Anterograde axonal tract tracing.

The mammalian brain contains a myriad of interconnected regions. An examination of the complex circuitry of these areas requires sensitive neuroanatomical tract tracing techniques. The anterograde tracers, Phaseolus vulgaris leucoagglutinin (PHA-L) and biotinylated dextran amines (BDA) are powerful tools that can be used to label fiber tracts that project from one particular brain region. When injected iontophoretically, PHA-L and BDA are readily taken up by neurons and transported anterogradely along their axonal tracts. Combined with immunocytochemistry for neurotransmitters, neuropeptides, and receptors, tract tracing methods may be used to elucidate the phenotype of synapses that form the microcircuitry of specific neural systems.