In vitro induction of radial-like cells by leptomeningeal and cortical astroglial conditioned media. Effect of protease inhibitors.

A population of subcultured astroglia from rat fetal cortex was transformed into radial-like cells after exposure to cerebral cortex astroglial conditioned medium in vitro. Such changes were also induced by basal medium modified by fetal leptomeningeal subcultures, but not by postnatal leptomeninges nor by fetal skin fibroblasts. The radializing effects of astroglial conditioned medium were inhibited by previous heat treatment. The addition of protease inhibitors to the basal medium did not cause spontaneous radialization of subcultured cortical astroglia, but increased the length of cell processes and incidence of radial-like forms when added to cortical astroglial conditioned medium. It is concluded that cortical astroglia and leptomeningeal cells share the capability of synthesizing and releasing diffusible molecules into the culture medium which act as morphogenetic inducers in vitro. Based on the present results, it is suggested that such effects would depend on the presence of instructive factor(s) in the conditioned medium which are able to induce rearrangement of the cytoskeleton, rather than on secreted molecules able to modify cell adhesion to the substrate.