MECHANISMS OF ASTROCYTE-DIRECTED NEURITE GUIDANCE

Astrocytes have recently become better recognized as playing vital rol es in regulating the patterning of central nervous system neurites dur ing development and following injury. In general, astrocytes have been shown to be supportive of neurite extension, but alterations in the b iochemical properties of astrocytes in particular areas during develop ment and in gliotic tissue may act to confine neurite outgrowth and th us provide guidance cues. In vivo studies indicate that restrictive as trocytes function through their altered expression of specific extrace llular matrix molecules, including tenascin, chondroitin, and keratan sulfate proteoglycans. In addition, several in vitro models suggest th at other cell surface molecules are utilized by restrictive astrocytes to direct neurite trajectories.