Enhancement of the periodic acid--Schiff (PAS) and periodic acid--thiocarbohydrazide--silver proteinate (PA-TCH-SP) reaction in LR white sections.

LR White is a well-suited resin for the demonstration of carbohydrates with the PAS or PA-TCH-SP reaction in semithin and ultrathin sections. The intensity of these reactions can be greatly enhanced by using 3 steps in tissue preparation, either singly or in combination: 1) The PAS reaction in semithin sections turns out stronger after partial (70% ethanol) than complete (100% ethanol) dehydration of the tissue before its transfer to 100% LR White. 2) Silver enhancement of the PA-TCH-SP reaction product can simply be effected by physical development of ultrathin sections (PA-TCH-SP-SE reaction). Least precipitates are formed in this procedure, when sections are mounted on uncoated gold grids, processed for cytochemistry, and thinly coated with carbon in the end. 3) The use of hot silver proteinate (50 degrees C) plus strong silver enhancement (15-20 min silver lactate developer) reveals minute concentrations of TCH-labelled aldehyde groups in the tissue that do not react with silver proteinate at room temperature.--Silver enhancement and the use of hot silver proteinate do not depend on LR White, but may also be applied to ultrathin sections of tissue embedded in other resins.