Phase Of Retraction Research Articles

Tau regulates the microtubule-dependent migration of glioblastoma cells via the Rho-ROCK signaling pathway.

The pathological significance of Tau (encoded by MAPT) in mechanisms driving cell migration in glioblastoma is unclear. By using an shRNA approach to deplete microtubule-stabilizing Tau in U87 cells, we determined its impact on cytoskeletal coordination during migration. We demonstrated here that the motility of these Tau-knockdown cells (shTau cells) was significantly (36%) lower than that of control cells. The shTau cells displayed a slightly changed motility in the presence of nocodazole, which inhibits microtubule formation. Such reduced motility of shTau cells was characterized by a 28% lower number of microtubule bundles at the non-adhesive edges of the tails. In accordance with Tau-stabilized microtubules being required for cell movement, measurements of the front, body and rear section displacements of cells showed inefficient tail retraction in shTau cells. The tail retraction was restored by treatment with Y27632, an inhibitor of Rho-ROCK signaling. Moreover, we clearly identified that shTau cells displayed relocation of the active phosphorylated form of p190-RhoGAP (also known as ARHGAP35), which inhibits Rho-ROCK signaling, and focal adhesion kinase (FAK, also known as PTK2) in cell bodies. In conclusion, our findings indicate that Tau governs the remodeling of microtubule and actin networks for the retraction of the tail of cells, which is necessary for effective migration.

Modeling length-tension properties of RCPm muscles during voluntary retraction of the head

Head retraction exercises are one of several commonly used clinical tools that are used to assess and treat patients with head and neck pain and to aid in restoration of a normal neutral head posture. Retraction of the head results in flexion of the occipitoatlantal (OA) joint and stretching of rectus capitis posterior minor (RCPm) muscles. The role that retraction of the head might have in treating head and neck pain patients is currently unknown.RCPm muscles arise from the posterior tubercle of the posterior arch of C1 and insert into the occipital bone inferior to the inferior nuchal line and lateral to the midline. RCPm muscles are the only muscles that attach to the posterior arch of C1. The functional role of RCPm muscles has not been clearly defined.The goal of this project was to develop a three-dimensional, computer-based biomechanical model of the posterior aspect of the OA joint. This model should help clarify why voluntary head retraction exercises seem to contribute to the resolution of head and neck pain and restoration of a normal head posture in some patients.The model documents that length-tension properties of RCPm muscles are significantly affected by variations in the physical properties of the musculotendonous unit. The model suggests that variations in the cross sectional area of RCPm muscles due to pathologies that weaken the muscle, such as muscle atrophy, may reduce the ability of these muscles to generate levels of force that are necessary for the performance of normal, daily activities. The model suggests that the main benefit of the initial phase of head retraction exercises may be to strengthen RCPm muscles through eccentric contractions, and that the main benefit of the final phase of retraction may be to stretch the muscles as the final position is held.

SASI ACTIVITY IN THREE-DIMENSIONAL NEUTRINO-HYDRODYNAMICS SIMULATIONS OF SUPERNOVA CORES

ABSTRACT The relevance of the standing accretion shock instability (SASI) compared to neutrino-driven convection in three-dimensional (3D) supernova-core environments is still highly controversial. Studying a 27 M ☉ progenitor, we demonstrate, for the first time, that violent SASI activity can develop in 3D simulations with detailed neutrino transport despite the presence of convection. This result was obtained with the Prometheus-Vertex code with the same sophisticated neutrino treatment so far used only in one-dimensional and two-dimensional (2D) models. While buoyant plumes initially determine the nonradial mass motions in the postshock layer, bipolar shock sloshing with growing amplitude sets in during a phase of shock retraction and turns into a violent spiral mode whose growth is only quenched when the infall of the Si/SiO interface leads to strong shock expansion in response to a dramatic decrease of the mass accretion rate. In the phase of large-amplitude SASI sloshing and spiral motions, the postshock layer exhibits nonradial deformation dominated by the lowest-order spherical harmonics (ℓ = 1, m = 0, ±1) in distinct contrast to the higher multipole structures associated with neutrino-driven convection. We find that the SASI amplitudes, shock asymmetry, and nonradial kinetic energy in three dimensions can exceed those of the corresponding 2D case during extended periods of the evolution. We also perform parameterized 3D simulations of a 25 M ☉ progenitor, using a simplified, gray neutrino transport scheme, an axis-free Yin-Yang grid, and different amplitudes of random seed perturbations. They confirm the importance of the SASI for another progenitor, its independence of the choice of spherical grid, and its preferred growth for fast accretion flows connected to small shock radii and compact proto-neutron stars as previously found in 2D setups.

Targeted subendothelial matrix oxidation by myeloperoxidase triggers myosin II-dependent de-adhesion and alters signaling in endothelial cells

During inflammation, myeloperoxidase (MPO) released by circulating leukocytes accumulates within the subendothelial matrix by binding to and transcytosing the vascular endothelium. Oxidative reactions catalyzed by subendothelial-localized MPO are implicated as a cause of endothelial dysfunction in vascular disease. While the subendothelial matrix is a key target for MPO-derived oxidants during disease, the implications of this damage for endothelial morphology and signaling are largely unknown. We found that endothelial-transcytosed MPO produced hypochlorous acid (HOCl) that reacted locally with the subendothelial matrix and induced covalent cross-linking of the adhesive matrix protein fibronectin. Real-time biosensor and live cell imaging studies revealed that HOCl-mediated matrix oxidation triggered rapid membrane retraction from the substratum and adjacent cells (de-adhesion). De-adhesion was linked with the alteration of Tyr-118 phosphorylation of paxillin, a key adhesion-dependent signaling process, as well as Rho kinase-dependent myosin light chain-2 phosphorylation. De-adhesion dynamics were dependent on the contractile state of cells, with myosin II inhibition with blebbistatin attenuating the rate of membrane retraction. Rho kinase inhibition with Y-27632 also conferred protection, but not during the initial phase of membrane retraction, which was driven by pre-existing actomyosin tensile stress. Notably, diversion of MPO from HOCl production by thiocyanate or nitrite attenuated de-adhesion and associated signaling responses, despite the latter substrate supporting MPO-catalyzed fibronectin nitration. These data show that subendothelial-localized MPO employs a novel “outside-in” mode of redox signaling, involving HOCl-mediated matrix oxidation. These MPO-catalyzed oxidative events are likely to play a previously unrecognized role in altering endothelial integrity and signaling during inflammatory vascular disorders.

Changing dendritic field size of mouse retinal ganglion cells in early postnatal development

During early postnatal development, dendrites of retinal ganglion cells (RGCs) extend and branch in the inner plexiform layer to establish the adult level of stratification, pattern of branching, and coverage. Many studies have described the branching patterns, transient features, and regulatory factors of stratification of the RGCs. The rate of RGC dendritic field (DF) expansion relative to the growing retina has not been systematically investigated. In this study, we used two methods to examine the relative expansion of RGC DFs. First, we measured the size of RGC DFs and the diameters of the eyeballs at several postnatal stages. We compared the measurements with the RGC DF sizes calculated from difference of the eyeball sizes based on a linear expansion assumption. Second, we used the number of cholinergic amacrine cells (SACs) circumscribed by the DFs of RGCs at corresponding time points as an internal ruler to assess the size of DFs. We found most RGCs exhibit a phase of faster expansion relative to the retina between postnatal day 8 (P8) and P13, followed by a phase of retraction between P13 and adulthood. The morphological alpha cells showed the faster growing phase but not the retraction phase, whereas the morphological ON-OFF direction selective ganglion cells expanded in the same pace as the growing retina. These findings indicate different RGCs show different modes of growth, whereas most subtypes exhibit a fast expansion followed by a retraction phase to reach the adult size.

Studies on the loops of amphibian lampbrush chromosomes during the phase of retraction

Flannery, A.V. and Hill, R.S. 1987. Studies on the loops of amphibian chromosomes during the phase of retraction. —Herediras 106: 209–218. Lund, Sweden. ISSN 0018–0661. Received August 8, 1986 The process of loop retraction in lampbrush chromosomes of Triturus cristastus carnifex, during oocyte maturation, has been investigated by studying the morphology of the loops isolated under different monovalent cation conditions, using a combination of light and electron microscopy. When lampbrush chromosomes bearing retracted loops were prepared in buffer containing reduced levels of monovalent cations (0.7 mM), the mean axial loop length was increased by at least 2.5 times over the mean length of loops prepared under ionic conditions which stabilize normal lampbrush structure (i.e., 70 mM cations). This cation-dependent change in loop structure indicates that the retracted appearance of the loops in maturing oocytes involves the folding of the loop axis. RNA transcription appears to continue during retraction since ribonucleo-protein transcripts are clearly present on the loop axes at all ionic concentrations used and in Miller spreading studies. In Miller spreading preparations, however, the density of transcripts is clearly less in transcription units from retracted loops. Direct evidence concerning the structure of the loop axis at cation concentrations of 0.7 mM and above has not been obtained because the axis remains obscured by RNP transcript under these conditions. However, a model is proposed which accounts for the folding of the loop axis and its simultaneous transcription by RNA polymerases.

A CPG Component LE Generates Depolarization of Buccal Neurons by Producing Constant Plateau Potentials During Feeding Responses of Aplysia kurodai

In the buccal ganglia of Aplysia kurodai we have identified neurons (here termed LE neurons, or LE) producing plateau potentials lasting several seconds by application of short depolarizing currents. Results obtained from experiments using various bath solutions suggest that generation of these plateau potentials may be an endogenous property of LE. Application of various intensities or lengths of depolarizing currents induced in LE almost constant plateau potentials with fixed duration and depolarizing size. LE spikes produced monosynaptic EPSPs in the ipsilateral multi-action neuron (MA) and the jaw-closing motor neuron (JC) in the buccal ganglia. Conversely, MA spikes produced monosynaptic IPSPs in LE. There was electrical coupling between LE and both MA and JC. During the feeding-like response elicited by electrical stimulation of the nerve, LE showed rhythmic depolarization almost simultaneously with MA and JC, and firing on the plateau potentials occurred during the period of JC firing, the later phase of radula retraction. Hyperpolarization of LE during the feeding-like response suppressed generation of plateau potentials, though rhythmic small depolarization was still induced. During LE hyperpolarization, the duration of the depolarization of MA and JC was shortened. These results suggest that LE may be an element of the feeding CPG circuit and may contribute to part of the depolarization of MA and JC by generating constant plateau potentials during the feeding response, though LE may not have rhythm-generating ability.

Advances in Intracerebral Hemorrhage Management

Recent advances in the evaluation and management of intracerebral hemorrhage (ICH) include: the identification of molecular markers that correlate with events in its early course, complications, and outcome; the impact of previous treatment with antiplatelet or anticoagulant agents on the outcome after ICH; the analysis of the results of the large international STICH (Surgical Trial in Intracerebral Hemorrhage) study; and the publication of the results of the recombinant activated Factor VII trial in ICH. Recent research interest in ICH has attempted to produce a better understanding of the events that occur early in its course, including hematoma growth, development of perihematoma edema, and the resultant tissue injury, factors that can cause early neurological deterioration and can have impact on its long-term outcome.1–3 These interrelated processes are accompanied by a cascade of events that correlate with elevation of certain molecular markers in serum. The process of perihematoma edema formation starts early after ICH onset, generally within 3 hours,4 and it increases gradually in severity for at least 72 hours.5 Several mechanisms in sequence contribute to the formation of edema, including: a first phase of clot retraction with extrusion of serum; a second phase (for the first 2 days) of activation of the coagulation cascade with production of thrombin; and a final phase (after 3 days from onset) of red blood cell lysis with hemoglobin-induced neuronal damage.5 The central role of thrombin in promoting perihematoma edema has been documented in both experimental6 and human7 ICH, with evidence of reduced edema formation after administration of thrombin inhibitors. The deleterious effects of thrombin in the perihematoma tissues are mediated by inflammation, cytotoxicity, and disruption of the blood-brain barrier.8–10 The molecular correlates of perihematoma edema include elevated levels of glutamate, tumor necrosis factor-α, interleukin-1, and intercellular adhesion molecule-1, …

Cytoskeletal and Morphological Alterations Underlying Axonal Sprouting after Localized Transection of Cortical Neuron AxonsIn Vitro

We examined the cytoskeletal dynamics that characterize neurite sprouting after axonal injury to cortical neurons maintained in culture for several weeks and compared these with initial neurite development. Cultured neocortical neurons, derived from embryonic day 18 rats, were examined at 3 d in vitro (DIV) and at various time points after axotomy at 21 DIV. The postinjury neuritic response was highly dynamic, progressing through an initial phase of retraction, followed by substantial axonal sprouting within 4-6 hr. Postinjury sprouts were motile and slender with expanded growth cone-like end structures. Microtubule markers were localized to sprout shafts and the proximal regions of putative growth cones and filamentous actin was distributed throughout growth cones, whereas neurofilament proteins were restricted to sprout shafts. A similar distribution of cytoskeletal proteins was present in developing neurites at 3 DIV. Exposure of developing and mature, injured cultures to the microtubule stabilizing agent taxol (10 microg/ml) caused growth inhibition, process distension, the transformation of growth cones into bulbous structures, and abnormal neurite directionality. Microtubule and neurofilament segregation occurred after taxol exposure in developing neurites and postinjury sprouts. Exposure to the microtubule destabilizing agent nocodazole (100 microg/ml) resulted in substantial morphological alteration of developing neurons and inhibited neurite growth and postinjury axonal sprouting. Our results indicate that the axons of cortical neurons have an intrinsic ability to sprout after transection, and similar cytoskeletal dynamics underlie neurite development and postinjury axonal sprouting.

Reconfiguration of the high-security hospitals: some lessons from the mental hospital retraction and reprovision programme in the United Kingdom, 1960-2000

The high-security hospitals of England and Wales are entering a phase of major retraction, with local security services embarking upon the reprovision of services for patients with longer-term needs who do not require high security. The large area mental hospitals underwent similar changes and the lessons that may be learnt from this process are relevant to proposed changes in forensic services. These lessons include: (1) the risk of over-optimistic predictions concerning the time-scale and resources required for major bed reduction; (2) the problems associated with 'creaming off', with the risk of increasing acuity in the residual inpatient population accompanied by deterioration in the quality of the retracting services; (3) the risk of 'silting up' in the reprovided services in the absence of an appropriate community infrastructure; and (4) the importance of quality of life for longer-stay secure inpatients. This paper urges caution in view of the potentially serious clinical and organizational risks associated with these major changes in forensic services.

Contribution of the Plasmin/Matrix Metalloproteinase Cascade to the Retraction of Human Fibroblast Populated Collagen Lattices

To assess the contribution of the plasmin/matrix metalloproteinase cascade in lattices retraction, human gingival fibroblast-populated collagen lattices were supplemented with plasminogen. The rate of lattice retraction was enhanced by addition of plasminogen. This effect was concomitant to plasmin generation, prostromelysin-1 and procollagenase activation. Plasminogen-mediated initiation of that proteolytic cascade was accompanied by conspicuous changes in cell morphology and collagen fibers organization. At day 1 of culture fibroblasts shifted from a rounded (control) to an elongated (in presence of plgn) shape. At the latest stage of retraction, intense vacuolization around fibroblasts was noticed in plgn-supplemented lattices which paralleled the increased collagen degradation. Plgn-enhancing influence on the initial phase of lattice retraction could be totally annihilated by either aprotinin or Batimastat. Those data emphasize the crucial importance of the plasmin–MMP proteolytic cascade in granulation tissue retraction in a healing wound.

Practical problems in the teaching of ethics to medical students.

Some practical problems in the teaching of ethics to medical students are described. The definition of the objectives of the course remains the central aspect, and is more important than the specific content. The use of student projects, buzz groups, case histories and discussion points is described. There is a need for student assessment or examination at the end of the course. The teachers require a broad background in philosophy, clinical medicine and teaching skills. The learning of the teachers may be as important as that of the students.

Circulation, respiration and fluid dynamics in the gastropod mollusc, Hemifusus tuba (Gmelin)

Cardiac activity, respiratory rate, and fluid movements in and out of the shell and tissues of Hemifusus tuba (Gmelin) have been investigated. Estimates of cardiac output (Q̇) were in the range 0.1 to 2.22 ml·min −1 (in individuals of 7.0 to 14.2 cm shell length). Maximum systolic ventricular pressure was between 6.4 to 11.4 cm H 2O, with highest values being recorded from large, partially-retracted specimens. Respiratory rate (V̇ 2) increased with size according to V̇ O2 α dry weight (g) −0.43. This mass exponent is low compared with that for many other species. Perfusion indices ( Q ̇ V ̇ o2 ) increased with size indicating that del was less efficient in larger Hemifusus. During retraction, two phases of fluid expulsion were recognized. The first allowed Hemifusus to retreat rapidly within the confines of its shell. The second, slower phase of retraction drew up the operculum to form a tight, protective seal with the shell. Expelled fluid, particularly from the second phase, contained blood proteins, suggesting that fluid is lost from the blood system during full retraction.

Serotonin has both excitatory and inhibitory modulatory effects on feeding muscles in Aplysia.

Serotonin (10(-8) M) produced opposite long-lasting (up to 10 min) effects on acetylcholine-elicited contractions of different buccal mass muscles of Aplysia. Contractions of the dorsal extrinsic muscle and accessory radula closer muscle were enhanced by serotonin; whereas contractions of the ventral extrinsic muscle were inhibited by serotonin. The effect of higher concentrations of serotonin on dorsal and ventral extrinsic muscles was in the same direction as at 10(-8) M but was greater in both magnitude and duration. The phase of feeding-protraction or retraction--during which a muscle is active--is not correlated with the direction of modulation produced by serotonin.

Mechanism of retraction of the trailing edge during fibroblast movement.

Retraction of the taut, trailing portion of a moving chick heart fibroblast in vitro is an abrupt dynamic process. Upon retraction, the fibroblast tail always ruptures, leaving a small amount of itself attached to the substratum by focal contacts. Time-lapse cinemicrography shows that retraction produces a sudden, massive movement of both surface and cytoplasmic material toward a cluster of focal contacts near the main body of the cell. The appearance of folds on the upper cell surface at this time and the absence of endocytotic vesicles are consistent with this forward movement. Retraction of the trailing edge, either occurring naturally or produced artificially with a microneedle, consists of an initial fast component followed and overlapped by a slow component. Upon artificial detachment in the presence of iodoacetate, dinitrophenol, and sodium fluoride, and at 4 degrees C, the slow component is strongly inhibited and the fast one only slightly inhibited. Moreover of the bundles of microfilaments oriented parallel to the long axis of the tail seen in TEM. Most of the birefringence is lost during the fast phase and the rest during the slow phase of retraction. Concurrently, the bundles of microfilaments disappear during the fast phase of retraction and are replaced by a microfilament meshwork. All of these results are consistent with the hypothesis that the initial fast component of retraction is a passive elastic recoil, associated with the oriented bundles of microfilaments, and that the slow component of retraction is an active contraction, associated with a meshwork of microfilaments.

Self-contact inhibition of movement in cultured chick heart fibroblasts

Collisions between two lamellar processes extended from a single locomoting cultured cell were examined by time-lapse cinemicrography and transmission electron microscopy. In most cases after contact the forward movement of either one or both of the lamellae ceased and was followed by a phase of retraction of the lamellae resulting in the breaking of the contact. The events correspond well to the contact inhibition of movement expressed when two cells collide. The similarity is also shown in the ultrastructure of the cell contacts which exhibit a close parallel arrangement of the apposed cell membranes and an alignment of microfilaments in the regions of the cytoplasm at the contacts.

Clot retraction: II. Theoretical model of platelet filamentogenesis

The degree of clot retraction is dependent upon platelet number, in that a higher concentration of platelets brings about a greater amount of retraction. Ultrastructural studies indicate that a new population of microfilaments occurs within platelets after clot formation, and their appearance corresponds to the most active phase of retraction. On the basis of the experimental results, a mathematical formula is proposed which correlates platelet contractility and clot retraction. This formula emulates the crystallization model in metallurgy, and the calculated percentages of retraction correlate well with the experimental data. According to the mathematical model, clot retraction could be a function of platelet filamentogenesis.

Sudden Destruction of Motor End Plates by Lactic Acid

SummaryLactic acid in concentrations of 0.05 to 0.3% injected into the exposed zone of innervation of the sternomastoid muscle in the white rat produced sudden destruction of most of the motor end plates within 30 seconds to 25 minutes dependent upon the concentration of the acid. This liquefaction of the hypolemmal axons of the end plates was preceded by a first phase of retraction and a second phase of expansion and fragmentation. Lactic acid caused a progressive depletion, in both the hypolemmal and the epilemma1 axons, of auriphilous substances. The blood vessels were enlarged, hyperemic, and contained clumps of agglutinated red blood cells in the rigorous muscle paralyzed by lactic acid. I t is suggested that the acid metabolites which accumulate during rigor mortis of muscle are responsible for the destruction of the end plates and that during life certain processes that result in the intramuscular accumulation of acid, such as vascular congestion and anoxia, likewise may result in the destruction o...