The Marchi method introduced in 1885 stained the degenerating myelin . The Nauta method , introduced in the 1950s, and the Fink-Heimer method , introduced in 1967, use silver impregnation of degenerating axons. The reason why the silver impregnation works is unknown. Newer methods took advantage of the intrinsic transport machinery of neurons. This machinery uses the microtubules and neurofilaments we talked about before.
Neurons have three types of axonal transport .
Fast anterograde which uses microtubules and ATPase motors , slow axoplasmic with an unknown mechanism, and fast retrograde which uses microtubules also. These transport mechanisms are used to supply organelles to the axon terminals and to return compounds to the cell body for degradation. A method introduced in 1971 took advantage of the endocytosis of the enzyme horseradish peroxidase which catalyses the oxidation of certain compounds. These compounds appear opaque in the light microscope. HRP is taken up by the cell bodies of cells and transported to the axon terminals and is also transported from axons to the cell bodies.