We have investigated the factors controlling both the morphological transformation of glial processes into endfeet and the deposition of extracellular matrix molecules into the overlying basement membrane by destroying meningeal cells over the hamster cerebellum by 6-hydroxydopamine administration on the day of birth. We report that within 24 h of destruction of meningeal cells, the concentrations of fibrillary collagens types I, III and IV in the glia limitans externa and the associated basement membrane molecules laminin, collagen type IV, and fibronectin are greatly diminished, resulting in the development of focal gaps in the basement membrane. The immunohistochemical integrity of the basement membrane is restored within 3 days over those surfaces of the folial apices where meningeal cells reappear. Likewise, the fibrillary collagens of the associated interstitial matrix are re-established in the same amounts as in controls. However, meningeal cells remain permanently absent from fissures and all extracellular matrix molecules tested disappear from rostral cerebellar folia covered by the anterior medullary velum. Moreover, the glial endfeet make up the superficial glia limitans only on folial apices, while they disappear from the fissural surfaces. In primary cultures, meningeal cells produce the fibrillary collagens type I, III, and VI, and the matrix molecules fibronectin and laminin, collagen type IV, nidogen, and heparansulphate proteoglycan. These findings indicate that meningeal cells (i) produce molecular components of both the interstitial matrix and the basement membrane, and (ii) are involved in the morphological transformation of glial fibres into the endfeet which constitute the superficial glia limitans.

The histogenesis of the hamster dentate gyrus was studied with light and electron microscopy and antisera against the astrocyte-associated antigens vimentin and GFAP, in order to follow the differentiation of radial glial cells and astrocytes. The formation of the stratum granulosum is preceded by the establishment of successive dentate matrices, which are formed by cells that leave the ventricular neuroepithelium and occupy positions above the fimbria (suprafimbrial), below the pial surface (subpial), and within the dentate hilus (hilar dentate matrix). The subpial dentate matrix invades the marginal zone of that region of the cerebral wall, where the stratum granulosum will later develop. From the beginning of its existence on embryonal day 13 (E13) up to its disappearance about postnatal day 7 (P7), it is characterized by a high content of GFAP-positive cells and mitoses. This indicates early gliogenesis in the dentate anlage, long before the appearance of the stratum granulosum. Many of the bipolar GFAP-positive cells are oriented parallel to the pial surface and have focal contacts to the pial basement membrane. The establishment of the subpial dentate matrix splits the primordial radial glial scaffold of the hippocampal/dentate anlage into two bundles: 1) the suprafimbrial bundle that retains its original radial position between ventricle and pial surface; and 2) the dorsal glial bundle that traverses the ventral tip of the pyramidal cell layer of future CA3. The latter is pushed dorsolaterally, away from the pial surface, by the enlargement of the subpial dentate matrix and, later, by the suprapyramidal blade. The latter emerges around birth as small radial columns of granule cells located between the bent basal parts of the ventralmost fibers of the dorsal glial bundle and the subpial dentate matrix. From the beginning of its existence it is traversed by unipolar "secondary" radial glial fibers that appear to originate from the subpial dentate matrix. Both the supra- and the infrapyramidal blades seem to elongate by the addition of postmitotic granule cells and "secondary" radial glial cells from the subpial dentate matrix to the growing end of the primordial stratum granulosum. The hilar dentate matrix that is localized in the prospective hilar region, inside the growing stratum granulosum, also contains glial cells that seem to be incorporated into the stratum granulosum. The dentate gyrus is demarcated from the CA1 region of the hippocampus proper by GFAP-positive cells that populate the hippocampal fissure, and that also originate from the subpial dentate matrix.(ABSTRACT TRUNCATED AT 400 WORDS)

Meningeal cells participate in the development of the cerebellum both by stabilizing the extracellular matrix of the pial surface and by organizing the radial glial scaffold and the lamination of the cerebellar cortex. In the present study we investigated possible influences of meningeal cells on the development of the dentate gyrus, whose ontogenesis has many similarities to that of the cerebellum. Meningeal cells were selectively destroyed by injecting newborn hamsters with 25 micrograms 6-hydroxydopamine (6-OHDA) into the interhemispheric fissure. Twenty-four hours postinjection (p.i.) the meningeal cells over the medial cerebral hemispheres were completely destroyed. Thirty days p.i. the infrapyramidal blade of the dentate gyrus was almost completely missing, while the suprapyramidal blade was hypertrophied, extending with its medial tip almost up to the medial surface of the cortex. In order to ascertain that this maldevelopment was caused by the destruction of meningeal cells, another group of hamsters was pretreated with normetanephrine (NMN) which inhibits the extraneuronal uptake of 6-OHDA into meningeal cells. In this group the meningeal cells were unaffected by the treatment, and the morphology of the dentate gyrus was normal 30 days p.i. of 6-OHDA plus NMN. When the meningeal cells were destroyed in later stages of development (postnatal days 1-5), alterations of the dentate gyrus could be induced only up to the fourth postnatal day; thereafter, 6-OHDA treatment left it unchanged. This indicates a critical period of meningeal cell influence that coincides with the period of existence of the subpial dentate matrix. Analysis of the time course of the defective development revealed that in the first 5 days p.i. 1) meningeal cells over the medial cerebral hemisphere were destroyed and removed, 2) the pial basement membrane over both the dentate anlage and the diencephalon thinned and ruptured, and the adjacent brain parts fused focally, 3) many cells of the subpial dentate matrix disappeared from their subsurface position, 4) the number of "immature" cells increased in the hilus and the subgranular zone of the suprapyramidal blade, 5) the suprapyramidal blade elongated and thickened considerably, while the infrapyramidal blade did not form. Beyond 5 days p.i. those parts of the pial surface of the dentate anlage that had not fused with the diencephalon were repopulated with meningeal cells. This reappearance of meningeal cells was accompanied by 1) the restitution of the normal morphology of the basement membrane, 2) the reappearance of neuronal and glial cells below the pial surface, and 3) the formation of fragments of the infrapyramidal blade which later developed a normal appearing lamination.(ABSTRACT TRUNCATED AT 400 WORDS)

We have investigated the influence of meningeal cells on the development of the cerebellum by destroying these cells with 6-hydroxydopamine in hamsters of different ages. The ensuing foliation and lamination disruption in the cerebellar vermis is attributed to a disintegration of the cerebellar surface and a disorganization of the glial scaffold of the cerebellar cortex due to a loss of meningeal-glial interaction in stabilizing the extracellular matrix at the glia limitans superficialis (v. Knebel Doeberitz et al. 1986, Neuroscience 17:409-426). The severity of these cerebellar defects is correlated with the ontogenetic stage at which meningeal cells are destroyed, being greatest after treatment at postnatal day 1 and decreasing thereafter until day 5 and beyond, when no abnormalities occur, although all meningeal cells are destroyed throughout. The absence of cerebellar defects after destruction of meningeal cells at day 5 or later is associated firstly with the end of the period of branching morphogenesis of the cerebellum when all folial primordia are established, and, secondly, with the maturation of the glia limitans superficialis. These findings indicate that meningeal cells stabilize the cerebellar surface and glial scaffold over a critical period that ends, when the pattern of cerebellar foliation is established, and when the glia limitans superficialis has reached a mature state. Beyond this stage glial end-feet alone are sufficient to maintain the epithelial integrity of the cerebellum.

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