Visualization of migration of transplanted astrocytes using polystyrene microspheres.

Fluorescent polystyrene microspheres have been used to mark rat astrocytes for transplantation. Highly fluorescent cells were generated by incorporation of microspheres over periods of the order of 10 h. Microspheres ranging in average diameter from 50 to 200 nm and derivatized with either rhodamine or fluorescein have been used to label cells. There were no apparent cytotoxic effects of microsphere incorporation. Loaded astrocytes retained their complement of microspheres over periods of at least several weeks. The microspheres could be visualized in the transmission electron microscope. They were most likely phagocytosed by a coated-pit mechanism and accumulated in various types of lysosomal vesicles. Labelled astrocytes from neonatal PVG rats were implanted stereotaxically (as a plasma clot) into hippocampi of recipient syngeneic adult rats. Donor cells migrated from transplant to host over about 7 days. Transplant cells tended to be close to blood vessels over this period. Their location in paravascular spaces was determined from observation of microsphere-bearing cells in electron microscopy. Microsphere-loading of astrocytes is a simple method for marking cells for extended periods of time for transplantation which allows direct identification of marked cells with both fluorescence and electron microscopes.