Axonal Patterns in the Prosencephalon of the Human Developing Brain

Abstract

In the second half of gestation the human fetal brain is characterized by prominent transient structures, i.e. subplate, ganglionic eminence and perireticular nucleus. These structures are involved in the formation of projections by acting as intermediate targets. This study is aimed at demonstrating axonal patterns and their reorganization in the human fetal brain using the antibody mixture SMI 312 which immunolabels phosphorylated neurofilaments predominantly found in axons. In the immunosections, a laminar- and nuclear-specific labeling is present. The subplate contains diffusely arranged fibers and conspicuous obliquely oriented fibers. The internal capsule harboring the perireticular nucleus is characterized by dense fiber clusters which display interwoven fibers at high magnification. Near the ganglionic eminence, fibers are seen that are directed towards its periphery. The latter, i.e. the margins of the ganglionic eminence, display fiber terminations. The results demonstrate characteristic transient axonal patterns which are linked to transient projections known from animal studies. It is obvious that the functional organization of the fetal brain distinctly differs from that of the mature brain.