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Biomedical subjects

M Geier

Publications and source records attributed to M Geier.

17 recordsLinked to original sources
PubMed2002

L-lactic acid: a human-signifying host cue for the anthropophilic mosquito Anopheles gambiae.

Using a dual-choice olfactometer, the role of L-lactic acid was investigated in relation to host-seeking and selection by female Anopheles gambiae Giles sensu stricto (Diptera: Culicidae) mosquitoes in a Y-tube bioassay. L-lactic acid alone was not attractive, but it significantly augmented the attractiveness of CO2, skin odour and skin-rubbing extracts from humans and other vertebrates. Comparing the left and right index fingers of the same person, one could be made more attractive than the other by adding L-lactic acid to the air stream over that finger. The difference in L-lactic acid concentration between the two air streams offered to the mosquitoes fell within the natural range of variation emanating from a human hand, suggesting that L-lactic acid modulates intraspecific host selection by An. gambiae. Analysis of skin rubbings from various vertebrates (carnivores, chickens, primates, rodents, ungulates) indicated that humans have uniquely high levels of L-lactic acid on their skin. Tests with extracts of skin rubbings from cows and humans, with and without added L-lactic acid, suggest that naturally lower levels of L-lactic acid contribute to the lesser attractiveness of non-humans to An. gambiae s.s.

Animals↗
PubMed2001

The effect of lactic acid on odour-related host preference of yellow fever mosquitoes.

In a behavioural study we have investigated the role of lactic acid for the host preferences of yellow fever mosquitoes (Aedes aegypti) by comparing the attractiveness of rubbings from the hands of different human individuals and extracts obtained from skin rubbings from different mammals (Bos primigenius f. taurus, Capra aegagrus f. hircus, Felis silvestris f. catus and Homo sapiens). Certain human individuals were consistently more attractive to mosquitoes than others. Addition of lactic acid markedly increased the degree of attractiveness of formerly less attractive human odour samples and they were preferred over those which were originally the most attractive. There was almost no response to animal odour samples. In contrast to human samples, which contain a high amount of lactate, this compound could not be detected in samples from animals. When skin emanations from animals were combined with lactic acid, however, as many mosquitoes responded to odour samples of B. primigenius f. taurus and C. aegagrus f. hircus as did to human odours. All these data demonstrate that olfactory-based host preference of the anthropophilic mosquito A. aegypti is to a large extent due to differences in the amount of lactic acid in the odour samples.

Aedes↗
PubMed2000

An easy and accurate agarose gel assay for quantitation of bacterial plasmid copy numbers.

An assay for quantitation of plasmid copy numbers in bacterial cell cultures has been developed and validated. The method combines isolation of total bacterial DNA (including both plasmid and genomic DNA), running a series of twofold dilutions of total DNA in an agarose gel followed by ethidium bromide staining, and subsequent scanning of the gel picture negatives. We have developed a novel set of rules for integration of the scan data that allows us to achieve high assay precision, accuracy, and sensitivity. The assay validation results were as follows: intra- and interassay precision with %CV of 8.2-9.9 and 7.1-9.8%, respectively; ruggedness with %CV of 9.3-17.5%; spike recovery of 80-102%; and sensitivity of 1 plasmid copy per genome.

DNA, Bacterial↗
PubMed2000

Contribution of fatty acids to olfactory host finding of female Aedes aegypti.

Single carbon to 18 carbon n-aliphatic carboxylic acids were tested for their attractive effects on female Aedes aegypti in a Y-tube olfactometer. Each acid was tested over a wide range of concentrations together with L-(+)-lactic acid, the indispensable synergist for other attractive components emitted from human hosts. The attractiveness of lactic acid was significantly augmented when combined with fatty acids of chain length C(1)-C(3), C(5)-C(8) and C(13)-C(18), respectively. The addition of the C(9) and C(11) acids reduced the attractive effect of lactic acid. According to experiments showing a further increase of attractiveness by adding a second fatty acid, we suggest two groups of attractive carboxylic acids: C(1)-C(3) and C(5)-C(8). The addition of a fatty acid from one group to a mixture of lactic acid and an acid from the other group augmented the attraction to the mixture. Together with ammonia, a previously demonstrated attractant for Aedes aegypti, lactic acid plus two fatty acids from the different groups formed the hitherto most attractive, artificially composed blend. Two of the carboxylic acids which were found to be attractive together with lactic acid were also tested alone and in combination with CO(2), the major attractant in human breath. In both cases no attractive effect of the carboxylic acids could be observed.

Aedes↗
PubMed1999

Ammonia as an attractive component of host odour for the yellow fever mosquito, Aedes aegypti.

Behavioural responses of Aedes aegypti mosquitoes to ammonia were investigated in a modified Y-tube olfactometer. Ammonia was attractive in concentrations from 17 ppb to 17 ppm in air when presented together with lactic acid. Aqueous solutions of ammonia salts in concentrations comparable to those found in human sweat also increased the attractiveness of lactic acid. The role of lactic acid as an essential synergist for ammonia became further apparent by the fact that ammonia alone or in combination with carbon dioxide was not effective, even though the synergistic effect of carbon dioxide and lactic acid was corroborated. An extract from human skin residues, which attracts approximately 80% of the tested mosquitoes, contains both lactic acid and ammonia. The combination of these compounds, however, attracts no more than 45%, indicating that other components on human skin also play a role in host finding. Preparative liquid chromatography of the skin extract yielded three behaviourally active fractions which work together synergistically. Fraction III contains lactic acid as the effective principle; the compositions of the other two have not been clarified yet. The attractiveness of fraction I was augmented considerably when ammonia was added, whereas the effect of fraction II was not influenced by ammonia. These results suggests that ammonia is part of the effective principle of fraction II and contributes to the attractive effect of host odours.

Aedes↗
PubMed1999

Influence of odour plume structure on upwind flight of mosquitoes towards hosts

Both the concentration and the fine-scale plume structure of host odours influence the upwind flight of female mosquitoes Aedes aegypti (L.) (Diptera: Culicidae) in a wind tunnel. The attractive effects of carbon dioxide, human skin odour and l-(+)-lactic acid were tested in homogeneous, turbulent and filamentous odour plumes. With carbon dioxide, the percentage of upwind-flying mosquitoes increased with the increasing fluctuations in concentration that occur in turbulent and filamentous plumes. In homogeneous plumes, an initial activation effect was observed, but sustained upwind flights were less frequent than in the other plumes. The opposite was found with plumes of human skin odour: the highest number of mosquitoes flew upwind in the homogeneous plume, whereas in turbulent or filamentous plumes their numbers were significantly lower. Regardless of plume type, the percentage of upwind-flying mosquitoes increased with increasing concentrations of carbon dioxide and of skin odour. With l-(+)-lactic acid, the dose-response characteristics were not consistent, and the relative effects of different plume types upon upwind flights differed within different ranges of concentration. Even maximum reactions to this compound were modest compared with those to carbon dioxide or to skin odour. Our findings demonstrate (1) that mosquitoes are able to orient upwind under continuous odour stimulation and (2) that upwind flight is dependent upon plume structure in different ways for different host odour components.

Journal Article↗
PubMed1996

A search for components in human body odour that attract females of Aedes aegypti.

In a new type of wind tunnel, mosquitoes fly upwind towards host odour sources and towards human skin wash extracts obtained by rubbing the skin with a pad soaked in ethanol. We used this behavioural response as a bioassay to identify attractants in liquid chromatography fractions of such extracts. L-Lactic acid is a major constituent of skin wash extracts and it is a necessary component for the extract's effectiveness. As a single stimulus, however, L-lactic acid is only slightly effective. This indicates that the extract's high degree of effectiveness is based on a synergism of L-lactic acid and other odour components. The separation of the extract by liquid chromatography revealed three distinct regions of active fractions, only one of which contained L-lactic acid. The components of the other two regions have not yet been determined. A combination of fractions in these two regions together with L-lactic acid is as attractive as the complete extract.

Aedes↗
PubMed1996

Responses of antennal olfactory receptors in the yellow fever mosquito Aedes aegypti to human body odours.

Recent behavioural studies have demonstrated that human body odours which female Aedes aegypti find attractive exert their effects as complex mixtures of synergistically acting components. We have attempted to clarify the sensory mechanisms underlying the perception of these complex host odours by studying the responses of sensory cells underneath the A3-type sensilla of the mosquito antenna to both a human skin wash extract and the extract's active chromatographic fractions. The reaction patterns show that the host stimuli elicit responses from several types of receptor cells in a typical across-fibre pattern mode. It seems as if this is another case where the essential message in a biologically significant odour consists of a complex pattern of compounds that is encoded in an according complex response pattern by a cooperating set of primary sensory neurons of different odour specificities.

Aedes↗
PubMed1994

[Control system for a complete artificial heart based on a mean value model of the cardiovascular system].

The reliable use of an artificial heart in patients requires a control strategy that is able to monitor and realistically regulate the different loads of the cardiovascular system. The model outlined in the following article was created in an interdisciplinary environment with heart specialists and automation engineers. A control system for an artificial heart, in the form of a peristaltic pump, was created with the help of a load-dependent mean-value model of the cardiovascular system. The resistance of the arterioles in the systemic vascular system RA was chosen as the parameter for the adaptation of the cardiac output. This parameters can be easily and accurately estimated through the measurement of pressures and flows, and it is a very good indicator for the load of the organism. The results, obtained through simulation of the overall system, show a very fast and accurate adaptation of the cardiac output to the needs of the body at changing loads over a large range of workloads. At the same time, the protection of the lungs from excessive pressure is ensured by balance control of the outputs of the two halves of the artificial heart. The control system outlined here needs only pressure and flow sensors, which can be integrated into the pump housing.

Cardiac Output↗
PubMed1989

Accumulation of colony-stimulating factor 1 in amniotic fluid during human pregnancy.

Colony-stimulating factor 1 is a hematopoietic growth factor that increases 1000-fold in the uteri of pregnant mice, and its receptor is abundantly expressed in the human placenta. The concentration of colony-stimulating factor 1 in amniotic fluid at 33 to 40 weeks (9.0 +/- 1.1 ng/ml) was twofold higher than that at 16 to 18 weeks gestation (4.1 +/- 0.5 ng/ml), whereas maternal serum colony-stimulating factor 1 levels did not rise significantly. Colony-stimulating factor 1 was detected in endometrial extracts from pregnant women and levels were higher than those in extracts from nonpregnant women.

Amniotic Fluid↗
PubMed1986

Radioimmunoassay of relaxin in pregnancy with an analogue of human relaxin.

A radioimmunoassay for relaxin was developed in which a synthetic analogue of human relaxin was used as standard, tracer, and immunogen. Relaxin could not be measured in sera from men or non-pregnant women, but was measurable in pregnant women from the tenth week of gestation until term. Concentrations ranged from 0.19-1.18 ng/ml, with highest levels measured in the first trimester.

Animals↗