Histochemical Use of Borohydrides as Aldehyde Blocking Reagents

Complete blocking of the Schiff reaction applied after HIO₄ oxidation is attained by 1%, 0.5% or 0.2% NaBH₄ in 1% Na₂HPO₄ with a 1 min exposure, 0.1% NaBH₄ requires 2 min. KBH₄ was also completely effective in the same solvent at 1, 0.5 and 0.25% in 1 min. The solutions deteriorate on standing, so that 0.5% NaBH₄ is effective in 1 min at 7 hr but 5 min is needed at 24 hr and is ineffective at 36 hr; 1% KBH₄ requires 4 min at 24 hr when fresh, and showed deterioration in 2-4 days. Saturated (0.4%) isopropanol and 1% pyridine solutions required 10-15 min when fresh and showed deterioration in 2-4 days. No satisfactory results were obtained with 80% or absolute dioxan or with methyl cellosolve in times of an hour or less; even a 24 hr exposure was ineffective with 0.2% in 80% dioxan.