Figure 2.

SynCAM 1-dependent changes in mossy fiber projections and target innervation in the hippocampal CA3 area. A, Calbindin immunostaining of hippocampal sections to label mossy fibers in WT (left) and SynCAM 1 KO mice (right) at P28. Bundle width was measured as marked by the dashed line above the genu in the left panel. Representative, anatomically matched sections are shown. Scale bar, 500 μm, applies to both panels. B, Quantification of images as in A showed in WT a width reduction of the suprapyramidal mossy fiber bundle between P14 and P28. Mossy fibers in SynCAM 1 KO mice did not undergo this developmental pruning, resulting in widened bundles at P28 (n = 4 male mice each, 24 measurements per animal; 2-way ANOVA with Bonferroni's post test) C, Compared with WT mice at P28, SynCAM 1 KO animals showed increased Timm's staining of mossy fiber terminals in CA3 stratum lucidum (sl; marked by dashed lines). Representative, anatomically matched sections are shown. Scale bar, 500 μm, applies to both panels. D, Timm's staining measured from images as in C was increased in the KO compared with WT littermates. Intensity was normalized to background in CA1 (n = 4 male mice each, 2–3 sections per animal; Student's t test). E, Density of NeuN-positive neuronal nuclei in DG was unaffected by loss of SynCAM 1 (n = 7 sections each from 2–3 male mice per genotype; Student's t test).