The retrograde transport method.

After an injection of horseradish peroxidase into the brain, the enzyme product can later be found in cell bodies of neurons which project axons to the injection site. The use of the tracer has now been adapted as a means of identifying neurons on the basis of their efferent fiber projections. In this review particular attention is paid to characteristics of the phenomenon of retrograde transport, such as diffusion of the marker from the injection site and the region of effective uptake, uptake by injured axons of passage as well as by axon terminals and the preterminal portions of axons, and the anterograde movement of peroxidase. The retrograde transport method is compared to the previously available method of retrograde cell degeneration and the advantages and limitations of both techniques are considered.