Observations of HRP labeling following injection through a chronically implanted cannula--a method to avoid diffusion of HRP into injured fibers.

One of the limitations of the horseradish peroxidase (HRP) tracer method is the diffusion of HRP into injured axons resulting in unintended labeling of neurons not terminating in the injection area. To overcome this limitation, an experiment was designed to inject the HRP through an implanted cannula after degeneration and healing had taken place. It was shown that implantation of a cannula into the internal capsule significantly decreased the number of labeled axons in the injection site, thus limiting the unintended labeling of neurons from that injection.