Correlative ultrastructural and immunohistochemical study of developing vascular basement membrane in postnatal rat spinal cord.

We investigated the development of vascular basement membrane in immature spinal cord vessels during rat spinal cord myelination. Correlative ultrastructural and immunohistochemical study indicated that fibronectin was the first component of extracellular matrix. Then, on the 9th postnatal day, laminin appeared. At that time, lamina lucida of vascular basement membrane was not detectable. On the 15th day, when collagen IV was visible, lamina densa and lamina lucida were occasionally observed. All components of basement membrane--fibronectin, laminin, collagen IV, alpha-2 laminin (merosin)--and ultrastructural division into two layers were detected on the 25th postnatal day. The results of this study indicates that a gradual development of endothelium in immature rat spinal cord blood vessels leads to a gradual increase of synthesis of extracellular matrix components.