Cell Migration of Neural and Neoplastic Cells Transplanted into the Adult Rat Brain

During embryonic development a complex interplay takes place between the primitive neural ectoderm and surrounding mesodermal tissues. This process is characterized by generation of neuroblasts from the early neuroepithelium which first migrate and then differentiate into mature neural cells in the various regions of the central nervous system (CNS). Extensive cell migration, as observed for fetal cells during development, is a property which is also observed in malignant brain tumor cells in vivo [2–4, 9, 13, 22]. Glioma cells, for instance, show a tendency to migrate along fiber tracts of the white matter and along blood vessels [2, 9], and it is at present unclear whether this migration is enhanced by specific biological properties of the tumor cells or by specific anatomical structures in the brain itself. Of particular interest is the fact that also fetal brain cells, upon transplantation into the adult brain, show a tendency for extensive migration within the CNS [11, 12, 18]. In addition, it has been shown that tumor cells can possess specific fetal phenotyp-ic properties [14, 19] which may be acquired during the process of transformation and differentiation. In the present study we therefore compared the migratory patterns of fetal brain cells and glioma cells transplanted into the adult CNS. To visualize the transplanted cells within the brain they were stained with the carbocyanine dye 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine Perchlorate (DiI), which is nontoxic and integrates within the plasma membrane of individual living cells [15–17].