Pathway tracing using biotinylated dextran amines

Biotinylated dextran amines (BDA) are highly sensitive tools for anterograd e and retrograde pathway tracing studies of the nervous system. BDA can be reliably delivered into the nervous system by iontophoretic or pressure inj ection and visualized with an avidin-biotinylated HRP (ABC) procedure, foll owed by a standard or metal-enhanced diaminobenzidine (DAB) reaction. High molecular weight BDA (10 k) yields sensitive and exquisitely detailed label ing of axons and terminals, while low molecular weight BDA (3 k) yields sen sitive and detailed retrograde labeling of neuronal cell bodies. The detail of neuronal cell body labeling can be Golgi-like. BDA tolerates EM fixatio n and processing well and can, therefore, be readily used in ultrastructura l studies. Additionally, BDA can be combined with other anterograde or retr ograde tracers (e.g. PHA-L or cholera toxin B fragment) and visualized eith er by multi-color DAB multiple-labeling - if permanent labels are desired, or by using multiple simultaneous immunofluorescence - if fluorescence view ing is desired. In the same manner, BDA pathway tracing and neurotransmitte r immunolabeling can be combined. Note that BDA pathway tracing can also be combined with anterograde or retrograde labeling with fluorescent dextran amines, if one wishes to exclusively use tracers with the favorable transpo rt properties and sensitivities of dextran amines. In this case, the BDA ca n be visualized together with the fluorescent dextran amines using fluoresc ence labeling for the BDA, or the fluorescent dextran amines can be visuali zed together with the BDA by multicolor DAB labeling via immunolabeling of the fluorescent dextran amines using anti-fluorophore antisera. BDA is, thu s, a flexible and valuable pathway tracing tool that has gained widespread popularity in recent years. (C) 2000 Elsevier Science B.V. All rights reser ved.