The anterograde neuroanatomical tracer biotinylated dextran-amine: comparison with the tracer Phaseolus vulgaris-leucoagglutinin in preparations for electron microscopy.

We investigated the properties of biotinylated dextran-amine (BDA) as a neuroanatomical tracer at the electron microscopic level and we compared the results with those obtained previously with another tracer, the lectin Phaseolus vulgaris-leucoagglutinin (PHA-L). BDA was injected into various brain areas of rats. Following survival and fixation, vibratome sections were cut, subjected to a freeze-thaw treatment, and incubated overnight with avidin-biotin complex (ABC). Following reaction with diaminobenzidine (DAB)-hydrogen peroxide, the sections were processed for electron microscopy. In the electron microscope we observed that the reaction product occurred in the cytoplasm of cell bodies and in the matrices of dendrites, axons and axon terminals following ABC histochemistry of BDA-containing brain sections. The ultrastructural details of BDA-labelled neurones were generally better preserved than in PHA-L-labelled material, whereas at the same time penetration of the reagent into the sections was complete (incomplete in sections of PHA-L material). We conclude that the use of BDA as a neuroanatomical tracer in electron microscopy is a good substitute for PHA-L. The detection method for transported BDA is much faster and less complicated than that for PHA-L, while the results are better; that is, there is improved penetration coinciding with good preservation of ultrastructure. Keeping the limitations of BDA as a neuroanatomical tracer in mind, e.g., retrograde transport into local collaterals of axons that intermingle with anterogradely labelled axons, BDA seems well suited as a neuroanatomical tracer for electron microscopy.