Differential Cellular Dynamics of Platelet‐Derived Growth Factor Receptor β Cells and Macrophages After Complete Spinal Cord Transection in Neonatal and Juvenile Rats

Lesion morphology after complete spinal cord transection (CST) varies depending on the time of injury. Following CST, the stumps are connected by fibrous tissue in adult and juvenile rats, whereas they are connected by thin meningeal tissue in neonatal rats. Here, we compared the cellular dynamics after CST in neonatal and juvenile rats to investigate factors contributing to the morphologic differences between the two groups. The intensity of PDGFRβ-positive structures associated with fibrotic scar formation at the lesion core was significantly higher in juvenile CST rats than in neonatal CST rats. In neonatal rats, the intensity gradually decreased, whereas in juvenile rats it peaked at 7 days and then decreased. Pro-inflammatory CD11c-positive macrophages were abundant in the lesion core 2 days after CST, then rapidly decreased in both neonatal and juvenile CST rats. Anti-inflammatory CD163-positive macrophages in the lesion core were significantly more abundant in neonatal CST rats than in juvenile CST rats and remained elevated until 14 days after CST. Neonatal CST rats exhibited less fibroblast accumulation and higher CD163-positive macrophage density in the lesion core compared with juvenile CST rats. These differences may be associated with morphologic differences in the lesion core between the two groups. CD163-positive macrophages in the neonatal CST rats may primarily promote meningeal remodeling rather than fibrous tissue proliferation leading to fibrous scar formation.