Meningeal cells influence cerebellar development over a critical period

Summary 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 scaf-fold 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.     

Destruction of meningeal cells over the newborn hamster cerebellum with 6-hydroxydopamine prevents foliation and lamination in the rostral cerebellum

Intracisternal injection of 30 micrograms 6-hydroxydopamine was used to destroy meningeal cells in the newborn hamster. After 20 or 30 days the cerebella of treated animals showed severe morphological alterations including: an absence of distinct folia anterior to the primary fissure; a disruption of lamination in the same region by the displacement of both Purkinje cells and cerebellar interneurons; a reduction in size and frequency of branching of the medullary tree with anomalous anterobasal branches and splaying; reductions in the area of the molecular layer, the total area occupied by granule cells, the length of the pial surface and the length of the Purkinje cell layer of 29, 21, 57 and 27%, respectively; disorganization of the radially organized glial scaffold by outgrowth of Bergmann glial fibers and displacement of their cell bodies, the Golgi epithelial cells, and anomalous orientation, polarity, size and branching frequency of Purkinje cell dendritic trees. These findings support our earlier hypothesis that the initial destruction of meningeal cells destabilizes the cerebellar surface (basal lamina and glia limitans superficialis) and disorganizes the glial scaffold, while the neuronal cerebellar malformations are secondary to this glial defect.     

Destruction of meningeal cells over the medial cerebral hemisphere of newborn hamsters prevents the formation of the infrapyramidal blade of the dentate gyrus.

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)     

The development of the radial glial scaffold of the cerebellar cortex from GFAP-positive cells in the external granular layer

Summary We have reinvestigated the origin and genesis of the radial glia of the cerebellar cortex in the hamster using three astroglial markers, vimentin, GFAP, and S-100 protein antibodies. On embryonic day 12 (E12), before the emergence of the external granular layer, the cerebellar anlage is traversed from the ventricle to the pial surface by a primordial radial glial scaffold which is vimentin-positive, but GFAP and S-100 negative. With the formation of the external granular layer on E13, a few GFAP positive cells appear among the unstained external granular layer cells. First seen within the germinal trigone and caudalmost part of the external granular layer, they then develop rostrally, amongst the cells of the expanding external granular layer, proliferating adjacent to the basement membrane. Beginning on E15, cells that are positive for the S-100 protein also appear within the external granular layer and the molecular zone. In later stages, S-100 is strongly expressed in Golgi epithelial cells, so we have considered it to be a marker for these cells. By contrast, the primordial radial glial cells were not stained with this marker. On the day of birth (E16/PO) many S-100 positive cells also appear at intermediate levels between the EGL and the Purkinje cell plate. They are unipolar and bear a single radial process that is directed towards the pial surface. The caudorostral appearance of S-100-positive cells firstly in the external granular layer, then in the molecular zone and finally in the Purkinje cell plate is identical to the temporal sequence of development of these layers, and suggests that S-100-positive cells are at first integral constituents of the external granular layer, but later descend through the molecular zone, to colonize the Purkinje cell plate. Here they proliferate and ultimately differentiate into Golgi epithelial cells, their numerous short radial glial processes traversing the molecular zone and the external granular layer to fill the interstices between the primordial radial glial fibres. At birth, S-100-positive Golgi epithelial cells have progressively colonized the Purkinje cell plate from the germinal trigone rostrally, up to a region midway between primary fissure and anterior medullary velum and, between P2 and P3, the rostralmost part of the cerebellum has become populated. GFAP- and S-100-positive cells remain in the external granular layer up to the end of the first postnatal week. In the same interval, the number of Golgi epithelial cells and Bergmann glial fibres increases rapidly in the expanding cerebellar cortex. Our results suggest that the majority of the Golgi epithelial cells are not translocated, morphologically transformed primordial radial glial cells, but derive from the external granular layer, translocate into the Purkinje cell layer and differentiate into the secondary radial glial cells which intercalate with the basal processes of primordial radial glia. The latter are thus supplemented by the former, providing a radially organized substrate allowing granule cells produced in the secondary proliferative zone of the EGL to migrate through the molecular zone into the IGL.     

Meningeal cells organize the superficial glia limitans of the cerebellum and produce components of both the interstitial matrix and the basement membrane

Summary We have investigated the factors controlling both the morphological transformation of glial processes into end feet 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 fissurai 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.     

Valproic acid-induced pancreatitis: 16 new cases and a review of the literature

Background Acute pancreatitis is rarely seen in children, and, in contrast to cases in adults, it is often drug induced. One possible medication is the antiepileptic drug valproic acid (VPA), which is commonly prescribed for generalized and focal epilepsy, migraine, neuropathic pain, and bipolar disorder. The common side effects associated with VPA are typically benign, but less common but more serious adverse effects may occur. These include hepatotoxicity, hyperammonemic encephalopathy, coagulation disorders, and pancreatitis. Since 1979, a few cases of pancreatitis induced by VPA have been published in the medical literature. Methods We mailed a questionnaire to all members of the “German Section of the International League against Epilepsy,” asking about VPA-induced side effects. We also reviewed the medical literature for VPA-induced pancreatitis. Results Fifty-three publications (90 patients) published from 1979 to 2005 were found. Our survey in Germany, however, yielded 16 cases of pancreatitis from 1994 to 2003 whose original files we could study in detail. None of these patients had been published previously. Conclusions The difference between 90 patients reported worldwide from 1979 to 2005 and the 16 new documented cases from only Germany over 10 years corroborates that the occurrence of this severe side effect is under reported.     

Development of astroglial cells in the proliferative matrices, the granule cell layer, and the hippocampal fissure of the hamster dentate gyrus.

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)     

A time course study of the alterations in the development of the hamster cerebellar cortex after destruction of the overlying meningeal cells with 6-hydroxydopamine on the day of birth

Summary This study is a chronological analysis of 6-hydroxydopamine-induced alterations in development of the hamster cerebellar cortex. This treatment destroys the overlying meningeal cells, the sequelae of which include (i) a thinning of the external granular layer over the folial apices and a thickening in the region of the prospective fissures, reflecting a retardation of the growth of the cerebellar cortex, accompanied by displacement of the normally superficialmost GFAP-positive external granular layer cells into deeper parts of the external granular layer; (ii) a retardation of multiplication of Golgi epithelial cells which colonize the rostral third of the Purkinje cell layer so that their numbers decrease in the rostralmost folia; (iii) disturbed morphological and biochemical differentiation of the Golgi epithelial cells and their processes, the growing radial Bergmann glial fibres which detach from the pial surface and branch within the external granular layer, causing a failure in endfeet formation at the superficial glia limitans, loss of characteristic radial morphology, with the adoption of a multipolar form, and normal or increased GFAP expression and decreased S-100 expression; (iv) fragmentation of the external granular layer beyond P5 to P7 with loss of the regular lamination and foliation of the cerebellar cortex, characterized by a completely random distribution of fragments of Purkinje cell layer, molecular zone and internal granular layer. We conclude that the destruction of meningeal cells interferes with the establishment and stabilization of both the external granular layer and the secondary radial glial scaffold composed of Golgi epithelial cells, whose proliferation, growth and differentiation is subsequently disturbed. The failure to stabilize the external granular layer and to form a normal secondary radial glial scaffold is, in turn, responsible for the disruption of the regular laminar deposition of the neurons of the cerebellar cortex.