Heparan sulfate proteoglycan and laminin mediate two different types of neurite outgrowth.

Spinal cord neurons cultured in vitro have been shown to respond to changes in their environment by means of 2 different types of neurite outgrowth: (1) neurite elongation and (2) emergence and branching of newly formed neurites. Culture of spinal cord neurons with heparan sulfate proteoglycan (HSPG) medium resulted in a 3-fold increase in neurite elongation compared to the control. Extensive branching was seen when neurons were cultured in laminin-supplemented culture medium. HSPG-induced elongation and laminin-induced branching of neurites were blocked by specific anti-HSPG and antilaminin sera, respectively. Furthermore, laminin antibodies did not inhibit neurite elongation and HSPG antibodies did not block neurite branching. Conditioned medium from primary embryonic rat muscle cultures (MCM) mimicked the effects of both HSPG and laminin on neurite outgrowth. Immunoprecipitation with anti-HSPG and antilaminin antibodies demonstrated that MCM contains these 2 basal lamina components. Our observations suggest that HSPG and laminin might be highly effective molecules for promoting neurite outgrowth of rat spinal cord neurons in vitro.