Dissociated cell cultures initiated from whole forebrains of E12.5 wild-type mice (A,B,C) or from the ventral portion of the forebrain from E11.5 wild-type mice (D) were grown in defined media in the presence or absence of a chemical inhibitor of Fgfrs [PD173074; 150 nM (A–C), 100 nM (D) or 300 nM (B)], inhibitor of all hedgehogs (cyclopamine; 1uM) or both. OLP development was analyzed by immunolabeling with specific marker of early OLPs (PDGFRa) at 6 DIV (A,B,C) or 9 DIV (D), late OLPs (O4) at 9 DIV (A,B) double labeled with the nuclear marker Hoechst (blue). The total numbers of PDGFRa- or O4-positive cells were counted and expressed as a percent of control. Error bars represent S.E.M. (N=3). Each experiment was performed at least two to three times. Scale bars, 50 um. Note that OLP generation is strongly inhibited by either of the inhibitors.