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At least 1,009 records · Page 56Linked to original sources
PubMed1977

Secondary sensory cells in the gravity receptor system of the statocyst of Octopus vulgaris.

The presence of secondary sensory cells in the Octopus gravity receptor system has been demonstrated. In serial thin sections of the receptor cells (hair cells) no axons were found leaving the cells. Instead, synapses were observed with synaptic vesicles lying inside the receptor cells. Both data clearly indicate that the receptor hair cells represent secondary sensory cells. In addition, efferent contacts to the receptor cells could be confirmed.

Animals↗
PubMed1991

Glucose-6-phosphate dehydrogenase activity and protein turnover in erythroblasts separated by velocity sedimentation at unit gravity and Percoll gradient centrifugation.

This work was undertaken to improve a separation method for preparation of large amounts of erythroid cells of different age with homogeneous and minimal contamination of myeloid cells. Our method was suitably employed in the study of the decay mechanism of glucose-6-phosphate dehydrogenase (G6PDH) during the erythroid cell maturation. Twenty fractions of erythroid cells at different advancing stages of maturation were prepared by fractionating, at unit gravity, bone marrow cells from anaemic rabbit. The specific activity of the G6PDH was assayed and plotted vs the fraction number and the typical sigmoid curve of the activity decay was drawn. The separated cells were then grouped in three sets of fractions following the three phases of the sigmoid curve and the fractions of each set were combined. From the cytochemical analysis of the three main fractions so obtained, we found a 25-30% myeloid cell contamination in the first fraction, while in the other two fractions the myeloid contamination was 10% or less. For this reason we performed a rapid separation of the first fraction on a discontinuous percoll gradient. By this method, the myeloid cell contamination of the first fraction was levelled down to the other two. The fractions, so obtained, (I, II and III in order of increasing cell maturation) showed a four fold decrease of glucose-6-phosphate dehydrogenase activity expressed both per cell number and on protein base. On the contrary the concentration of the total soluble proteins did not change significantly in the three fractions. The three purified cellular populations were used to provide information on the protein turnover of the erythroid cells during their development. We measured, in intact cells, the rate of synthesis and degradation of total proteins and then, in cell lysates, we determined the rate of degradation of G6PDH, purified from rabbit RBC and radiolabeled by reductive methylation with C14-formaldehyde. The rates of proteolysis obtained with total proteins and methyl-G6PDH clearly indicate that the proteolytic machinery of the erythroblasts reduces its activity during the cell maturation.

Anemia↗
PubMed1994

Orientation of human optokinetic nystagmus to gravity: a model-based approach.

Optokinetic nystagmus (OKN) was induced by having subjects watch a moving display in a binocular, head-fixed apparatus. The display was composed of 3.3 degrees stripes moving at 35 degrees/s for 45 s. It subtended 88 degrees horizontally by 72 degrees vertically of the central visual field and could be oriented to rotate about axes that were upright or tilted 45 degrees or 90 degrees. The head was held upright or was tilted 45 degrees left or right on the body during stimulation. Head-horizontal (yaw axis) and head-vertical (pitch axis) components of OKN were recorded with electro-oculography (EOG). Slow phase velocity vectors were determined and compared with the axis of stimulation and the spatial vertical (gravity axis). With the head upright, the axis of eye rotation during yaw axis OKN was coincident with the stimulus axis and the spatial vertical. With the head tilted, a significant vertical component of eye velocity appeared during yaw axis stimulation. As a result the axis of eye rotation shifted from the stimulus axis toward the spatial vertical. Vertical components developed within 1-2 s of stimulus onset and persisted until the end of stimulation. In the six subjects there was a mean shift of the axis of eye rotation during yaw axis stimulation of approximately 18 degrees with the head tilted 45 degrees on the body. Oblique optokinetic stimulation with the head upright was associated with a mean shift of the axis of eye rotation toward the spatial vertical of 9.2 degrees. When the head was tilted and the same oblique stimulation was given, the axis of eye rotation rotated to the other side of the spatial vertical by 5.4 degrees. This counterrotation of the axis of eye rotation is similar to the "Müller (E) effect," in which the perception of the upright is counterrotated to the opposite side of the spatial vertical when subjects are tilted in darkness. The data were simulated by a model of OKN with a "direct" and "indirect" pathway. It was assumed that the direct visual pathway is oriented in a body, not a spatial frame of reference. Despite the short optokinetic after-nystagmus time constants, strong horizontal to vertical cross-coupling could be produced if the horizontal and vertical time constants were in proper ratio and there were no suppression of nystagmus in directions orthogonal to the stimulus direction. The model demonstrates that the spatial orientation of OKN can be achieved by restructuring the system matrix of velocity storage. We conclude that an important function of velocity storage is to orient slow-phase velocity toward the spatial vertical during movement in a terrestrial environment.

Adult↗
PubMed1996

Blood vessel adaptation to gravity in a semi-arboreal snake.

The effects of vasoactive agonists on systemic blood vessels were examined with respect to anatomical location and gravity acclimation in the semi-arboreal snake, Elaphe Obsoleta. Major blood vessels were reactive to putative neurotransmitters, hormones or local factors in vessel specific patterns. Catecholamines, adenosine triphosphate, histamine and high potassium (80 mM) stimulated significantly greater tension per unit vessel mass in posterior than anterior arteries. Anterior vessels were significantly more sensitive to catecholamines than midbody and posterior vessels. Angiotensin II stimulated significantly greater tension in carotid artery than in midbody and posterior dorsal aorta. Arginine vasotocin strongly contracted the left and right aortic arches and anterior dorsal aorta. Veins were strongly contracted by catecholamines, high potassium and angiotensin II, but less so by adenosine triphosphate, arginine vasotocin and histamine. Precontracted vessel were relaxed by acetylcholine and sodium nitroprusside, but not by atrial natriuretic peptide or bradykinin. Chronic exposure of snakes to intermittent hypergravity stress ( + 1.5 Gz at tail) did not affect the majority of vessel responses. These data demonstrate that in vitro tension correlates with that catecholamines, as well as other agonists, are important in mediating vascular responses to gravitational stresses in snakes.

Adaptation, Physiological↗
PubMed1977

Isolation of osteoclasts by velocity sedimentation at unit gravity.

A method is presented for separating osteoclasts from the heterogeneous population of bone and marrow cells. Cell suspensions were prepared from femora of young rabbits by mechanical dispersion. The starting cell suspension typically contained only 1.0% +/- 0.5 osteoclasts. Following an initial 45 min of unit gravity sedimentation in a lucite chamber osteoclasts were primarily distributed in fractions 2-5. A second 45-min sedimentation of these pooled fractions yielded cell suspensions containing greater than 30% osteoclasts (as much as a 50-fold increase over starting percentages). Linear scan analysis, however, revealed that osteoclasts accounted for 73.14% +/- 0.58 of the cell colume. Subsequent in vitro experiments demonstrated linear incorporation of 3H-leucine into TCA precipitable protein for cells comprising the osteoclast fraction. Concomitant radioautographs revealed radioactive label in isolated osteoclasts.

Animals↗
PubMed2004

Analysis of the effects of gravity and wall thickness in a model of blood flow through axisymmetric vessels.

The effects of gravitational forces and wall thickness on the behaviour of a model of blood flow through axisymmetric vessels were studied. The governing fluid dynamic equations were derived from the Navier-Stokes equations for an incompressible fluid and linked to a simple model of the vessel wall. A closed form of the hyperbolic partial differential equations was found, including a significant source term from the gravitational forces. The inclination of the vessel is modelled using a slope parameter that varied between -1 and 1. The wave speed was shown to be related to the wall thickness, and the time to first shock formation was shown to be directly proportional to this thickness. Two non-dimensional parameters were derived for the ratio of gravitational forces to viscous and momentum forces, respectively, and their values were calculated for the different types of vessel found in the human vasculature, showing that gravitational forces were significant in comparison with either viscous or momentum forces for every type of vessel. The steady-state solution of the governing equations showed that gravitational forces cause an increase in area of approximately 5% per metre per unit slope. Numerical simulations of the flow field in the aorta showed that a positive slope causes a velocity pulse to change in amplitude approximately linearly with distance: -4% per metre and +5% per metre for vessels inclined vertically upwards and downwards, respectively, in comparison with only +0.5% for a horizontal vessel. These simulations also showed that the change relative to the zero slope condition in the maximum rate of change of area with distance, which was taken to be a measure of the rate of shock formation, is proportional to both the slope and the wall thickness-to-inner radius ratio, with a constant of proportionality of 1.2. At a ratio of 0.25, typical of that found in human arteries, the distance to shock formation is thus decreased and increased by 30% for vessels inclined vertically downwards and upwards, respectively. Gravity and wall thickness thus have a significant impact on a number of aspects of the fluid and wall behaviour, despite conventionally being neglected.

Aorta↗
PubMed1982

Characterization of subpopulations of OC and OB bone cells obtained by sedimentation at unit gravity.

Immediately after isolation from calvaria, OC and OB bone cells populations 1-6 were individually characterized by sedimentation at unit gravity. This procedure was used to generate from each population 4 fractions that contained cells of different sizes. Sedimentation results suggested that freshly isolated OC cell populations consisted of cells that were generally smaller and demonstrated less size heterogeneity than OB cells. After sedimentation the cells in each fraction were cultured for 6 days and then characterized with regard to cell separation based on basal biochemical characteristics and hormonal responses to PTH and CT. The largest cells in the later released OC cells appeared to be a mixture of OC and OB cells (approx. 15% of populations 2 + 3). All OB cell fractions appeared to be free of OC cells. The highest basal OC activities and hormonal responses occurred in the larger cells of population 2, whereas in OB cells (populations 5 and 6), this occurred in the cells of small to intermediate size. Finally, although the absolute size of the cells in each fraction increased during culture, the size differential within the fractions and between OC and OB cells was maintained even after 6 days.

Acid Phosphatase↗
PubMed1988

Cell sedimentation with gravity activation.

Murine monoclonal antibody T101 has been coupled to thinly polymer-coated heavy alloy particles (LaMn2Ge2). These conjugates are coupled to cultured cells of the human T-cell leukemia line RPMI 8402 (T8402). The sedimentation velocities of cells, of particles, and of cells with particles attached are measured. After determining the mean radii of cells, of particles, and of cells with particles attached, one may compute a mean number of 33 particles attached to a cell. Independently one may compute a mean number of 144 particles/cell for surface saturation. The Appendix handles the underlying theory in three parts: number of particles/cell, saturation number of particles/cell, and resolution for gravity activation. Regarding the latter, cell radii from 4 to 10 microns and particle radii from 0.01 to 1 micron are considered.

Cell Line↗
PubMed2004

[Gravity valves for idiopathic normal pressure hydrocephalus. A Prospective study of 60 patients].

OBJECTIVE: Are hydrostatic valves superior to conventional differential pressure shunts in patients with normal- pressure hydrocephalus, with regard to the postoperative results of treatment and possible complications? METHODS: From September 1997 to January 2002, 60 patients with idiopathic normal-pressure hydrocephalus were treated by surgical implantation of a hydrostatic valve (Miethke dual-switch valve) at the Unfallkrankenhaus Berlin. RESULTS: One year after the shunt operation, the clinical picture was very good for 33% of the patients, good for 33%, satisfactory for 17%, and poor for 17%. At 20%, the rate of postoperative complications (catheter dislocations, valve infections, underdrainage and overdrainage) is still relatively high. The opening pressure of the Miethke dual-switch valve did not correlate with the postoperative results of treatment. CONCLUSION: According to our experience, hydrostatic Miethke dual-switch valves are superior to conventional differential pressure shunts without an additional gravity unit, especially with regard to the treatment of patients with idiopathic normal -pressure hydrocephalus, concerning both the postoperative results of the treatment and the incidence of possible complications. With differentiated diagnosis and therapy, a clinical improvement can be achieved for 83% of such patients.

Adult↗
PubMed2005

Gravity-assisted pivot-shift test for anterior cruciate ligament injury: a new procedure to detect anterolateral rotatory instability of the knee joint.

The denominated gravity-assisted pivot-shift test was introduced as a new procedure to detect anterolateral rotatory instability of the knee joint. The patient lies in the supine position or slightly rotated onto the affected side. The affected knee flexed approximately 60 degrees and the ipsilateral hip flexed, abducted and externally rotated so that the plane of the knee motion runs parallel to the floor. The examiner instructs the patient to raise the affected leg off the examining table and to extend the affected knee gradually. If the lower leg is internally rotated suddenly, with the knee subluxated at an angle of approximately 20 degrees , followed by the reduction in flexion, this test is regarded as positive. This test was investigated on 51 anterior cruciate ligament (ACL) deficient knees, being positive in 30 knees (Group P) and negative in 21 (Group N) with the positive rate of 59%. There was no significant correlation between the result of this test and the clinical features, but Group N included relatively small number of females and recurrent injuries tended to occur more frequently in Group P. Thirty-six knees received ACL reconstruction subsequently. There was no statistically significant difference between the groups in the side-to-side difference in anterior knee laxity at one year postoperatively. However, three patients with the side-to side difference of more than 3 mm belonged to Group P. Relatively low positive rate in ACL deficient knees suggests that it may not be used as a diagnostic procedure for ACL injury. It is possibly used for the prediction of high risk patients for symptomatic giving-way and/or patients with poor prognosis after ACL reconstruction.

Adolescent↗
PubMed1999

Ultrasound evaluation of gravity induced anterior drawer following anterior cruciate ligament lesion.

Ultrasound is not so far a standard procedure to visualize the anterior drawer following anterior cruciate ligament (ACL) lesions. This is because the described techniques are either technically difficult or depend on the experience of the performer and are not standardized. The purpose of this prospective analysis on ACL intact, ACL deficient and ACL reconstructed knees was to compare the diagnostic accuracy of prone ultrasonographic Lachman testing with KT-1000 measurements in the same study population. Our technique is based on a prone position of the patient. The thigh lies on the table surface such that the patella has no contact. The lower leg is placed on a roll in the ankle area and flexed to 30 degrees . The transducer (5 MHz) is positioned over the medial aspect of the popliteal fossa to visualize the femoral condyle as well as the tibial head. Under ultrasound control the lower leg is manually lifted as far the thigh stays in contact with the surface defining the start position. The lower leg is then released and drawn by gravity into the anterior drawer position, the final position. The distance between the posterior tangent from the medial femoral condyle to the medial tibial plateau was registered by three independent ultrasound measurements of the injured knee. The uninvolved opposite knee served as an internal control. The same procedure was done using a KT-1000 device (89 and 133 Newton and manual maximum force). The patients were split into two groups: acute injury (A), and (B) 6 months following ACL repair with a patellar tendon graft. All patients then underwent arthroscopy. In group A with acute ACL lesions the anterior drawer resulted in 14.1 mm (+/- 3.5) and was significantly (P < 0.001) different from the contralateral knee (7.7 mm +/- 2.9). The KT 1000 showed a comparable difference with 14.4 mm (+/- 3.9) for the injured knee and 8.3 mm (+/- 3.4) for the uninjured (P < 0.001). Sonometrically, group B patients showed no clear difference between the repaired (9.9 mm +/- 2.7) knee and its control (8.1 mm +/- 2.5). This was found for the KT-1000 results as well. The results derived from the ultrasound evaluation of the anterior drawer correlated well with those from the KT-1000 (r = 0.46). Based on a minimum intra-individual difference of 5 mm in the ultrasound measured anterior drawer, the sensitivity of the test in group A resulted in 0.96, and the specificity in 0.98. The described technique is reproducible, painless and easy to perform in order to evaluate acute ACL tears using any commercially available ultrasound device. The reproducibility is similar to the KT-1000 device. We recommend this technique for use in cases of acute ACL tears as well as in the follow-up of ACL repair.

Adolescent↗
PubMed2002

The effects of a change in gravity on the dynamics of prehension.

Investigating cyclic vertical arm movements with an instrumented hand-held load in an airplane undergoing parabolic flight profiles allowed us to determine how humans modulate their grip force when the gravitational and the inertial components of the load force are varied independently. Eight subjects participated in this study; four had already experienced parabolic flights and four had not. The subjects were asked to move the load up and down continuously at three different gravitational conditions (1 g, 1.8 g, and 0 g). At 1 g, the grip force precisely anticipated the fluctuations in the load force, which was maximum at the bottom of the object trajectory and minimum at the top. When gravity changed, the temporal coupling between grip force and load force persisted for all subjects from the first parabola. At 0 g, the grip force was accurately adjusted to the two load force peaks occurring at the two opposite extremes of the trajectory due to the absence of weight. While the experienced subjects exerted a grip force appropriate to a new combination of weight and inertia since their first trial, the inexperienced subjects dramatically increased their grip when faced with either high or low force levels for the first time. Then they progressively released their grip until a continuous grip-load force relationship with regard to 1 g was established after the fifth parabola. We suggest that a central representation of the new gravitational field was rapidly acquired through the incoming vestibular and somatic sensory information.

Acceleration↗
PubMed2004

Motor control goes beyond physics: differential effects of gravity and inertia on finger forces during manipulation of hand-held objects.

According to basic physics, the local effects induced by gravity and acceleration are identical and cannot be separated by any physical experiment. In contrast-as this study shows-people adjust the grip forces associated with gravitational and inertial forces differently. In the experiment, subjects oscillated a vertically-oriented handle loaded with five different weights (from 3.8 N to 13.8 N) at three different frequencies in the vertical plane: 1 Hz, 1.5 Hz and 2.0 Hz. Three contributions to the grip force-static, dynamic, and stato-dynamic fractions-were quantified. The static fraction reflects grip force related to holding a load statically. The stato-dynamic fraction reflects a steady change in the grip force when the same load is moved cyclically. The dynamic fraction is due to acceleration-related adjustments of the grip force during oscillation cycles. The slope of the relation between the grip force and the load force was steeper for the static fraction than for the dynamic fraction. The stato-dynamic fraction increased with the frequency and load. The slope of the dynamic grip force-load force relation decreased with frequency, and as a rule, increased with the load. Hence, when adjusting grip force to task requirements, the central controller takes into account not only the expected magnitude of the load force but also such factors as whether the force is gravitational or inertial and the contributions of the object mass and acceleration to the inertial force. As an auxiliary finding, a complex finger coordination pattern aimed at preserving the rotational equilibrium of the object during shaking movements was reported.

Acceleration↗
PubMed2000

The effect of gravity on the horizontal and vertical vestibulo-ocular reflex in the rat.

Horizontal and vertical eye movements were recorded in alert pigmented rats using chronically implanted scleral search coils or temporary glue-on coils to test the dependence of the vestibulo-ocular reflex (VOR) upon rotation axis and body orientation. The contributions of semicircular-canal versus otolith-organ signals to the VOR were investigated by providing canal-only (vertical axis) and canal plus otolith (horizontal axis) stimulation conditions. Rotations that stimulated canals only (upright yaw and nose-up roll) produced an accurate VOR during middle- and high-frequency rotations (0.2-2 Hz). However, at frequencies below 0.2 Hz, the canal-only rotations elicited a phase-advanced VOR. The addition of a changing gravity stimulus, and thus dynamic otolith stimulation, to the canal signal (nose-up yaw, on-side yaw, and upright roll) produced a VOR response with accurate phase down to the lowest frequency tested (0.02 Hz). In order to further test the dependence of the VOR on gravitational signals, we tested vertical VOR with the head in an inverted posture (inverted roll). The VOR in this condition was advanced in phase across all frequencies tested. At low frequencies, the VOR during inverted roll was anticompensatory, characterized by slow-phase eye movement in the same direction as head movement. The substantial differences between canalonly VOR and canal plus otolith VOR suggest an important role of otolith organs in rat VOR. Anticompensatory VOR during inverted roll suggests that part of the otolith contribution arises from static tilt signals that are inverted when the head is inverted.

Animals↗
PubMed2000

Human orientation and movement control in weightless and artificial gravity environments.

Our goal is to summarize what has been learned from studies of human movement and orientation control in weightless conditions. An understanding of the physics of weightlessness is essential to appreciate the dramatic consequences of the absence of continuous contact forces on orientation and posture. Eye, head, arm, leg, and whole body movements are discussed, but only experiments whose results seem relatively incontrovertible are included. Emphasis is placed on distinguishing between virtually immediate adaptive compensations to weightlessness and those with longer time courses. The limitations and difficulties of performing experiments in weightless conditions are highlighted. We stress that when astronauts and cosmonauts return from extended space flight they do so with both physical "plant" and neural "controller" structurally and functionally altered. Recent developments in adapting humans to artificial gravity conditions are discussed as a way of maintaining sensory-motor and structural integrity in extended missions involving transitions between different force environments.

Humans↗
PubMed1998

The collicular code of saccade direction depends on the roll orientation of the head relative to gravity.

This paper investigates the influence of static head tilt on the relation between activity in the motor layers of the superior colliculus (mSC) and saccadic oculomotor output. Based on single-unit recordings and electrical microstimulation in awake rhesus monkeys, we report that head roll changes the direction of the saccade vector generated by the mSC, with respect to a head-fixed coordinate system. Typically, the vector rotates in a direction that is opposite to the head roll direction. This rotation exceeds the amount of ocular counterroll that is observed as a result of difference in static head roll positions. We find that the mSC works in an oculocentric coordinate system that is biased in the direction of gravity. It is argued that the modification is a result of processes that occur downstream of or parallel to the mSC.

Animals↗