PubMed Health⌕ Search

Biomedical subjects

K Meller

Publications and source records attributed to K Meller.

At least 37 records · Page 2Linked to original sources
PubMed1984

Cyclic morphological changes of glial cells in long-term cultures of rat brain.

Brain cells from embryonic rats were dissociated with trypsin, cultivated under constant conditions in Falcon flasks, and studied for periods of one year or more. Antisera against glial fibrillary acidic protein (GFA) and myelin basic protein (MBP) were used to identify glial cell types. For scanning electron microscopical (SEM) observation an embedding method in resin was developed that allows good preservation of the fine ultrastructural features of the cultivated cells and precise characterization of the cell types. Under our culture conditions, after four subcultures and 8-10 weeks of cultivation, the following cell types can be distinguished. (a) Flat epitheloid cells. From an immunocytological point of view these cells form a heterogeneous population composed of GFA- and MBP-positive and negative cells. They are the precursors of the following cell types. (b) Astroglial cells. SEM observations show a characteristic network of radially orientated prolongations. 92% of these cells are GFA-positive. (c) Oligodendroglial cells with characteristic dichotomously dividing branches. Secondary and tertiary branches end in flat amoeboid prolongations. These cells are MBP-positive. After approximately six weeks the most prominent cells are the flat epitheloid cells. The astroglial cells originate continuously from the epitheloid cells during the whole cultivation time. The formation of oligodendroglial cells, on the other hand, takes place at relatively precise intervals of time (approximately every 20-30 days) over the entire cultivation period (of more than one year).

Animals↗
PubMed1983

Ultrastructural aspects of rapid-frozen, deep-etched and rotary-shadowed synaptosomes.

Isolated synaptic terminals were rapid-frozen with a liquid-propane jet, deep-etched, and rotary-shadowed replicas produced. The replicas show a three-dimensional view of the cytoplasmic components. Intraterminal mitochondria display a rough inner membrane with numerous stalked globular particles. Microfilaments connect the diverse organelles of the nerve terminal. The main cytoplasmic structure is a tubular membrane system, probably formed by the smooth endoplasmic reticulum (SER). Rapid-frozen synaptosomes reveal sparse profiles of synaptic vesicles in contrast to the current structural features shown by the techniques employing cryoprotectants and/or fixatives. The structural lability of these SER-profiles seems to be very high, to the extent that varying morphological features are observed in the same replica. It is proposed that the synaptic vesicles originate from cisternae of the SER, and that the synaptic vesicles and the SER are in close structural and functional relation. The morphological relationship of both structures to the cell membrane still remains unclear.

Animals↗
PubMed1983

A quantitative freeze-etching study on the effects of cytochalasin B, colchicine and concanavalin A on the formation of intercellular contacts in vitro.

The effects of concanavalin A (conA), cytochalasin B (CB), and colchicine acting on cell membrane-associated structures, such as surface receptors or submembranal cytoskeletal components, were studied in trypsin-isolated plexus cells reaggregated in vitro. Following reaggregation, these cells form intercellular contacts, i.e. a zonula occludens (ZO) and integrated nexus (gap junctions, GJ). In the control cultures the GJ occupied 4.7%, the tight junctions (TJ) occupied 14 microns/microns2 of the surface of the zonula occludens (ZO). All the drugs/lectins studied inhibit contact formation in a characteristic manner. ConA inhibits the formation of GJ (1% of the ZO) and causes 5 times more defective TJ strands than the controls. CB inhibits the assembly of the TJ (75% of the controls) and the GJ (1% of the ZO) when it is administered during the period of contract formation. Colchicine inhibits the formation of GJ (1% of the ZO) and produces 2.5 times more open-end strands of TJ than the controls. All effects are reversible with the exception that integrated GJ are not re-formed after colchicine administration. It is suggested that an intact interaction between surface receptors, intramembranous particles and associated cytoskeletal structures is necessary for remodelling cellular contacts.

Animals↗
PubMed1981

Effects of colchicine on gap junction formation during retinal neurogenesis.

Colchicine, injected into the amniotic cavity of 3 to 10 day-old chick embryos, has the following effects on the developing retina: 1. Cells in arrested metaphase accumulate in the ventricular portion of the matrix region. If colchicine is applied at the end of the first week of incubation, the kinetic migration of the cell nuclei is inhibited. 2. The cells lose their typical slender, bipolar shape to become ovoid to spherical. These morphological changes are more obvious when colchicine acts during the first week of incubation. 3. The formation of temporary gap junctions between the matrix cells of the retina occurs during the first week of development. When colchicine is administered around the 3rd day of incubation, the assembly of intramembranous particles (IMPs) during gap junctions formation is incomplete. These results suggest that an intact microtubular system within the submembranous cytoskeleton is essential for the assembly of these intercellular contacts.

Animals↗
PubMed1981

Effects of concanavalin A on developing ganglion cells in the retina of chick embryos.

The administration of concanavalin A (Con A) (50-200 microgram/egg) to chick embryos between the third and the seventh day of incubation has the following effects on the retina: (1) Con A causes the degeneration of a large number of ganglion cells and consequently the layer that should be formed by these cells is not present or is constituted only by a small number of ganglion cells. (2) The lectin seems to be effective only when it is administered during the postmitotic phase of the ganglion cells. (3) The degenerated cells are phagocytosed by the Müller cells in a manner similar to that occurring during the natural cell death in normal retinal development. (4) The differentiation of other retinal elements (photoreceptors, bipolar, amacrine and Müller cells) is not affected by the lectin administration. (5) The administration of Con A in later stages of development, even at ten times higher dosages (2000 microgram/egg), fails to affect retinal neurogenesis. It is suggested that Con A binding to receptor sites of the cell membrane affects the distribution or mobility of surface components producing an alteration in the mechanism by which the developing cells regulate positional information during retinal neurogenesis.

Animals↗
PubMed1979

The formation of gap and tight junctions between retinal pigment cells in cell cultures.

The reformation of the junctional complex of retinal pigment cells was studied after trypsin disaggregation and in vitro reaggregation. Control specimens show a zonula occludens (tight junction) with integrated gap junctions and very large macular gap junctions. Isolation after trypsination results in disaggregation of the large gap junctions and fragmentation of the tight junctions with disaggregation of their integrated gap junctions. After two to four days of incubation the restoration of the zonula occludens is complete. After approximately five days of incubation, large gap junctions are found with a patchy arrangement of particles similar to that seen in vivo.

Animals↗
PubMed1977

In vivo and in vitro formation of the junctional complex in choroid epithelium. A freeze-etching study.

The junctional complex of choroid epithelial cells was studied during in vivo formation, disaggregation after trypsin treatment, and in vitro reaggregation. The in vivo formation begins with the occurrence of amorphous patches of particles followed by the formation of small particulate rows and polygonal-ordered particle assemblies. Further arrangement of the zonula occludens continues with the confluence of particles and smooth contoured ridges. At the 9th day stage a fully developed zonula occludens has developed. In a subsequent step nexus become integrated within the tight junction formation. Disaggregation after trypsination results in fragmentation of the zonulae occludentes. Parts of the disassembling aggregates become incorporated in vacuoles indicating an endocytotic mode of "digestion". The in vitro reconstruction of the zonula occludens proceeds from remnants of the former zonula occludens. On the 3rd to 4th day of cultivation mature tight junctions are visible. In vitro integrations of nexus were observed during a later phase. On the 7th day, cultivated choroid epithelial cells reveal well differentiated junctional complexes consisting of continuous zonulae occludentes and integrated gap junctions.

Animals↗
PubMed1977

The development of membrane specializations in the receptor-bipolar-horizontal cell synapse of the chick embryo retina. A freeze-fracture study.

Retinae of chick embryos and chicks one to six weeks after hatching were examined in ultrathin sections and in freeze-etch specimens. The development of the synaptic contacts between receptor cells and bipolar cells starts at the end of the second week of incubation with the enclosure of the dendritic prolongations, invaginating receptor terminals accompanied by the appearance of electron dense material at the synaptic contact sites. Subsequently receptor terminals become filled with synaptic vesicles which surround the synaptic lamellae that appear on the 16th day of incubation. The application of the freeze-fracture technique demonstrates that the differentiation of the synaptic membranes continues into the first week post hatching. E-fracture faces of the presynaptic membranes are characterized by crater-like structures, called synaptopores. Their number is rather small during incubation and increases after hatching. In the P-fracture faces of the dendrites, which are enclosed by the receptor terminals, small particle aggregations appear on the 16th day of incubation. These small particle clusters increase by the apposition of further particles which become arranged in lines and bring out a lattice-like aspect. This arrangement of particles in the inner part of the cell membrane is the morphological expression of the maturation process. The significance of these aggregations as a postsynaptic receptor for neurotransmitters in excitatory cells is discussed.

Animals↗
PubMed1976

Scanning electron microscopic studies on the development of the chick retina.

Fixed retinae of chick embryos and chicks of the first week after hatching were fractured and examined with the scanning electron microscope. The matrix cells of the retina proliferate up to the beginning of the second week. The migrating cells are oriented in cell cords. This columnar organizaion prevails up to the development of the plexiform layers formed as a consequence of the outgrowth of the dendritic and axonal cell processes. Special attention was paid to the differentiation of the ganglion, bipolar and receptor cells, and the radial fibers (Müller cells). Two main morphological patterns are significant for the organization of the retina during neurogenesis: a)the cell to cell contacts of migrating cells and b)the spatial arrangement of Müller cells which could provide guidelines for migration of neuronal elements.

Animals↗
PubMed1975

Neuronal migration during the early development of the cerebral cortex: a scanning electron microscopic study.

Fixed cerebral vesicles of mouse foetuses were fractured and examined with the scanning electron microscope. This method provides a study of the three dimensional developmental features of the pseudostratified columnar epithelium up to the formation of the early cortex plate. Matrix cells are a cell population of homogeneous shape, however, mitotic cells are easily identified by their spherical form. The external surface of the brain is formed by the closely packed end feet of these cells covered by a basal membrane. The formation of the cortical plate is the result of a continuous cell migration in columnar arrangement towards the pia. Glioependymal cells extend along the whole brain wall and most likely provide guidance for the migrating cell cords. The formation of the so-called migratory zone is a consequence of the growth of the basal and the horizontal prolongations of emigrating cells. The significance of the cell to cell contacts for the neuronal migration processes is discussed.

Animals↗
PubMed1975

Changes in glia-neuron relationships in cell cultures of spinal ganglia caused by puromycin.

Dorsal root ganglia of chick embryos were cultured for one to four weeks on Maximow-slides. Puromycin was added to cultures for a pulse of 30' in a dose of 100 mug/ml medium. Particular interest was given to the ultrastructural features of the glia-neuron relations. Puromycin caused a shrinkage of the glial processes and consequently the continous glial envelope of the spinal ganglion neurons disappeared. These changes of glia-neuron contacts were reversible after a few days when puromycin was withdrawn from the medium. The newly formed glial sheaths around the neurons were comparable to those in untreated cultures and to those in vivo. The effects of an inhibition of protein synthesis caused by puromycin are discussed in relation to the effects on the cell motility, on the renewal of cell membranes and on the formation of cell contacts in nervous tissue.

Animals↗