X-ray microanalysis of biological specimens by high voltage electron microscopy

For the purpose of analyzing and imaging chemical components of cells and tissues at the electron microscopic level, 3 fundamental methods are available, chemical, physical and biological. Among the physical methods, two methods qualifying and quantifying the elements in the structural components are very often employed. The first method is radioautography which can demonstrate the localization of radiolabeled compounds which were incorporated into cells and tissues after the administration of radiolabeled compounds. The second method is X-ray microanalysis which can qualitatively analyze and quantify the total amounts of elements present in cells and tissues. We have developed the two methodologies in combination with intermediate high or high voltage transmission electron microscopy (200-400 kV) and applied them to various kinds of organic and inorganic compounds present in biological materials. As for the first method, radioautography, I had already contributed a chapter to PHC (37/2). To the contrary, this review deals with another method, X-ray microanalysis, using semi-thin sections and intermediate high voltage electron microscopy developed in our laboratory. X-ray microanalysis is a useful method to qualify and quantify basic elements in biological specimens. We first quantified the end-products of histochemical reactions such as Ag in radioautographs, Ce in phosphatase reaction and Au in colloidal gold immunostaining using semithin sections and quantified the reaction products observing by intermediate high voltage transmission electron microscopy at accelerating voltages from 100 to 400 kV. The P/B ratios of all the end products Ag, Ce and Au increased with the increase of the accelerating voltages from 100 to 400 kV. Then we analyzed various trace elements such as Zn, Ca, S and Cl which originally existed in cytoplasmic matrix or cell organelles of various cells, or such elements as Al which was absorbed into cells and tissues after oral administration, using both conventional chemical fixation and cryo-fixation followed by cryo-sectioning and freeze-drying, or freeze-substitution and dry-sectioning, or freeze-drying and dry-sectioning producing semithin sections similarly to radioautography. As the results, some trace elements which originally existed in cytoplasmic matrix or cell organelles of various cells in different organs such as Zn, Ca, S and Cl, were effectively detected. Zn was demonstrated in Paneth cell granules of mouse intestines and its P/B ratios showed a peak at 300 kV. Ca was found in human ligaments and rat mast cells with a maximum of P/B ratios at 350 kV. S and Cl were detected in mouse colonic goblet cells with maxima of P/B ratios at 300 kV. On the other hand, some elements which were absorbed by experimental administration into various cells and tissues in various organs, such as Al in lysosomes of hepatocytes and uriniferous tubule cells in mice was detected with a maximum of P/B ratios at 300 kV. From the results, it was shown that X-ray microanalysis using semi-thin sections observed by intermediate high voltage transmission electron microscopy at 300-400 kV was very useful resulting in high P/B ratios for quantifying some trace elements in biological specimens. These methodologies should be utilized in microanalysis of various compounds and elements in various cells and tissues in various organs.

Radioautographology general and special

A new concept, termed "radioautographology" is advocated and its contents are reviewed. This term is the coinage synthesized from "radioautography" and "(o)logy", expressing a new science derived from radioautography. The concept of radioautographology (RAGology) is a science to localize the radioactive substances in the biological structure of the objects and to analyze and to study the significance of these substances in the biological structure. On the other hand, the old term radioautography (RAG) or autoradiography (ARG) is the technique to demonstrate the pattern of localization of various radiolabeled compounds in biological specimens. The specimens used in biology and medicine are cells and tissues. They are fixed, sectioned and made contact with the radioautographic emulsions, exposed and developed to produce metallic silver grains. Such specimens are designated as radioautographs (or autoradiographs) and the patterns of pictures made of silver grains are named radioautograms. Those people who produced radioautographs were formerly named radioautographers (or autoradiographers) who were only technicians, while those who study RAGology are not technicians but scientists and should be called as radioautographologists. The science of radioautographology was developed in the 20th century and can be divided into two parts, general radioautographology and special radioautographology, as most natural sciences usually can. The general radioautographology is the technology of RAG which consists of 3 fields of sciences, physics concerning radioactivity, histochemistry treating the cells and tissues and photochemistry dealing with the photographic emulsions. The special radioautographology, on the other hand, consists of applications of general radioautographology to various biological and medical sciences. The applications can be classified into several scientific fields, i.e., cellular molecular biology, anatomy, histology, embryology, pathology and pharmacology. Studies carried out in our laboratory were summarized and reviewed. The results obtained from the technology includes 4-dimensional structures of the organs taking the time dimension into account by labeling cells and localizing the sites of incorporation, synthesis, discharge of the labeled compounds in connection with the time lapse and aging of animals. All the results obtained from such applications should be systematized as a new filed of science in the future in the 21st century.