Formic acid is essential for immunohistochemical detection of aggregated intraneuronal Aβ peptides in mouse models of Alzheimer's disease

The staining protocols so far applied to study intracellular Aβ accumulation in human tissue have been inconsistent with varying use of heat and formic acid (FA) for antigen retrieval. Microwave heat treatment has been reported to enhance the staining of intraneuronal Aβ as compared to no or enzymatic pretreatment. FA is widely used to increase the staining of plaque pathology in AD, yet the effect of FA on intraneuronal Aβ staining has been reported to be low and similar to the effect of heat or even to counteract the enhancing effect of heat pretreatment on intraneuronal Aβ immunohistochemical detection. To overcome these inconsistencies, there is a need for optimization of the staining protocol for intraneuronal Aβ detection and more knowledge is required concerning the effects of the different antigen retrieval methods. In the present work, we optimized the staining protocol for intraneuronal Aβ in paraffin-embedded sections in relation to heat and FA using four different mouse models known to accumulate intraneuronal Aβ peptides. It was found that FA is essential for the staining of highly aggregated intraneuronal Aβ peptides in AD transgenic mouse tissue.