Fig. 1.

Schematic representation of outgrowth and guidance factors involved in the developing corticospinal tract in rat spinal cord. Vimentin immunoreactive astroglial cells (a) are situated in longitudinal tiers with their processes perpendicular to the outgrowing CST pioneer fibers and their growth cones (gc) (Joosten and Gribnau 1989a, b). The embryonic form of N-CAM is present on the growth cones of the pioneer CST fibers. The later-arriving CST fibers are guided by the cell adhesion molecule L1. During spinal gray matter target innervation, mainly through the formation of so-called back-branches, a tropic factor, probably NT-3, is released by either the CST target (inter)-neurons (in) or astroglial cells (a). Adapted from (Joosten 1997), with permission