Current concepts in neuroanatomical tracing

The development of new axonal tract tracing and cell labelling methods has revolutionised neurobiology in the last 30 years. The aim of this review is to consider some of the key methods of neuroanatomical tracing that are cu rrently in use and have proved invaluable in charting the complex interconn ections of the central nervous system. The review begins with a short overv iew of the most frequently used tracers, including enzymes, peptides, biocy tin, latex beads, plant lectins and the ever-increasing number of fluoresce nt dyes. This is followed by a more detailed consideration of both well est ablished and more recently introduced neuroanatomical tracing methods. Tech nical aspects of the application, uptake mechanisms, intracellular transpor t of tracers, and the problems of subsequent signal detection, are also dis cussed. The methods that are presented and discussed in detail include: (1) anterograde and retrograde neuroanatomical labelling with fluorescent dyes in vivo, (2) labelling of post mortem tissue, (3) developmental studies, ( 4) transcellular tracing (phagocytosis-dependent staining of glial cells), (5) electrophysiological mapping combined with neuronal tract tracing, and (6) simultaneous detection of more than one axonal tracer. (7) Versatile pr otocols for three-colour labelling have been developed to study complex pat terns of connections. It is envisaged that this review will be used to guid e the readers in their selection of the most appropriate techniques to appl y to their own particular area of interest. (C) 2000 Elsevier Science Ltd. All rights reserved.