Fig. 5. Effects of IGF-I on dendrites by branch order.A, Analysis of the mean number of apical branches of each order for control and IGF-I-treated neurons indicated there were significant effects of treatment and branch order (p < 0.005, ANOVA). Post hoctests demonstrated that IGF-I produced significant increases in the mean number of branches of the first through sixth orders (*p < 0.05, **p < 0.01, SNK).B, Consistent with the increased number of branches at several orders, IGF-I increased the percentage of neurons that included apical dendritic branches of higher orders (fourth through eighth).C, Analysis of the mean length of branches of each order revealed no apparent changes in length in response to IGF-I (the absence of higher-order branches in many neurons, particularly from control slices, precludes statistical analysis like that inA). D, Comparison of the mean number of basal branches at each order within each treatment group demonstrated that there was increased branching (p < 0.005, ANOVA) of intermediate (third through sixth order) branches; IGF-I increased fourth through sixth order branches, NT-3 third and fourth order, and BDNF only third order (*p < 0.05, SNK).E, Consistent with the increased number of branches at intermediate orders, the growth factors increased the percentage of neurons bearing basal branches of the highest orders. F, There was no apparent change in the mean length of basal dendritic branches of any order after treatment with any growth factor.