Neuroanatomical tract-tracing using biotinylated dextran amine.

Biotinylated dextran amine (BDA) is a highly efficient and powerful marker for bidirectional tracing of nerve pathways in a wide variety of species at the light and electron microscopic level. The BDA tract-tracing method can readily be combined with other anterograde or retrograde tracers for multiple neuroanatomical labeling studies to map the neuronal connectivity, or with immunocytochemistry for neurotransmitters and their receptors to reveal details of synaptic specializations within the multisynaptic neuronal circuits. Here, we describe an experimental protocol for anterograde and retrograde tracing using BDA. By applying BDA 10 kDa as an anterograde tracer, we demonstrate the existence of a direct bilateral nigro-trigeminal pathway in the rat.