Dextran amines: Versatile tools for anterograde and retrograde studies of nervous system connectivity

Abstract

Dextran amines are versatile and sensitive tools for anterograde and retrograde investigation of neural connectivity. Because of their tolerance of diverse fixatives, they are ideal for various light and electron microscopic studies. They can be iontophoretically or pressure-injected, and then depending on the type of dextran amine used and the type of detection method, visualized by transmitted light microscopy, fluorescence microscopy, or electron microscopy. High-molecular-weight biotinylated dextran amines (BDAs; 10 kDa) yield sensitive and exquisitely detailed labeling of axons and terminals, while low-molecular-weight BDAs (3 kDa) yield sensitive and detailed Golgi-like retrograde labeling of neurons. Labeling with the BDAs can be visualized with an avidin-biotinylated horseradish peroxidase (ABC) procedure followed by a standard or a metal-enhanced diaminobenzidine (DAB) reaction, or with any of several fluorescent probes that bind to biotin. Fluorescent dextran amines can be directly visualized by fluorescence microscopy or rendered suitable for transmitted light or electron microscopic viewing by immunohistochemical detection of the given fluorophore. The variety of dextran amines and the methods for their visualization make them well-suited for multiple-label studies. The dextran amines can also be combined with other anterograde or retrograde tracers, or intracellular labeling, and the disparate markers separately visualized either by multicolor DAB or by DAB-VIP® labeling, or by multiple fluorescence viewing. In the same manner, pathway tracing with dextran amines and immunohistochemical labeling can be combined. The dextran amines are thus flexible and valuable pathway-tracing tools that have gained widespread popularity since being introduced.