Effects of the Age of Donor or Host Tissue on Astrocyte Migration from Intracerebral Xenografts of Corpus Callosum

Our previous studies in which neural tissue was transplanted into neonatal rat brains have demonstrated that the patterns of astrocyte migration are stereotypic and are mainly influenced by local factors in the host brain. Here we examine how these patterns are affected by the relative maturity of donor cells and recipient brains. In one group of animals, adult mouse corpus callosum was transplanted into the cortex or midbrain of neonatal rat brains; in a second group, corpus callosum from 2- to 3-day-old mice was placed in adult rats. The location of the grafts and the distribution of donor astrocytes were defined by using a monoclonal antibody (anti-M2) specific for mouse astrocytes. In marked contrast to previous studies involving transplantation into neonatal hosts, very few neonatal astrocytes placed into adult brains invaded the gray matter and these never migrated more than 250 μm from the graft. The migration in adult brains also failed to show targeted migration to regions such as the substantia nigra. In the second group, astrocytes from adult grafts implanted in neonatal hosts migrated in both gray and white matter of brains in patterns similar to those of neonatal cells placed in neonatal brains. These observations suggest that the astrocyte migration in the white and gray matter is guided by different cues and that the maturation of host brain environment, but not the age of donor cells, influences the pattern of cell migration.