Your browser does not allow saving data (e.g. private mode): bookmarks will be lost when the tab closes.
Search PubMed
Keywords, author, journal, years — results from PubMed, abstracts with Russian translation, bookmarks in your browser.
Found: 5 464
Page 146 of 547-
Morphogenetic movements during the early development of the chick eye. An ultrastructural and spatial reconstructive study. B. Invagination of the optic vesicle and fusion of its walls.
Cell death as occurring in the developing optic cup of two to three-day-old chick embryos was investigated with the transmission electron microscope. Two circumscribed areas of cell death were found: The first appears during phase 1 (18 somites, stage 13-) in the middle of the invaginating optic vesicle wall; the second appears during phase 3 (24-28 somites, stages 15 and 16) in the optic stalk where it is connected with the diencephalon. Ultrastructural observations of dead cells with clumped nuclei are phagocytosed by neighbouring neuroepithelial cells. No invasion of macrophages from the mesenchyme was observed. Necrotic cells were occasionally found in the optocoel. After the invagination of the optic vesicle has been completed (at the end of the third day incubation) the layers of the optic cup meet, but there is no real cytoplasmic fusion. Some intercellular junctions are suggested to be precursors of gap junctions occurring in later stages. The role of changing cellular connections between lateral cell surfaces during invagination of the optic vesicle is discussed. Such a process could be responsible for the lengthening of the non-invaginating optic vesicle wall, i.e. the outer layer of the optic cup.
-
Ultrastructural development of raphe nuclei in the bat (Myotis myotis).
The development and ultrastructural features of the raphe nuclei of Microchiroptera Myotis myotis have been studied. Fetuses of different ages, newborn, young and adult bats were examined. Important fetal features were abundant mitoses and an incomplete cytokinesis between daughter cells. A medialward migration of reticular formation neurons was observed. The migration began in the third week of intrauterine life and continued through the sixth week of intrauterine life. In six-week-old fetuses it was possible to distinguish neuronal groups, although the delineation of borders for specific raphe nuclei was still arbitrary. Two types of neurons were distinguished at this stage and at all later stages, and both were present at all levels of the raphe complex. In the nine-week-old fetus the eight raphe nuclei were well-delineated. Newborn bats showed a great increase in cytoplasmic organelles and, also, in the myelination of neuronal fibers. No essential differences between young and adult bats were found.
-
Serialized on-grid lift-in sectioning for tomography (SOLIST) enables a biopsy at the nanoscale.
Cryo-focused ion beam milling has substantially advanced our understanding of molecular processes by opening windows into cells. However, applying this technique to complex samples, such as tissues, has presented considerable technical challenges. Here we introduce an innovative adaptation of the cryo-lift-out technique, serialized on-grid lift-in sectioning for tomography (SOLIST), addressing these limitations. SOLIST enhances throughput, minimizes ice contamination and improves sample stability for cryo-electron tomography. It thereby facilitates the high-resolution imaging of a wide range of specimens. We illustrate these advantages on reconstituted liquid-liquid phase-separated droplets, brain organoids and native tissues from the mouse brain, liver and heart. With SOLIST, cellular processes can now be investigated at molecular resolution directly in native tissue. Furthermore, our method has a throughput high enough to render cryo-lift-out a competitive tool for structural biology. This opens new avenues for unprecedented insights into cellular function and structure in health and disease, a 'biopsy at the nanoscale'.
-
Proliferation, migration and invasion of human glioma cells exposed to antifolate drugs.
The present study describes the effects of 2 folate antagonists, methotrexate (MTX) and the lipophilic antifolate trimetrexate (TMX) on 2 permanent human glioma cell lines (GaMg and D-54Mg) grown as monolayers and as multicellular tumor spheroids. In addition, the effects of drug exposure on tumor cell invasion was studied using a three-dimensional organ co-culture system. In monolayer cultures, TMX was a more potent inhibitor of cell growth than MTX, especially towards the GaMg cell line. The 2 drugs, however, showed similar cytotoxicity as assessed by the plating efficiency assay. Reduced ability of directional migration of cells on a plastic surface was seen by either antifolate usually at concentrations to 10-fold higher than those exerting a cytotoxic effect in the plating efficiency assay. TMX was somewhat more potent than MTX as an inhibitor of spheroid growth. When tumor spheroids were exposed to MTX or TMX at concentrations that caused 65 to 70% inhibition of cell migration, there was a latent period of 4 to 5 days before inhibition of spheroid growth ensued. Invasion was investigated in a co-culture system, where tumor spheroids were confronted with fetal rat brain cell aggregates. Neither drug reduced tumor cell invasion, although histological examination revealed toxic effects both in GaMg and in D-54Mg spheroids. We conclude that spheroids from human glioma cells were less sensitive to the antifolates than monolayers. For both drugs a latency period was observed before inhibition of spheroid growth. The spheroids retained their ability to invade normal brain tissue when exposed to levels of folate antagonists inhibiting spheroid growth.
-
The lack of a structured blood-brain barrier in the onychophoran Peripatus acacioi.
Onychophorans are 'living fossils' frequently purported to have evolved from the same ancestor as the arthropods and annelids. In the CNS of Peripatus acacioi, beneath an outer acellular neural lamella, glial cells ensheath the cerebral ganglion and the nerve cords. These glial cells are, however, attenuated and rather few in number and, although they interdigitate with one another, they seem to lack intercellular junctions. Exogenous tracers penetrate between them and into the underlying neuropile, suggesting that there is no structural blood-brain barrier. Throughout the nervous tissue, extracellular spaces occur which contain banded collagen fibrils embedded in a matrix material. Thin glial cell processes, characterized by dense filaments, surround these regions and frequently form hemi-desmosomes with the extracellular matrix. The peripheral nerve cell bodies have a range of diameters; some have the characteristics of neurosecretory neurons. Granules in such neurons are produced by the Golgi saccules and associated fenestrated membranes which also possess many coated vesicles. Comparable granules are also found in axonal tracts, but no distinct peripheral neurohaemal areas have been found. Lysosomes are common in the nerve cell bodies and are frequently in the form of multivesicular bodies or large phagocytic vacuoles. Beneath the outer nerve cells lie many tracheae, arranged as a ring around the central neuropile which consists of glial processes, extracellular matrix, axons and nerve terminals. These nerve terminals occur throughout the central neuropile and are characterized by dense pyramidal presynaptic specializations and postsynaptic subsurface cisternae. The nervous system of Peripatus is relatively simple in its organization, in the lack of glial intercellular junctions and in the ready accessibility of substances from the external milieu.
-
s-Collidine as a buffering system for glutaraldehyde perfusion of the central nervous system.
-
Improvement of the electron microscopic detection of peroxidase activity by means of the silver intensification of the diaminobenzidine reaction in the rat nervous system.
For the detection of the peroxidase activity at the electron microscopic level, a recently developed post-intensification method is applied, which plates metallic gold onto the end-product of the diaminobenzidine (DAB) reaction. Ultrastructural analysis of rat hypoglossal neurons labeled with horseradish peroxidase (HRP) through axonal transport reveals that the method is highly specific and more sensitive than the classical HRP--DAB--OsO4 sequence. Gold grains of 2--15 nm in diameter are present in the HRP-containing organelles of the neuron, whereas other elements of the brain tissue do not contain metallic gold.
-
Ependymal tanycytes of the rabbit third ventricle: a scanning electron microscopic study.
-
From Human Pluripotent Stem Cells to Cortical Circuits.
Understanding the development of the human brain in relation with evolution is an important frontier field in developmental biology. In particular, investigating the mechanisms underlying the greatly increased relative size and complexity of the cerebral cortex, the seat of our enhanced cognitive abilities, remains a fascinating yet largely unsolved question. Though many advances in our understanding have been gained from the study of animal models, as well as human genetics and embryology, large gaps remain in our knowledge of the molecular mechanisms that control human cortical development. Interestingly, many aspects of corticogenesis can be recapitulated in vitro from mouse and human embryonic or induced pluripotent stem cells (PSCs), using a variety of experimental systems from 2D models to organoids to xenotransplantation. This has provided the opportunity to study these processes in an accessible and physiologically relevant setting. In this chapter, we will discuss how conserved and divergent features of primate/human corticogenesis can be modeled and studied mechanistically using PSC-based models of corticogenesis. We will also review what has been learned through these approaches about pathological defects of human corticogenesis, from early neurogenesis to late neuronal maturation and connectivity.
-
Membrane morphology of the vertebrate nervous system. A study with freeze-etch technique.