The cavity volume was measured and calculated as described previously (Nakano et al., 2013 (link)). In brief, three rats each from CPEC-transplanted and PBS-injected groups were used at 5 w-TP. Horizontal cryostat sections of the spinal cord were stained by hematoxylin and eosin (HE) on the slide glass. After staining, the sections were embedded in Canada balsam (Wako, Osaka), and used for measurement of the volume of cavities. The border of cavities was traced to measure the areas of the cavities using the Image Filing System (Flovel, Tokyo, Japan) equipped on a microscope (Olympus, CKX41, Tokyo, Japan). The areas of the cavities were measured in every third section. Since the sections were ca. 10 μm thick, the total volume of the cavities was calculated by multiplying the average area of the cavities by the depth of the sections examined. The relative volume of the cavities was obtained by dividing the values of the total cavity volume by those of the whole spinal cord volume at the corresponding level.