c-kit immunohistochemistry was performed on unfixed frozen sections of human small (duodenum, jejunum, and ileum) and large intestine (ascending, transverse, descending, and sigmoid colon). The c-kit immunoreactive cells in the muscularis externa of the intestinal wall were identified as interstitial cells of Cajal (ICC) and mast cells. ICC were identified by their morphology, localization, and organization based on previous light and electron microscopic studies. In the small intestine, ICC were located primarily in relation to the myenteric plexus of Auerbach, but also in septa between circular muscle lamellae. In the large intestine, ICC were seen in relation to Auerbach's plexus, but also and in great numbers in the circular muscle layer and in teniae of the longitudinal muscle layer. The morphology of the ICC was similar in the small and large intestine, but the pattern of distribution was obviously different. c-kit immunoreactive mast cells were found predominantly in the inner part of the circular muscle layer. The anti-c-kit method is found to be an easy and reliable method to study at least most of the interstitial cells of Cajal and thereby contribute to further normal and pathological studies.

The plasma membrane permeabilization obtained by exposure of hepatocytes to digitonin is utilized in the so-called digitonin-pulse perfusion of rat liver (Quistorff and Grunnet 1987). Brief pulses of digitonin applied with antegrade and retrograde perfusion of the liver caused selective elution of cytosolic enzymes and metabolites from the periportal and the perivenous zone of the same liver. In the present study a light microscopical examination of the liver fixed immediately after the digitonin pulse confirmed the very high zonal selectivity of the method inferred from the marker enzyme pattern of the eluates: Only cells around the port of entry of digitonin were affected and the borderline between affected and non-affected cells was always sharp. The typical periportal lesion was triangular in shape, enclosing the portal space, while the perivenous lesion was roughly circular, concentric with the hepatic vein. Assuming that the digitonin lesion reflects the microcirculatory flow pattern these findings seem to be at variance with the acinar model of Rappaport (Rappaport et al. 1954). The lesion in the lobuli near the surface of the liver as reflected by the discoloration pattern observed on the surface was the same as the lesion of deeper lobuli. The conducting vessels of the liver were only insignificantly affected by digitonin. At the cellular level only the sinusoidal luminal surface of the hepatocytes was affected. The cytoplasmic matrix of the cells including glycogen appeared thinned. All cell types of the liver parenchyma seemed to be equally affected by the digitonin treatment.

The distribution and endocytotic function of Kupffer cells in the rat liver were studied after administration of fibrinogen stabilized colloidal gold suspensions either by injection directly into the circulatory system of anaesthetized rats or by application to the isolated perfused liver. After exposure to gold particles the livers were perfused with fixative and studied using several microscopic techniques. Gold was predominantly endocytosed by a highly active population of Kupffer cells surrounding the portal spaces resulting in distinct dark patterns around the terminal portal veins. In cross-sections of lobules the pattern appeared as incomplete networks composed of dark triangular areas with distinct borderlines towards light areas concentric with the terminal hepatic veins (central veins). The light areas contained few and relatively inactive small Kupffer cells. A wide variation of conditions gave essentially the same uptake pattern compatible with the concept of microcirculatory zones concentric with the terminal hepatic veins (Lamers et al., 1989; Quistorff and Rømert, 1989), but contradicting the traditional view of microcirculatory zones advanced by Rappaport et al. (1954). Since the same pattern developed during conditions of anoxia, it seems that oxygen is not the stimulus for the developmental distribution of Kupffer cells with high endocytotic activity. In vivo and perfusion experiments gave identical patterns, but a higher endocytotic activity of endothelial cells was found in perfused isolated livers.

– An electron microscopic, study on silver methenamine staining of hard dental tissues was made on a material that comprised human permanent teeth and primary tooth germs from human and porcine fetuses. It was demonstrated that silver‐stained material consisted of collagen fibrils. In predentin and precementum all collagen fibrils were stained, while collagen fibrils of dentin and cementum were unstained except for some fibrils of minor special areas such as Owen's contour lines, interglobular dentin, Tomes's granular layer, and in cementum small “interglobular‐like” areas. It is concluded that silver methenamine visualizes collagen fibrils of hypo‐ and unmineralized areas in dental hard tissues and therefore may be used to demonstrate abnormal patterns of mineralization. Finally variations of silver methenamine stainability in relation to differences in material and methods were studied and discussed.

After addition of ethanol to the ordinary fodder of pregnant mini-pigs, ultrastructural changes were found in secretory ameloblasts from tooth germs of their mid-term fetuses. Compared with controls, many mitochondria showed abnormal shape and size, and some exhibited deposition of paracrystalline material in the matrix. An abnormal deposition of stippled material intercellularly was also observed. These changes were interpreted as signs of an abnormal secretory function.