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DISCUSSION
Glial cells are structurally and functionally linked to neuronal tissues, including the optic nerve and retina. The transition of quiescent mature astrocytes to the activated phenotype represents one of the earliest and most dominant responses of the central nervous system to injury. Pathologically, the activated cells may be characterized by increased size and number, by altered cellular properties, such as upregulation of glial fibrillary acidic protein (GFAP), and by additional cellular changes that may cause or relieve neuronal impairment [4,6,7]. Such astrocytic changes have been found in the glaucomatous optic nerve and retina as well as in experimental glaucoma models [8,9].
Figure 2Details in dissection fragment a: retina on the face of optic nerve head; b: optic nerve head; c: lamina tissue including prelamina and postlamina; d: myelinated optic nerve fibers (20×)（略）
Figure 3 A:2nd passage of AST cells after FBS free selection. Morphological characters (arrows) showed typical starshaped with long extension processes; B: 1st passage of 2nd day growth LC cells with flat body of polygonal short processes (200×)（略）
In the optic nerve, glial cells include astrocytes, oligodendrocytes and microglia. Astrocytes are the major glial cells type in the nonmyelinated optic nerve head in most mammalian species. In the human optic nerve head, two subpopulations of astocytes are distinguished. Type 1A astroctyes are interspersed in the glial columns and at the edge of cribriform plates. They express GFAP but not neural cell adhesion molecule (NCAM). Type 1B astrocytes express both GFAP and NCAM. They are the major glial cell population in this region and are the primary cells involved in synthesis of the optic nerve head ECM during development and throughout life [10]. At the vitreal surface of the optic disc, which is lined with Type 1B astrocytes, is the source of the cells used for this study (see materials and methods). In our results, Type 1B astrocytes showed a starshaped morphology, and positive characterization will be shown in our next paper where were GFAP and NCAM positive. The results are consistent with those of Hernandez [11]. The method we used is economical and easy to perform because the astrocytes grow well in AGM without FBS while the LC cells cannot survive in this medium. The precise dissection of explant from ONH is quite important to get the purified cells.
The function of Type 1B astrocytes is to form the glial columns, surround blood vessels in the prelaminar region, form the cribriform plates in the lamina cribrosa and separate the sclera from the optic nerve in the insertion area. Under normal intraocular pressure, the astrocytes remain quiescent. In glaucoma, the lamina cribrosa undergoes significant deformation in response to changes in intraocular pressure (IOP), which generates biomechanical stress on astrocytes and other cell types of LC [12,13], leading to the reactive astrocyte phenotype, optic nerve head remodelling and loss of retinal ganglion cell axons. Histopathologic studies in human donor eyes also demonstrate that astrocytes undergo an activation process in glaucoma1 [14].
Cultures of adult human ONH astrocytes as a useful in vitro model have been reported in several studies. Several studies will be done using the cultured cells to simulate the physical stresses caused by elevated IOP. Such in vitro experiments will help us to understand the mechanisms involved in the remodelling of ECM in glaucoma and provide us a model with which to research medications for optic nerve protection in the future [1517].
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