Neurite outgrowth from mammalian CNS neurons on astrocytes in vitro may not be mediated primarily by laminin.

A number of in vitro studies suggest that certain components of the extracellular matrix (ECM), such as the glycoprotein laminin, can promote neurite outgrowth. In the present study the presence of laminin and heparan sulphate proteoglycan, another ECM molecule, on CNS glial (astrocytes) and non-glial (leptomeningeal) cells in vitro was examined. In addition, the ability of these cells and laminin-coated tissue culture substrates to promote neurite outgrowth from developing mammalian cerebellar cortical neurons was also assayed. Leptomeningeal cells were found to be labelled much more intensely with antibodies against laminin and heparin sulphate proteoglycan than were astrocytes. However, the proportion of neurons extending neurites was fourfold greater on astrocyte monolayers than on leptomeninges, and twofold greater than that on laminin. In addition, the length of the neurites growing on astrocyte monolayers was three- to fourfold greater than that on laminin or leptomeninges. Neurite outgrowth on leptomeninges and laminin could not be enhanced by culturing in astrocyte conditioned medium. The ability of various antibodies to block neurite outgrowth on these monolayers was also studied. These results suggest that the robust neurite outgrowth from mammalian CNS neurons plated on astrocytes may be mediated via an astrocyte surface molecule distinct from laminin.