Fig. 1

CC sampling for light and electron microscopy study. Diffusion tensor imaging and fiber tractography-based vertical partitioning of the CC into five segments corresponding to interhemispheric cortical connections (a). Celloidin embedded brain hemisphere was cut into 200-μm-thick gapless serial sections (b). From thirteen equidistant CC samples representing all segments (b) a 2-mm-wide CC sample was cut off and embedded in Epon (c1). Semithin sections were cut (c2) and stained with PPD (c3) for light microscopy morphometric studies [56]. For the EM morphometric study of axons Epon blocks were trimmed and 60-nm-thick sections were cut and stained with uranyl acetate. The calibrated electron micrographs obtained at 15,000x magnification were used for manual delineation of the axon border (c4) to estimate the diameter and crossectional area of the axon, as well as to estimate the thickness of the myelin sheath measured at four equidistant points. The measurements were performed with Image J software