American Journal of Anatomy最新文献

The ultrastructure of nucleoli was examined in developing rat spermatocytes and spermatids, with the help of serial sections. In addition, the radioautographic reaction of nucleoli as examined in rats sacrificed 1 hr after intratesticular injection of 3H(5')-uridine and taken as an index of the rate of synthesis of ribosomal RNA (rRNA). Primary spermatocytes from preleptotene to zygotene have small nucleoli typically composed of fibrillar centers, a fibrillar component, and a granular component, within which are narrow interstitial spaces. During early and mid-pachytene, nucleoli enlarge to about nine times their initial size, with the fibrillar and granular components forming an extensive network of cords--a nucleolonema--within which are wide interstitial spaces. Meanwhile, there appear structures identical to the granular component but distinct from nucleoli; they are referred to as extranucleolar granular elements. Finally, from late pachytene to the first maturation division, nucleoli undergo condensation, as shown by contraction of fibrillar centers into small clumps, while fibrillar and granular components condense and segregate from each other, with a gradual decrease in interstitial spaces. In secondary spermatocytes, nucleoli are compact and rather small, while in young spermatids they are also compact and even smaller. Nucleoli disappear in elongating spermatids. In 3H-uridine radioautographs, nucleolar label is weak in young primary spermatocytes, increases progressively during early pachytene, is strong by the end of mid pachytene, but gradually decreases during late pachytene up to the first maturation division. In secondary spermatocytes and spermatids, there is no significant nucleolar label. In conclusion, rRNA synthesis by nucleoli is low in young spermatocytes. During pachytene, while nucleoli enlarge and form a lacy nucleolonema, rRNA synthesis increases gradually to a high level by the end of mid pachytene. However, during the condensation and segregation of nucleolar components occurring from late pachytene onward, the synthesis gradually decreases and disappears. The small, compact spermatids arising from the second maturation division do not synthesize rRNA.

The ultrastructure of the thyroid epithelial cell was examined at various time intervals after induction of involution of the hyperplastic thyroid gland. Thyroids were made hyperplastic by the feeding of thiouracil in a Remington low-iodine diet to male Fischer rats for 3 weeks. Involution was induced by replacing the thiouracil-containing diet with Purina Laboratory Chow, a high-iodine diet. During involution, organelles that play a role in the synthesis and secretion of thyroglobulin, such as the rough endoplasmic reticulum, Golgi apparatus, and apical vesicles, were well preserved and prominent features of the epithelial cell. The apical plasma membrane of many cells was highly irregular for approximately 2 weeks with signs suggesting rapid discharge of apical-vesical contents into the lumen of the follicle. Pseudopods and colloid droplets were present but were not very prominent features of the cell. No signs of extensive autophagy or obvious increased incidence of lysosomes were present, although there was an elevation in the incidence of small dense bodies starting about day 8, and prominent by 15 days. Some of these may be phagosomes formed from luminal debris. The observations indicate that involution of the hyperplastic thyroid in which there is maintenance of the protein synthetic apparatus and little sign of autophagy or death of the epithelial cells is remarkably different from phenomena occurring during involution of prostate or mammary glands.

Male Fischer rats were fed a low-iodine diet containing thiouracil for 21 days to produce hyperplastic thyroid glands, and then fed a high-iodine diet for various time intervals, from 5 hr to 180 days, in order to study the morphological changes that occur during involution. Thyroids were fixed by perfusion fixation and embedded in Epon. Sections were examined by light microscopy. Initially at 0 days of involution (at the time of the change to the high-iodine diet), follicular lumens were very narrow and capillary lumens were very wide. The capsule was thick and infiltrated with mononuclear leukocytes. No obvious changes occurred for 1 day after the change in diet, but shortly thereafter capillary lumens began to narrow. By 4 days, most capillary lumens were close to normal size; capillaries formed a more or less normal bed except that many were embedded in a relatively thick or wide interfollicular matrix. This matrix was largely gone by 21 days. Between 1 and 21 days, follicular lumens dilated progressively as colloid accumulated. The density of staining of the accumulated colloid varied from follicle to follicle, and this variation was also observed in older controls. Inflammatory cells gradually disappeared from the capsule and most were gone by 15 days. Starting at approximately 15 days and continuing to 180 days, one or more disintegrating cells were found in some lumen profiles. Colloid goiters were not observed in these rats even after several months of involution. Some lumens were rather large, however, and small fractions of the follicles, both small and large, were bounded by flat cells and resembled "cold" follicles morphologically.

In this study measurements were obtained from 359 vertebrae and 215 intervertebral discs in an attempt to classify discs by their size. At the cervical and thoracic levels, this attempt was unproductive because of extensive variations. In the lumbar spine, discs were allocated to six size-matched groups and to two height-matched groups. The breadth of marginal rims were also measured with a view to provide surgeons operating on the spine with precise data on disc morphology to facilitate disc replacement.

Ultrastructural alterations induced by colchicine were investigated to determine the secretory activities of odontogenic cells during formation of tooth enameloid matrix in skates. Treated skate inner dental epithelial (IDE) cells did not display dilated cisternae of the granular endoplasmic reticulum (GER) nor accumulate Golgi-associated secretory granules at any dose level or time interval examined. This response was markedly different from that observed in teleost IDE cells synthesizing the enameloid collagen matrix. Treated skate IDE cells did show increased accumulations of glycogen-containing vesicles and intercellular glycogen associated with amorphous material, compared to controls. Additionally, the aberrant occurrence of large intracellular glycogen pools and amorphous material suggested that carbohydrate processing was a major function of skate IDE cells. Treated odontoblasts associated with enameloid matrix formation sometimes showed dilated GER cisternae, but procollagen secretory granules were not observed. Instead, electron dense material was present within the Golgi cisternae, tubular granules, and large granules. Some electron-dense material appeared to be shunted to a resorptive pathway via multivesicular bodies in treated odontoblasts. The continuity of tubular granules with the enameloid matrix suggested that they contained precursors of the enameloid matrix, and possibly the periodic, 17.5-nm cross-striated, "giant" fibers. Treated odontoblasts associated with predentin collagen matrix deposition showed dilated GER cisternae and accumulations of procollagen secretory granules, features consistent with the function of active collagen synthesis and secretion. The findings indicate that (1) skate IDE cells do not synthesize enameloid collagen as found in bony fish tooth development; (2) skate IDE cells do process glycogen for secretion into the enameloid matrix; (3) collagen, although present, is not a major constituent of skate enameloid matrix; (4) enameloid "giant" fibers are unique to elasmobranchs; and (5) odontoblasts synthesize and secrete proteins other than collagen into the enameloid matrix.

In male Fischer rats, a class of follicles with flat epithelium is present as a minor component of thyroid glands in which most of the follicles have cuboidal epithelium. These follicles occur in thyroids that have been made hyperplastic by feeding the rats thiouracil for 21 days and then allowing involution for 21 days or more. They also occur in older control rats. The follicles resemble in morphology, at the light-microscope level, the so-called "cold" follicles that occur in aged mice. We have examined the ultrastructure of the flat cells in these follicles and compared it with that of the flat cells occurring in the thyroid follicles of hypophysectomized rats. The cells in involution have abundant rough endoplasmic reticulum (RER) and few lysosomes and, in these respects, differ markedly from cells in hypophysectomized rats. The follicles with flat cells are surrounded by a normal incidence of blood capillaries, so that the cells do not appear to be deprived of access to an adequate supply of materials necessary to satisfy their metabolic requirements. Their abundant RER suggests that they have thyroid-stimulating hormone (TSH) receptors, so that the flat cell may be the result of some process occurring at a step distal to receptor coupling with TSH. Their occurrence in young rats after the induction of hyperplasia may be a consequence of cell multiplication producing a clone of neighboring abnormal cells that have an abnormally small cell height.

Mitochondrial structure has been examined in three dimensions using high-resolution scanning electron microscopy in cells from rat liver, retina (photoreceptors and retinal pigment epithelium), and kidney (proximal convoluted tubular cells and podocytes). Tissues were prepared by aldehyde-osmium fixation and freeze cleavage using a cryoprotectant, followed by removal of the cytosol by immersion in a dilute osmium tetroxide solution. The microscope used (Hitachi S-570) was equipped with a secondary electron detector located in the column above the specimen, situated within the objective lens. Mitochondria in all tissues examined were found to have only tubular cristae, which in some instances could be seen to span the entire diameter of the organelle. The walls of the tubular cristae, when unfractured, were in contact with the inner mitochondrial membrane; and their lumens were open to the intermembranous space. We hypothesize that in cells of many, perhaps most tissues, mitochondrial cristae are not shelf-like but are, in fact, tubes which span the mitochondrial matrix and are continuous with the inner mitochondrial membrane at both ends.

The endodermal layer of the human yolk sac was examined three-dimensionally with light microscopy on serial sections using scanning electron microscopy and transmission electron microscopy to find the origin of hemopoiesis in the yolk sac. Cell-labelling techniques were also employed using the monoclonal anti-transferrin receptor antibody. Orifices of the endodermal and intracellular tubules facing the yolk-sac cavity were demonstrated on the endodermal surface. Various-sized blood cells in various stages of differentiation and maturation were distributed in the yolk-sac cavity and tubules and were observed also at the orifices of the tubules. The morphological and the immunological findings suggest that blood cells with large nuclei in the endodermal layer are the most immature. The present results suggest that blood cells originate from the endodermal layer and are carried to the embryo through the yolk sac cavity and the vitelline duct. It is probable that the endodermal and intracellular systems of tubules have an important role in the transport of blood cells, including stem cells.

An immunohistochemical and ultrastructural study of human melanoma colonies grown in soft agar for up to 50 days was performed. Three morphological variants of developing tumor colonies are reported: 1) large light colonies, 2) small dark colonies, and 3) smooth-edged colonies. The large light colony variant is the most frequently observed in the soft agar assay (approximately 70%), followed by the dark colony variant (approximately 27%), and the smooth-edged colony variant (approximately 3%). Major morphological characteristics are associated with each variant, as shown with light microscopy (LM) and transmission electron microscopy (TEM). Both LM and TEM analyses demonstrated that the large light colony variant was hypomelanotic and contained a microfibrillar extracellular matrix (ECM). The small dark colony variant was found to be hypermelanotic and contained a less demonstrable ECM. The smooth-edged variant has an encapsulated periphery, no demonstrable ECM, and tightly packed cells with desmosome-like junctions. In order to characterize further the ECM in the most commonly observed variant, the large light colony, specific antibodies to fibronectin (FN) and collagen types IV and V (COLs IV and V) were applied and observed with immunofluorescence microscopy and immunoperoxidase. In paraffin sections of melanoma colonies, FN was observed associated with both the cell surface and the ECM. However, no specific staining was seen for COLs IV and V. In addition, ruthenium red was used to preserve and selectively bind to glycosaminoglycans (GAGs) and proteoglycans (PGs). TEM studies reveal GAG-like granules stained with ruthenium red in the fibrillar ECM and a dotted, punctate staining of the cell surface. Understanding the biological and architectural composition of developing melanoma tumor colonies in soft agar could contribute to the development of more efficient chemotherapeutic strategies.

Cryostat- and vibratome-cut sections of rat kidneys were singly or doubly labeled to visualize immunoreactive tyrosine hydroxylase (THI), dopamine beta-hydroxylase (DBHI), vasoactive intestinal peptide (VIPI), and neuropeptide Y (NPYI). Rats were perfusion fixed with 2-4% paraformaldehyde with or without 0.15% picric acid and rinsed in buffer for 18-48 hr. Single antigens were labeled with horseradish peroxidase in vibratome sections, whereas cryostat sections were used to label one antigen with peroxidase and another with a fluorophore in the same tissue section. A dense plexus of DBHI noradrenergic nerves innervates the renal arterial tree, and such nerves innervate the interlobar veins and renal calyx as well. Immunoreactive NPY is colocalized in most of these nerves, but some intrarenal noradrenergic nerves do not contain NPY but do contain VIP immunoreactivity. The distribution of NPYI nerves resembles that of DBHI nerves, whereas most perivascular noradrenergic nerves immunoreactive for VIP innervate selected arcuate and interlobular arteries. A small population of nonadrenergic, VIPI nerves innervates the renal calyx.