The extracellular matrix molecule, laminin, induces purkinje cell dendritic spine proliferation in granule cell depleted cerebellar cultures.

Granule cells and glia were eliminated or reduced in organotypic cerebellar cultures exposed to cytosine arabinoside. Transplantation of such granuloprival cultures with glia or exposure to astrocyte conditioned medium in the absence of parallel fibers (granule cell axons) resulted in proliferation of Purkinje cell dendritic spines. The aim of the present study was to identify specific astrocyte secreted factors that induced dendritic spine proliferation. Known astrocyte secreted, neurite promoting factors were screened by application to granuloprival cultures and assayed for dendritic spine proliferation by electron microscopy. An extracellular matrix molecule, laminin, evoked sprouting of Purkinje cell dendritic spines. Dendritic spine proliferation was not associated with known neurite promoting parts of the laminin molecule, as two laminin-derived peptides with identified neurite promoting domains did not induce dendritic spine sprouting. The purpose of laminin-induced dendritic spine proliferation may be to elaborate postsynaptic membrane, thereby increasing the target area for arriving axon terminals during development or regeneration, both of which have been associated with the presence of laminin secreting astrocytes.