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Biomedical subjects

A F Brown

Publications and source records attributed to A F Brown.

At least 55 records · Page 3Linked to original sources
PubMed1989

Microinterferometry of the movement of dry matter in fibroblasts.

We describe the use of interferometric microscopy coupled with a novel application of Sénarmont compensation for detecting and quantifying the distribution of dry matter in cultured cells. In conjunction with video techniques and digital image processing, a two-dimensional, calibrated map of the dry mass distribution in an isolated cell can be obtained and digitally recorded. We have called the technique Digitally Recorded Interferometric Microscopy with Analyser Shift (DRIMAS). The method greatly facilitates the automatic recognition of cells by computer. Recorded time-lapse sequences can be used to establish a database of the growth and motility of specific cells in given experimental conditions. Databases of this type can be analysed to reveal the patterns of growth and locomotory behaviour of individual cells. We describe a systematic method of obtaining parameters of cell size, shape, spreading, intracellular motility and translocation. Auto-correlations and cross-correlations between these parameters can be detected and quantified using time series analysis, revealing potential cause/effect relationships in the mechanisms of growth and motility. Besides characterizing the overall pattern of cell behaviour, these data can also yield information about the instantaneous pattern of intracellular motility. We describe the use of finite element analysis to reveal the dynamics of the intracellular transport of dry matter. This yields the pattern of the minimum flow of dry matter required to account for the changes in its distribution. Most of this flux is not associated with the movement of visible structures and possibly represents the transport of dissociated components of the cytoskeleton. In chick heart fibroblasts, surprisingly high velocities of nearly 2.0 microns s-1 were detected during the period of increased motility following tail detachment. The total kinetic energy associated with the dry mass flux is a single parameter, which characterizes the instantaneous motility of the cell. We found that the kinetic energy of intracellular motility can be several hundred times greater than the kinetic energy of translocation. Kinetic energy may prove to be a very informative single measure of intracellular motility for assessing the effects of malignant transformation, genetic manipulations, and other experimental treatments on the locomotory machinery of the cell.

Animals↗
PubMed1989

The polarization of fibroblasts in early primary cultures is independent of microtubule integrity.

Fibroblasts in culture apparently require an intact system of microtubules in order to adopt and maintain a polarized morphology. In contrast, the polarization of a number of epithelial cell types has been shown to be microtubule-independent. Reconciliation of these apparently contradictory data is difficult, however, because the epithelial cells were studied in short-term primary cultures while the fibroblasts were studied in secondary or longer-term cultures. To clarify the situation we have examined the effects of the microtubule-disrupting drugs, colcemid and nocodazole, on the polarization of a single cell type, the chick heart fibroblast (HF), maintained in both primary (1 degree) and secondary (2 degree) cultures. Immunofluorescence observations of both types of culture showed that in control medium the cells contained abundant microtubules, which were absent if the cells were cultured in medium containing either colcemid or nocodazole. The effects of microtubule-disrupting drugs on the polarization of the cells were quantified using two measures of cell shape, elongation and dispersion, both of which increase with increasing polarization. The results show that microtubule-disrupting drugs do not have a significant effect on the polarization of HF spreading in 1 degree culture but significantly reduce the polarization of HF spreading in 2 degree cultures. The effects of microtubule disruption on HF that had been maintained in 1 degree culture for 6 h, 24 h or 48 h were also quantified.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

The shape of cultured epithelial cells does not depend on the integrity of their microtubules.

Fibroblasts are thought to require an intact system of cytoplasmic microtubules in order both to adopt and to maintain a polarized morphology in culture, but whether the same is true for epithelial cells is not clear. We therefore compared the effects of the microtubule-disrupting drugs, colcemid and nocodazole, on the morphology of isolated embryonic chick heart fibroblasts (HF), corneal epithelial (CE) and epidermal epithelial (EE) cells. Immunofluorescence observations showed that all three cell types contained abundant microtubules when cultured in control medium and that these were absent from cells cultured in medium containing either colcemid or nocodazole. Qualitative observations suggested that these drugs inhibited the polarization of spreading HF but had no effect on the morphology of either of the epithelial cell types. We confirmed this observation quantitatively using two measures of cell shape, elongation and dispersion, both of which increase with increasing polarization. Our measurements show that microtubule-disrupting drugs significantly reduce both the elongation and dispersion of spreading HF but do not have a significant effect on either of these measures for the epithelial cell types. We quantified in a similar way the effects of microtubule-disrupting drugs on the morphology of all three cell types that had previously spread in control medium. We found that transferring spread HF to colcemid-containing medium significantly reduced both the elongation and dispersion of these cells but that the same treatment had no effect on these measures for either of the epithelial cell types. Our observations suggest that, unlike the fibroblasts, the epithelial cell types we have studied do not require microtubules either to adopt or to maintain a polarized morphology.

Animals↗
PubMed1987

A unified approach to analysing cell motility.

The quantitative analysis of cell motility in culture has several important functions. First, it gives a concise and accurate description of the motile process and can detect subtle differences in motility due to different genetic makeup or experimental conditions. Second, its objectivity means that results can be communicated precisely and used unambiguously to test hypotheses about motility. Third, it may be used to derive a mathematical model with the same statistical properties as the motile process and thus elucidate the mechanism of motility. In this paper, we introduce a general procedure for analysing cell motility in a wide variety of circumstances. We describe a pilot project for the analysis of simple geometrical data obtained from randomly moving fibroblasts. Finally, as an example, we show how an analysis of the translocation of the fibroblasts can lead to insights into the mechanism of motility that are arguably not obtainable by any other approach.

Animals↗
PubMed1986

Alignment of fibroblasts on grooved surfaces described by a simple geometric transformation.

The response of chick heart fibroblasts to grooved substrata was studied using microfabricated grooves and new measures of shape and alignment derived from the moments of cell shapes. Cell shape and alignment were measured on 23 different sets of regular, parallel grooves, which ranged in width from 1.65 to 8.96 micron, and in repeat spacing from 3.0 to 32.0 micron. The grooves were of constant depth, 0.69 micron. Digitized video images were analysed to extract the zero-, first- and second-order moments of the cell shapes, from which were calculated three measures of cell shape, and three measures of cell alignment. Regression analyses of the measures against parameters of the substratum such as groove width, repeat spacing and the ridge width between grooves show that ridge width is the main parameter affecting cell alignment (alignment being inversely proportional to ridge width), although groove width has a small additional effect. All the differences in cell shape between the different grooves can be summarized to a very good approximation as simple geometrical stretch transformations of the shapes of cells on planar surfaces. Our principal measure of cell alignment, paraxial elongation, is a measure of the necessary transformation. This finding has the interesting biological implication that the shape and orientation adopted by cells, in response to the grooves, are not governed by independent cellular mechanisms.

Animals↗
PubMed1985

Epidemiology of tick-borne diseases of cattle in Zimbabwe. III. Theileria parva group.

A survey of the occurrence of antibodies to Theileria parva using the IFA test in calves up to one year old at 244 localities in Zimbabwe revealed that the parasite occurred throughout the country although the prevalence of positive serological reactors was generally low. Outbreaks of theileriosis in high rainfall areas in the north, east and west of the country were attributed to Theileria parva bovis transmitted from cattle to cattle by Rhipicephalus appendiculatus. Outbreaks in high and low rainfall areas in the south and west of the country were attributed to Theileria parva lawrencei transmitted from buffalo to cattle by Rhipicephalus zambeziensis or R. appendiculatus. R. appendiculatus was not uniformly distributed in Zimbabwe. It occurred very commonly in foci in the commercial farming areas but was rare in most overgrazed communal farming areas. Outbreaks of disease attributed to T. parva bovis were recorded in some but not all the R. appendiculatus foci. The disease was present in areas infested with R. zambeziensis but it did not cause cattle deaths in these areas.

Animals↗
PubMed1985

Studies on the locomotory behaviour and adhesive properties of mononuclear phagocytes from blood.

Mononuclear phagocytes isolated from peripheral blood move slowly on albumin-, collagen- and fibronectin-coated glass, as judged by analysis of time-lapse film, although their movement is stimulated somewhat by serum. When a differential-adhesion method is used to purify monocytes from a crude mononuclear cell fraction it appears to select a particularly slow-moving sub-group. Despite their slow rate of movement (especially in comparison with neutrophils) monocytes move over and penetrate monolayers of endothelial cells, apparently without difficulty; they are, however, restricted to the upper surface of a fibroblast monolayer. Penetration of reconstituted collagen gels by freshly isolated monocytes was not observed but cultured monocytes, which spontaneously detached from the culture substratum over a 48 h period, did invade collagen gels. The adhesive properties of these cultured cells, measured in a flow-chamber assay, did not differ from freshly isolated monocytes purified on serum-coated dishes and detached with EDTA, and their invasive capacity does not seem to be a consequence of altered adhesive properties. The behavioural differences between monocytes and neutrophils are considerable, although both cell types have to leave the circulation and penetrate tissues in vivo.

Animals↗
PubMed1985

A simple chamber for observing microscopic specimens in both top and side views.

A method is described which permits the observation of microscopic specimens in both top and side views, a rapid change between the two views being possible without disturbing the specimen. The system requires the introduction of simple optical components into a culture chamber, does not restrict the types of microscopy that may be used, and does not necessitate modification of the microscope itself. The technique is discussed in relation to the study of tissue cells in culture, but may find applications in other areas.

Culture Techniques↗
PubMed1984

Epidemiology of tick-borne diseases of cattle in Zimbabwe. II. Anaplasmosis.

A survey on the incidence of antibodies to Anaplasma marginale in one- to three-year-old cattle was carried out in Zimbabwe using the capillary tube agglutination test. Antibodies were detected in all but one of 118 batches of sera collected from different localities throughout the country. There was no clear relationship between the frequency of occurrence of positive serological reactors, which was similar in both commercial and communal farming areas, and the incidence of clinical anaplasmosis. However, the highest numbers of cattle exhibiting positive reactions were generally recorded from the areas that were most heavily tick infested. There was evidence that wild ungulates may serve as reservoirs of infection as antibodies to A. marginale were detected in sera from buffalo (Syncerus caffer) and impala (Aepyceros melampus).

Anaplasma↗
PubMed1984

Neutrophil and monocyte behaviour in three-dimensional collagen matrices.

Neutrophil granulocytes migrate rapidly into three-dimensional gels of native collagen fibres, the leading front of the cell population moving approximately 100 micron/hour when the cells are unstimulated. Migration occurs in the apparent absence of adhesion to collagen fibres, as neutrophils do not adhere to collagen-coated glass and are unable to locomote over collagen-coated surfaces, probably due to lack of traction with the substratum. It would appear, therefore, that the mechanism of neutrophil movement through three-dimensional collagen gels is fundamentally different to the mechanism of migration over a planar substratum. Freshly isolated blood monocytes do not invade collagen gels. However, if monocytes are cultured on serum-coated plastic, approximately 80% of the cells spontaneously detach from the culture surface over a 48 hour period: these detached cells invade collagen gels, although at a much slower rate than neutrophils.

Animals↗
PubMed1983

Analysis and microbiological stability of an isosorbide 50% mixture.

Isosorbide mixture containing 50% w/v isosorbide and 5% w/v sorbitol is used in the treatment of hydrocephalus. The G.L.C. analysis of the mixture is described and its antimicrobial properties investigated. Results for the determination of lead in the mixture are given and the significance of the levels discussed with relevance to the treatment of infants.

Bacteria↗
PubMed1983

Neutrophil behaviour in the presence of protease inhibitors.

Neutrophil leucocytes circulate in plasma, which contains broad-spectrum antiproteases such as alpha-2-macroglobulin and alpha-1-antitrypsin, and move into environments in which antiproteases are present. Plasma antiproteases significantly reduce the adhesiveness of leucocytes in both static and dynamic adhesion assays, although their action does not seem to depend upon their anti-protease capacity. Contrary to expectation, leucocyte movement over surfaces and through both rigid and deformable three-dimensional matrices (micropore filters and collagen gels) is unaffected by antiproteases. This renders the idea that forward movement depends upon the proteolytic cleavage of redundant adhesion sites less probable. Various non-physiological antiproteases (chloromethyl ketones, soya bean trypsin inhibitor, and epsilon-aminocaproic acid are also ineffective in reducing locomotion, although they do cause minor changes in adhesiveness.

Cell Adhesion↗
PubMed1982

Neutrophil granulocytes: adhesion and locomotion on collagen substrata and in collagen matrices.

Neutrophil granulocytes (PMNs) adhere poorly to and are unable to locomote on collagen-coated glass; they are able to attach to and invade three-dimensional matrices of collagen fibres. Invasion is largely independent of adhesion to the fibres, does not occur by proteolysis of the gel, and is not affected by the presence of fibronectin or chondroitin sulphate. Invasion is reduced by increasing the concentration of collagen in the gel or by the presence of hyaluronic acid. It is proposed that in both these situations there is physical obstruction of PMN movement. The ability to locomote through tissues of very variable properties in vivo is important in the role of the PMN in inflammation.

Animals↗