Glia

doi: 10.1002/glia.440090101pmid: N/A

Ghooray, Ganesh T.; Martin, George F.

doi: 10.1002/glia.440090102pmid: 8244526

We have shown previously that rubrospinal axons grow around a lesion of their pathway in developing opossums and that a critical period exists for that plasticity. As a first step toward addressing the possibility that glial maturation and/or the development of an astrocytic response to lesioning contribute to loss of rubrospinal plasticity, we have studied the normal development of radial glia and astrocytes in the spinal cord of the opossum by immunostaining for vimentin (Vim) and glial fibrillary acidic protein (GFAP). Vim‐like immunoreactivity (Vim‐LI) was present in radial glia throughout the spinal cord at birth (12 days after conception), whereas GFAP‐like immunoreactivity (GFAP‐LI) was limited to cells of comparable morphology in the ventral part of the cervical cord. The subsequent appearance of GFAP‐LI followed ventral to dorsal and rostral to caudal gradients and by postnatal day (PD) 15, it was found in radial glia throughout the cord. At the same age, processes immunostained by either antibody had lost their radial orientation in the ventral horn of the cervical cord. The subsequent transformation from radial glia to astrocytes also followed ventral to dorsal and rostral to caudal gradients. By PD30, mature appearing astrocytes were immunostained by both antibodies at thoracic levels of the spinal cord, the levels lesioned in the plasticity experiments referred to above, and by PD41, they were found at all levels of the cord. Since rubral axons are able to grow around a lesion of the thoracic cord until PD26–30, there is a rough temporal correlation between the transition from radial glia to mature appearing astrocytes and the end of the critical period for plasticity. © 1993 Wiley‐Liss, Inc.

Ghooray, Ganesh T.; Martin, George F.

doi: 10.1002/glia.440090103pmid: 8244527

We have shown previously that rubral axons grow around a lesion of their pathway in developing opossums and that a critical period exists for that plasticity. The critical period begins when rubral axons first reach the level of the lesion and ends sometime between postnatal days (PD) 26 and 30. The aim of the present study was to examine the development of an astrocytic response to lesioning the spinal cord to determine if there is a temporal correlation between the development of such a response and the end of the critical period. The astrocytic response was examined immunohistochemically, 2 and 4 weeks after hemisecting the thoracic spinal cord, using an antibody to glial fibrillary acidic protein (GFAP). A response was first seen at PD21 in the 2‐week series. The response was relatively mild, however, and limited to the white matter. When the lesion was made at PD26. the response was still restricted to the white matter, but hypertrophied astrocytes were found at the gray/white matter junction and cystic cavities were present. When the lesion was made at PD41, the response had spread to the gray matter and it occupied a larger area rostral and caudal to the lesion than at earlier ages. The animals allowed to survive 4 weeks after lesioning were subjected to a second operation 4‐5 days before sacrifice so that Fast Blue could be injected bilaterally two to three segments caudal to the lesion. When the hemisection was made at PD15, a response was present in the ventral and ventrolateral funiculi, but not in that part of the lateral funiculus that contains rubrospinal axons. As expected from previous studies, rubral neurons were labeled contralateral to the lesion, suggesting that their axons had grown around it. When the lesion was made at PD21, the glial response was still limited to the white matter, but it extended into that part of the lateral funiculus that contains rubral axons. In spite of the presence of a glial response, rubral neurons were still labeled contralateral to the lesion. When the lesion was made at PD26, hypertrophied astrocytes were present at the gray/white matter junction and small cavities were noted at the lesion site. In such cases, there was no evidence for rubrospinal plasticity. An astrocytic response was not observed in the gray matter of the dorsal horn, an area used by rubral axons to grow around a lesion of their pathway, until well after the end of the critical period. We conclude that the initial development of a glial scar in the white matter after lesioning does not determine the end of the critical period for rubrospinal plasticity. Loss of rubrospinal plasticity correlates most closely with the appearance of hypertrophied astrocytes at the gray/white matter junction and the formation of cystic cavities.

Hatton, James D.; Finkelstein, Jeremy P.; Sang U, Hoi

doi: 10.1002/glia.440090104pmid: 8244528

While transplanted astrocytes migrate in specific patterns in therecip‐ient brains, it is not known whether native astrocytes behave similarly. The ability of normal astrocytes to migrate under non‐transplant condition was therefore explored. Native astrocytes were labelled in situ with fluorescent latex beads. These latex spheres were actively endocytosed by astrocytes in vitro, and it was therefore anticipated that these spheres would also be endocytosed by native astrocytes exposed to them. Labelling was accomplished by dissecting the pia mater away from a small region of the cerebral cortex and overlaying the area with Gelfoam containing fluorescent beads. After 2–4 h, the Gelfom was removed and the wound was cloesd. At the end of 2–4 weeks, manipulated brains were harvested for fluorescence microscopy. In this analysis, fluorescent polyspheres had been taken up by both pial fibroblasts and astrocytes at the pial‐glial margin. Labelled astrocytes (identified by glial fibrillary acidic protein (GFAP) staining) were neither hyperplastic nor hypertrophic. They were confined to the area of the original labelling site, and did not migrate either laterally across the pial margin or ventrally into the cortical layers. Knife wounding at the time of label application, either in the region of the label or distant from it, produced reactive astrocytes that were hypertrophic. These cells also did not migrate from the label site. These results suggest that astrocytes labelled by this method do not migrate in the absence of some transplant‐derived stimulus even when stimulated by local wounding. © 1993 Wiley‐Liss, Inc.

Trotter, Jacqueline; Crang, A. John; Schachner, Melitta; Blakemore, William F.

doi: 10.1002/glia.440090105pmid: 8244529

Immortalised lines of murine glial precursor cells expressing the neomycin resistance gene and a temperature‐sensitive mutation of the SV 40 T oncogene were established from cultures of oligodendrocytes and precursor cells infected with a replication‐incompetent, helper‐free retrovirus. At the permissive temperature (33°C), they could be continually propagated in vitro and cells were present expressing the 04 antigen specific for glial precursor cells and oligodendrocytes. At 38°C, where the expression of the T antigen is down regulated, cell division largely ceased. During early passage in vitro, limited differentiation to a more mature phenotype, as evidenced by expression of GFAP and the oligodendrocyte marker O1 was observed at both 33°C and 38°C. When transplanted into demyelinating lesions in the spinal cords of adult rats early passages of the lines yielded myelin‐forming oligodendrocytes and astrocytes. Cells from later passages of the lines although failing to synthesise myelin still associated specifically with the demyelinated axons. These experiments demonstrate the retention of physiological properties of these oncogene‐carrying glial cells when transplanted in vivo and suggest that such immortalised populations can be used for the isolation of molecules regulating glial cell function. © 1993 Wiley‐Liss, Inc.

Rubio, Nazario; Sierra, Angeles

doi: 10.1002/glia.440090106pmid: 8244530

Theiler's murine encephalomyelitis virus (TMEV) is known to interact with cells of the central nervous system (CNS). Here we report that, interestingly, it is a potent inductor of interleukin‐6 (IL‐6) in the CNS of infected animals and in pure cultures of astrocytes. Maximal IL‐6 gene transcription in glial cells, as detected by bioassay and ELISA, was observed at 6 and 24 h after infection. Astrocytes from both SJL/J and Balb/c (strains of mice susceptible and resistant, respectively, to TMEV‐induced demyelination) produced similar amounts of IL‐6, measured in tissue culture supernatants. These results indicate that although an immunomodulatory effect can be exercised by IL‐6 synthesized by astrocytes, it does not play a crucial role in immune‐mediated demyelination induced by TMEV. © 1993 Wiley‐Liss, Inc.

Nakamura, Yoichi; Iga, Kozo; Shibata, Taiho; Shudo, Masachika; Kataoka, Kiyoshi

doi: 10.1002/glia.440090107pmid: 7902337

By a Percoll density‐gradient centrifugation of rat hippocampal ho‐mogenate, We found a novel subcellular fraction (specific gravity ≈ 1.046 g/ml), besides synaptosomes (≈1.060 g/ml), which showed a high activity of Na+‐dependent glutamate uptake. The initial rate of the glutamate uptake in this fraction was as high as twice that in synaptosomes. Activities of choline acetyltransferase and high affinity choline uptake were, on the other hand, much lower. γ‐Aminobutyric acid uptake activity was nearly equivalent in both fractions. Electron microscopic observations revealed that the fraction was morphologically different from synaptosomal or myelin fractions, but mainly consisted of two different types of empty membrane vesicles; irregular (0.3−0.8 μm in diameter) and spheroid type (0.2 μm). The immunoreactivity to glial fibrillary acidic protein was appreciably high in this fraction. The marker enzyme analysis showed the fraction was rich in plasma membranes. On the basis of these results, the fraction is termed glial plasmalemmal vesicles(GPV). We analyzed kinetically the reaction of Na+ ‐dependent glutamate uptake by GPV comparing with that by synaptosomes. Km values for glutamate in GPV was 4.7 μM and Vmax was 33 nmol/mg/min, while in synaptosomes 11 μM and 17 nmol/mg/min, respectively. Hill coefficients of Na+ activation in GPV and synaptosome were 1.1 and 2.0, respectively. Thus, the mechanism or transporter molecule in glial cells for Na+‐dependent glutamate transport is likely to be different from that in neurons. © 1993 Wiley‐Liss, Inc.

Bartsch, Udo; Pesheva, Penka; Raff, Martin; Schachner, Melitta

doi: 10.1002/glia.440090108pmid: 8244531

We have analyzed the expression of the oligodendrocyte‐derived extracellular matrix molecule janusin (previously termed J1–160/180) in the retina and optic nerve ofdeveloping and adult mice using indirect light and electron microscopic immunocytochemistry, immunoblot analysis, and enzyme‐linked immunosorbent assay. In the optic nerve, janusin is not detectable in neonatal and only weakly detectable in 7‐day‐old animals. Expression is at a peak in 2‐ or 3‐week‐old animals and subsequently decreases with inceasing age. In the retina, expression inceases until the third postnatal week and then remains at a constant level. In immunocytochemical investigations at the light microscopic level, janusin was found in the myelinated regions of the nerve with spots of increased immunoreactivity possibly corresponding to an accumulation of the light microscopic level, janusin was found in the myelinated regions of the nerve with sports of increased immunoreactivity possibly corresponding to an accumulation of the molecule at the nodes of Ranvier. At the electron microscopic level, contact sites between unmyelinated axons, between axons, and glial cells, and between axons and processes of myelinating oligodendrocytes were immunoreactive. Cell surfaces of astrocytes at the periphery of the nerve and forming the glial‐limiting membrane, in contrast, were only weakly immunopositive or negative. In cell cultures of young postnatal mouse or rat optic nerves, oligodendrocytes and type‐2 astrocytes, but not type‐1 astrocytes were stained by janusin antibodies. In the oligodendrocyte‐free retina, janusin was detectable in association with neuronal cell surfaces, but not with cell surfaces of Muller cells or retinal astrocytes. Our observations indicate that expression of janusin in the optic nerve and in the retina is developmentally differentially regulated and that other cell types, in addition to oligodendrocytes, express the molecule. Since the time course of janusin expression in the optic nerve coincides with the appearance of oligodendrocytes and myelin and since janusin is associated with cell surfaces of oligodendrocytes and outer aspects of myelin sheaths and is concentrated at nodes of Ranvier, we suggest that janusin is functionally involved in the process of myelination. © 1993 Wiley‐Liss, Inc.

Kageyama, Glenn H.; Robertson, Richard T.

doi: 10.1002/glia.440090109pmid: 7503953

Topographically distinct populations of radial glial cells in the diencephalon and mesencephalon of neonatal rats and hamsters were transcellularly labeled with wheat germ agglutinin conjugated to horseradish peroxidase (WGA‐HRP) and with the lipophilic tracer DiI. A comparison of the histological distribution of the two tracers is suggestive of two different mechanisms of transcellular labeling. Intraocular injections of WGA‐HRP resulted in the uptake of exogenously applied WGA‐HRP by retinal ganglion cells, followed by anterograde axonal transport and exocytosis within the optic target nuclei. In addition to the transneuronal labeling, which is typical of such injections, we observed the transcellular labeling of the processes and somata of radial glial cells that were topographically associated with the terminal fields of the labeled axons. Similar transcellular labeling of radial glial cells associated with the axon terminal fields of the colliculogeniculate projection to the medial geniculate nucleus was observed following injections of WGA‐HRP in the inferior colliculus. The transcellular labeling within the radial glial cells was discontinuous and somatopetally concentrated, indicating the existence of a retrograde active transport mechanism within the radial glial processes subsequent to its uptake following release of tracer from axons. This type of labeling can be referred to as transcellular retrograde glioplasmic transport. In contrast, DiI was used as a tracer through its capacity to diffuse within the plasmalemma. Topographically distinct populations of radial glial cells were transcellularly labeled following placements of DiI in the retina, inferior colliculus, or dorsal thalamus of fixed brains. The radial processes of labeled radial glial cells consistently extended into regions that also contained labeled axons. It is likely that the transcellular radial glial labeling with DiI occurred via transmembranous diffusion. These data indicate that a close structural and functional relation exists between axons and glial cells in the developing brain. © 1993 Wiley‐Liss, Inc.