Application of Grimelius argyrophil staining to the study of tumour ultrastructure. I. Effects of fixatives

Electron Microscopic Study Using Formalin-fixed, Paraffin-embedded Material, with Special Reference to Observation of Microbial Organisms and Endocrine Granules

In the diagnostic pathology practice, specimens for electron microscopy (EM) are not necessarily handled and fixed under the ideal condition. In the present article, the author describes ultrastructural study using formalin-fixed and/or paraffin-embedded material. The fine morphologic preservation is often acceptable, particularly when small cubes are dug out of paraffin blocks. Particulate structures such as neuroendocrine granules and microbes are consistently observed even using paraffin sections. Paraffin sections signalized with silver particles in Grimelius and Grocott stains or diaminobenzidine products in immunostaining and in situ hybridization are applicable to EM evaluation by using a pre-embedding sequence. The practical merit includes the targeted approach: highly accurate sampling from focal lesions can be achieved for EM analysis, after observing hematoxylin and eosin-stained or specific-signalized paraffin-sections. This allows us pathologists a convenient and practical way for identifying focally infected pathogens, as well as a retrospective ultrastructural analysis of rare lesions long kept as a form of paraffin blocks.

Application of Grimelius argyrophil staining to the study of tumour ultrastructure. III. Effects of osmium tetroxide

The results obtained in electron microscopy for Grimelius (1968) argyrophil staining by the en bloc staining of Vassallo and the staining on section of Håkanson were compared on tumoral and non-tumoral tissue samples and were found to lead to different results. Our earlier results for the en bloc staining method indicated that the fixative used in this process was important and that embedding in resin followed by staining of section weakened silver impregnation. We examined here the effects of OsO4 post-fixation combined with such embedding and found that staining was obtained within a shorter period and was more intense. This staining on section was not specific enough, since it was observed in secretory granules of non-argyrophil cells such as those containing somatostatin. In addition, this staining was not confined to specific peripheral zone as it occurred after en bloc staining; particularly in secretory granules with double structure including a core such as those containing glucagon in the pancreas or certain granules in tumoral carcinoid tissue. Consequently silver deposits were located both in the core and peripheral zone of such granules. Moreover, after OsO4 post-fixation, embedding in resin, and staining on section, argentaffin and argyrophil properties intermingle.

Application of Grimelius argyrophil staining to the study of tumour ultrastructure. II. Effects of resin embedding: Epon

2 methods have so far been proposed for staining samples by the argyrophil technique of Grimelius for electron microscopy. Vassallo et al. (1971) used en bloc staining after fixation with a mixture of glutaraldehyde and formaldehyde, then Håkanson et al. (1971) stained sections from samples previously fixed by double formaldehyde/OsO4 treatment and embedding in resin. Another investigation that concerned glutaraldehyde fixation showed the effect of this fixative in sample staining (Soranzo and Roland 1987). The present experiments demonstrated that Epon intervenes directly in argyrophil staining of sections. With this resin, the staining process lasted longer than with paraffin embedding materials and offered no guarantee of positivity. Granules with a double structure and dense core displayed different locality of argyrophilia before and after embedding.