Protargol impregnation of plastic-embedded semi-thin sections: a simple method to select degenerative areas for electron microscopy.

0.5 mu plastic-embedded sections, obtained from aldehyde-osmium fixed rat and cat spinal cord, were impregnated in a 0.5% Protargol solution for 24 hours at 56 degrees C. Reduction was performed in a sodium sulphite- (5%) hydroquinone (1%) developer. Terminals undergoing Wallerian degeneration stand out as easily discernible black dots; corresponding osmiophilic degenerative patterns are demonstrated in consecutive thin electron microscopic sections. This simple technique enables successful trimming of blocks to obtain areas with the highest frequency of terminal degeneration.