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Biomedical subjects

F N Low

Publications and source records attributed to F N Low.

At least 37 records · Page 2Linked to original sources
PubMed1979

Scanning electron microscopy of the subarachnoid space in the dog: evidence for a non-hematogenous origin of subarachnoid macrophages.

Injection of viable BCG into the subarachnoid space of immunized and non-immunized dogs produced a 10-fold increase in the populations of pial free cells. In immunized animals injected three days previously with BCG, stereoscopic SEM revealed that many pial cells had rounded up and were protruding into the subarachnoid space. With continued rounding these cells took on amoeboid characteristics, with shapes that suggested a capacity for cell movement. Internally, these pial cells possessed an increased volume of perinuclear cytoplasm and organelles. Reactive pial cells could be distinguished from macrophages of presumed hematogenous origin on the basis of their surface morphology. These findings suggested that pial cells had the ability to alter their normal structural and behavioral characteristics and to become macrophage-like under these conditions of secondary challenge by BCG.

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PubMed1978

Effects of cytochalasin B on the fine structure of organized endodermal cells of the early chick embryo.

Fresh pullet eggs (White Leghorn) were incubated for 36 to 48 hours. The blastoderms were exposed to cytochalasin B (CB), 10 or 40 microgram/ml, for 2, 5, and 15 minutes prior to fixation by immersion in buffered chick Ringers solution containing CB, previously dissolved in dimethysulfoxide (DMSO), or by sub-blastodermic injection. Controls fixed in ovo possess relatively flat surfaces with bulges due to uptake of yolk. Numerous microappendages (blebs, microvilli and ruffles) are present, especially at cell margins. DMSO-controls present a similar cell surface except that small blebs are more prominent. The plasmalemmas of CB-treated endodermal cells possess numerous large blebs (2-10 micron in diameter), smaller blebs (0.2 micron) and microvilli. Cell dissociation occurs in selected areas resulting in rounded cells, devoid of microappendages, with peripheral processes. Transmission electron microscopic preparations of tissues similar to those used for scanning electron microscopy reveal that large blebs are filled with membranous material. Microfilaments are present but lack their normal subplasmalemmal arrangement. Microtubules and other cell organelles are apparently unaffected by CB. Evidence in this study supports the concept that cytochalasin B exerts its influence through alteration of the plasmalemma.

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PubMed1977

Scanning electron microscopy of the subarachnoid space in the dog. V. Macrophages challenged by bacillus Calmette-Guerin.

Mongrel dogs were anesthetized intraperitoneally with pentobarbitol. One cc of cerebrospinal fluid was drawn through a needle inserted into the cisterna magna and mixed with 1 cc (4-9 million viable BCG organisms) of freeze-dried bacillus Calmette-Guerin. One minute later this mixture was injected by the same needle into the cisterna magna. At 1 and 12 days postinjection, experimental animals were perfused with buffered aldehydes. Samples of the leptomeninges were post-fixed in OsO4 and routinely prepared for scanning and transmission electron microscopy. Leptomeningeal samples of untreated, control animals were similarly prepared. Scanning and transmission microscopy confirm that free cells resting on the subarachnoid linings and within the subpial connective tissue space of control animals possess the morphology of macrophages (Malloy and Low, '76). Viable BCG in the subarachnoid space produces a 3-fold increase in the free cell population of the leptomeninges in 24 hours and a 10-fold increase in 12 days. These cells tend to form associations varying from loose aggregates to tight clusters. Approximately 80% of these free cells express macrophage morphology, with abundant plasma-lemmal microappendages and cytoplasmic vacuoles. Transmission electron microscopy of the free cell population of BCG-stimulated animals reveals at least two other members of the leukocyte series on the leptomeningeal linings.

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PubMed1977

Glutaraldehyde fixative tonicity for scanning electron microscopy of delicate chick embryos.

Fresh pullet eggs (White Leghorn strain) were incubated from 19-2ldium-gold and observed in a Cambridge S4 scanning electron microscope. Shrunken cells with intracellular yolk granules embossed on the surface are produced by the strongly hypertonic Karnovsky's fixer (Final: 2010 mOsm). Embryos fixed with modified Karnovsky's fixer (Final: 373 mOsm) possess surfaces with irregular microappendages. Swollen cells with few microappendages are observed when embryos are fixed in a hypotonic environment (Final: 250 mOsm or less). Ideal fixatives preserve a relatively flat surface, with cells bordered by smoothsurface microappendages. For adequate SEM fixation, fixative vehicle should be approximately isotonic for tissue, with aldehyde (2% or less) added to vehicle.

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PubMed1977

Identification of challenged subarachnoid free cells.

Three distinct types of free cell contours are recognizable in scanning electron microscopy (SEM) on the leptomeningeal sheaths of dogs twelve days after an intrathecal injection of bacillus of dogs twelve days after an intrathecal injection of bacillus Calmette-Guerin (BCG). Macrophages posses abundant plasmalemnal blebs which are shown in transmission electron microscopy (TEM) to be composed of large membrane-bound vacuoles. Smooth surfaced lymphoblasts exhibit many basal microvilli that rest upon and often indent the plasmalemma of an underlying pial cell. Neutrophils display many microvilli over their rounded, chrysanthemum-like surfaces. The consistency with which these external features are expressed suggests that each cell type possesses characteristic surface topography, at least under these conditions of challenge.

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PubMed1977

High-voltage electron microscopy of extracellular fibrillogenesis.

High-voltage electron microscopy was employed to observe developing extracellular connective tissue elements in the cervical perinotochordal and perivertebral regions in the chick embryo from 2 through 15 days' incubation. During days 2 and 3, small (10 nm) and large (18-20 nm) microfibrils surrounded the notochord, becoming evident around fibroblast-like cells in day 4. Amorphous material, globular granules and microfibrillar bundles were present at this time. Microfibrillar length increased as did the total population of microfibrils. At four days microfibrils 3-5 nm in diameter arose in all directions from globular granules. During day 9 and thereafter to day 15, microfibrillar diameters increased. This growth formed unit collagenous fibrils 30 nm in diameter or greater. Axial periodicity became evident at day 14. Small microfibrils appear to be composed largely of glycoproteins and do not contain a significant amount of collagen. The globular granules and associated filaments are probably proteoglycans. The amorphous material is believed to provide molecular collagen to developing fibrils. Large microfibrils and unit collagenous fibrils contain significant amounts of molecular collagen.

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PubMed1976

Scanning electron microscopy of the subarachnoid space in the dog. IV. Subarachnoid macrophages.

Young dogs of both sexes were used in this study. Transmission and scanning electron microscopy were utilized for the examination of the spinal cord and choroid plexus with emphasis on the study of free cells. These procedures were modified so that, in certain cases, the same cells observed in scanning electron microscopy could be analyzed internally by transmission electron microscopy. One half of the animals were injected under anesthesia with horseradish peroxidase for observation of phagocytosis. This study confirms that the free cells observed in the subarachnoid space with the scanning and transmission electron microscopes are identical. The internal morphology of these cells corresponds to that of macrophages. This is further substantiated by the ability of these cells to localize horseradish peroxidase in discrete vacuoles within their cytoplasms. Both pial macrophages and epiplexus cells localize peroxidase in an identical manner in the same animal after one injection. In addition macrophages on the surface of the pia mater respond to extravasated red blood cells in a characteristic manner including phagocytosis. The plentiful population of macrophages on the surface of the pia mater supports the concept that these cells are of major importance in maintaining asepsis in the subarachnoid space.

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PubMed1975

Scanning electron microscopy of the subarachnoid space in the dog. III. Cranial levels.

Young dogs were anesthetized by intrathoracic injection of sodium pentobarbital and perfused with buffered aldehydes. Lining tissue samples from the cranial subarachnoid space were prepared for scanning electron microscopy (SEM) by postfixing in buffered OSO4. Samples were then dehydrated, dried in a Critical Point Drying System, and coated with carbon and palladium-gold. Specimens were viewed in a Cambridge S4 scanning electron microscope. After thorough scanning, selected samples were routinely prepared for transmission electron microscopy (TEM) and viewed in a Philips EM-200 transmission electron microscope. This study depicts the surface morphology of the meningeal linings of the cranial subarachnoid space. The cranial pia mater possesses natural gaps or fenestrations between cells. SEM reveals a more complex morphology of arachnoid trabeculae than previously interpreted from light and transmission electron microscopy. Many free cells are observed on the meningeal linings of the subarachnoid space. The present study establishes that these free cells are macrophages by means of definitive TEM correlates. Microvillous-like processes extending between macrophages and the pial surface are present. The frequency and the nature of these thin processes suggest the possibility of a plasmalemma-mediated system of communication.

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PubMed1975

Scanning electron microscopy of cardiac endothelium of the dog.

Tissue obtained from young dogs was fixed in buffered aldehydes by vascular perfusion or direct immersion. Selected hearts were maintained in modified mammalian Ringer's solution for three to five minutes prior to fixation. The chambers of the heart and related valves were exposed by dissection and prepared by routine techniques for observation by scanning electron microscopy (SEM). Subsequent to SEM studies, selected specimens were embedded in Epon 812 and sectioned for transmission electron microscopy (TEM). The cardiac endothelium, when fixed immediately in buffered aldehydes, presents an essentially invariable surface throughout the interior of the heart. The predominant nuclear bulges and attenuated peripheral plasmatemma are consistently smooth, with occasional marginal ruffles, scattered microvilli and small blebs. Apart from the higher population of nuclear bulges on valvular surfaces, local variations in SEM of endocardium occur in response to the various stages of systole and diastole encountered. These physiological changes do not produce microappendages. Immersion for three to five minutes in (Chenoweth's) Ringer's solution, prior to fixation, produces a substantial population of microappendages. The cellular surface acquires a swirled appearance erupting in microvilli, blebs and ruffles. These exhibit considerable pleomorphism. There is great lability of the endocardial surface in response to a classic "holding solution" widely used in preparatory techniques. In preparing soft tissues for SEM caution must be used if physiological "holding solutions" are used prior to fixation.

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PubMed1975

Scanning electron microscopy of volk absorption in early chick embryos.

Fresh pullet eggs (White Leghorn Strain) were incubated from 6-19 hours. Blastoderms were fixed in situ with aldehyde fixative, post-osmicated in 2% OsO4, dehydrated in acetone, critical-point-dried, mounted ventral side up, coated with palladium-gold wire and observed in a Cambridge Stereoscan S4 scanning electron microscope. Large extracellular yolk granules had a smooth surface and appeared to break up into smaller particles. Similar particles have been observed intracellularly in transmission electron microscopy. Numerous microappendages, mostly ruffles, suggest phagocytosis as a method of absorption of yolk granules into the cells. Absorption of yolk by the cells of the blastoderm involves an initial break up of yolk granules followed by phagocytosis.

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PubMed1975

An unusual type of cilium.

The connective tissue cells of the dentinal pulp of unerupted dog teeth possess occasional cilia. Internally there are 4 to 8 peripheral doublets and one central doublet. Nine peripheral doublets are observed only close to or near the basal body.

Animals↗
PubMed1975

Mitotic cells and their microappendages in the primitive streak of the chick embryo.

Fresh pullet eggs (White Leghorn Strain) were incubated to the primitive streak stage of development. Blastoderms were fixed in situ with isotonic aldehyde fixatives and prepared for scanning electron miscropy by means of post-osmication, critical point drying and gold-palladium coating. Cells judged to be in various stages of mitosis by their surface contours were numerous on the ventral surface of the chick blastoderm. Cells which were in the late preparatory stages for mitosis had rounded up from their surroundings. Microvilli dominated the surface. The degree of separation and number of microvilli increased until late metaphase or anaphase. Mitotic cells did not completely separate themselves from adjacent cells. Ruffles and blebs were not prominent during mitotis and long filopodia were absent. A definite localization of microappendages (microvilli, blebs, ruffles) to the area of cytokinesis was evident in early telophase and persisted through daughter cell formation.

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PubMed1975

Morphological and histochemical evidence of mitoribosomes in Manduca sexta.

The mitochondria found in the neurons of the frontal ganglion of Manduca sexta contained numerous mitoribosomes. The mitochondria of the glial and perineural cells did not contain mitoribosomes. The mitoribosomes were digested in RNase whereas phospholipase C digested the cellular membranes but had no effect on the mitoribosomes.

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