In vitro proliferation of cortical cells extracted from E17–20. Cortical cells were incubated in supplemented Neurobasal medium. Data are presented as fold of control (day 0 luminescence value) means ± S.E.M. of a minimum of five experiments each performed in triplicate. *** P < 0.001, *P < 0.05 compared to day 0 as determined by t-test analysis.