Biotin-dextran: a sensitive anterograde tracer for neuroanatomic studies in rat and monkey.

The properties of a new anterograde tracer, biotin-dextran (BD), are reported. Iontophoretic or pressure injections of BD in the spinal cord of rats and monkeys revealed terminal-like BD label in many regions of the brain. The BD label was visualized by an avidin-biotin reaction combined with diaminobenzidine, with and without nickel enhancement. This reaction resulted in permanent label and revealed the fine morphology of terminal boutons and en-passant endings. Biotin-dextran is an excellent anterograde tracer that can also be visualized at the electron microscopic level, used in combination with other retrograde and anterograde tracers and with immunohistochemical labeling of neurotransmitters.