Discussion

Abstract

In the fetal spinal cord WGA-HRP injection site borders are diffuse. Since exact determination of the injection site was impossible, the injection sites sizes were overestimated by including all sections in which evenly spread, fine-grained TMB deposit was present. This way the injection site size mainly represented the extent of the area of diffusion of the injected tracer, and not necessarily the extent of the area from which tracer is effectively taken up and transported. The latter area is probably smaller than the former one. The position intervals of the descending fiber fronts (Fig. 4) were derived from the positions of the rostral borders of these overestimated injection sites. Since the rostral borders of the effective injection sites are probably located more caudally along the spinal cord, the actual descent (e.g., of the rubrospinal fibers) could actually be slightly more advanced than depicted here.