Fixation artifacts in transmission electron microscopy
Cell and tissue preparations for transmission EM contain artifacts introduced at each step of the preparative method. Fixation, as a first and crucial step, is subject to both gross and subtle artifact. For familiar tissues, gross artifacts are easily recognized. Artifacts in unfamiliar cells and subtle distortions or alterations of structure or localizations of molecules of interest are more difficult to assess.Three general approaches are useful for identification of fixation artifacts. Especially in the case of single cells, it is possible to make direct comparison of living and fixed specimens. Advanced light microscopic methods allow very high-resolution imaging of cells and comparison of structure before and after fixation. Light microscopic observation during fixation has documented examples both of creation of structure and disappearance of structure. A more widely applicable approach is the comparison of structure in the same tissue after fixation by different procedures.