Ultrastructural observations on blood vessels surrounding normal and regenerating spinal cord in newt

The ultrastructural analysis of capillaries surrounding normal and regenerating caudal spinal cords of two species of newt (Triturus vulgaris and T. cristatus) is reported. Around normal spinal cords, capillaries were generally continuous. Surrounding the regenerating spinal cords the various capillaries of the regenerating blastema appeared discontinuous with small or broad gaps along the capillary wall. This was seen even after two months of tail regeneration when the spinal cord was similar to the normal and many axons were myelinating. These morphological findings suggest that during tail regeneration in newts the blood-brain barrier is not very effective. Also extravasating mature and immature blood cells were observed inside regenerating capillaries. Therefore growing capillaries can exchange metabolites and, possibly, growth factors with the nervous tissue and the other regenerating tissues.