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The epithelial basal lamina of the small intestine has numerous fenestrations for intraepithelial migration of leukocytes. We have reported dynamic changes of fenestrations in dietary conditions. To investigate this phenomenon, we performed statistical analyses using scanning electron microscopy images of the epithelial basal lamina of rat intestinal villi after removal of the villous epithelium by osmium maceration. We examined structural changes in the number and size of fenestrations in the rat jejunum and ileum under fasted and fed states for 24 h. Our findings revealed that, in the jejunum, the number of free cells migrating into the epithelium through fenestrations increased from 2 h after feeding, resulting in an increase in the fenestration size of intestinal villi; the number of free cells then tended to decrease at 6 h after feeding, and the fenestration size also gradually decreased. By contrast, the increase in the fenestration size by feeding was not statistically significant in the ileum. These findings indicate that the number of migrating cells increases in the upper part of the small intestine under dietary conditions, which may influence the absorption efficiency of nutrients including lipids, as well as the induction of nutrient-induced inflammation.

The basal lamina of the villous epithelium in the small intestine has numerous fenestrations, which are produced by leukocytes for their intraepithelial migration. We previously showed that these fenestrations change due to the dynamics of migrating leukocytes in response to dietary conditions and suggested the possibility that this change is related to the regulation of the absorption of large-sized nutrients such as chylomicrons. The present study was, thus, designed to investigate structural changes in basal lamina fenestrations in response to a high-fat diet. The ultrastructure of the intestinal villi in the rat upper jejunum was investigated by electron microscopy of tissue sections in both the normal and the high-fat diet groups, and the fenestrations in the villous epithelium of rat upper jejunum were studied by scanning electron microscopy of osmium macerated/ ultrasonicated tissues. The present study showed that free cells adhering to the fenestrations increased in the upper jejunum two hours after feeding high-fat diet and the size of the fenestrations in this region also increased after feeding high-fat diet for 2 days. This enlargement of fenestrations may play an important role in increasing the efficiency of lipid absorption by facilitating the movement of chylomicrons from the intercellular space to the lamina propria.

The epithelial basal lamina of the small intestine forms a felt-like sheet at the base of the epithelium. Previous studies have shown that the basal lamina has numerous fenestrations, which are produced by leukocytes penetrating through the basal lamina. In this study, we aimed to directly visualize fenestrations of the rat basal lamina in intestinal villi by scanning electron microscopy (SEM) after removal of the villous epithelium by osmium maceration and ultrasonic treatment. Structural changes in fenestrations were then investigated in relation to dietary conditions. SEM of these tissues revealed the presence of fenestrations in the villous epithelial basal lamina in all segments of the small intestine, although the number was the highest in the jejunum. The present study also showed that the number and size of fenestrations increased after feeding in the jejunum, whereas changes were unclear in the ileum. These findings suggested that the basal lamina fenestrations were changed through the dynamics of migrating leukocytes in dietary conditions and may also be related to the regulation of nutrient absorption, particularly as lipids are transported from the intercellular space of the epithelium to the lamina propria.

In the cochlea, a high K + environment in the endolymph is essential for the maintenance of normal hearing function, and the transport of K + ions through gap junctions of the cochlear epithelium is thought to play an important role in endolymphatic homeostasis. The aim of the present study was to demonstrate the three-dimensional (3D) ultrastructure of spiral ligament root cells and interdental cells, which are located at both ends of the gap junction system of the cochlea epithelium. Serial semi-thin sections of plastic-embedded rat cochlea were mounted on glass slides, stained with uranyl acetate and lead citrate, and observed by scanning electron microscopy (SEM) using the backscattered electron (BSE) mode. 3D reconstruction of BSE images of serial sections revealed that the root cells were linked together to form a branched structure like an elaborate "tree root" in the spiral ligament. The interdental cells were also connected to each other, forming a comb-shaped cellular network with a number of cellular strands in the spiral limbus. Furthermore, TEM studies of ultra-thin sections revealed the rich presence of gap junctions in both root cells and interdental cells. These findings suggest the possibility that both root cells and interdental cells contribute to K + circulation as the end portion of the epithelial cell gap junction system of the cochlea.

Thiamine pyrophosphatase (TPPase) cytochemistry is an established method for specific labeling of the trans-Golgi cisterns in tissue sections. Herein, we combined this enzyme cytochemical method with array tomography using scanning electron microscopy (SEM), a new imaging technique based on collection of backscattered electron (BSE) images of consecutive resin-embedded sections on glass slides, to detect the entire three-dimensional (3D) organization of the Golgi apparatus with sufficient spatial resolution. As the signal intensity of BSE depends on the atomic number of the materials, lead precipitates confined to the trans-Golgi cisterns after TPPase cytochemistry were clearly observed by BSE-mode SEM. The mild fixative used for TPPase cytochemistry also enabled accurate identification of target gonadotropes in the composite pituitary tissue by immunocytochemical staining. By 3D reconstruction of the entire trans-Golgi cisterns based on serial ultrathin section images of tissues after TPPase cytochemistry, we detected ultrastructural differences in the 3D configuration of the Golgi apparatus between cerebellar Purkinje cells and pituitary gonadotropes. The appropriate combination of enzyme cytochemistry and/or immunostaining with array tomography will further clarify the relationship between the organization and functional states of the Golgi apparatus.

The increased discharge of gonadotropin releasing hormone (GnRH) from hypothalamic neurons after castration specifically stimulates pituitary gonadotropes. To elucidate the putative effects of GnRH on the three-dimensional ultrastructure of gonadotropes, we examined osmium-macerated pituitary tissues of male rats at various time points after castration by high resolution scanning electron microscopy (SEM) combined with immunocytochemistry. Two days after castration, the Golgi apparatus was disassembled into small stacks; patch-like, tubuloreticular clusters of endoplasmic reticulum (ER) membranes were present; and spherically enlarged mitochondria were accumulated in the central area of the stimulated gonadotropes. These acute changes were indiscernible by 1 week after castration, and then the pituitary gonadotropes of castrated animals gradually became hypertrophic, finally exhibiting the characteristic "signet-ring" appearance, with markedly dilated cisterns of the rough ER. Upon SEM observation, the inner surface of the cavity was mostly flat, and openings connecting adjacent lumens of the ER were sparse. Proliferation of the osmiophilic tubular network of the ER-Golgi intermediate compartment was observed in the persistently stimulated gonadotropes, indicating a marked increase in trafficking of secretory proteins between the Golgi and ER. The acute and chronic changes in the gonadotropes after castration revealed in the present study by SEM provide evidence for a putative link between the intracellular signaling events evoked by GnRH and the ultrastructural dynamics of the organelles of the secretory pathway.

Although a number of papers have given useful information on splenic microcirculation by light and/or scanning electron microscopy, controversies remain as to the vascular arrangement, especially in the human spleen. The present study re-examined the microvasculature of the human spleen using a three-dimensional reconstruction of immunohistochemically stained tissue sections, and showed that the central artery does not directly issue follicular arteries in the human spleen; follicular arteries are derived from penicillar arteries outside the follicle and end in the white pulp. We found that the splenic follicle is surrounded by an elaborate system of anastomosed capillaries in both the marginal zone and the superficial layer of the white pulp. Most of these capillaries are also branches of the penicillar arterioles that are issued from the central artery in the same, or a different, white pulp system. Because the endothelia of these capillaries are widely open in the marginal zone, this vascular network may play a major role in supplying blood to the marginal zone. The accumulation of sialoadhesin-positive macrophages was also observed around the vascular network, suggesting an important role for this structure as the front line of immune response.