Structure and behavior of rat primary and secondary Schwann cells in vitro

The structure and motility of isolated rat primary (I) Schwann cells (SC) have been compared to that of subcultured (II) SC during and after mitotic stimulation. I SC contain myelin components which persist for 2 weeks in serum-free medium while they rapidly disappear in medium containing serum and high glucose concentration. These components were never detected in II SC. Both I SC and II SC after their mitotic phase are spindle-shaped, contain many intermediate and actin filaments, have no basement membrane but show intense migratory and undulatory activities. Rare fibroblasts in I cultures are recognized by their extremely variable shape, the presence of Thy 1.1 antigen in their membrane and their intense edge ruffling alternating with abrupt translocation. In contrast, I SC movements consist of intracellular translocation of nuclei along SC processes, which retract and extend constantly, and in slow rhythmic undulation episodes (2.3 ± 0.2/min) alternating with migration at 135 ± 50 μ/h. The total number of these episodes per day in serum-free medium is rigorously identical for different cells (166.3 ± 0.2) and this uniformity of frequency suggests a genotypic basis. Cycles, consisting of an undulation episode followed by a resting interval, have mean durations of 8.6 ± 4.1 min and a sharp peak of occurrence at 6 min, with exponential distribution of the longer periods. Motility of II SC is considerably inhibited during mitotic stimulation by cholera toxin and a pituitary extract while SC phenotype has changed to a flat multipolar cell with prominent Golgi and ribosomes. Migration is reduced to 24 ± 2 μ/h and only 2% of the SC show pulsations of the same periodicity as the I SC undulations. A dramatic increase in pulsation frequency occurs 6–12 h after removal of mitogenic factors when 80% of II SC start pulsating twice as fast for 2–3 days. When mitoses cease, SC quickly recover their SC phenotype with rhythmic undulations while migration speed increased to 92 ± 20 μ/h. Thus, in spite of dramatic modification of shape, structure and behavior during mitotic stimulation, SC subsequently recover their unique motility pattern which might be essential for their myelinating functionPeer reviewe

Jókai regényének kétrészes, szines, magyar filmváltozata

[grafika] Ernyei S. J

The effects of the off-road vehicle on the soil cohesion and internal friction

The movement of the off-road vehicle on a deformable track such as soil and grass modifies the soft soil profile and mechanical properties - cohesion and internal friction - of the soil. It is assumed there is a dynamic physical change in the tire-soil interface, the cohesion and internal friction soil properties being also not constant. In our paper we summarize the most important methods which can be applied to compute the towed force in tire-soil interface situations. We have carried out many in situ soil shearing tests with different soil moisture contents and in different soil depressions. We conducted the soil shearing test before and after the vehicle movement, which means there are different soil compactions. Based on our soil shearing tests we can say that the soil cohesion increase depends on the soil depth. The value of the increase depends on the soil compaction and the soil depth. The soil internal friction hardly decreases and its changing value is less than that of soil cohesion. The soil cohesion and shearing values decrease as a function of soil moisture content. The higher values of both soil cohesion and soil shearing are characteristics of compacted soil. The results of our tests were as follows: soil cohesion and soil shearing values are not constant with different types of soil. Both of them change as a function of the soil moisture content and soil depth. The equation for the towed force which occurs during the tire-soil interface is more precise if the soil cohesion would be a function of the soil moisture content and the soil depth in the equation. Soils are multifarious, hence our results are accurate for the above soil conditions and test methods