Fixation artifacts

French J (2008) Retinal folding in the term rabbit fetus developmental abnormality or fixation artifact. Reprod Toxicol 26 262-266... 

Caveats include minor differences in size and shape from muscle to muscle, and fixation artifacts that can eliminate staining, especially presynaptically. In general, defects in the presynaptic terminal, such as partial retraction, are reflected less-precise definition in the postsynaptic receptors. 

Cellular and nuclear localization of autoantibodies was initially described three decades ago (A7, A8, A9). However, some argued that they only represent a fixation artifact, with movement of immunoglobulins into cells during tissue preparation... 

Already in 1965, Ryser and Hancock provided evidence that histones and polyamino acids could greatly enhance albumin uptake by cultured tumor cells (6). More recently, several polybasic peptides (so-called protein transduction domains, PTDs or cell-penetrating peptides, CPPs) have been shown to efficiently mediate uptake of nucleic acids, bioactive peptides, phage particles, and liposomes into a wide variety of mammalian cells. The initially proposed ability of CPPs to penetrate plasma membranes via a temperature-independent, non-endocytotic pathway was later shown to be a fixation artifact, and it is currently widely accepted that CPP-mediated macromolecular delivery follows energy-dependent endocytotic pathways that in most cases depend on the expression of cell-surface heparan sulfate proteoglycans (HSPGs) (7). 

The distribution of cannabinoid receptors has been extensively mapped by quantitative autoradiography, in situ hybridization, and immunocytochemistry. Each of these techniques has its strengths and weaknesses. Properly calibrated, quantitative autoradiography provides the best measure of absolute receptor density. Nonetheless, its spatial resolution is limited and specificity depends on the ligand used. In situ hybridization identifies the cells synthesizing CB i mRNA. However, mRNA levels and protein levels may not necessarily correlate. Immunocytochemistry provides outstanding spatial resolution however, fixation artifacts and unanticipated antibody crossreactivity must be assiduously avoided. For the most... 

FIGURE 1.27 Section of lymph node stained with CD45 showing variable fixation artifact. Well-defined cytoplasmic membrane staining is seen in the subcapsular region (A) and toward the periphery of the section (B), where the tissue is adequately fixed. 

FIGURE 1.28 Another lymph node section stained with Bcl-2 showing similar variable fixation artifact with gradual loss of staining appreciated toward the center of the node. 

Early microscopists described the spindle long ago. In 1952 it was seen in live cells in the shape of birefrin-gent fibers, thus excluding the possibility of fixation artifacts. Electron microscopists helped to clarify knowledge of the spindle when they showed that the fibers were essentially composed of microtubules. 

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