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Biomedical subjects

A S Curtis

Publications and source records attributed to A S Curtis.

At least 19 recordsLinked to original sources
PubMed1992

Making real neural nets: design criteria.

Neural nets may be assembled with living nerve cells in vitro to test theories about neural processing and the ways in which patterns develop in the nervous system, and to test ideas about plasticity and learning in processing systems. This may benefit the design of computer systems and prosthetic devices. Extracting information from such nets can be achieved by means of intracellular and extracellular electrodes and fluorescent dyes. Patterning of cells may be achieved using microfabrication techniques, and extracellular electrodes can be combined within the patterned substrate.

Humans↗
PubMed1992

Dendritic processing: using microstructures to solve a hitherto intractable neurobiological problem.

In vivo, intracellular recordings of mammalian brain stem motoneurones, followed by peroxidase staining and tridimensional reconstruction, suggest that the shape of the dendritic tree plays an important role in the processing of neural information. To test this hypothesis attempts were made to guide, in culture, the growth of neuritic branches of neurones dissociated from the hypoglossal nucleus of rat brain stem. This was performed using topographical and adhesive microstructures which were designed to control the shape of the neuritic tree. Guidance of the neuritic processes can be observed with small grooves engraved on quartz and plastic substrates, and simple shapes with few processes and bifurcations on each neurite could be obtained using adhesive microstructures. These procedures, which allow the shape of a neurone to be controlled, are very promising in the study, by means of classical electrophysiological methods as well as optical recordings, of the involvement of dendritic architecture in the processing of neural information.

Animals↗
PubMed1992

Modulation of adhesion of lymphocytes to murine brain endothelial cells in vitro: relation to class II major histocompatibility complex expression.

Adhesion of lymphocytes to mouse brain endothelial cells was studied after treatment of the endothelium with 1000 U/ml gamma interferon (IFN-gamma) for 1 h to 2 days. Adhesion was not significantly different from controls after 1 h but at 4 h and thereafter, adhesion increased in a time-related manner. IFN-gamma also increased the expression of class II major histocompatibility complex (MHC) and murine intercellular adhesion molecule-1 (ICAM-1) molecules on the endothelial cells. The level of expression of class II MHC molecules was related to the length of exposure to IFN-gamma. MAb blocking studies suggested that class II molecules were responsible for the IFN-gamma-induced increase in lymphocyte-endothelial cell adhesion. Transfection of a murine lung endothelial cell line with cDNA for the class II MHC molecule also produced a significant increase in lymphocyte-endothelial cell adhesion, suggesting that the class II MHC molecule may have a role in adhesion which is distinct from antigen presentation.

Animals↗
PubMed1992

Localised application of an activating signal to a cell: experimental use of fibronectin bound to beads and the implications for mechanisms of adhesion.

Small beads derivatised with fibronectin or with bovine serum albumin are allowed to attach to BHK cells in suspension at low ratios of beads to cells. In this way populations of cells bearing predominantly one bead per cell can be prepared. We show that the attachment of one bead per cell affects the adhesion and spreading of that cell on substrata, raising adhesion and increasing spreading if the signal molecule is fibronectin, decreasing these quantities if the bead bears BSA. The experiments are conducted in the absence of other sources of exogenous fibronectin and in some cases in the additional absence of endogenous sources. The effects are especially marked if the substratum is adsorbed haemoglobin on which control cells show little attachment or spreading. We further show by interference reflection microscopy and by scanning electron microscopy that the beads are found on the non-adhering side (uppermost or outer) of the cell when fibronectin-bearing beads are used, presumably because fibronectin will not attach to haemoglobin. The increased adhesion and spreading found in such cases must be attributed to an activation produced by the bead, which spreads to other parts of the cell and which activates a fibronectin-independent mode of adhesion.

Animals↗
PubMed1991

Cell guidance by ultrafine topography in vitro.

Laser holography and microelectronic fabrication techniques have been employed to make grating surfaces in fused quartz with ultrafine period (260 nm) in an attempt to mimic the topography of aligned fibrillar extracellular matrix (ECM), which, in the past, has been shown to affect the behaviour of cells in vitro and in vivo. The alignment of BHK cells, MDCK cells and chick embryo cerebral neurones on 260 nm period grating surfaces (130 nm grooves separated by 130 nm) of various depths (100, 210 and 400 nm) was examined. While all gratings aligned BHK cell populations, the degree of alignment was dependent on depth. The response of single MDCK cells to the grating patterns was both to align precisely to the direction of the gratings, and to elongate; only their elongation was depth-dependent. MDCK cells that were part of epithelial cell islands, and the outgrowth of neurites from chick embryo neurones, were mainly unaffected by the grating surfaces. It is clear that topography on this scale can control cell behaviour, but guidance of this type is strongly dependent on cell type and cell-cell interactions.

Animals↗
PubMed1979

H-2 restriction of contact inhibition of epithelial cells.

Medawar has suggested that the major histocompatibility gene complex (MHC) might be involved in the contact inhibition of movement shown by fibroblasts and epithelia. Contact inhibition of movement is that reaction of cells which stops the movement of one cell over another and thus leads to monolayering and other features of morphology typical of cells in culture and in vivo. By confronting epithelial outgrowths we have compared contact inhibition between syngeneic cells with that between allogeneic cells. Contact inhibition was more marked between allogeneic combinations than syngeneic combinations, when the genetic mismatch lay in certain parts of the MHC complex.

Animals↗
PubMed1979

The H-2 histocompatibility system and lymphocyte adhesion: interaction modulation factor involvement.

The effects of thymocyte interaction modulation factor on the adhesion of mouse allogeneic thymocytes and B-cells are reported. This glycoprotein, produced by short term cultures of thymocytes, has already been described as reducing the adhesion of syngeneic B-cells, leucocytes and macrophages. Adhesion was measured in suspension culture using the collision efficiency method. This paper reports that: 1. In addition to the syngeneic effect of thymocyte IMF in reducing adhesion of certain unlike cell types there is also an allogeneic effect in which an allogeneic T-IMF will diminish the adhesion of a thymocyte population, or still further reduce the adhesion of a B-cell population than would a syngeneic T-IMF. 2. Thymocyte IMFs were prepared from different congenic strains and tested on the adhesion of syngeneic and allogeneic thymocytes. When factor and cells were syngeneic or matched at any H-2 locus except H-2 D there was no effect on adhesion since it remained at the same value as in controls in their own IMF. But whenever factor and cells were mismatched at H-2 D there was a marked diminution in the adhesion of the cells. 3. Antibodies raised against specific thymocyte IMFs could be used to detect the presence of T-IMF binding to the surface of cells by immunofluorescence or immune cytolysis. These systems show that the antibodies against thymocyte IMF can be used to type the H-2 D type of a cell and that these factors are present at the surface of thymocytes and certain other cell types. They confirm that the thymocyte IMF is either in H-2 D product or is closely associated with H-2 D locus in its binding and action. They also show that the T-IMF antigen on non-lymphocytic types is produced by T-cells or thymocytes. 4. The general relevance of these results is discussed in relation to cell recognition phenomena.

Animals↗
PubMed1979

Cell surface lipids and adhesion. IV. The effects of trypsin on lipid turnover by the plasmalemma.

Trypsin treatment of intact cells or isolated plasmalemmae from embryonic chick neural retinae leads to an accumulation of lysophospholipids in the plasmalemmae. Trypsin was used at activities commonly used in cell disaggregation techniques. This accumulation appears to result from the decrease in acyltransferase activity in the plasmalemma produced by enzyme treatment. Plasmalemmal CoA ligase activity is not affected by trypsin treatment. Trypsinization has little effect on plasmalemmal phospholipase A2 activity. These results are discussed in relation to (a) the effects of trypsinization on cell adhesion, and (b) the theory that cells cannot adhere to lecithins because of their fluidity or surface-free-energy values. We propose that the effects of trypsinization on adhesion may in large part be due to the effects on other plasmalemmal proteins. Similarly the inability of cells to adhere to lecithin substrates is simply explained as being due to the lysolecithin that contacting cells release from these substrates.

Acyltransferases↗
PubMed1978

Cell adhesiveness and embryonic differentiation.

The aim of the investigation was to decide whether changes in cell to cell adhesiveness took place during embryonic differentiation. The technique of Curtis (1969) was used to measure the adhesive behaviour of several types of ectodermal, neural and mesodermal cells of the chick embryo at stages 7 and 12 of differentiation. Cells dissected from segmented mesoderm were found to be more adhesive than cells from unsegmented mesoderm. Cells from the ectoderm were more adhesive than those from the neural tissue, at both stages 7 and 12. Cells from both ectoderm and neural tissue became more adhesive between stages 7 and 12. It is concluded that an increase in adhesiveness may play a role in somite segmentation, but not in neural tube formation.

Animals↗
PubMed1975

Cell surface lipids and adhesion. I. The effects of lysophosphatidyl compounds, phospholipase A2 and aggregation-inhibiting protein.

Aggregation-inhibiting protein (AIP: Curtis & Greaves, 1965), which diminishes the adhesiveness of cells, particularly at low temperatures, is identified in the present paper as phospholipase A2 (EC. 3.1.1.4). Our reasons for this identification are because phospholipase activity parallels AIP activity on cell adhesion, and because various inhibitors and sera act in a parallel manner on adhesion in the presence of AIP or phospholipase. We suggest that the enzyme acts on adhesion by producing lysolecithin and other lysolipids in the plasmalemma. Addition of lysolipids diminishes cell adhesion in a manner similar to phospholipase A. Incubation of cells in Hanks' medium at 37 degrees C has a parallel effect. Conditions which would be expected to stimulate reacylation of lysolipids in the plasmalemma, i.e. incubation of cells in the external presence of CoA, ATP and a fatty acid, lead to a recovery or maintenance of adhesion after or during Hanks' incubation at 37 degrees C. All these results suggest that lipid components of the cell, probably in the plasmalemma, are of importance in adhesion. The results are discussed in relation to the long-standing controversy about the effects of low temperatures and trypsinization on cell adhesion, for phospholipase treatment of cells affects adhesion in a manner similar to trypsinization.

Acylation↗
PubMed1975

Cell surface lipids and adhesion. II. The turnover of lipid components of the plasmalemma in relation to cell adhesion.

The preceding paper showed that those conditions that ought to stimulate reacylation of lysolipids in cells can increase cell adhesions. Similarly we found that conditions that would be expected to lead to the accumulation of lysolipids in the cell surface diminish cell adhesion. This paper reports on the answers to the following questions. (1) Is reacylation of lysolipids in the cells stimulated by an external supply of CoA, ATP and a fatty acid? (2) Does this reacylation lead to the incorporation of exogenous fatty acid in the plasmlemma? (3) What range of fatty acids can be incorporated into the plasmalemma and into what compounds? (4) Does the plasmalemma contain the enzyme systems to effect this turnover, namely phospholipase A2, a CoA-ligase and an appropriate acyl transferase(s)? (5) Do lysolipids accumulate in the plasmalemma under conditions which diminish cell adhesion? We find that saturated fatty acids in the range C14--C18, and some unsaturated fatty acids are incorporated into the plasmalemmae of these neural retina cells. About 20% of the plasmlemma content of fatty acids can be turned over in 30'. Incorporation is mainly into phosphatidyl choline, serine and ethanolamine in both R1 and R2 positions. The plasmalemmae contain the enzymes to effect the turnover. Isolated plasmalemmae are active in this turnover. Incubation of the plasmalemmae with phospholipase A2 leads to an accumulation of lysolipids. Very low levels of phospholipase stimulate turnover, possibly endogenous phospholipase activity is the rate-limiting step in the system. These findings are discussed in relation to the possible mechanisms by which lipids might affect adhesion.

Acyltransferases↗