Electron microscopic classification of amine-producing endocrine cells by selective staining of ultra-thin sections

Rat stomach ECL cells up-date of biology and physiology

The ECL cell is the predominant endocrine cell type in the oxyntic mucosa, displaying typical ultrastructure with numerous cytoplasmic vesicles and electron-dense granules. ECL cells have many features in common with neurons and other peptide hormone-producing endocrine cells, including the ability to produce, store, and secrete chromogranin-A and chromogranin A-derived peptides. In addition, they produce and store histamine and respond with activation and growth to a gastrin challenge. ECL cells are stimulated to secrete histamine as well as other products by gastrin and PACAP and are inhibited by somatostatin, galanin, and prostaglandins. The cytoplasmic vesicles are thought to contain histamine and other secretory products. Mature secretory vesicles occur in the docking zone of the ECL cells, where they constitute the releasable pool of secretory products. Gastrin stimulation will induce exocytosis and degranulation. Histamine released from ECL cells plays a key role in the regulation of parietal cell activity (the gastrin-ECL cell-parietal cell axis). In response to long-term gastrin stimulation, vacuoles and lipofuscin bodies develop in the ECL cells, forming part of a crinophagic pathway by which the ECL cell strives to eliminate superfluous secretory products.

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.

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

Two methods have so far been proposed for staining samples by the argyrophil technique of Grimelius for electron microscopy. For Håkanson glutaraldehyde prevented argyrophilia, so the author stained sections from samples previously fixed by double formaldehyde/osmium tetroxide treatment and embedding. Vassallo used en bloc staining after fixation with glutaraldehyde-formaldehyde mixtures. We examined each factor which could directly interfere in argyrophil staining en bloc and on section. In the present experiment we compared effects of fixatives after staining en bloc. Glutaraldehyde prevented argyrophilia in 1 case out of 15, that of A-like cells in the oxyntic gland of the rat positivity was maintained in EC-like cells of this gland and adrenalin cells of the adrenal gland contrary to the previous description.

Studies on in vitro effect of serotonin on calcitonin secretion by rat thyroid C cells

Thyroid glands of young rats were incubated for 3 h in Eagle's solution supplemented with 5-hydroxy-l-tryptophan (5-HTP) or with serotonin. Following control incubations or incubations with serotonin, no serotonin could be demonstrated in C cells using immunocytochemical techniques. However, serotonin was demonstrated in the secretory granules of all C cells following incubation with 5-HTP. The secretory function of C cells was evaluated by ultrastructural and immunocytochemical studies, and by calcitonin radioimmunoassays of the incubation medium. Following incubation with 5-HTP, the secretory function of the majority of C cells was inhibited, and calcitonin levels in the media were decreased. Incubation with serotonin produced an increased secretory function of C cells and higher calcitonin levels in the media. The results indicate that serotonin and its direct precursor, 5-HTP, affect calcitonin secretion by rat thyroid C cells by distinct mechanisms.

Enteroglucagon and substance P-like immunoreactivity in argentaffin and argyrophil rectal carcinoids

A specific immunofluorescence for enteroglucagon or substance P or for both hormones was demonstrated in nine out of 12 examined rectal carcinoids. One tumor was argentaffin, contained ultrastructurally pleomorphic granules of the entero-chromaffin cell type, and showed immunofluorescence for substance P. The rest were non-argentaffin but were argyrophil with the Grimelius technique and contained round granules. The argyrophil carcinoids were immunoreactive to one or both hormones in eight cases and not fluorescent in three cases. In two of the non-argentaffin carcinoids a small number of argyrophil cells was found with the method of Sevier-Munger.

Intestinal endocrine cells of chicks around the time of hatching

The duodenum of 16-day Black Australorp chick embryos, and the duodenum, ileum, large intestine and caeca of 18-day embryos and of chicks within 30 h of hatching, have been studied by electron microscopy. Cells were found with secretory granules resembling those in mammalian EC, S, A-like, EG and D cells (terminology of Solcia et al., 1973), and were on this basis tentatively identified accordingly. The distribution and frequency of the chick cells in different parts of the tract correspond well to the situation in mammals.

Staining procedures for the endocrine cells of the upper gastrointestinal mucosa: light-electron microscopic correlation for the gastrin-producing cell

Although histochemical, immunohistochemical, and electron microscopic methods have led to the identification of a large variety of endocrine cells in the upper gastrointestinal mucosa, no conventional light microscopic technique capable of the simultaneous identification of these cells has been reported. Such a staining method would be of considerable value to the pathologist as the malfunction of the endocrine cells of the gut, which produce numerous digestive hormones and biogenic amines, is closely related to a number of clinical conditions afflicting man. In this work, after testing three different polychrome staining methods, it has been concluded that a slightly modified Herlant's tetrachrome in tissues fixed in Zenker-formol is the procedure of choice. This method allows the distinction of several different cell types in the upper gastrointestinal mucosa of man and dog and permits the easy identification of the gastrin-producing cells on a routine basis. This identification has been confirmed in the case of two patients with gastrin cell hyperplasia, seen by both light and electron microscopy. Herlant's tetrachrome has proven valuable in the screening of human as well as experimental gastrointestinal tissues and it has been found to be very suitable for recognizing gastrin-producing cell hyperplasias. The usefulness of this method is expected to increase with the establishment of further correlations between the light and electron microscopy of the endocrine cells of the gut.