To determine whether or not the portal vessels play any essential role on the cytogenesis of adenohypophysis through the mediation of hypothalamic neurohormones, chronological and topographical relations between the portal system and adenohypophysial cells have been studied in fetal rats aged from 14.5 to 18. 5, by vascular infusion with India ink and by immunohistochemistry. On day 14.5, the intraglandular fossa (Atwell's recess) receives several blood vessels (primitive portal vessels) from the subtuberal capillary plexus and a pair of fine branches from the internal carotid arteries: those blood vessels anastomose within the recess. On day 15.5, the recess becomes narrow but the vasculature extends posteriorly into the growing anterior wall of the Rathke's pouch, in which they sprout short branches showing terminal dilations. Immunoreactive ACTH cells first appear in the ventral-middle portion of the pars distalis, where the vascular sproutings are not evident. On day 16.5, the intraglandular blood vessels spread through the pars distalis and connect occasionally with extraglandular venous system suggesting the initiation of the hypophysial portal circulation. TSH cells first appear sporadically in the posterior part of the pars distalis, where blood vessels are still scarce and very occasional cells abut on the sinusoids. On day 17.5, the recess becomes indistinct and pituitary acquires the mature shape. The intraglandular vasculature of the portal system makes a dense meshwork in the adenohypophysis except the pars intermedia. LH cells appear first in the ventral region of the anterior half of the adenohypophysis, where occasional cells appear abutting on the sinusoids. The conclusion is that the portal blood supply, which might convey hypothalamic neurohormones, is not essential for initial cytogenesis of the adenohypophysial cells studied here.

View full abstract

The alveolar epithelium of larval and adult caecilians is composed of one cell type only, the cytoplasm of which, however, is divided into two divisions: an organellerich part containing the nucleus and a flattened peripheral part which covers the blood capillaries. Apically the cells bear variously shaped microvilli, which are sparse on the flattened areas of the cells. Among the cytoplasmic structures electron-dense bodies and lamellated bodies are prominent. Morphological observations suggest that in the adult the lamellated bodies are derived from the dense ones, which presumably represent lysosomes. Acid phosphatase and unspecific esterase are present in the entire alveolar epithelium. The lamellar material is extruded by exocytosis. A close structural relation between lamellated bodies and multivesicular bodies-as to be found in many mammals-does not exist. In the larvae among others there exists an extensive lateral labyrinth between neighboring alveolar cells and a considerable variability of the lamellated bodies. The latter frequently arise within or near fields of glycogen or presumably also within membrane systems.
The thickness of the air-blood barrier measures in the thinnest parts about 1μm. In the subepithelial connective tissue, beside the spacious blood and lymphatic capillaries, smooth muscle cells, fibrocytes, collagen and elastic fibers, mast cells and nerve fibers (with granule-containing varicosities) are found. Within the low septa, which divide the inner surface of the wall of the lung into flat polyangular chambers (=alveoli), pieces of hyaline cartilage occur in the proximal parts of the lung. Macrophages are of rare occurrence in the caecilian lung. They contain acid phosphatase, β-glucosaminidase and unspecific esterase and are located in the connective tissue and within the alveolar epithelium near epithelial cells exhibiting structural alterations. The epithelium covering the gills of young larvae is composed of two layers of squamous cells. The cells of the surface layer contain large secretory granules.

View full abstract

The toxic effect on area CA3 of the hippocampus of the rat of small doses of kainic acid (KA) injected into the lateral ventericles was examined by electron microscopy. The most characteristic feature revealed was degeneration in the pyramidal cell somata and in their dendrites from as early as 3hr after injection. We found four types of degenerating pyramidal cells probably corresponding to their susceptibility to KA intoxication. We also detected degenerating preterminal axons and terminals in addition to degenerating pyramidal cells and dendrites. Temporary structural alterations of the mossy fiber endings and intimate adhesional contacts between the mossy fiber endings were also observed. The response of the glia to the damage area CA3 was an increase in the number of astroglia and macrophages in the early stage followed later by mobilization of microglia and astroglia for the formation of scar tissue.

View full abstract

Merkel cell development was studied in the regenerative labial mucous membrane of adult rabbits. Fullthick wounds were made on the inferior labial mucous membrane of the rabbits, then the regenerative mucous membrane was examined by electron and light microscopy at time intervals of 2, 7, 10, 14, 21 and 30 days after the injury. By 7 days, the regenerative area of the mucous membrane was replaced with a dense lamellar connective tissue, which was mainly composed of alternately arranged collagen fiber layers and fibroblasts, and an overlying stratified squamous epithelium. No Merkel cell was found 7 days after the injury. Ten days after the injury, a few very immature Merkel cells were identified in the regenerative epithelium. The Merkel cells increased in number and matured in structure during the course of the following regenerative period. Thirty days after the injury, the wounded area healed without forming a scar tissue, and the regenerated epithelial ridges usually included regular type Merkel cells. As adult animals were used in this experiment, the reproduction of the Merkel cell in the regenerative epithelium seemed to be independent of the undifferentiated neuroectodermal tissue.

View full abstract

Electron microscopic study showed the presence of macrophages in the retina in postnatal rat. These phagocytic cells were localized predominantly in the nerve fiber layer between the ganglion cells and the inner limiting membrane. They were pleomorphic, some displayed typical features of tissue macrophages bearing prominent cytoplasmic inclusions, others resembled monocytes or microglial cells. Their cytoplasm contained a variable number of electron-dense granules of size 0.15μm and these exhibited peroxidase activity.

View full abstract

Age related changes of TSH-responsiveness and the iodinating capacity of thyroid follicles in mice 3, 10 and 19-20 months of age were investigated by light and electron microscopy partly using ¹²⁵I radioautography. In 3-month-old mice almost all the thyroid follicles respond to exogenous TSH stimulation and many reabsorbed colloid droplets appear in most follicle epithelial cells. In aged mice extremely large follicles appear in the thyroid. Though some of them react to TSH, others do not show any responsibility to repeated injections of TSH. In 10-month-old mice, TSH-unresponsive follicles occupy about 4.5% of the total number of follicles, and in 19-20-month-old animals about 20%. The follicles of this type, named “cold” follicles, are very large in size and fail to concentrate radioiodine even after repeated injections of TSH. The large lumina of these follicles are surrounded by strongly attenuated epithelial cells. The apical surfaces of these atrophied cells are almost flat. The cytoplasm is occupied by large mitochondria, large secondary lysosomes, rough endoplasmic reticulum with dilated cisternae, and small Golgi apparatus. Some cells in normal follicles are degenerated without losing their cuboidal or columnar shape, showing swelling of the cisternae of rough endoplasmic reticulum and accumulation of secondary lysosomes. The present study indicates that the aging of the thyroid may be manifested by two changes: one is the appearance of “cold” follicles surrounded by attenuated and atrophied cells, and the other is degeneration in normal-shaped, TSH-reactive follicles.

View full abstract

Glutaraldehyde-fixed tissues were treated with HCl and tween 20 to remove such extracellular materials as collagen fibers and basal laminae. In the HCl-treatment the collagen fibers were digested, while in the tween-treatment the basal laminae were removed. By this method the basal interdigitations of cells of the proximal tubule and the pericytes on the capillary wall were clearly demonstrable by scanning electron microscopy (SEM).

View full abstract

Segi's cap, a huge aggregation of basal-granulated cells on the top of the intestinal villi has been known only in human fetuses. This study reveals that the peculiar structure occurs also in cattle and pig fetuses. Segi's cap in these animals mainly consists of argyrophil endocrine cells and, in the cattle fetus, includes gastrin-, somatostatin-, motilin- and secretin-immunoreactive cells.

View full abstract