Genetic deletion of NeuroD2 leads to reduced density of thorny excrescence spine heads. (A, C) Hoechst nuclear staining of the hippocampus from post-embryonic day (P)21 littermate, WT and NeuroD2 null (knockout (KO) OK) mice. (B, D) CTIP2 immunostaining, specific for DG and CA1 neuron nuclei, shown for the same sections as in (A, C). (E) P21 CA3 pyramidal neuron filled in coronal hippocampal section from transcardially perfused mouse by targeted microinjection of Lucifer Yellow dye. Inset indicates individual TE spine heads in a single confocal plane (white arrowheads). (F) Representative proximal dendritic segments with TE spines in WT and NeuroD2 null mice (KO) at P7, P14 and P21 time points. (G) TE elaboration quantified by counting the density of individual spine heads on primary and secondary dendritic branches in 60X confocal stacks (P7, n = 6 per condition; P14, 21, n ≥ 15). (H) Individual TE spine head width quantified in confocal stacks as the width of the head in the confocal plane where it was largest (n ≥ 6 per condition). *P < o.05, t-test. Scale bars: 130 μm (A); 75 μm (E); 5 μm (F, I). Error bars represent ± standard error of the mean. N.S., not significant.