COCULTURES OF MENINGEAL AND ASTROCYTIC CELLS - MODEL FOR THE FORMATION OF THE GLIAL-LIMITING MEMBRANE

The glial-limiting membrane at the border of the central nervous syste m (CNS) consists of glial endfeet covered by a basal lamina. The forma tion of the glia limitans seems to be controlled by adjacent meninges but only little is known about this interaction. In the present study astrocytes and meningeal cells were investigated in vitro to see if co cultures of these cells can serve as a suitable model for the differen tiation of the glial-limiting membrane and can be used to define the c onditions under which the glial-limiting membrane develops. The follow ing observations were made in cocultures of meningeal and astrocytic c ells of two-day-old rats: (i) epithelioid astrocytes were transformed into stellate cells; (ii) single colonies of proliferating epithelioid astrocytes were generated; (iii) the area around these colonies becom es devoid of meningeal cells, which seem to form a circular border aro und the astroglial islands; (iv) from the glial colonies long thin gli al processes grow towards the surrounding meningeal cells, terminating at the site of contact; (v) in the contact zone between meningeal cel ls and astrocytes irregular shaped deposits of electron dense material resembling a basal lamina were seen. These observations indicate that indeed a structure resembling a glial-limiting membrane develops in c ocultures of meningeal and astrocytic cells. Its formation depends on the balance of growth promoting effects of meningeal cells on astrocyt es and growth inhibiting effects of astrocytes on meningeal cells. Bot h activities can be enriched from conditioned media of pure astrocytic or meningeal cell culture. The proposed model of meningo-astrocytic c ocultures may be a helpful instrument for further investigations on th e formation of the glia limitans.