Fig. 7. Histograms of thalamic axons sprouting on membranes from distinct cortical layers with PI-PLC enzyme treatment (A) and in the presence of soluble ephrin-A5-Fc (B). Bars represent the percentage of branches formed on membranes from cortical layer 4 (black bars) and cortical layer 5 (white bars). Data are presented in percentage and normalized to 100% for values obtained on membranes from layer 5. The ability of layer 4 membranes to support thalamic axons sprouting decreases after removal of GPI-anchored molecules and after exposure to ephrin-A5-Fc fusion protein. By contrast, none of these treatments influences the branching of thalamic axons on layer 5 membranes. (C) Histogram of branch formation of thalamic axons cultured on cortical membranes from layer 4 (black bar), layer 5 (white bar), and on a mixture (1:1) of both types of membranes (gray bar). On the latter substrate, thalamic axons exhibit a branching density similar to the density observed on layer 5 membranes alone, suggesting that the branch-promoting activity in membranes from layer 4 is inhibited by the membrane extracts from layer 5. n, number of fibers examined.

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