Staining sections of water‐miscible resins 2. Effects of staining‐reagent lipophilicity on the staining of glycol‐methacrylate‐embedded tissues

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Abstract
SUMMARY: Glycol methacrylate (GMA) sections of animal tissues were stained with a group of twenty‐seven reagents of very varied chemical characteristics. The artefactual background staining of the resin was found to be dependent on the hydrophilic/lipophilic character of the staining reagent, as estimated from the logarithm of its octanol‐water partition coefficient (log P). Intense background staining occurred with lipophilic stains, whose log P>2. In keeping with this, use of GMA semi‐permeable membranes for enzyme histochemistry failed to give staining when using a lipophilic substrate, probably because the substrate was trapped in the membrane. An analysis of other routine histochemical stains—in terms of the probable occurrence of high resin background staining and low tissue sensitivity—is made. A numerical guide is provided to help avoid artefacts resulting from hydrophobic and size effects. Note: small, hydrophilic reagents (log P P > 2; 550 < ionic weight < 1000 Da), give strong background staining.