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Biomedical subjects

R D Allen

Publications and source records attributed to R D Allen.

At least 199 records · Page 11Linked to original sources
PubMed1982

Optical sectioning of HRP-stained molluscan neurons.

The use of high-resolution differential interference contrast(DIC) microscopy on cleared whole-mounts of the circumesophageal nervous system from Hermissenda crassicornis permits visualization of neuronal morphology in detail without the need for physical sectioning. Such optical sectioning, when preceded by intracellular iontophoresis of horseradish peroxidase (HRP) permits rapid and accurate examination of the arborization of electrically characterized neurons. Details such as varicosities and terminal swellings can readily be resolved. This method has revealed new morphological features of neurons implicated in training-specific behavioral modification in Hermissenda, and promises to be of further general use for the quantitative morphometry of electrically identified neurons.

Animals↗
PubMed1982

Meal stimulated gastrin and pancreatic polypeptide levels before and after partial gastric transection for morbid obesity.

The aim of the study was to determine the basal and meal stimulated plasma gastrin and pancreatic polypeptide levels in six morbidly obese patients before and after partial gastric transection (gastroplasty), an operation which results in the distention of the stomach with a small volume of food. The partial gastric transection involved the creation of a proximal gastric pouch of approximately 100 ml, with a 1.2 cm diameter lumen between the proximal and distal gastric pouch. Basal gastrin and pancreatic polypeptide were not altered by the operation. The magnitude of the pancreatic polypeptide response to the mean was significantly depressed, although the time course was not changed. Inhibition of pancreatic secretion is thought to be a physiological function of pancreatic polypeptide, hence its decreased release warrants further investigation in relation to the effect of partial gastric transection on pancreatic function.

Adult↗
PubMed1982

Phagosomal-phagolysosomal membrane dynamics of stimulated mouse peritoneal macrophages.

Freeze-fracture replication was used to study the membrane events of stimulated mouse peritoneal macrophages during phagocytosis. An increase in intramembrane particles (IMPs) was observed on the protoplasmic fracture (PF) face of the freeze-fractured plasma membrane of phagocytosing macrophages as compared to those of the plasma membrane of nonphagocytosing cells. On the basis of freeze-fracture patterns of membranes, three types of phagosomal membranes were found following the ingestion of the streptomycin-dependent mutant (avirulent) of Salmonella typhimurium (SMD). Most phagosomes 10 min after bacterial uptake had membranes that were structurally similar to the plasma membranes of phagocytosing cells. Structural transformations, i.e., changes in IMP number and size distribution, were observed in phagosomal membranes as the time from bacterial uptake increased. Similar types of phagosomal membranes were also found in phagocytosing macrophages when wild-type Salmonella typhimurium (virulent) was used as the phagocytic challenge. Some indirect morphological evidence suggested that membranes may be pinched off from the phagosomes-phagolysosomes which would be available for recycling back to the cell surface. In the systems studied thus far it appears that the freeze-fracture structure of phagolysosomal membranes is significantly different from that of the plasma membranes. In addition, freeze-fracture evidence suggested that fusion can take place between adjacent phagosomes or phagolysosomes.

Animals↗
PubMed1981

Quantitation of human platelet transformation on siliconized glass: comparison of "normal' and "abnormal' platelets.

A series of typical morphological stages, representing progression of transformation, may be defined following adhesion of platelets to a siliconized glass surface. Platelets are visualized by new light microscopic techniques that allow quantitative categorization of transformation of large platelet populations by morphological stage, and thus the detection and elucidation of platelet defects which influence transformation. Living platelets form each of five subjects with bleeding disorders, due to platelet defects, exhibited a pattern of morphologic transformation which differed from normal. In addition, the pattern observed with the platelets from a subject with Glanzmann's thrombasthenia was sufficiently different from that observed with the platelets from four subjects with thrombopathy, so as to point to a qualitative difference in the activity of the platelets in the two disorders. These findings indicate that the analysis of platelet transformation in vitro through the use of light microscopy may allow for detection and further classification of platelet abnormalities.

Blood Platelet Disorders↗
PubMed1981

Video-enhanced contrast polarization (AVEC-POL) microscopy: a new method applied to the detection of birefringence in the motile reticulopodial network of Allogromia laticollaris.

A new method is described for recording rapid processes of cell motility in polarized light. The Allen video-enhanced contrast (AVEC-POL) method of polarization microscopy achieves significant improvements in resolution, contrast, and the visibility of fine detail by a combination of novel adjustments to a standard (unrectified) polarizing microscope and video camera. Using the full working aperture of a high-power planapochromatic objective lens and compensator setting of lambda/9-lambda/4, visible images appear lacking in contrast. However, the same images viewed with an appropriate video camera equipped with an electronic offset adjustment can be made to appear with as much contrast as desired, revealing a significantly greater amount of fine detail in the image than can be seen by high extinction visual microscopy alone. At bias retardations between one-ninth and one-quarter wave, the diffraction anomaly observed near extinction disappears. Consequently, polarizing rectifiers are not required with the AVEC-POL method, and images previously requiring photographic exposures of around 20 seconds are sufficiently bright to be registered on the video monitor in 1/60 second. Using an intensity monitor, quantitative measurements of cellular birefringence can be retrieved from live or videotaped images displaying a linear relationship between contrast and phase retardation due to birefringence. The AVEC-POL method also renders accessible to polarized light analysis a number of objects that scatter or depolarize too much light to be studied by high extinction methods. The method is demonstrated on model objects and applied to the highly motile reticulopodial network of Allogromia laticollaris. Rapid motion in close association with microtubules can now be analyzed in greater detail at a significant reduction in the cost of recording.

Animals↗
PubMed1981

Video-enhanced contrast, differential interference contrast (AVEC-DIC) microscopy: a new method capable of analyzing microtubule-related motility in the reticulopodial network of Allogromia laticollaris.

A new method called Allen Video-enhanced Contrast, Differential Interference Contrast (AVEC-DIC) microscopy is shown to be sufficiently sensitive to detect several new features of microtubule-related motility in the reticulopodial network of the foraminifer, Allogromia. The method takes advantage of the variable gain and offset features of a binary video camera to operate the DIC microscope under conditions highly favorable for video imaging, but in which the optical image is virtually invisible to the eye yet retains its full information when viewed by a suitable video camera. The improvements are made possible by setting a dé Senarmont compensator to lambda/9-lambda/4 at maximal working aperture of internally corrected planapochromatic objectives. Under these conditions, the offset feature of the video camera can reject so much stray light from the instrument and specimen that contrast compares favorably with that observed in high-extinction images, and polarizing rectifiers offer scarcely any advantage. Freed from the constraints of the light-limited conditions of DIC microscopy, video images can be recorded 60 times per second, or over 1,000 times the rate of photomicrographs at comparable magnifications under high-extinction conditions. Application of this method to the reticulopodial network of Allogromia has shown that cytoplasmic organelles are translocated only in contact with single microtubules or bundles of microtubules, and that these organelles fail to move when separated from microtubules. Microtubules themselves undergo both axial translatory ("sliding") and lateral "zipping and unzipping" movements that have been suggested to occur during mitosis and other biological processes.

Animals↗
PubMed1981

Digestive system membranes: freeze-fracture evidence for differentiation and flow in Paramecium.

Freeze-fractured membranes of digestive vacuoles of randomly feeding Paramecium caudatum exhibit dramatic differences in intramembrane particle (IMP) number and distribution on both E- and P-fracture faces. By pulse-feeding latex spheres to cells we have demonstrated that these differences are related to the age of the digestive vacuoles, and that the membranes of such vacuoles undergo a specific sequence of changes during the digestive cycle. Young digestive vacuoles (DV-I; less than or equal to 6 min), nascent vacuoles still connected to the cytopharynx, and discoidal vesicles, from which vacuole membrane is derived, all have a highly particulate E face and a less particulate P face. As early as 3 min after feeding, a second category of digestive vacuoles (DV-II) can be recognized, which are both considerably smaller in diameter and lack particles on their E face. These findings suggest that the endocytic removal of DV-I membrane material associated with the formation of DV-II vacuoles involves a concomitant and selective removal of E-face particles, as essentially no changes are seen in the density of P-face particles on the two types of vacuoles. Beginning at 10 min the first DV-III vacuoles are encountered. These are both larger than the DV-II vacuoles and possess very prominent E-face particles, which resemble those on the E face of the numerous lysosomes bordering the digestive vacuoles. DV-III vacuoles also exhibit a substantial increase in P-face particles. These membrane changes closely parallel, and are probably correlated with, the physiological events occurring within the vacuole lumen: concentration of food, killing of prey, and digestion. Calculations of the amount of membrane removed from DV-I to form DV-II and of the increase in membrane surface area during the transition from DV-II to DV-III indicate that as much as 90% of the initial phagosome (DV-I) membrane can be removed before digestion begins. The enlargment of DV-II must be caused by fusion with adjacent lysosomes which also contribute the new populations of IMPs to the DV-III membrane. The appearance of numerous endocytic structures on older DV-III vacuoles suggests that membrane is retrieved from DV-III before defecation.

Animals↗
PubMed1981

Studies on the motility of the foraminifera. I. Ultrastructure of the reticulopodial network of Allogromia laticollaris (Arnold).

Allogromia laticollaris, a benthic marine foraminifer, extends numerous trunk filopodia that repeatedly branch, anastomose, and fuse again to form the reticulopodial network (RPN), within which an incessant streaming of cytoplasmic particles occurs. The motion of the particles is saltatory and bidirectional, even in the thinnest filopodia detected by optical microscopy. Fibrils are visible by differential interference microscopy, and the PRN displays positive birefringence in polarized light. These fibrils remain intact after lysis and extraction of the RPN in solutions that stabilize microtubules (MTs). Electron micrographs of thin sections through these lysed and stabilized cytoskeletal models reveal bundles of MTs. The RPNs of living Allogromia may be preserved by standard EM fixatives only after acclimatization to calcium-free seawater, in which the streaming is normal. The MTs in the RPN are typically arranged in bundles that generally lie parallel to the long axis of the trunk and branch filopodia. Stereo electron micrographs of whole-mount, fixed, and critical-point-dried organisms show that the complex pattern of MT deployment reflects the pattern of particle motion in both flattened and highly branched portions of the RPN. Cytoplasmic particles, some of which have a fuzzy coat, are closely associated with, and preferentially oriented along, either single MTs or MT bundles. Thin filaments (approximately 5 nm) are also observed within the network, lying parallel to and interdigitating with the MTs, and in flattened terminal areas of the filopodia. These filaments do not bind skeletal muscle myosin S1 under conditions that heavily decorate actin filaments in controls (human blood platelets), and are approximately 20% too thin to be identified ultrastructurally as F-actin.

Actins↗
PubMed1981

Motility.

Explore the source record for details and available documents.

Amoeba↗
PubMed1981

Axenic Paramecium caudatum. III. Biochemical and physiological changes with culture age.

As Paramecium caudatum passes through the lag, log and stationary phases of the culture cycle, cellular protein content, polar (PL) and neutral (NL) lipid contents, marker enzyme activities, rate of digestive vacuole formation and cellular viability undergo characteristic changes. Maximal protein content (60 ng/cell) and enzyme activities ranging from 7 nmoles for catalase to 0.2 pmoles/cell/min for alkaline phosphatase were observed between days 2 and 4. This active metabolism paralleled the fine structure of 1 to 3 day-old cells which contained extensive foci of rough endoplasmic reticulum (RER) partially bordered by Golgi stacks and the rapid depletion of those lipid fields accumulated during day 1. Decrease in protein content and enzyme activities in late log phase indicated a slowing of cellular synthesis. The lipids in the medium were largely depleted and accounted for the low lipid uptake of 14 ng/cell on day 5 as compared with 615 ng/cell on day 1. Yet a vast amount of protein lysate was still available in the culture medium. During stationary phase, catalase activity remained constant, but activities of alkaline and acid phosphatases and 5'nucleotidase declined gradually to low levels, while those of Ca2+-ATPase and malate dehydrogenase declined precipitously. Only 25% of the maximal activities of the latter two enzymes remained by the end of stationary phase. A ten-fold increase in the cellular PL and NL content was already observed 24 h postinoculation. This accumulation was used for subsequent growth and cell divisions; PL declined exponentially and NL less steeply between days 1 and 6. PL remained level (5 ng/cell) throughout stationary phase while NL declined further to 1 ng/cell by day 11. The rate of digestive vacuole formation was constant (6.3 +/- 0.5 DV/5 min pulse) during the entire log phase, then declined from 4.4 on day 6 to 0.22 on day 11. When early to mid-stationary-phase cells were subcultured, some lag in growth was seen; a definite lag was observed when inoculating with late-stationary-phase cells. When early-death-phase cells were given fresh nutrients, many died; the surviving ones became fully rejuvenated after 48 h. The biochemical and physiological data from this study are correlated with the morphological study of the companion paper.

Alkaline Phosphatase↗
PubMed1981

Axenic Paramecium caudatum. II. Changes in fine structure with culture age.

The fine structure of axenically grown Paramecium caudatum undergoes characteristic changes which reflect the cell's nutritional and metabolic conditions. Cells in early log phase of growth contain large lipid accumulations and extensive foci of rough ER bordered by Golgi stacks, indicating an active metabolism. Lipid bodies and ER foci are reduced during mid log phase. By days 5 and 6 (late log phase) some rough ER and a few lipid bodies are found in the cortex while the endoplasm is filled with free ribosomes and small vesicles. Conjugating cells, observed at the onset of stationary phase (day 6), show an accumulation of secondary lysosomes concomitant with a lack of digestive vacuoles. Lipofuscin-like granules and autophagosomes appear on day 7 and increase in number throughout the stationary and death phases. Immature autophagosomes are smaller and are bounded by a "thin" membrane lacking a glycocalyx. Mature autophagosomes (autophagolysosomes) containing partially digested mitochondria have a "thicker" membrane with a glycocalyx, a characteristic of lysosomes. Fusion of lysosomes with autophagosomes is verified by the presence of the natural lysosomal marker, the paracrystalline sheets, in the autophagolysosomes. The residue remaining from the lipid fields on days 5 to 20 includes highly convoluted membrane-like patches with long non-membrane-bound cylinders. Concomitant with the decrease in the number of digestive vacuoles, lysosomes, autophagosomes and lipofuscin-like granules proliferate from day 7 and become the striking feature of death-phase cells. With increased culture age the cisternae of Golgi stacks become dilated and decrease in diameter, and the number of ribosomes on the ER at the cis-face of these stacks is reduced. Mitochondria sometimes increase in density, and some have multi-lamellar whorls extending from their outer membrane.

Cell Survival↗
PubMed1980

Membrane recycling and endocytosis in Paramecium confirmed by horseradish peroxidase pulse-chase studies.

Paramecium caudatum cells were pulse-chased in horseradish peroxidase (HRP) using pulses of 30 s to follow endosome (endocytotic vesicle) formation from defaecating digestive vacuoles and 3-min pulses to follow the movement and fate of these vesicles in the cell. Endosomes formed during the 30 s in HRP are heavily labelled with HRP reaction product and are mostly flattened. Some align along microtubules that point toward the cytopharynx. Diskoidal vesicles at the cytopharynx are unlabelled in unchased cells. Cells exposed to a 3-min HRP pulse contain varied amounts of HRP-labelled diskoidal vesicles at the cytopharynx but no labelled vesicles near their closed cytoprocts. Labelled vesicles are also found aligned along the cytopharyngeal microtubular ribbons. Diskoidal vesicles are no longer labelled after a 47-min chase. Use of pulse-chase HRP cytochemistry supports the hypothesis that the membrane of digestive vacuoles retrieved at the cytoproct is moved along microtubular ribbons directly to the cytopharynx where the membrane enters the diskoidal vesicle pool. This membrane appears to enter neither the Golgi nor lysosomal systems in its passage. HRP reaction product is also found in vesicles near the parasomal sacs, in some secondary lysosomes and in small spherical vesicles that are probably trichocyst membrane fragments. Possibly some membrane from parasomal sacs or condensing digestive vacuoles may also enter the diskoidal vesicle pool but apparently not membrane from trichocysts.

Animals↗
PubMed1979

Transformation and motility of human platelets: details of the shape change and release reaction observed by optical and electron microscopy.

Blood platelets from 10 normal human subjects have been examined with a sensitive differential interference contrast (DIC) microscope. The entire transformation process during adhesion to glass is clearly visible and has been recorded cinematographically, including the disk to sphere change of shape, the formation of sessile protuberances, the extension and retraction of pseudopodia, and the spreading, ruffling, and occasional regression of the hyalomere. The exocytosis of intact dense bodies can be observed either by DIC microscopy, or by epifluorescence microscopy in platelets stained with mepacrine. Details of fluorescent flashes indicate that the dense bodies usually release their contents extracellularly, may do so intracytoplasmically under the influence of strong, short wavelength light on some preparations of mepacrine-stained platelets. The release of one or more dense bodies leaves a crater of variable size on the upper surface of the granulomere. Such craters represent the surface component of the open canalicular system and their formation and disappearance can be directly observed. Because these techniques permit quantitation of several parameters of motility which are not readily observable by other techniques, it is suggested that high extinction DIC microscope examination may become a rapid and useful method of studying congenital and acquired platelet disorders. Many features of platelet transformation have been confirmed and extended by scanning electron micrographs. These can in turn be interpreted by reference to time-lapse films of living platelets.

Blood Platelets↗