Improved vessel painting with carbocyanine dye-liposome solution for visualisation of vasculature.

Vessel painting is one of the most accessible and cost-effective techniques for visualising vasculature by fluorescence microscopy. In this method, the hydrophobic carbocyanine dye DiIC18 labels the plasma membrane via insertion of its alkyl chains into the lipid bilayer. A major disadvantage of this procedure is that it does not stain veins and some microvessels in mouse brain. Furthermore, DiIC18 molecules can aggregate during perfusion, thereby occluding arteries and reducing the success rate and reproducibility of the experiment. To overcome these problems, we developed an improved vessel painting procedure that employs neutral liposomes (NLs) and DiIC12. NLs prevented DiI aggregation under physiological conditions whereas DiIC12 showed enhanced dye incorporation into liposomes and consequently increased staining intensity. Using this method, we successfully labelled all major blood vessel types in the mouse brain, including both veins and microvessels. Thus, liposome-mediated vessel painting is a simple and efficient method for visualising vasculature.