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At least 955 records · Page 53Linked to original sources
PubMed1997

The beta-amyloid precursor protein of Alzheimer's disease enhances neuron viability and modulates neuronal polarity.

beta-Amyloid precursor protein (betaPP) can reside at neuron and glial cell surfaces or undergo proteolytic processing into secreted fragments. Although betaPP has been studied extensively, its precise physiological role is unknown. A line of transgenic knock-out mice selectively deficient in betaPP survive and breed but exhibit motor dysfunction and brain gliosis, consistent with a physiological role for betaPP in neuron development. To elucidate these functions, we cultured hippocampal neurons from wild-type and betaPP-deficient mice and compared their ability to attach, survive, and develop neurites. We found that hippocampal neurons from betaPP-deficient mice had diminished viability and retarded neurite development. We also compared the effects of betaPP secretory products, released from wild-type astrocytes, on process outgrowth from wild-type and betaPP-deficient hippocampal neurons. Outgrowth was enhanced at 1 d in the presence of wild-type astrocytes, as compared with betaPP-deficient astrocytes. However, by 3 d, neurons had shorter axons but more minor processes with more branching when cocultured with wild-type astrocytes, as compared with betaPP-deficient astrocytes. Our data demonstrate that cell-associated neuronal betaPP contributes to neuron viability, axonogenesis, and arborization and that betaPP secretory products modulate axon growth, dendrite branching, and dendrite numbers.

Alzheimer Disease↗
PubMed1997

Crosslinking of the U5 snRNP-specific 116-kDa protein to RNA hairpins that block step 2 of splicing.

Step 2 of pre-mRNA splicing has characteristics that are suggestive of a 5' to 3' scanning process from the branch point to locate the 3' splice site. Specifically, the 3' splice site is almost always at the first AG downstream of the branch point even when the two elements are separated by hundreds of nucleotides. Insertion of new AGs between the branch and 3' splice site, or mutation of the wild-type 3' splice site, usually results in use of the new first AG as the 3' splice site. Finally, insertion of stable secondary structure between the branch point and 3' splice site, but distant from both elements, results in a block to step 2. We have sought to complement this circumstantial evidence by detecting physical contacts between the spliceosome and the RNA substrate in regions that are not themselves important for splicing, other than that they lie between the branch point/polypyrimidine tract and the 3' splice site. We have blocked step 2 of splicing by insertion of hairpin structures between the branch point and 3' splice site and applied methylene blue-mediated crosslinking, which is specific for protein-dsRNA interactions. Using this approach, we have detected a 116-kDa crosslinked protein that appears after step 1 of splicing with all transcripts containing a hairpin downstream of the branch point. The protein was identified as the 116-kDa U5 snRNP protein, which is a GTP-binding protein involved in step 2 of splicing. The crosslinking characteristics of U5 p116 are consistent with it having a role in locating the 3' splice site AG prior to step 2 of splicing.

HeLa Cells↗
PubMed1998

[Quantification of pericentral NADPH-diaphorase neurons in the spinal cord of rabbits].

BACKGROUND: The freely diffusible radical nitric oxide is generated by nitric oxide synthase, and is bioregulatory molecule that functions as a major neurotransmitter. Constitutive nitric oxide synthase exhibits NADPH-diaphorase activity that can be demonstrated histochemically. OBJECTIVE: The purpose of the present investigation was to characterize and determine number of NADPH-diaphorase positive neurons around the central canal in all segments of the rabbit spinal cord. METHODS: Rabbits Chinchilla were used in this experiment. After intracardiac perfusion the spinal cords were removed, cut into slices and histochemical analysis of NADPH-diaphorase activity was performed. Sections were evaluated by using light microscope. RESULTS: NADPH-diaphorase positive pericentral neurons were present in cervical, thoracic, lumbar; sacral and coccygeal segments. They differed in the shape of their bodies and in length and branching of their processes. The main differentiation was observed in their number depending on the place of localisation. The highest number of these NADPH-diaphorase positive neurons was in sacral part (6 in average), the lowest one was noticeable in thoracic spinal cord (1-2 in average). CONCLUSION: Thus, our study suggests that pericentral neurons of the rabbit spinal cord which are capable of synthesizing nitric oxide, differs in number amount depending on the place of their localization in each spinal cord segments. (Tab. 2, Fig. 9, Ref. 21.)

Animals↗
PubMed1993

False pancreas divisum: not a difficult diagnosis.

OBJECTIVE: To study the clinical and cholangiopancreatographic features in cases of false pancreas divisum. METHODS: Six patients with pancreatic duct block to the right of the spine detected among 300 consecutive endoscopic retrograde cholangiopancreatograms (ERCP) done during April 1990 to March 1992 formed the basis of the study. The clinical and radiological features of these six cases of false pancreas divisum were analyzed. OUTCOME MEASURES & RESULTS: The causes of false pancreas divisum were carcinoma of pancreas (3 patients), pancreatic trauma (2) and pancreatitis with infected pseudocyst (1). Three patients presented with obstructive jaundice and three with pain in the abdomen. On ERCP, the pancreatic duct length varied from 3.5 cm to 5.0 cm and the diameter ranged from 2.0-6.5 mm. Terminal arborization of pancreatic duct was absent in all cases. In both patients with pancreatic trauma there was displacement of the pancreatic duct towards the common bile duct. A branch to the uncinate process originating from the main pancreatic duct was seen in 4 patients and contrast spilling at the site of block was seen in two patients. CONCLUSION: History of abdominal trauma; demonstration of space occupying lesion in the pancreas; displaced, dilated pancreatic duct which terminates without arborization with or without leakage of contrast; and presence of a branch to the uncinate process arising from the pancreatic duct on pancreatography strongly suggest a diagnosis of false pancreas divisum.

Adult↗
PubMed1983

Surface view of strial vessel, prominence vessel, and external sulcus cells as revealed by scanning electron microscopy.

The stria vascularis and the spiral prominence in the lateral cochlear wall were observed with scanning electron microscopy (SEM) after dissolving out the epithelial layer and the basement membrane by tryptic digestion and HCl hydrolysis. The external sulcus cells have regularly arranged pegs and a fine basal interdigitation on the cell surface. The strial vessel and the spiral prominence vessel could be visualized well and the characteristic surface view of their periendothelial cells presented. The former has cytoplasmic processes with a fine branching appearance similar to red coral and the latter has bulged popcorn like processes. Their functional significance is discussed.

Animals↗
PubMed1988

Antibodies to cell surface ganglioside GD3 perturb inductive epithelial-mesenchymal interactions.

Most epithelial sheets emerge during embryogenesis by a branching and growth of the epithelium. The surrounding mesenchyme is crucial for this process. We report that branching morphogenesis and the formation of a new epithelium from the mesenchyme in the embryonic kidney can be blocked by a monoclonal antibody reacting with a surface glycolipid, disialoganglioside GD3. In contrast, a more than 10-fold excess of antibodies to adhesive glycoproteins (N-CAM, L-CAM, fibronectin) fails to inhibit morphogenesis. Although the anti-GD3 antibody affected epithelial development, the disialoganglioside GD3 was expressed not in the epithelium, but in the mesenchyme surrounding the developing epithelia. The data raise the intriguing possibility that the anti-GD3 antibody inhibits epithelial development by interfering with epithelial-mesenchymal interactions.

Animals↗
PubMed1992

[Acute and subacute dissection of the thoracic aorta: diagnostic importance of magnetic resonance tomography].

The purpose of this study was to retrospectively assess the reliability of ECG-triggered magnetic resonance imaging (MRI) for the diagnosis of acute and subacute thoracic aortic dissection and associated clinical epiphenomena. 67 patients were subjected to MRI; the diagnostic results were compared with morphological standards. 25 patients had type A, 12 patients type B dissection. In 30 cases a dissection was excluded. 17 patients with aortic dissection had acute onset of symptoms, 10 patients had subacute onset of symptoms. 17 patients revealed thrombosis of the false lumen, which was found in the descending aorta in 59% of the cases. Aortic regurgitation and pericardial effusion was most often associated with type A dissection (Table 1). Three patients were studied while on mechanical ventilation. Scan time for MRI ranged from 15 to 71 minutes with an average of 46 +/- 18 minutes. In this series no deleterious events were encountered related to MRI diagnostics. In contrast to previously published data using other noninvasive techniques the sensitivity of MRI was 100% for detecting a dissection in the ascending segment of the thoracic aorta. Moreover, the specificity of MRI for a dissection was 100% and thus higher than previously published data using transesophageal echocardiography. Sensitivity and specificity for detection and correct classification of type B dissection was 100% and 100% respectively (Table 2). In addition, MRI proved to be sensitive in detecting the formation of thrombus material in the false lumen of the ascending aorta (92%), the aortic arch (100%) and the descending segment (88%). Specificity for exclusion of suspected thrombus material even proved to be slightly higher with 100% in the ascending and descending aorta and 96.1% in the aortic arch (Table 3). The site of entry to a dissection was detected in 78%, with a sensitivity of 76% in the ascending and 92% in the descending aorta. The involvement of side branches in the dissecting process was identified in 60%. There were no false positive findings concerning side branch involvement. Aortic regurgitation and pericardial effusion were detected in 100% and 100%, respectively (Tables 1 and 2). MRI performed even in acute cases proved to be a atraumatic, safe and highly sensitive method to identify and classify acute and subacute dissections of the entire thoracic aorta. Limited patient access was not associated with an increased risk and mechanical ventilation did not interfere with MRI. These results may establish MRI as a valid and promising noninvasive technique to establish the diagnosis in patients with thoracic aortic dissection.(ABSTRACT TRUNCATED AT 400 WORDS)

Acute Disease↗
PubMed1979

[The human dental pulp as viewed through a scanning electron microscope (author's transl)].

The human dental pulp was examined using a scanning electron microscope. The odontoblasts are pear-shaped and have a fine-grain surface structure. Tomes' process divides into fine branches before entering the predentin. Very few fibroblasts were found. These had stronger cell processes at the two terminal poles. Adhering to their surfaces were fine fibers. Collagenous and nerve fibers could not be accurately identified in the rich fibrillary network of the pulp. Stronger nerve fasciculi were readily observable through longitudinal sulci. Thinner fibers were seen to spread out in branches from some nerve bundles. The capillaries were observed to be surrounded by a sheath of fine fibrils.

Capillaries↗
PubMed1986

Identification of a novel Y branch structure as an intermediate in trypanosome mRNA processing: evidence for trans splicing.

We present evidence that addition of the 35 nucleotide spliced leader (SL) to the 5' end of T. brucei mRNAs occurs via trans RNA splicing. A 100 nucleotide fragment of the 135 base SL RNA (100-mer) is revealed by S1 nuclease analysis of total and poly(A)+ RNA. This 100-mer is not detected by Northern hybridization analysis, indicating that it does not exist free in the cell. The 5' end of the 100-mer maps precisely to the conserved splice junction sequence of the SL RNA. Purified debranching enzyme releases this 100-mer RNA as a free, 100 nucleotide species. This indicates that the 100-mer is covalently linked to poly(A)+ RNA by a 2'-5' phosphodiester bond, that the branched intermediate has a discontinuous intron or Y structure (rather than a lariat), which is expected of a trans-spliced mRNA, and that the SL RNA is indeed the donor of the SL sequence to trypanosome mRNAs.

Animals↗
PubMed1989

Distribution and spatial geometry of dopamine interplexiform cells in the rat retina: I. Developing retina.

The morphology and distribution of dopaminergic interplexiform cells were analyzed in 9-day-old rat retinas processed as wholemounts for tyrosine hydroxylase immunohistochemistry. The mean number of dopaminergic interplexiform cells was estimated as about half of the total number of dopaminergic neurons in the immature retina, with a higher density in the temporal retina. Four interplexiform cells were individually analyzed and reconstructed with a computer system. Their arborizations could be divided into three different regions based on both their morphological features and their position within the retinal layers: (1) an internal arborization, spreading at the margin between the inner nuclear layer and the inner plexiform layer, composed of long, thick, somatofugal dendrites branching at acute angles, (2) an external arborization in the middle of the inner nuclear layer, formed by short, thin, varicose, recurved, axon-like processes branching at right angles, (3) and one or more scleral process(es), originating either from the cell body or from the internal arborization, running toward the outermost cell row of the INL, some of which reached the outer plexiform layer. Finally, analysis of the arborization network by computer simulations based on the 4 digitalized cells was compared with a nearest-neighbour analysis of cell body distribution. It showed that cell bodies are almost randomly distributed--at least in the inferior retina--but that an adjustment of dendritic growth and orientation probably occurs to ensure a homogeneous coverage of the retina with a constant degree of overlap in the adult. This report represents the first three-dimensional computer reconstruction of chemically identified neurons in the retina.

Animals↗
PubMed2006

Astrophysical reaction rate for the neutron-generator reaction 13C(alpha,n)16O in asymptotic giant branch stars.

The reaction 13C(alpha,n) is considered to be the main source of neutrons for the s process in asymptotic giant branch stars. At low energies, the cross section is dominated by the 1/2+ 6.356 MeV subthreshold resonance in (17)O whose contribution at stellar temperatures is uncertain by a factor of 10. In this work, we performed the most precise determination of the low-energy astrophysical S factor using the indirect asymptotic normalization (ANC) technique. The alpha-particle ANC for the subthreshold state has been measured using the sub-Coulomb alpha-transfer reaction ((6)Li,d). Using the determined ANC, we calculated S(0), which turns out to be an order of magnitude smaller than in the nuclear astrophysics compilation of reaction rates.

Journal Article↗
PubMed2002

Branching, segmentation and the metapterygial axis: pattern versus process in the vertebrate limb.

Explanations of the patterns of vertebrate fin and limb evolution are improving as specific hypotheses based on molecular and developmental data are proposed and tested. Comparative analyses of gene expression patterns and functions in developing limbs, and morphological patterns in embryonic, adult and fossil limbs point to digit specification as a key developmental innovation associated with the origin of tetrapods. Digit development during the fin-to-limb transition involved sustained proximodistal outgrowth and a new phase of Hox gene expression in the distal fin bud. These patterning changes in the distal limb have been explained by the linked concepts of the metapterygial axis and the digital arch. These have been proposed to account for the generation of limb pattern by sequential branching and segmentation of precartilagenous elements along the proximodistal axis of the limb. While these ideas have been very fruitful, they have become increasingly difficult to reconcile with experimental and comparative studies of fin and limb development. Here we argue that limb development does not involve a branching mechanism, and reassess the concept of a metapterygial axis in limb development and evolution.

Animals↗
PubMed1980

The projections of neurosecretory cells in the brain of the North-American medicinal leech, Macrobdella decora, using intracellular injection of horseradish peroxidase.

The projections of four anatomically distinct groups of putative neurosecretory cells found within the supra-oesophageal ganglion of the leech Macrobdella decora were studied by intracellular injection of horseradish peroxidase. All four groups have their own characteristic branching pattern while sharing the common feature of possessing primary branches that project into the dorsal commissure. Numerous secondary processes extend from these primary branches to terminate within the neural lamella, as well as within the neuropile. Electron microscopy of the regions into which these secondary processes project reveals numerous neurosecretory terminals. The data suggests that the midregion of the dorsal commissure constitutes a neurohemal complex. These observations strengthen the argument that the four groups of identified cells are indeed neurosecretory.

Animals↗
PubMed2006

Mycobacteriophage exploit NHEJ to facilitate genome circularization.

Ku-dependent nonhomologous end joining (NHEJ) is a double-strand break repair process conserved in all branches of cellular life but has not previously been implicated in the DNA metabolic processes of viruses. We identified Ku homologs in Corndog and Omega, two related mycobacteriophages of Mycobacterium smegmatis. These proteins formed homodimers and bound DNA ends in a manner identical to other Ku's and stimulated joining of ends by the host NHEJ DNA ligase (LigD). Omega and Corndog are unusual in having short 4 base cos ends that would not be expected to self-anneal and would therefore require NHEJ during phage genome circularization. Consistently, M. smegmatis LigD null strains are entirely and selectively unable to support infection by Corndog or Omega, with concomitant failure of genome circularization. These results establish a new paradigm for sequestration of the host cell NHEJ process by bacteriophage and provide a framework for understanding similar transactions in eukaryotic viral infections.

Antigens, Nuclear↗
PubMed1980

Initial observations on the ocular microcirculation in man. I. The anterior segment and extraocular muscles.

Gold-coated, plastic corrosion casts of the human ocular microcirculation were studied by scanning electron microscopy to define the angioarchitecture of the anterior segment, ciliary processes, and extraocular muscles. Several arterial branches from the major arterial circle (MAC) supplied each ciliary process. The afferent arterial supply may be regulated by a sphincter mechanism at its branch point from the MAC. The ciliary processes and ciliary muscle seem to be drained by iris veins and prominent venules, one of which is present between each pair of ciliary processes, and directly into pars plana veins. The predominant drainage channel of the ciliary processes is directly into the pars planar veins; the ciliary muscle seems to be drained by the other two routes primarily. The extraocular muscles possess a rich blood supply. No anastomoses of the anterior ciliary arteries with the MAC were noted, although they did contribute to the blood supply of the iris, ciliary muscle, and episcleral vascular complex.

Aqueous Humor↗
PubMed1989

Monensin influences basal and human growth hormone-releasing hormone 44-induced release of stored and new rat growth hormone and prolactin.

When previous data suggested a growth hormone-releasing factor (GRF)-sensitive branch in intracellular hormone processing, the monensin-sensitive Golgi apparatus seemed a likely candidate. We examined monensin's effect on basal and GRF-stimulated release of newly synthesized and stored rat growth hormone (rGH) and rat prolactin (rPRL). 14C-Pre-labeled, perifused rat pituitary fragments were exposed to [3H]leucine in 0-10 microM monensin; a pulse of 3 nM GRF assessed subsequent secretory responsivity. Monensin dose-dependently reduced basal release of stored [14C]rGH and [14C]rPRL. GRF-stimulated release of stored [14C]hormone was doubled after 0.03 microM and 0.1 microM monensin; higher concentrations diminished stored hormone release. Low concentrations of monensin accelerated basal (0.03 microM and 0.1 microM) and GRF-stimulated (0.03 microM) [3H]rGH and [3H]rPRL release without altering recovery; higher monensin concentrations (greater than or equal to 1 microM) reduced basal, and abolished GRF-stimulated, new hormone release and reduced total [3H]rGH and [3H]rPRL recovery. These data are consistent with a GRF-sensitive and monensin-influenced branch in intracellular hormone processing that regulates the fraction of new hormone exiting the cell without prior immersion in storage compartments.

Animals↗
PubMed1994

Compartmental modeling of rat macular primary afferents from three-dimensional reconstructions of transmission electron micrographs of serial sections.

1. We cut serial sections through the medial part of the rat vestibular macula for transmission electron microscopic (TEM) examination, computer-assisted three-dimensional (3-D) reconstruction, and compartmental modeling. The ultrastructural research showed that many primary vestibular neurons have an unmyelinated segment, often branched, that extends between the heminode [putative site of the spike initiation zone (SIZ)] and the expanded terminal(s) (calyx, calyces). These segments, termed the neuron branches, and the calyces frequently have spinelike processes of various dimensions that morphologically are afferent, efferent, or reciprocal to other macular neural elements. The purpose of this research was to determine whether morphometric data obtained ultrastructurally were essential to compartmental models [i.e., they influenced action potential (AP) generation, latency, or amplitude] or whether afferent parts could be collapsed into more simple units without markedly affecting results. We used the compartmental modeling program NEURON for this research. 2. In the first set of simulations we studied the relative importance of small variations in process morphology on distant depolarization. A process was placed midway along an isolated piece of a passive neuron branch. The dimensions of the four processes corresponded to actual processes in the serial sections. A synapse, placed on the head of each process, was activated and depolarization was recorded at the end of the neuron branch. When we used 5 nS synaptic conductance, depolarization varied by 3 mV. In a systematic study over a representative range of stem dimensions, depolarization varied by 15.7 mV. Smaller conductances produced smaller effects. Increasing membrane resistivity from 5,000 to 50,000 omega cm2 had no significant effect. 3. In a second series of simulations, using whole primary afferents, we examined the combined effects of process location and afferent morphology on depolarization magnitude and latency, and the effect of activating synapses individually or simultaneously. Process location affects peak latency and voltage recorded at the heminode. A synapse on a calyceal process produced < or = 8% more depolarization and a 23% increase in peak latency compared with a synapse on a process of a neuron branch. For whole primary afferents, depolarization decreased 40% between simulations of the smallest and largest afferents. Simulations in which membrane resistivity and synaptic conductance were varied while afferent geometry was kept constant indicated that use of 5,000 omega cm2 and 1.0 nS produced results that best fit electrophysiological findings. Synaptic inputs activated simultaneously did not sum linearly at the heminode. Total depolarization was approximately 14% less than a simple summation of responses of synapses activated one at a time.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Maculae↗
PubMed1998

Histotomography of the odontoblast processes at the dentine-enamel junction of permanent healthy human teeth in the confocal laser scanning microscope.

The translucency of teeth allows the non-destructive subsurface visualisation of their microstructure by confocal laser scanning microscopy (CLSM) at a level of about 150 microns below the surface. The dentine-enamel junction (DEJ) is accessible only directly adjacent to the cervix of the tooth. Therefore teeth have to be sectioned for studying marginal areas of the dental hard tissue. The potential of the technique for (pseudo) three-dimensional visualisation allows the study of an array of individual confocal images, the interpretation of which is similar to that of macroscopic tomographs (CT-scan, MRI). Additionally, the extended focus mode yields the overlay of individual confocal images in the form of a two-dimensional projection. This mode of operation proved to be particularly suited for the visualisation of odontoblast processes in their whole extension. The three-dimensional junction between enamel and dentine, the branches of the odontoblast processes and their interactions with the DEJ is demonstrable by CLSM without staining or other procedures of sample preparation. The direct microscopic comparison between samples, either fresh or kept in a humid chamber, and Technovit-embedded sample blocks gives evidence that the risk of artefacts by sample storage or by the embedding procedure is minimal. The tomographs limited to subsurface areas of the tissue also exclude mechanical surface artefacts due to grinding or cutting.

Dental Enamel↗