Hello Bob:

You can suppress normal axon staining by oxidation or by lowering the pH of the
impregnation solution.
Great reference
STAIN TECHNOLOGY, Vol.55, no. 5  1980.
EXPERIMENTAL STUDIES OF MECHANISMS INVOLVED IN METHODS DEMONSTRATING AXONAL AND
TERMINAL DEGENERATION by F. Gallyas, L. Zaborszky, and J.R. Wolff  pages
281-290.
If you cannot locate this reference  or need more information, let me know.
Lynn Brennan
City of Hope Med Center
Division of Neuroscience
Duarte, California  
lbrennan@coh.org