The organization of astrocytes in organotypic mouse spinal cord culture: an electron microscope study

Measles virus antigen in macrophage/microglial cells and astrocytes of subacute sclerosing panencephalitis

In two patients with subacute sclerosing panencephalitis (SSPE) of 10 and 25 months duration we demonstrated by immunohistochemistry the presence of measles-virus nucleocapsid antigen (MVNA) in CD68+ cells and astrocytes of brain tissues. In both cases, CD68+ hematogenous monocyte/ macrophages and perivascular microglial cells (Mphi) were found infiltrating the brain parenchyma, and often partially or completely invested by perivascular reactive astrocytes expressing glial fibrillary acidic protein (GFAP). Mphi with cytoplasmic MVNA were often seen in the Virchow-Robin spaces and in close association with perivascular astrocytes, which often also contained MVNA+ intracytoplasmic inclusions. Reactive astrocytosis was more severe in the patient with long-standing illness, and a correspondingly elevated number of strongly GFAP+ MVNA+ or MVNA- perivascular binucleated astrocytes was observed. An uptake of MVNA+ cell debris by reactive astrocytes was evident in areas of white matter displaying extensive demyelination and necrosis. Taken together, these observations seem to indicate that the brain infiltration by Mphi carrying measles virus could represent one pathway of virus entry and dissemination in the central nervous system. Virus transfer to perivascular astrocytes via cell-to-cell contacts with infected macrophages is also suggested.

Some unusual responses of astrocytes to ghost tangles in a long duration case of juvenile Alzheimer's disease: an electron microscopic study

The ghost tangles (GTs) in usual Alzheimer's disease are separated into small bundles of abnormal straight filaments by many invading astrocytic processes lacking a basal lamina (BL). An electron microscopic study of GTs in the Ammon's horn of a case of juvenile Alzheimer's disease of 25 years' duration, however, revealed that only a small number of astrocytic processes had infiltrated the GTs, resulting in the GTs being composed of large bundles. Moreover, the majority of glial processes that had invaded or apposed GTs possessed an interrupted but still fairly well-developed BL with hemidesmosome-like profiles. Although pia-arachnoid cells are required for astrocytes to form a continuous BL, astrocytes can have a segmental BL on their surface facing even empty intercellular spaces within the brain parenchyma. The much greater frequency and better development of the GT-associated BL in our case indicate that the GT filaments somehow increased the ability of astrocytes to form a BL. On the other hand, the scarcity of GT-invading astrocytic processes implies that many of the glial processes that had once penetrated GTs had been withdrawn, with the result that GTs escaped expectable endocyto-phagocytosis by astrocytes.

Astrocytes alter their polarity in organotypic slice cultures of rat visual cortex

The ultrastructure of astrocytes in an organotypic slice culture of the rat visual cortex was investigated using ultrathin sections and freeze-fracture replicas. After a culture period of 9-15 days, a glial scaffold formed that separated the bulk of the slice neuropil from the medium and the underlying plasma clot. However, the glial cells and processes did not build a dense barrier but allowed the outgrowth of neurites. A basal lamina covering the medium-oriented surface of the astrocytes was not found. In freeze-fracture replicas, orthogonal arrays of particles (OAP) were characteristic components of astrocytic membranes. The OAP density in membranes bordering the medium was 35 +/- 13 OAP/microns 2, corresponding to 2.5% of this membrane area; the OAP density in membranes within the slice neuropil was 22 +/- 12 OAP/microns 2, corresponding to 1.4% of this membrane area. Although the difference was significant, it was greatly reduced when comparing OAP densities in endfoot and non-endfoot membranes in vivo. Another node of polarity was recognized in astrocytes of the organotypic slice culture. In membranes of astrocytes bordering upon the medium, the density of non-OAP intramembranous particles (IMP) was clearly higher (1130 +/- 136 IMP/microns 2) than in membranes of astrocytes in the center of the slice (700 +/- 172 IMP/microns 2). This pronounced IMP-related polarity was observed neither in vivo nor in cultured astrocytes. The present study suggests, together with data from the literature, that the distribution of astrocytic OAP across the cell surface is influenced by the existence of a basal lamina and neuronal activity, and that astrocytes possess a more remarkable plasticity of membrane structure than previously suspected.

Transformation of cells of astrocyte lineage into macrophage-like cells in organotypic cultures of mouse spinal cord tissue

Phagocytic cells on the surface of the explants and their relationships to the surface were examined morphologically and immunocytochemically in organotypic cultures of mouse spinal cord tissue. Phagocytic cells were rounded, had smooth cytoplasmic surfaces and were occasionally closely apposed to underlying cells by junctional complexes. These cells contained dense bodies, vacuoles, smooth and coated vesicles, a few microtubules and bundles of intermediate filaments similar to astroglial filaments. The superficial layer of the explant which usually consisted of astroglial cell bodies and their processes, sometimes contained immature neuroepithelial cells with numerous free ribosomes, centrioles, Golgi apparatus, microtubules and infrequently, intermediate filaments. Overall, the cells resembled poorly differentiated astrocytes. Numerous dense bodies and coated vesicles were observed in some of these immature cells as well as in astrocytes in the surface layer of the explant. Cytoplasmic bridges between immature cells within the explant and phagocytic cells on the surface were observed. Immunocytochemistry revealed the presence of glial fibrillary acidic protein within these surface phagocytic cells. It thus appears that immature neuroepithelial cells of astrocytic lineage are capable of transforming into macrophage-like cells in organotypic culture.

Cell and tissue culture of the central nervous system: recent developments and current applications

A survey of methods for cell and tissue culture of the central nervous system (CNS) is given. This includes a brief historical outline and description of methods in current use. Recent methodological improvements are emphasized, and it is shown how these are applied in modern neurobiological research. Both monolayer cell cultures and three-dimensional organ culture systems are widely used, each having advantages and limitations. In recent years, there has been considerable improvement of culture for prolonged periods in chemically defined media. Brain tissue from a wide spectrum of species have been used, including different types of human brain cells which can be propagated for several months. At present, these culture systems are employed for dynamic studies of the developing, the adult and ageing brain. It is possible to select neurons and the different classes of glial cells for culture purposes. Cell culture of the CNS has given new insights into the biology of brain tumours. Culture systems for experimental tumour therapy in vitro are also available. Recently, it has been shown that organ cultures of brain tissue can be used as targets for invasive glioma cells, enabling a direct study of the interactions between tumour cells and normal tissue to take place.

Fine structure of astrocytic processes during serum-induced demyelination in vitro

Astrocytic changes were examined ultrastructurally during serum-induced demyelination in organotypic cultures of mouse spinal cord tissue. The myelin sheaths of most myelinated fibers showed myelin breakdown. Sheet-like astrocytic processes completely and closely surrounded the demyelinating fibers and frequently engulfed myelin fragments. These processes were virtually devoid of glial filaments or microtubules and contained flocculogranular material, round and elongated cisterns and glycogen granules. Penetration of the myelin sheath by astrocytic processes was only rarely found. The cell body of the astrocyte was never insinuated between the myelin sheath and the axon. No endocytosis of myelin droplets via coated pits on the surface of astrocytes was observed. In comparison with phagocytic mononuclear cells in vivo, astrocytes in vitro dispose of myelin debris less actively. Astrocytes in serum-induced demyelination probably play a nonspecific but fundamental role during degeneration in segregating damaged nerve fibers from surrounding neuronal elements.