Revealing the three-dimensional murine brain microstructure by contrast-enhanced computed tomography

To improve our understanding of the brain microstructure, high-resolution 3D imaging is used to complement classical 2D histological assessment techniques. X-ray computed tomography allows high-resolution 3D imaging, but requires methods for enhancing contrast of soft tissues. Applying contrast-enhancing staining agents (CESAs) ameliorates the X-ray attenuating properties of soft tissue constituents and is referred to as contrast-enhanced computed tomography (CECT). Despite the large number of chemical compounds that have successfully been applied as CESAs for imaging brain, they are often toxic for the researcher, destructive for the tissue and without proper characterization of affinity mechanisms. We evaluated two sets of chemically related CESAs (organic, iodinated: Hexabrix and CA4+ and inorganic polyoxometalates: 1:2 hafnium-substituted Wells-Dawson phosphotungstate and Preyssler anion), for CECT imaging of healthy murine hemispheres. We then selected the CESA (Hexabrix) that provided the highest contrast between gray and white matter and applied it to a cuprizone-induced demyelination model. Differences in the penetration rate, effect on tissue integrity and affinity for tissue constituents have been observed for the evaluated CESAs. Cuprizone-induced demyelination could be visualized and quantified after Hexabrix staining. Four new non-toxic and non-destructive CESAs to the field of brain CECT imaging were introduced. The added value of CECT was shown by successfully applying it to a cuprizone-induced demyelination model. This research will prove to be crucial for further development of CESAs for ex vivo brain CECT and 3D histopathology.

The choice of a masking agent in the histochemical staining of metals

The masking effects of standard masking agents (aminopolycarboxylic acids, carboxylic acids and phosphates) have been investigated in both test-tube experiments and tissue sections in order to ascertain the factors which must be considered when choosing a masking agent for the histochemical staining of a metal. The masking effects in vitro were determined by spectrophotometry through the complexing of the dye Chrome Azurol S with aluminium, beryllium, and iron at pH 5 and 7. The effects were also examined by staining metal-containing tissue sections in a Chrome Azurol S masking agent system at the same pH values. In many cases, the masking effects observed in sections did not agree with those obtained in the test-tube experiments. This means that the published values of stability constants are not a sufficient guide for choosing a suitable masking agent for the staining of metals. The discrepancy is mainly attributable to the presence of protein in a solid state when metals are stained in sections. Therefore, in the future, consideration should be given to a metal-protein or masking agent-protein interaction using a model compound such as a chelate resin. The polyphosphates are among the most useful masking agents for metal staining in acidic solutions from a practical standpoint.

Structure-staining relationships in histochemistry and biological staining. I. Theoretical background and a general account of correlation of histochemical staining with the chemical structure of the reagents used

A description is given of the choice, rationale and calculation of several numerical coefficients for describing the chemical structures of staining reagents such as dyestuffs, enzyme substrates, diazonium and tetrazolium salts. Using such coefficients, structure-staining correlations may be made for many staining systems. Examples include the structural correlations of the quantitative affinity measurements of the staining of chromatin with basic dyes, the tetrazolium salts for use as visualizing agents in enzyme histochemistry, and the use of bis-azo compounds as acid or basic dyes, or as fat stains. The value of such structure-staining correlation models for assisting the rational selection and design of new histochemical reagents, and for understanding old reagents and procedures, is discussed.