NCAM as a differentiation marker of postmigratory immature neurons in the developing human nervous system

The regional distribution and cellular localization of the neural cell adhesion molecule were investigated in the developing nervous system of human embryos and fetuses, by using immunocytochemistry with antibodies against the human neural cell adhesion molecule. Embryos and fetuses with crown-rump lengths ranging from 15 to 80 mm (corresponding approximately to 6-12 ovulation weeks) were examined. In the telencephalon, immunoreactivity was found in the primordial plexiform layer and in the early cortical plate. During later stages, immunoreactivity was present in the marginal zone, cortical plate, developing subplate zone and radiations of the internal capsule. In the mesencephalon and rhombencephalon, neuronal perikarya were outlined and strong staining was present in fiber bundles. In the spinal cord, strong immunostaining was present in fiber tracts and in dorsal and ventral roots. Immunostaining outlined perikarya of dorsal and ventral gray columns; the neuropil of the developing gray matter was also stained. Contrary to findings in some other species, precursor cells in the proliferating zones, i.e. all cells of ventricular zones and the external granular layer in the proliferation were not stained. Reactivity, however, was also observed in single mature-looking nerve cell bodies and their processes, which were localized in proliferating zones. All peripheral nervous structures including nerve fibers and peripheral nervous tissue components derived from the neural crest (i.e. sensory and autonomic ganglia) expressed the neural cell adhesion molecule. At the cellular level staining always appeared to be associated with the entire cell membrane of a given neuron including its outgrowing processes. Immunocytochemical staining for neural cell adhesion molecule is an excellent method for the identification of single nerve fibers, nerves and nerve cell bodies in situ in the developing peripheral and early central nervous system. The neural cell adhesion molecule is suggested as a marker of postmigratory immature neurons in the developing human nervous system.