A quantitative and morphological study of vascularisation of the developing mouse spinal cord.

Vascularisation of the mouse spinal cord was examined by both quantitative histology and electron microscopy from E10 up to adult life, with particular emphasis on embryonic development. Blood vessels were present at all stages examined. From E10 to E14 blood vessels were most numerous in the ependymal layer. Ependymal layer vascularity declined as the layer itself decreased in size. Two rapid phases of vascularity were found. The first, from E14 to E18, coincided with the cessation of neuron production and early differentiation of grey matter. From E18 to P5 the volume density of blood vessels declined due to rapid growth of grey matter, presumably due to differentiation of the neuropil. A second rapid phase of vascularisation, associated with myelination, occurred between P5 and P15. The volume density of blood vessels declined between P15 and P150, probably due to a combination of cord growth and an actual decrease in size and/or number of blood vessels. The volume density of vessels in white matter increased from E14 to E18 and remained constant until P5. Since white matter volume increased rapidly between E18 and P5 due to the onset of myelination, the constant volume density indicated a substantial increase in the number of vessels during this time. The rapid increase in vascularisation noted in the grey matter between P5 and P15 also occurred in white matter, as did the later decline. It is suggested that there is a transient increase in vascularity associated with myelin production. At all stages spinal cord endothelial cells are joined by tight junctions. Primitive dark endothelial cells are present at E11 but many pale, well differentiated endothelial cells are also present. A basement lamina appears to be present on parts of vessels in contact with glioblasts. By E15 endothelial cells are well differentiated.