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Biomedical subjects

L Gorski

Publications and source records attributed to L Gorski.

9 recordsLinked to original sources
PubMed2001

Configuration specificity in bisection acuity.

Crucial for the perception of form are the spatial relationships between the elements of a visual stimulus. To investigate the mechanisms involved in coding the distance between visual stimuli, thresholds for detecting whether a central marker accurately bisects a spatial interval were compared for a variety of configurations. Thresholds are best when all three members of the bisection configuration are identical. Performance is impaired, often by as much as a factor of two, when the outer delimiters of the spatial interval differ from the central marker in either length, orientation or contrast polarity. Illusory contours act poorly as borders for bisection by a central line. Disparity thresholds are not affected by orientation differences between test and flanking lines. Because in peripheral vision bisection acuity improves with practice, transfer of training between configurations can be used to gauge overlap of neural processing mechanisms. Transfer is complete only between patterns where all markers are similar, reduced when the outer markers differ by 20 degrees in orientation and absent when they are orthogonal. The dependence of bisection discrimination on similarity between the elements of the stimulus demonstrates that the encoding of spatial location and spatial extent are coupled to the coding of other stimulus properties.

Contrast Sensitivity↗
PubMed2000

A common step for changing cell shape in fruiting body and starvation-independent sporulation of Myxococcus xanthus.

Myxococcus xanthus can sporulate in either of two ways: at the end of the program of fruiting body development or after exposure of growing cells to certain reagents such as concentrated glycerol. Fruiting body sporulation requires starvation, while glycerol sporulation requires rapid growth, and since the two types of spores are structurally somewhat different, it has generally been assumed that the two processes are different. However, a Tn5 Lac insertion mutation, Omega7536, has been isolated which simultaneously blocks the development of fruiting body spores as well as glycerol-induced spores. Both sporulation pathways are blocked in the mutant within the process that converts a rod-shaped cell into a spherical spore. The Omega7536 locus is expressed at the time of cell shape change appropriate to each process, early after glycerol induction and late after starvation induction. On the C-signal response pathway, it is possible to identify positions for the normal function of the Omega7536 locus and for the inducing stimulus from glycerol that are unique and consistent with the observations. Although the two sporulation pathways differ in certain respects, it is shown that they share at least one step for changing a rod-shaped cell into a spherical spore.

Bacterial Proteins↗
PubMed2000

A sigma(54) activator protein necessary for spore differentiation within the fruiting body of Myxococcus xanthus.

Insertion of an internal DNA fragment into the act1 gene, which encodes one of several sigma(54)-activator proteins in Myxococcus xanthus, produced a mutant defective in fruiting body development. While fruiting-body aggregation appears normal in the mutant, it fails to sporulate (<10(-6) the wild-type number of viable spores). The A and C intercellular signals, which are required for sporulation, are produced by the mutant. But, while it produces A-factor at levels as high as that of the wild type, the mutant produces much less C-signal than normal, as measured either by C-factor bioassay or by the total amount of C-factor protein detected with specific antibody. Expression of three C-factor-dependent reporters is altered in the mutant: the level of expression of Omega4414 is about 15% of normal, and Omega4459 and Omega4403 have alterations in their time course. Finally, the methylation of FrzCD protein is below normal in the mutant. It is proposed that Act1 protein responds to C-signal reception by increasing the expression of the csgA gene. This C-signal-dependent increase constitutes a positive feedback in the wild type. The act1 mutant, unable to raise the level of csgA expression, carries out only those developmental steps for which a low level of C-signaling is adequate.

Adaptor Proteins, Signal Transducing↗
PubMed1998

Targeted mutagenesis of sigma54 activator proteins in Myxococcus xanthus.

Myxococcus xanthus DNA segments related to the highly conserved central sequence of sigma54 activator proteins have been investigated. A genetic technique designed to inactivate a gene that encodes such an activator by inserting a plasmid-borne internal fragment of the putative gene has been tested. When the internal fragment inserted by homologous recombination into the corresponding chromosomal locus, the expected duplication of the gene was observed by Southern hybridization. The single restriction fragment characteristic of each segment was replaced in the insertion strains by two hybridizing fragments, and one of these fragments hybridized with the kanamycin resistance gene of the plasmid vector. The combined molecular weights of the two fragments from the insertion strains were equal to the molecular weight of the original fragment plus the expected molecular weight contributed by the vector. In the duplication, one copy is expected to have an N-terminal deletion and the other copy is expected to have a C-terminal deletion. In most cases, the net result should be loss of activator function. If an activator is essential for vegetative growth, then it should not be possible to obtain the insertion strain by plasmid integration. Indeed, integrants for three of the segments were not obtained in repeated trials; however, a plausible explanation for these results other than lethality can be offered. Of the seven insertions validated by Southern hybridization, four strains exhibited defects in the development of fruiting bodies. One of these failed to develop in submerged culture, though it developed normally on agar. The other three showed arrested development of fruiting bodies, each at a morphologically different stage of aggregation. One of the mutants may be defective in the reception pathway of A-signal.

Bacterial Proteins↗
PubMed1996

Resected sigmoid carcinoma with 13-year metastasis-free interval. Sternal recurrence detected by immunoscintigraphy.

Colorectal cancers rarely present with bone metastases. Regular postoperative monitoring after resection by conventional imaging techniques and carcinoembryonic antigen levels aids physicians in identifying such tumor recurrences. However, some recurrences might elude detection by bone scan, computed tomography, and magnetic resonance imaging, and newer tests such as immunoscintigraphy using radioimmune-tagged monoclonal antibodies may be more diagnostic. Here we report a case, presenting with delayed recurrence at a rare bony site, in which application of immunoscintigraphy helped in the definitive detection of the tumor recurrence.

Adenocarcinoma↗
PubMed1991

Temporal sequence of the recovery of traits during phenotypic curing of a Cytophaga johnsonae motility mutant.

The lack of cell translocation and the resulting formation of nonspreading colonies of mutants of the gram-negative gliding bacterium Cytophaga johnsonae have been correlated with the loss of cell surface features of the organism. These cell surface traits include the ability to move polystyrene-latex beads over the cell surface and the ability to be infected by bacteriophages that infect the parent strain. In order to assess whether these traits reflect structures or functions that actually play a role in gliding, we studied a mutant (21A2I) selected for its inability to form spreading colonies; it is deficient in sulfonolipid, lacks bead movement ability, and is resistant to at least one bacteriophage. The provision of cysteate (a specific sulfonolipid precursor) restores lipid content and gliding to the mutant; hence, the lipids are necessary for motility. Growth with cysteate also restores bead movement and phage sensitivity. In order to determine the temporal relationship of these traits, we undertook a kinetic study of the appearance of them after addition of cysteate to the mutant. One predicts that appearance of a trait essential for cell translocation will either precede or accompany the appearance of this ability, while a nonessential trait need not do so. Sulfonolipid synthesis was the only trait that appeared before gliding; this is consistent with its established importance for motility. Bead movement and phage sensitivity first appeared only after gliding started, suggesting that the machinery involved in those processes is not necessary, at least for the initiation of gliding.

Adsorption↗
PubMed1990

Outer membrane polysaccharide deficiency in two nongliding mutants of Cytophaga johnsonae.

Phenol-extractable polysaccharides firmly associated with the outer membrane of the gliding bacterium Cytophaga johnsonae could be resolved by gel filtration in sodium dodecyl sulfate (SDS) or by SDS-polyacrylamide gel electrophoresis into a high-molecular-weight (H) fraction (excluded by Sephadex G-200) and a low-molecular-weight (L) fraction. Fraction L was rich in components typical of lipid A and the core region of lipopolysaccharide (P, 3-hydroxy fatty acids, and 2-keto-3-deoxyoctonate) and evidently was a lipopolysaccharide with a limited number of distal, repeating polysaccharide units, as judged by SDS-polyacrylamide gel electrophoresis. In relation to total carbohydrate, the H fraction was rich in amino sugar but poor in (possibly devoid of) the lipid A and core components. Two nongliding mutants were highly deficient in the H fraction; one of these was deficient in sulfonolipid but could be cured by provision of a specific sulfonolipid precursor, a process that also resulted in the return of both the H fraction and gliding, as well as the ability to move polystyrene latex spheres over the cell surface. Hence, the polysaccharide may be the component that is directly involved in motility, and the presence of sulfonolipids in the outer membrane is necessary for the synthesis or accumulation of the polysaccharide. This conclusion was reinforced by the fact that the second nongliding, polysaccharide-deficient mutant had a normal sulfonolipid content.

Cell Fractionation↗
PubMedDate not supplied

Changes in the concentrations of certain biochemical parameters in the peripheral blood during exercise and restitution after bloodletting.

The reported investigations were carried out in 18 men aged 19 to 23 years in whom 400 ml of whole blood was removed. On the day before bloodletting, one hour and 24 hours after it the studied men carried out a 10 minute exercise on a Monark cycle ergometer at a workload raising the heart rate to 170/min. Before the exercise, immediately after it and in the 30th minute of restitution venous blood samples were taken for determinations of the concentrations of total protein, albumins, free fatty acids, glucose, lactate and pyruvate, and the activity of lactic dehydrogenase, alanine aminotransferase and aspartate aminotransferase. During that time the acid-base equilibrium was determined in capillary blood. After bloodletting the concentrations of albumins, total protein and free fatty acids were decreased parallelly to haematocrit value decrease (p less than 0.05) and glucose concentration increased slightly (p less than 0.05). Enzyme activity was decreased slightly (p greater than 0.05). The partial oxygen pressure decreased, that of carbon dioxide increased, and hydrogen ion concentration rose. These changes were more pronounced after 24 hours than 1 hour after bloodletting. After submaximal exercise and in the 30th minute of restitution as well as 1 and 24 hours after bloodletting the changes in the concentrations of the biochemical parameters, enzyme activity and acid-base equilibrium were similar as after bloodletting.

Acid-Base Equilibrium↗