A new method for visualization of endothelial cells and extravascular leakage in adult mouse brain using fluorescein isothiocyanate

We described a new method for the visualization of vasculature and endothelial cells and the assessment of extravascular leakage in adult mouse brain by using fluorescein isothiocyanate (FITC), or a reactive fluorescent dye. FITC is the fluorescein derivative that reacts covalently with amine groups at alkaline pH. In this method, strong fluorescence of FITC was seen at vasculature throughout the brain and spinal cord, when mice received intracardiac perfusion with FITC-containing saline at pH 7.0 followed by paraformaldehyde (PFA) fixative at pH 8.0. The fluorescence of FITC was faint when animals were fixed with PFA fixative at pH 7.0 after the perfusion of FITC-containing saline at pH 7.0. The fluorescence of FITC was not detected when mice was fixed with PFA fixative before the perfusion of FITC-containing saline. Double labeling immunohistochemistry using an endothelial cell marker CD31 or a pericyte marker desmin revealed that FITC was accumulated at nuclei of endothelial cells but not at those of pericytes. Extravascular leakage of FITC was prominent in the area postrema or a brain region of the circumventricular organs that lacks the blood-brain barrier. Moreover, strong extravascular leakage of FITC was detected at damaged sites of the cerebral cortex with cryoinjury. Thus, FITC method is useful technique for examining the architecture of brain vasculature and endothelial cells and the assessment of extravascular leakage in adult rodents. Moreover, FITC binds covalently to cellular components, so that makes it possible to perform double labeling immunohistochemistry and long-term storage of the preparation.