Fig. 9. Inhibiting PDGFR at st. 8 but not st. 10 blocks neurogenesis. (A) At st. 8, 1 µm (n=3) and 2.5 µm PIII (n=5 embryos) reduced neurogenesis by 70% compared with controls (n=6). Average number of triple positive Pax3/NF/Hu+ cells (at least 10 sections) was counted and cells/section normalized to controls. Error bars are s.e.m.; ^*P<0.05; ^**P<0.01. (B) For injections at st. 10, control or 2.5 µm PIII showed no significant differences in Pax3+ (white bars), Hu/NF+ (gray bars) or Pax3/Hu/NF+ (black bars) (P>0.05; n=6 each). Thus, once opV trigeminal placode cells are specified, neurogenesis is not blocked by inhibiting PDGFR.