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Biomedical subjects

A Czirók

Publications and source records attributed to A Czirók.

14 recordsLinked to original sources
PubMed2002

Multi-field 3D scanning light microscopy of early embryogenesis.

A computer-controlled microscopy system was devised to allow the observation of avian embryo development over an extended time period. Parallel experiments, as well as extended specimen volumes, can be recorded at cellular resolution using a three-dimensional scanning procedure. The resulting large set of data is processed automatically into registered, focal- and positional-drift corrected mosaic images, assembled as montages of adjacent microscopic fields. The configuration of the incubator and a sterile embryo chamber prevents condensation of the humidified culturing atmosphere in the optical path and is compatible with both differential interference contrast and epifluorescence optics. As a demonstration, recordings are presented showing the large-scale remodelling of the embryonic primordial vascular structure.

Animals↗
PubMed2001

Theory of periodic swarming of bacteria: application to Proteus mirabilis.

The periodic swarming of bacteria is one of the simplest examples for pattern formation produced by the self-organized collective behavior of a large number of organisms. In the spectacular colonies of Proteus mirabilis (the most common species exhibiting this type of growth), a series of concentric rings are developed as the bacteria multiply and swarm following a scenario that periodically repeats itself. We have developed a theoretical description for this process in order to obtain a deeper insight into some of the typical processes governing the phenomena in systems of many interacting living units. Our approach is based on simple assumptions directly related to the latest experimental observations on colony formation under various conditions. The corresponding one-dimensional model consists of two coupled differential equations investigated here both by numerical integrations and by analyzing the various expressions obtained from these equations using a few natural assumptions about the parameters of the model. We determine the phase diagram corresponding to systems exhibiting periodic swarming, and discuss in detail how the various stages of the colony development can be interpreted in our framework. We point out that all of our theoretical results are in excellent agreement with the complete set of available observations. Thus the present study represents one of the few examples where self-organized biological pattern formation is understood within a relatively simple theoretical approach, leading to results and predictions fully compatible with experiments.

Biofilms↗
PubMed2000

Proliferative and migratory responses of astrocytes to in vitro injury.

An in vitro "scratch-wound" model was used to evoke and investigate some astroglial responses to mechanical injury. The changes in the morphology, locomotion, and proliferation of injured astrocytes were analysed under culture conditions devoid of blood-derived cells responsible for activating the inflammatory cascade. The rate of proliferation was determined by immunocytochemical detection of BrdU-incorporating cells located next to or far from the wound. The motility of individual cells and the mass-advancement of cell-assemblies were monitored by computer controlled video-microscopy both in injured monolayers and in preparations of single cells or aggregates of astrocytes. The large sets of digitalized data allowed a reliable statistical evaluation of changes in cell positions providing a quantitative approach for studies on dynamics of cell locomotion. The results indicated that cultivated astrocytes respond to injury (1) with enhanced nestin immunoreactivity at the expanding processes, (2) with increased mitotic activity exceeding the rate caused by the liberation from contact inhibition, but (3) without specific, injury-induced activation of cell locomotion. Some advantages and drawbacks of "scratch-wound" models of astrocytic responses to mechanical injury are presented and discussed.

Animals↗
PubMed2000

Dynamics of cell aggregation during in vitro neurogenesis by immortalized neuroectodermal progenitors.

Early events of in vitro neuronal development were studied by inducing neuron formation in a neuroectodermal cell line, NE-4C/A3, derived from the embryonic forebrain vesicles of p53-deficient mice. Neuronal differentiation was initiated by treating the cells with all-trans retinoic acid (RA). By the second day of RA treatment compact cell aggregates were formed. The first signs of neuronal cell fate decision were revealed inside the aggregates. To elucidate the process of aggregate formation, the dynamics of cell clustering and the migration of individual cells were investigated by a novel computer-controlled videomicroscopic system. Besides real-time observation of cell motility, the system allowed statistical analysis of large sets of data providing quantitative evaluation of cell locomotion during an early, critical phase of RA induced neuron formation. The results showed that chemoattractants did not play a principal role in cell aggregation. Retinoic acid, on the other hand, was found to cause a rapid decrease in the average migratory velocity without changing the randomness of migratory routes. The data indicated that aggregation was facilitated by increased cohesion upon incident collision of randomly encountering cells. The resulting compact cell clusters provided the structural conditions for contact communication apparently needed for the neuronal differentiation of NE-4C/A3 cells.

Animals↗
PubMed2000

Bioconvective dynamics: dependence on organism behaviour.

Bioconvection occurs when a macroscopic nonuniformity of the concentration of microbial populations is generated and maintained by the directional swimming of the organisms. This study investigated the properties of the patterns near the onset of the instability and later during its evolution into a fully nonlinear convection regime. In suspensions of the bacteria Bacillus subtilis, which tend to swim upwards in a gradient of oxygen concentration that they create by consumption, we discovered that the dominant wavelength at the onset of the instability is determined primarily by the cell density and is influenced only weakly by the fluid depth. This observation contrasts strongly with previous observations on the gravitactic alga Chlamydomonas nivalis, in which the opposite dependence was found. Considerable differences were also found in the long-term evolution of the convection patterns. These results demonstrate the existence of readily distinguishable types of bioconvection systems, even at early stages of the instability. The observed differences are clearly and causally correlated with disparate reasons for upward swimming by these micro-organisms, leading to different geometric distributions of the density of the suspension.

Animals↗
PubMed2000

Locomotion and proliferation of glioblastoma cells in vitro: statistical evaluation of videomicroscopic observations.

OBJECT: The motility and doubling of human glioblastoma cells were investigated by means of statistical evaluation of large sets of data obtained using computer-aided videomicroscopy. METHODS: Data were obtained on cells in four established glioblastoma cell lines and also on primary tumor cells cultured from fresh surgical samples. Growth rates and cell cycle times were measured in individual microscopic fields. The averages of cell cycle time and the duplication time for the recorded cell populations were 26.2 +/- 5.6 hours and 38 +/- 4 hours, respectively. With these parameters, no significant differences among the cell lines were revealed. Also, there was no correlation in the cell cycle time of a parent cell and its progeny in any of the cultures. Statistical analysis of cell locomotion revealed an exponential distribution of cell velocities and strong fluctuations in individual cell velocities across time. The average velocity values ranged from 4.2 to 27.9 micro/hour. In spite of the uniform histopathological classification of the four tumors, each cell line produced by these tumors displayed distinct velocity distribution profiles and characteristic average velocity values. A comparison of recently established primary cultures with cell lines that had propagated multiple times indicated that cells derived from different tumors sustain their characteristic locomotor activity after several passages. CONCLUSIONS: It can be inferred from the data that statistical evaluation of physical parameters of cell locomotion can provide additional tools for tumor diagnosis.

Brain Neoplasms↗
PubMed1994

Generic modelling of cooperative growth patterns in bacterial colonies.

Bacterial colonies must often cope with unfavourable environmental conditions. To do so, they have developed sophisticated modes of cooperative behaviour. It has been found that such behaviour can cause bacterial colonies to exhibit complex growth patterns similar to those observed during non-equilibrium growth processes in non-living systems; some of the qualitative features of the latter may be invoked to account for the complex patterns of bacterial growth. Here we show that a simple model of bacterial growth can reproduce the salient features of the observed growth patterns. The model incorporates random walkers, representing aggregates of bacteria, which move in response to gradients in nutrient concentration and communicate with each other by means of chemotactic 'feedback'. These simple features allow the colony to respond efficiently to adverse growth conditions, and generate self-organization over a wide range of length scales.

Bacteria↗