Native extracellular matrix induces a well-organized dipolar outgrowth pattern with neurite extension and retraction in cultured neurons

Cultured anterior pagoda (AP) neurons from the leech develop characteristic outgrowth patterns that depend on the molecular composition of the substra te. This article analyzes how native substrates from the central nervous sy stem (CNS), such as the extracellular matrix (ECM) inside the capsules that enwrap the ganglia, determine the outgrowth patterns of AP neurons. When p lated on the internal side of ganglion capsules, the remaining primary port ion (stump) of AP neurons sprouted two main branches in opposite directions with bifurcations. This T-shaped pattern was distinctive for AP neurons an d was different from the patterns of the same cell type plated on the exter nal side of the capsule or on leech laminin extracts, in which they generat ed multiple neurites and branching points. AP neurons plated on tritonized CNS homogenates reproduced the outgrowth pattern displayed on ganglion caps ules, in terms of the number of primary neurites, their length, their orien tation, and the number of branch points. The development of the T-shaped ou tgrowth pattern of AP neurons on ganglion capsules and CNS homogenates star ted by the sprouting of one branch that later bifurcated, followed by a sec ond branch in the opposite direction after a lag of several hours. Extensio n of the second branch and retraction of secondary neurites of the first we re synchronous and contributed to refine the T-shaped pattern. These result s suggest that during development or regeneration of the CNS, particular se ts of ECM proteins have multiple effects regulating the number, direction, extension,: and retraction of neurites. (C) 2000 Wiley-Liss, Inc.