Timing and patterns of astrocyte migration from xenogeneic transplants of the cortex and corpus callosum

The timing, pattern, and pathway of astrocyte migration were investigated in vivo by transplantation of CD-1 mouse cerebral cortex (E13-14) or corpus callosum (P2-3) into neonatal rat cortex. A monoclonal antibody specific for a mouse astrocyte surface antigen (M2) was used to identify the location of the grafts and the migrated donor astrocytes. Within the host cortex, astrocytes from cortical grafts began migration at post-transplantation day (PTD) 7. Over the next 4 days, the most distant displaced donor cells were found progressively further away from the grafts, migrating at a rate of about 220 microns/day. After PTD 11, the migration rate for the farthest displaced donor cells slowed to 25 microns/day, and the cells appeared to stop at about PTD 16 at a distance of 1,100 microns from the edge of the graft. Astrocytes had a faster migration speed in the white matter and covered a longer distance (5 mm) than those in the gray matter, extending on occasion into the contralateral hemisphere. The patterns of astrocyte migration differed depending on local cues around the transplant. Donor astrocytes that had been implanted into the host cortex migrated toward the host cortical surface, sometimes in several radial lines. Astrocytes from grafts, especially callosal grafts, placed in the subcortical white matter migrated along the host fiber tracts. Many astrocytes transplanted into the hippocampus formed laminar patterns close to the hippocampal neuronal layers. These results suggest that the direction, pattern, and speed of astrocyte migration are influenced by local substrates in the host brain.