Ultrastructural aspects of human nonunion.

A histological study on the tissue of nonunion of tibias of two young patients was performed to evaluate the ability of cells to start the mineralization of the matrix. The observations can be summarized as follows: 1) Tissue vessels often appear occluded by thrombotic material; 2) Fibroblasts and chondrocytes found in the nonunion tissue seemed normal, with a good secretion apparatus; 3) The cell membranes were able to produce matrix vesicles; 4) Matrix vesicles and cell membrane looked positive to ALPase reaction, 5) Hydroxyapatite crystals could be observed in the cell matrix or inside matrix vesicles. It may be concluded that cells populating nonunion tissue are well equipped to induct the mineralization of the matrix, but the absence of a blood supply, enough to bring them a normal calcium amount, is the real reason for the nonunion.     

Ultrastructural aspects of the marine fungusJaponochytrium sp.

The morphology and ultrastructure of aJaponochytrium sp. has been studied by light, scanning and transmission electron microscopy. The wall has been shown to be multilamellate and persistent. Stages in zoospore cleavage are described and sagenogenetosomes reported in mature sporangia.     

Ultrastructural aspects of cryofixed nerves

Summary The ultrastructure of the optic and trigeminal nerves of the rat, cryofixed by use of a liquid nitrogenpropane jet, was examined, paying special attention to the myelin sheath and the cytoskeleton of the axoplasm. The cytoskeleton of the axoplasm is formed by a meshwork of neurofilaments and microtubules connected both to each other and also to the cell organelles and axolemma. These cross-linkers are fixed to the longitudinal neurofilaments in a helical arrangement, which could be a morphological substrate for the diverse axonal transport phenomena. The myelin sheath is formed by concentrically apposed membrane pairs, which are not fused together. The corresponding major and intraperiod lines seen using classical electron microscopy are in fact fissures that are obscured by the pattern of the selective deposition of osmium at certain sites and cannot be interpreted as specific structures. The cryofixed myelin membranes have the appearance of predominantly globular subunits arranged in an asymmetrical bilayer. The globular particles are of diverse diameter and occupy varying positions within the membrane. The tight junctions or zonulae occludentes of the myelin are formed by arrays of isolated particles, and consequently the fibril formation seems to be a result of the chemical fixation.     

Ultrastructural aspects of preglioma]

Investigation of submicroscopic changes in the astrocytes after the intracerebral injection of the carcinogen 9,10-dimethyl-1-2-benzanthracene suggested that the so-called substantial period of preglioma began from the 45th day of the experiment, when structurally atypical astrocytes appeared against the background of distrophic changes. The changes in the submicroscopic organization of the astrocytes during chemical carcinogenesis can be divided into three stages: 1) intracellular hyperplasia due to traumatic injury of the brain; 2) dystrophic changes connected with the vascular tissue disturbances and immediate action of the carcinogen on the tissue; 3) atypical ultrastructure reconstruction of the astrocytes.     

Ultrastructural aspects of cat submandibular glands

Submandibular glands of five adult female cats were examined by conventional electron microscopic techniques. All gland acini are mucous secreting and each acinus is capped with mucous secreting demilunar cells. Secretory product of demilunar cells is more electron lucent than that of acinar cells. The demilunes show intercellular tissue spaces and intercellular canaliculi whereas similar specializations are absent between acinar cells. Mitochondria and arrays of granular endoplasmic reticulum are more numerous in demilunar cells than in acinar cells. In acinar and demilunar cells secretory droplets first appear as enlarged Golgi saccules which subsequently become closely related to cisternae of the granular endoplasmic reticulum. Filamentous structures, interpreted as mucin molecules, are present in secretory droplets of acinar cells. Intercalated ducts are short, consisting of several junctional cells between acini and striated ducts. Striated ducts are long and tortuous and contain light cells, dark cells and basal cells. Light cells contain numerous membrane bound granules in their distal ends whereas dark cells show electron lucent vesicles in the same position. Basal cells contain a paucity of organelles and membrane plications but exhibit hemidesmosomes along their basal plasma membranes. Myoepithelial cells are abundant in relation to acinar and demilunar cells. Nerve terminals are present in some instances between acinar cells or between acinar and myoepithelial cells.     

Ultrastructural aspects of the earwig ovary

Ultrastructural studies of the pre-vitellogenic ovaries of Euborellia annulipes indicate an overall structure basically similar to that of other insect ovaries. The membrane surrounding the pore connecting the nurse cell and oöcyte is coated with a thick electron dense material, whereas the cytoplasmic bridge contains few microtubules. All evidence indicates a unidirectional flow of materials synthesized or assembled in the nurse cell into the developing oöcyte.     

Ultrastructural aspects of mouse cecal epithelium

Summary The ultrastructure of the cecal epithelium of the mouse resembles that of more distal parts of the colon. A brief discussion is presented of the possible significance of apical cytoplasmic granules to the glycocalyx and of the close association of microorganisms with the lining epithelium.This research was supported by N.I.H. grant GM-15289. The author thanks Dr. F. J. Agate for the scanning electron micrograph.     

Trout sperm chromatin. II. Ultrastructural aspects after salt dissociation of proteins

The ultrastructural organization of the trout sperm nucleus was studied in ultrathin sections and spread preparations after partial decondensation of the nucleus with increasing NaCl concentrations. The obtained results suggest that the organization of the trout sperm chromatin is much more complex than a pure nucleoprotamine. Three types of complexes were observed. The first one results from the association of DNA with protamines. This complex appears as a fibrous network when partially decondensed nuclei are digested with DNase I indicating that at least a part of DNA remains protected by protamines and favours models accepting a colinear alignment of the latter on the DNA molecules. The second type of structures represent the DNA-protamine fibers compacted into dense clumps which appear as separate compaction units seen upon partial decondensation of the sperm nucleus. A third type are complexes of the ring-shaped granular bodies tightly associated with DNA and resisting high salt-urea and detergent treatment.     

Ultrastructural aspects of Sertoli cells in infancy

In the present study some aspects of Sertoli cells of testicular-biopsy specimens of children from 0 to 8 years old are examined. We can distinguish two main morphological situations. In the first one, Sertoli cells with monomorphic aspect can be seen; in the second can be shown Sertoli cells with various aspects. In this polimorphic situation we can distinguish three Sertoli cell types differing in cellular shape, cytoplasme electron-density and amount of RER and Golgi complex.     

Ultrastructural aspects of wall regeneration byPythium protoplasts

Electron microscope studies were made of wall regeneration byPythium protoplasts. Wall regeneration began with the formation of a loose network of fibrils on the surface of the protoplast followed by increase in density of the fibrillar mesh and deposition of granular matrix material. The majority of the protoplasts did not develop beyond the loose fibrillar network stage, however a small percentage were able to complete wall formation and to form hyphal tubes. A clear zone of demarcation was visible between the fibrillar surface of the protoplast and the smooth surface at the base of the developing hyphal tube.     

Ultrastructural aspects of cell wall synthesis inSpirogyra

Summary Filaments ofSpirogyra were fixed in 2% osmium tetroxide dehydrated in alcohol and embedded in Araldite. The fine structure of cells with regard to wall synthesis was studied. The cell wall was shown to have four layers. The inner one contains microfibrils and is considered to be the cell wall proper. The outer three layers are components of the slime layer. The innermost of these, the second layer of the wall, was shown to be between 1m to 3m and the third 0.3m to 1m. The fourth layer appears as no more than a dark black line measuring 10 nm across. In the cytoplasm two types of vesicles were seen. The largest of these has contents similar in appearance to the slime layer of the wall. This same material was also seen in the large vesicles attached to the Golgi bodies. It is suggested that the smaller vesicles are derived from the larger vesicles and later fuse with the cell membrane. The Golgi bodies were found to be fairly large measuring up to 5m across. Small electron opaque blobs and flecks on the outside of the plasmalemma and in between the microfibrils of the cell wall proper are considered to be mucilage droplets travelling to the slime layer. It cannot be excluded that some of the material of the large vesicles is released directly into the cytoplasm and is transferred without vesicles through the plasma membrane. The negative contrast appearance of the microfibrils seen in the cell wall is thought to be due to the spaces between them being filled with this electron opaque mucilage.Intercisternal rodlets measuring 2.5 nm across were seen in the Golgi bodies.Transverse microtubules were found to occur near the plasmalemma having the same orientation as some of the microfibrils.Lomasome-like structures sometimes with many 5 nm fibrils in their vicinity were seen.