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PubMedDate not supplied

An inhibitor of the Ca(2+)-ATPases in the sarcoplasmic and endoplasmic reticula inhibits transduction of the gravity stimulus in cress roots.

Cress (Lepidium sativum L.) roots were treated with 20 microM cyclopiazonic acid (CPA), an inhibitor of the Ca(2+)-transporting ATPases present in the sarcoplasmic/endoplasmic reticulum of animals and the endoplasmic reticulum of plants, in order to investigate its effect on the gravitropic response. Root growth was not significantly reduced by the applied dose of CPA, but the gravitropic response (curvature) was drastically inhibited. We hypothesize that the ER Ca(2+)-ATPase of statocytes is involved in transduction of the gravity stimulus and that CPA disturbs a cytosolic Ca2+ signal necessary for graviperception.

Brassicaceae↗
PubMed1976

[The specific gravity of the excitation formation and conduction system of the heart compared to the working myocardium as an indication of differences in structure and composition (author's transl)].

Samples of heart conducting system tissue and samples of ordinary heart muscle (left heart, right heart, and septum interventriculare) were taken from the hearts of 50 prime-conditioned bulls. The specific gravity of the heart conducting system was significantly higher than that of ordinary heart muscle. This is surprising because it cannot be explained by a difference in water content. The question arises whether or not there are differences in the composition of protein and in the content of glycogen.

Animals↗
PubMed1997

Central root cap cells are depleted of endoplasmic microtubules and actin microfilament bundles: implications for their role as gravity-sensing statocytes.

Indirect immunofluorescence, using monoclonal antibodies to actin and tubulin, applied to sections of root tips of Lepidium, Lycopersicon, Phleum, and Zea, revealed features of the cytoskeleton that were unique to the statocytes of their root caps. Although the cortical microtubules (CMTs) lay in dense arrays against the periphery of the statocytes, these same cells showed depleted complements of endoplasmic microtubules (EMTs) and of actin microfilament (AMF) bundles, both of which are characteristic of the cytoskeleton of other post-mitotic cells in the proximal portion of the root apex. The scarcity of the usual cytosketetal components within the statocytes is considered responsible for the exclusion of the larger organelles (e.g., nucleus, plastids, ER elements) from the interior of the cell and for the absence of cytoplasmic streaming. Furthermore, the depletion of dense EMT networks and AMF bundles in statocyte cytoplasm is suggested as being closely related to the elevated cytoplasmic calcium content of these cells which, in turn, may also favour the formation of the large sedimentable amyloplasts by not permitting plastid divisions. These latter organelles are proposed to act as statoliths due to their dynamic interactions with very fine and highly unstable AMFs which enmesh the statoliths and merge into peripheral AMFs-CMTs-ER-plasma membrane complexes. Rather indirect evidence for these interactions was provided by showing enhanced rates of statolith sedimentation after chemically-induced disintegration of CMTs. All these unique properties of the root cap statocytes are supposed to effectively enhance the gravity-perceptive function of these highly specialized cells.

Actin Cytoskeleton↗
PubMed1993

Centrifugation causes adaptation of microfilaments: studies on the transport of statoliths in gravity sensing Chara rhizoids.

The actin cytoskeleton is involved in the positioning of statoliths in tip growing Chara rhizoids. The balance between the acropetally acting gravity force and the basipetally acting net outcome of cytoskeletal force results in the dynamically stable position of the statoliths 10-30 micrometers above the cell tip. A change of the direction and/or the amount of one of these forces in a vertically growing rhizoid results in a dislocation of statoliths. Centrifugation was used as a tool to study the characteristics of the interaction between statoliths and microfilaments (MFs). Acropetal and basipetal accelerations up to 6.5 g were applied with the newly constructed slow-rotating-centrifuge-microscope (NIZEMI). Higher accelerations were applied by means of a conventional centrifuge, namely acropetally 10-200 g and basipetally 10-70 g. During acropetal accelerations (1.4-6g), statoliths were displaced to a new stable position nearer to the cell vertex (12-6.5 micrometers distance to the apical cell wall, respectively), but they did not sediment on the apical cell wall. The original position of the statoliths was reestablished within 30 s after centrifugation. Sedimentation of statoliths and reduction of the growth rates of the rhizoids were observed during acropetal accelerations higher than 50 g. When not only the amount but also the direction of the acceleration were changed in comparison to the natural condition, i.e., during basipetal accelerations (1.0-6.5 g), statoliths were displaced into the subapical zone (up to 90 micrometers distance to the apical cell wall); after 15-20 min the retransport of statoliths to the apex against the direction of acceleration started. Finally, the natural position in the tip was reestablished against the direction of continuous centrifugation. Retransport was observed during accelerations up to 70 g. Under the 1 g condition that followed the retransported statoliths showed an up to 5-fold increase in sedimentation time onto the lateral cell wall when placed horizontally. During basipetal centrifugations > or = 70 g all statoliths entered the basal vacuolar part of the rhizoid where they were cotransported in the streaming cytoplasm. It is concluded that the MF system is able to adapt to higher mass accelerations and that the MF system of the polarly growing rhizoid is polarly organized.

Acceleration↗
PubMed1994

Gravity-regulated formation of the peg in developing cucumber seedlings.

It has been proposed that peg formation in the vascular transition region (TR zone) between the hypocotyl and the root in Cucurbitaceae seedlings is a gravimorphogenetic phenomenon. Initiation of the peg became visible 36 h after imbibition when cucumber (Cucumis sativus L. cv. Burpee Hybrid II) seeds were germinated in a horizontal position at 24 degrees C in the dark. Simultaneously, sedimented amyloplasts (putative statoliths) were apparent in the sheath cells surrounding the vascular strands, and in the cortical cells immediately adjacent to them, in the TR zone. In contrast, the other cortical cells, some of which were destined to develop into the peg, contained amyloplasts which were not sedimented. These results suggest that the graviperception mechanism for peg formation may be like that of statoliths in shoot gravitropism. By 48 h following imbibition, the cells of the TR zone still had sedimented amyloplasts but had lost their sensitivity to gravity, possibly because of their maturation.

Cucumis sativus↗
PubMed2002

CECILIA, a versatile research tool for cellular responses to gravity.

We describe a centrifuge designed and constructed according to current demands for a versatile instrument in cellular gravitational research, in particular protists (ciliates, flagellates). The instrument (called CECILIA, centrifuge for ciliates) is suited for videomonitoring, videorecording, and quantitative evaluation of data from large numbers of swimming cells in a ground-based laboratory or in a drop tower/drop shaft under microgravity conditions. The horizontal rotating platform holds up to six 8mm-camcorders and six chambers holding the experimental cells. Under hypergravity conditions (up to 15 g) chambers can be rotated about 2 axes to adjust the swimming space at right angles or parallel to the resulting gravity vector. Evaluations of cellular responses to central acceleration-- in the presence of gravitational 1 g--are used for extrapolation of cellular behaviour under hypogravity conditions. CECILIA is operated and monitored by computer using a custom-made software. Times and slopes of rising and decreasing acceleration, values and and quality of steady acceleration are supervised online. CECILIA can serve as an on-ground research instrument for precursor investigations of the behaviour of ciliates and flagellates under microgravity conditions such as long-term experiments in the International Space Station.

Acceleration↗
PubMed1998

Development of postural control of gravity forces in children during the first 5 years of walking.

The aim of this work was to propose developmental indexes relative to the control of balance and gravity forces, using force-plate data, for children in their first 5 years of independent walking. The first part of this paper is devoted to the definition of an index to quantify postural capacity during walking. Based on the assumption that the vertical acceleration of center of mass (CM) reflects the capacity of muscular forces between the head-arms-trunk and the stance leg segments to control the external forces, the value of the CM vertical acceleration at foot contact is proposed as a developmental index of the postural capacity of the child to control gravitational forces. This index was analyzed longitudinally in five children, over the course of eight experimental sessions. The children were examined during their first 5 years of independent walking (for a total of 457 step sequences). The covariation between the CM vertical acceleration at foot contact and the gait velocity was considered as a second index characterizing the development of coordination between the postural and dynamic requirements of body progression. From these indexes it was established that the postural capacity needed just to control balance with the leg muscles was not attained before 4-5 years of independent walking, i.e., at about 5-6 years of age.

Acceleration↗
PubMed1999

Kaolin-induced hydrocephalus in the hamster: temporal sequence of changes in intracranial pressure, ventriculomegaly and whole-brain specific gravity.

The development of kaolin-induced hydrocephalus in adult hamsters was monitored by measuring changes in intracranial pressure (ICP), ventriculomegaly (VG) and whole-brain specific gravity (SG). Controls were intact or sham operated animals. Relative to controls, ICP of experimental animals increased at 24 h post intracisternal kaolin injection (by approximately 7-fold), reached a maximum on day 6 (by approximately 12-fold) and remained markedly elevated through day 15 (by approximately 5-fold). Ventricles differed in time of onset of distension (third: day 1, lateral: day 2, fourth: day 4) and in time of maximum ventriculomegaly (fourth: day 6; third: day 7; and lateral: day 9). Ventricular distension resulted in alterations in the ependyma; cilia were lost and apical cell surfaces were distorted. The ependyma was ruptured and the subjacent neuropil was exposed to the cerebrospinal fluid in some regions. Whole-brain SG remained constant in controls but declined in hydrocephalic hamsters after day 3 post-kaolin injection and reached its nadir on day 9 when whole-brain water content was 18% greater than in controls. Consistent with the fact that causal relationships exist between increased ICP, ventricular distension and brain edema, the alterations in each parameter occurred sequentially rather than simultaneously, and the time-course of each manifestation of hydrocephalus differed. The data suggest that the pathophysiology of kaolin-induced hydrocephalus in the hamster is tri-phasic: an initial period of rapid change, a brief interval of maximum alteration, and a subsequent period of compensation.

Age Factors↗
PubMed2004

The effect of specific gravity of perfluorocarbon liquid on the retina after experimental vitreous substitution.

PURPOSE: To evaluate the histological changes in the retina after experimental vitreous substitution with various amounts of perfluorophenanthrene (PFPH). METHODS: Thirty-two rabbit eyes were mechanically vitrectomized and filled up with 0.8 cc or 0.2 cc highly purified PFPH. The substance remained for 1 week (4 eyes), 2 weeks (8 eyes), 4 weeks (10 eyes) or 8 weeks (10 eyes). Eight eyes underwent the same surgical procedure without PFPH exchange to serve as a control group. A histological comparison of corresponding areas in the center and in the periphery of the inferior retina ensued. RESULTS: After 2 weeks, nuclear drop-downs and irregularities of the outer plexiform layer and of both nuclear layers were observed centrally in the eyes with a 0.8 cc substitution. The changes proceeded to irregularities and cell loss of all retinal layers with focal areas of complete destruction of the retinal architecture after 8 weeks. In contrast, single nuclear drop-downs, wrinkling of the outer nuclear layer and cell loss in the photoreceptor layer were observed in the peripheral retina at the end of the observation period. In those eyes where 0.2 cc PFPH was exchanged nuclear drop-downs were found after 2 weeks, leading to focal thinning of the outer plexiform layer and irregularities of the outer nuclear layer after 4 weeks with an insignificant increase after 8 weeks. At this time these histological alterations were comparable with those that we observed after 2 weeks in the eyes with a 0.8 cc tamponade in a corresponding area. CONCLUSIONS: Even high purification of PFPH does not prevent retinal damage. The different results in different areas after vitreous substitution with 0.2 cc and with 0.8 cc demonstrate that the high specific gravity of the substance may also play a role in the development of histological changes after extended tamponade.

Animals↗
PubMed2005

Cross-correlation between EMG and center of gravity during quiet stance: theory and simulations.

Several signal processing tools have been employed in the experimental study of the postural control system in humans. Among them, the cross-correlation function has been used to analyze the time relationship between signals such as the electromyogram and the horizontal projection of the center of gravity. The common finding is that the electromyogram precedes the biomechanical signal, a result that has been interpreted in different ways, for example, the existence of feedforward control or the preponderance of a velocity feedback. It is shown here, analytically and by simulation, that the cross-correlation function is dependent in a complicated way on system parameters and on noise spectra. Results similar to those found experimentally, e.g., electromyogram preceding the biomechanical signal may be obtained in a postural control model without any feedforward control and without any velocity feedback. Therefore, correct interpretations of experimentally obtained cross-correlation functions may require additional information about the system. The results extend to other biomedical applications where two signals from a closed loop system are cross-correlated.

Computer Simulation↗
PubMed2002

Basipetal propagation of gravity-induced surface pH changes along primary roots of Lepidium sativum L.

While there is ample evidence for a role of auxin in root gravitropism, the seeming rapidity of gravi-induced changes in electrical parameters has so far been an argument against auxin being a primary signal in gravitropic signal transmission. To address this problem, we re-investigated the effect of gravistimulation on membrane voltages of Lepidium sativum L. and Vigna mungo L. root cells. In our hands, gravistimulation did not induce changes in membrane voltage in cells of the root cap statenchyma, root meristem or apical elongation zone that can be correlated with the orientation of the cells relative to the gravity vector. While these results challenge a model of rapid electrically based signal transmission, there is evidence for a slower signal propagation along gravistimulated L. sativum roots. Using multiple proton-selective microelectrodes to simultaneously measure surface pH on opposite root flanks at different distances from the root tip, we observed gravi-induced asymmetric pH changes at the surface of all investigated root zones. Upon gravistimulation, the surface pH decreased on the physically upper root flank and increased on the lower flank. The pH asymmetry appeared first [2.1+/-0.4 min (mean +/- SD) after tilting] at the root cap and then - with incrementing lag times - at the meristem (after 2.5+/-0.3 min at 300 micro m from root tip; after 3.7+/-0.4 min at 700 micro m) and apical elongation zone (4.8+/-0.5 min at 1,000 micro m), suggesting a basipetal progression of differential surface acidification at a rate of 250-350 micro m min(-1), consistent with reported auxin transport rates.

Biological Transport↗
PubMed1998

Growth dynamics and cytoskeleton organization during stem maturation and gravity-induced stem bending in Zea mays L.

Characterization of gravitropic bending in the maize stem pulvinus, a tissue that functions specifically in gravity responses, demonstrates that the pulvinus is an ideal system for studying gravitropism. Gravistimulation during the second of three developmental phases of the pulvinus induces a gradient of cell elongation across the non-growing cells of the pulvinus, with the most elongation occurring on the lower side. This cell elongation is spatially and temporally separated from normal internodal cell elongation. The three characterized growth phases in the pulvinus correspond closely to a specialized developmental sequence in which structural features typical of cells not fully matured are retained while cell maturation occurs in surrounding internodal and nodal tissue. For example, the lignification of supporting tissue and rearrangement of transverse microtubules to oblique that occur in the internode when cell elongation ceases are delayed for up to 10 d in the adjacent cells of the pulvinus, and only occurs as a pulvinus loses its capacity to respond to gravistimulation. Gravistimulation does not modify this developmental sequence. Neither wall lignification nor rearrangement of transverse microtubules occurs in the rapidly elongating lower side or non-responsive upper side of the pulvinus until the pulvinus loses the capacity to bend further. Gravistimulation does, however, lead to the formation of putative pit fields within the expanding cells of the pulvinus.

Cell Wall↗
PubMed1984

Specific gravity increases and brain water content decreases during short epileptiform seizures in discrete rabbit brain areas.

In rabbits subjected to bicuculline (BC)- or pentylenetetrazole (PTZ)-seizures of 3 or 20 min duration or to adrenaline-induced hypertension, specific gravity (SG) was measured bilaterally in 15 regional brain areas in order to detect possible associations between the regionally limited blood-brain barrier openings due to these insults (see Nitsch and Klatzo 1983) and the presence of brain edema. In controls, a large variation between regional SG levels became evident: between 1.0467 in cerebellum and 1.0417 in preoptic area. A seizure duration of only 3 min was not sufficient to change SG significantly. After 20 min of seizures independent from the inducing agent, SG increased in all brain areas. The degree of increase seemed to be unrelated to presence or absence of a blood-brain barrier opening. In an attempt to avoid the influence of blood impregnation on the SG value, blood was replaced by saline before measurement. In controls, saline perfusion decreased SG only in the two areas with the highest original levels, thus documenting the partial dependency of the regional SG on the hematisation of the tissue. After 20 min of PTZ-induced seizures, SG in saline-perfused rabbits increased, but no longer significantly in all brain areas. This suggests that a part of the seizure-induced SG increase can be attributed to the hyperemia of the brain during the convulsions. On the other hand, an increase in flow volume due to hypertension did not change SG with the exception of the septum, preoptic area and hypothalamus. The direct measurement of water content with the classical wet/dry method in 4 gross brain areas showed that early seizure periods are in fact associated with a dehydration of the brain. This phenomenon could be explained by a glucose- and lactate-induced rise in blood osmolarity which in turn might cause a dehydration of the brain tissue.

Animals↗
PubMed1975

The gravity suit: a useful device in complicated urologic hemorrhage.

External counterpressure with a gravity suit was used to control intractable postoperative bleeding in 4 urologic patients. Two patients had coagulation defects, and 2 had been unsuccessfully reexplored prior to application of the G-suit. The bleeding was controlled with preservation and restoration of vital signs in each case. In 3 cases external counterpressure may have been lifesaving.

Aged↗
PubMed1992

Artificial gravity in Space: vestibular tolerance assessed by human centrifuge spinning on Earth.

Artificial gravity created by the astronauts themselves, without any external power supply, by pedalling on coupled counterrotating bicycles along the inner wall of the space module (Twin Bikes System, TBS), was previously suggested (Antonutto et al., 1991) to prevent musculo-skeletal decay and cardiovascular deconditioning during long term space flights. To investigate whether this unusual rotating environment would determine abnormal stimulations of the vestibular system due to Coriolis cross coupled accelerations, thus leading to acute motion sickness (AMS), the conditions of a rotating environment were reproduced in a human centrifuge. A cycloergometer was fixed to the arm of the centrifuge, the rotation speed of which was equal to that yielding 1 g at the feet level in the TBS (i.e. ranging from 19 to 21 RPM). The ergometer position was such that the combination of the horizontal and gravitational acceleration vectors was 1.414 at the inner ear level and was aligned along the head to feet axis. Three subjects, pedalling at 50 W on a cycloergometer during centrifuge's spinning, were asked to move the head following an AMS' provocation protocol. None of them developed any AMS symptoms. This supports the look of the TBS as tool for avoiding musculo-skeletal and cardiovascular deconditioning during long term space flights.

Adult↗
PubMed1992

Gravity detection through bifurcation.

Bifurcation is a phenomenon in which a physical system is forced to make a choice between one of the several possible states to which it can evolve. In this process the system can become extremely sensitive to very small influences--smaller than the size of the fluctuations--that favor one of the states. A general theory of this sensitivity and a simple model for gravity detection is presented. The difference between systems in thermodynamic equilibrium and those that are far from equilibrium is also discussed.

Animals↗
PubMed1992

Perception of gravity by plants.

Physical principles can be used to predict some features about the gravity perception system in plants. The nature of the system has made it rather elusive, so this approach represents an additional source of information to help find it. For a gravitational stimulus to be detected, two masses must move relative to each other in a manner which causes a significant amount of work to be done on a receptor. Relative to cellular dimensions, the masses must be large, be dense and move noticeable distances. The main sources of noise are thermal motion and flexing of the plant tissue. Some new models for the function of amyloplasts as statoliths are presented.

Cell Size↗