Fluorescent imaging in vivo of developing blood vessels on the optic tectum of Xenopus laevis.

The growth and development of individual living capillaries, venules, and endothelial sprouts on the pial surface of the brain were examined with video microscopy and intravascular FITC-dextran in anesthetized tadpoles of pigment-deficient Xenopus laevis, stages 42-50. The fluorescent tracer, injected intracardially through glass micropipets, was well tolerated by the tadpoles and improved the visibility of vessels compared to transmitted light. Case histories of vascular development on the optic tectum confirmed the sprouting of new capillaries during angiogenesis. The caudal tectum and its vascular domains grew faster than the rostral, but the densities of caudal surface vessels were at least as high as rostral densities, indicating that angiogenesis was well matched to neural development. Internal capillary branches were further elaborated and pial venules increased in diameter in premetamorphic tadpoles and in Xenopus frogs.