regina M., were raised on different concentrations of sucrose. The thresholds of the behavioral responses to tarsal stimulation were elevated in blowflies raised on high concentrations of sucrose. The relationship between the median acceptance thresholds and the raising concentration of sucrose was logarithmically linear. Two groups of experimental flies were prepared: (1) coated flies, in which only D-type chemosensory hairs could respond physiologically, and (2) treated flies, in which all chemosensory hairs except D-type hairs functioned physiologically. Proboscis extension responses were ascertained in both groups. Median acceptance thresholds for the coated and treated flies, respectively, were presumed to be logarithmically linear in relation to the raising concentration of sucrose. It was supposed that D-type sugar receptor impulses initiate mainly the proboscis extension responses under the 0.01 M sucrose threshold and that B-type sugar receptor impulses initiate the responses above the 0.01 M sucrose threshold. Median acceptance thresholds for whole labellar stimulation were elevated to 0.026 M sucrose in blowflies raised on 1.0 M sucrose. Median acceptance thresholds were again lowered in blowflies raised on sucrose of more than 1.0 M.This research was supported in part by ITO foundation and Scientific Research Fund from the Ministry of Education of Japan.