Advanced fixation techniques for high-sensitivity molecular imaging: effectiveness of glyoxal fixation for immunostaining.

Chemical fixation is essential in immunohistochemistry for detecting molecular localization. The gold-standard fixative for immunohistochemistry is 4% paraformaldehyde (PFA); however, its properties-such as tissue shrinkage and protein cross-linking through methylene bridges-often restrict antibody access, posing challenges to achieving specific binding reactions. This is particularly true for receptors and ion channels condensed in the synaptic cleft, postsynaptic density, or trigger zone of action potentials. To overcome this problem, several laboratories have attempted antigen-exposure techniques. Recently, we demonstrated that fixation by glyoxal, a dialdehyde with two carbon atoms, enables specific detection of molecular groups that are difficult to be detected in PFA-fixed tissues. Here, we summarize the advantages and precautions in the use of glyoxal fixative.