A, Histogram summarizing the data shown in Table 1 and illustrating the proportion (percent) of olfactory bulb explants in which axons look attracted, repelled, or unaffected when co-cultured next to control COS cells, Sema A- or Sema IV-expressing cells, and olfactory epithelium. B, Histogram showing the axonal surface (mean ± SEM) in the different combinations of olfactory bulb explants and COS cells. All explants were fixed and stained with anti-β-tubulin antibodies. The axonal surface was measured in the distal (black bars) and proximal (gray bars) quadrants, as indicated in C. Olfactory bulb axons are strongly repelled by Sema IV but attracted by Sema A. Control COS cells have no effect. Theasterisks denote differences between both quadrants (proximal and distal) that are significant at the p = 0.0001 level (Mann–Whitney rank sum test and Wilcoxon signed rank test). C, Schema of the method used to quantify neurite outgrowth. An image analysis system was used to determine the overall area covered by neurites in the proximal (P, gray area) and distal (D, black area), as represented on theright. This gives an estimate of neurite lengths and numbers.