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Abstract
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 currently in use and have proved invaluable
in charting the complex interconnections of the central nervous system. The review
begins with a short overview of the most frequently used tracers, including enzymes,
peptides, biocytin, latex beads, plant lectins and the ever-increasing number of fluorescent
dyes. This is followed by a more detailed consideration of both well established and
more recently introduced neuroanatomical tracing methods. Technical aspects of the
application, uptake mechanisms, intracellular transport of tracers, and the problems
of subsequent signal detection, are also discussed. 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 protocols for three-colour
labelling have been developed to study complex patterns of connections. It is envisaged
that this review will be used to guide the readers in their selection of the most
appropriate techniques to apply to their own particular area of interest.