Cell Cycle Kinetics in Fetal Rat Cerebral Cortex: Effects of Prenatal Treatment with Ethanol Assessed by a Cumulative Labeling Technique with Flow Cytometry

The effects of ethanol on the cell cycle kinetics of cortical precursor cells during the period of cortical neuronogenesis [between gestational day (G) 12 and G21] was systematically examined. Samples of dissociated cortical cells were harvested from the cerebral cortices of 13‐, 15‐, 17‐, 19‐, and 21‐day‐old fetuses. The fetuses were obtained from pregnant rats: (a) fed a liquid diet containing 6.7% (v/v) ethanol (Et) ad libitum, (b) pair‐fed an Isocaloric liquid control diet (Ct), or (c) fed chow and water (Ch) ad libitum. Before harvesting the cells, the fetuses were administered a series of 1–5 injections of bromodeoxyuridine (BrdU). The proportion of cells that incorporated the BrdU was assessed. Using these raw data, the S‐phase length (T B , total cell cycle length (T c ), and the growth fraction (GF; the fraction of the total population that was actively cycling) were determined with a cumulative labeling procedure. The T 3 was –8–9 hr, regardless of either the date of the injection or the dietary treatment of the dam. On the other hand, the T c for the Ct‐ and Ch‐treated rats increased over the gestational period. That is, the T c was shortest on G13 and longest on G21. The T c for Et‐treated rats, however, did not change between G13 and G21. For the Ch‐ and Ct‐treated groups, the GF decreased > 15‐fold between G13 and G21. The decline (5‐fold) for the Et‐treated group over the same period, however, was not as great as it was for the Ct‐treated fetuses. Thus, by G17 (and thereafter), the GF for Et‐treated fetuses was significantly greater than it was for the Ct‐treated group. Ethanol treatment has opposite effects on the two cortical germinal zones; it stimulates the proliferation of subventricular cells, whereas it inhibits the proliferation of ventricular cells). Thus, the ethanol‐induced changes in the T c and the GF reflect the combined effects of ethanol on the two cortical proliferative zones.