Notes: 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.

Notes: 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.

Notes: 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.