Fluorescein labelled dextrans as tracers for vascular permeability studies in the nervous system

Golden hamsters received i.v. injections of dextrans labelled with fluorescein isothiocyanate (FITC-Dextran). After 4 hrs samples from the cerebral hemispheres, Gasserian ganglia and sciatic nerves were fixed either by immersion in formalin or by cardiac perfusion with the same fixative. The distribution of the tracer was then studied by fluorescence microscopy of thin frozen sections. With this simple technique FITC-Dextrans could easily be detected in tissue sections. The tracers used (mol. w. 19000 and 154000) spread in the same way as fluorochrome-labelled albumin, remaining in the lumen of cerebral vessels but leaking extensively from vessels in the ganglia. FITC-Dextrans thus appear to be very useful tracers for vascular permeability studies of nervous tissue since dextrans can be obtained in a wide range of molecular weights. FITC-Dextrans can also be subjected to microscopic and quantitative studies.