Differential migration of astrocytes grafted into the developing rat brain

Fetal and neonatal astrocytes migrate in specific patterns when transplanted into the adult rat host brain. However, it is unclear whether these astrocytes demonstrate the same degree of mobility during early brain development. In the present study, neonatal cortical, hippocampal, and hypothalamic astrocytes were collected from the brains of 1- to 3-day-old rats and placed in tissue culture. After 14 to 21 days, cultures enriched in astrocytes were harvested and labelled with either the fluorescent dye Fast Blue or fluorescein-labelled latex beads. They were then transplanted into the right frontal cerebrum of neonatal rats at 2, 5, 8, and 11 days postpartum. Seven days after transplantation, animals were sacrificed and their brains were fixed by immersion in aldehydes, sectioned on a cryostat, and examined with fluorescence microscopy. Transplanted astrocytes migrated along the corpus callosum, internal capsule, glial limitans, ventricular linings, and hippocampal structure. Labelled cells were also found in the contralateral hemisphere in day 2 brains. Migration in a radial fashion from the injection site toward the periphery was a particularly obvious pattern, and was most pronounced in these younger hosts. In days 5 and 8 rat brains, astrocyte migration became more restricted to the hemisphere of implantation. In 11-day-old host brains, hemispheric restriction and other region-specific influences became manifest and specifically modulated migration. Radial migration was absent in the 11-day-old host group except for cells of cortical origin. The observed results demonstrate that neonatal cortical, hippocampal, and hypothalamic astrocytes transplanted into the neonatal cerebrum migrate in patterns that are more extensive than in the adult brain.(ABSTRACT TRUNCATED AT 250 WORDS)