Astroglia proliferate during brain growth, and can divide again later, particularly during astrogliosis. We investigated whether astroglia in primary cultures of newborn rat brain similarly achieve a state of prolonged quiescence which enables re-entry into the cell division cycle. In cultures after 2 months, cell number plateaued and there were sharp decreases in [3H]thymidine incorporation (70 ± 5 vs 4 ± 0.5 cpm/ μg protein/h at 30 and 60 days, respectively) and in percentages of cell nuclei incorporating bromodeoxyuridine (BrDU) (from 46 ± 6% to < 1%). Replating at 104cells/cm2yielded secondary cultures which synthesized DNA actively. Forty-eight hours of serum deprivation at 2-3 days from subculturing, followed by addition of 10% serum (time 0), resulted in a return to quiescence which persisted until 12 h (G0 + G1). By 20 h (S phase), there were abrupt increases in DNA synthesis (5-fold) and in BrDU-labeled nuclei (from 19 ± 2 to 76 ± 8%) and the percentage of glial fibrillary acidic protein (GFAP)-positive cells declined to 14 ± 2%. Three days later, GFAP-positive cells numbered around 80%. Cell cycling after prolonged quiescence, in a manner similar to that in early astroglial cultures, required a non-sterol derivative of mevalonate in late G1. These data confirm that astroglia in primary cultures, like their counterparts in vivo, have a flexible capacity to enter and depart from quiescence, and most importantly, provide a system for examining regulation of this process. © 1991.
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