Microinjection methods for visualization of the vascular architecture of the mouse embryo for light and scanning electron microscopy.

Injection of certain materials into blood vessels enables three dimensional visualization of vascular architecture and has provided abundant information which is not available by reconstruction of serial sections. By injection methods, the vascular architecture can be visualized either with scanning electron microscopy (SEM) after injection of resin and tissue digestion or with light microscopy (LM) after injection of barium sulfate and tissue clearing. The author has successfully observed whole blood vessels of 13.5-18.5 day mouse embryos using the collodion cast method in SEM. In mouse embryos younger than 12.5 embryonic days, a part, not whole, of blood vessels was obtained using cast colloiding. When the X-ray contrast medium was injected, the whole vasculature of the 9.5 day embryo was elucidated with LM, and the backscattered electron image and the secondary electron image of the identical area in the lung alveolar capillaries of the 17.5 day embryo were obtained with SEM, which showed the spatial relationship between the capillaries and their circumferential cells three dimensionally. Cast and injection methods are reviewed with respect to their application for investigating the development of mouse embryo.