Serum and fibroblast growth factor stimulate quiescent astrocytes to re-enter the cell cycle

An in vitro model was used to study the cytokinetics of astroglial cells derived from neonatal rat cerebellum. Confluent monolayers of astrocytes (85% astroglial as assessed by GFAP immunoreactivity) were subcultured at low cell density and after 2-3 days growth were rendered quiescent by shifting them to low serum medium (0.25%) for several days. Cells could be stimulated to re-enter the proliferative compartment by challenging them with high concentrations of fetal bovine serum (5-10% FBS) or fibroblast growth factor (FGF). FGF added alone at a concentration of 25 ng/ml caused quiescent astrocytes to re-enter the cell cycle nearly as effectively as 5-10% serum. Moreover, when FGF (25 ng/ml) was combined with 0.5% serum there was a potentiation of the mitogenic effect seen with FGF alone. This synchronization scheme is an important tool for continuing studies of the growth factor and hormonal requirements for astroglial cell proliferation and differentiation.