Fig. 2. Responses of motor axons to Slit proteins in vitro. (A) Dissection of tissues for use in collagen gel co-cultures (see Materials and methods). (B,C,E) Trigeminal (r2+3) level explants co-cultured with cells transfected as indicated. (D) Histogram showing quantitation (mean % pixels on facing side of explant are on the y axis) of outgrowth from explants at r2-8 levels in the presence of transfected cell clusters; n>30 for each condition. Asterisks represent significant differences from the controls. (F-M) Semi-quantitative data. A shift to negative explant net scores indicates inhibition of outgrowth (see Materials and methods); inhibition was significant when P<0.1 in all cases, and significant when P<0.05 in G,H,I,K,M; n>25 for each condition. Scale bar: 400 µm.