EFFICIENT IMMUNODETECTION OF VARIOUS PROTEIN ANTIGENS IN GLUTARALDEHYDE-FIXED BRAIN-TISSUE

Optimal ultrastructural preservation of brain tissue for electron micr oscopy is best achieved with fixatives containing high concentrations of glutaraldehyde, which is generally considered detrimental to the im munogenicity of most protein antigens. We tested seventeen mono- or po lyclonal antibodies against peptide or protein antigens, including a m ajority for which immunoreactivity had previously been reported to be sensitive to glutaraldehyde fixation. Forebrain sections of rats or mi ce fixed by perfusion with 3.5% glutaraldehyde were processed for pre- embedding immunocytochemistry by the avidin-biotin method. The resulti ng immunostaining was in most cases at least similar to that obtained in sections fixed with paraformaldehyde. Immunoreactivity against the mouse or human neurofilament protein NF-L was even improved, being sim ilar to that previously reported for unfixed brain tissue. Of all anti gens tested, only choline acetyltransferase, phenylethanolamine-N-meth yl transferase, and neuropeptide Y were detected with lower sensitivit y than after paraformaldehyde fixation, which was attributed to a rath er restricted penetration of the primary antibody into glutaraldehyde- fixed tissue sections, These results indicate that glutaraldehyde may be envisaged as a possible fixative for optimal immunocytochemical det ection of any tissue antigen at the electron microscopic level, includ ing antigens which, on the basis of results obtained after fixation wi th paraformaldehyde-glutaraldehyde mixtures, were considered highly se nsitive to glutaraldehyde fixation.