Conjugated dimers of horseradish peroxidase as neuroanatomical tracers.

Horseradish peroxidase dimer (HRP-HRP) and monomer (HRP) were compared in their ability to act as neuroanatomical tracers. Dimers exhibited less diffusion at the site of injection. At 48-72 h survival periods, there were no appreciable differences in the retrograde neuronal labeling produced by these two compounds. However, at 7 days survival, there was little retrograde labeling due to the presence of monomer while dimer labeling was still intense.