Anterograde Tracing

Tracing is managed through a phenomenon called axonal transport or axoplasmic flow. Conventional tracing methods rely on cellular markers transported in axons in the anterograde or retrograde direction from the neuronal cell body. Minute quantities of these markers are injected into a specific peripheral or CNS site. Then, the animals are perfused with fixatives, and the distribution of the marker is studied in tissue sections after a sufficient time has elapsed for uptake and transport to occur. Considerable amounts of connectional data have been collected in this manner.

A series of tracers has been developed as anterograde tracing, which means that the labeling begins at the cell bodies and dendrites. The tracers are transported out to the axons and their terminals according to the preferential direction of their transport in the axon. Many classes of tracer tools are available, including fluorescent dyes (e.g., RITC), plant lectins [Phaseolus vulgaris leucoagglutinin (PHA-L)], dextrans [biotinylated dextran amine (BDA)].

Multi-level Labeling System

There is little doubt that modern tract-tracing protocols will continue to be very useful in basic neuroanatomical research. The further study of the complexity of brain circuits requires effective multi-labeling procedures to visualize several projections simultaneously because single-staining approaches may often not provide enough detail. Multiple-labeling strategies using different fluorescent dyes in vivo or in fixed tissues can be used to study divergent or convergent projections. A suite of tracers has been generated that could enable simultaneous multicolor labeling and tracing. Moreover, this procedure has advantages over the fluorescent markers nowadays commonly used in multiple neuroanatomical tract-tracing methods, such as the stability of the staining and compatibility with EM.

Learn more: Anterograde Multi-level Labeling System