Hierarchical clustering of samples. Hierarchical clustering tree of samples, corresponding to the different experimental points (treatments and times). The proNGF/NGF concentrations are expressed in ng/ml. The tree shows the gene expression similarity between samples, by using the “non-centered Pearson” correlation, as a metric to compare the expression profiles. The y-axis indicates the distance between samples. The colours of highlighted treatments correspond to those displayed in Figure 4. This diagram shows that the degree of similarity between the NGF and proNGF responses at 30 minutes is low.