Fig. 3. Responsiveness of motoneuron subpopulations to Slit proteins in vitro. (A,D,G) Immunostained trochlear axons from explants co-cultured with transfected cell clusters. (B) Histogram showing mean angle difference representing trochlear axon bundle chemorepulsion. Significant differences from controls represented by asterisks (P<0.05); n>20 in each condition. (C,F,I) Spinal cord explants growing in the presence of transfected cell clusters. (E,H) Histograms representing quantitation of mean % of axons facing cluster (y-axis) for retrogradely labelled dorsally projecting (BM/VM) axons (E) or ventrally projecting (SM) axons (H). Asterisks indicate significant deviations from the control values (P<0.05); n>10 for BM/VM labelled explants, n>25 for SM labelled explants. (J-L) Explants placed in apposition to Slit1-transfected cell clusters. (M-O) Explants facing mock-transfected control cell clusters. (J,M) Ventrally projecting abducens axons. (K,N) Dorsally projecting glossopharyngeal axons. (L,O) Dorsally projecting hypoglossal/cranial accessory axons. Scale bars: 400 µm in I for A,C,D,F,G,I; 400 µm in O for J-O.