Illusory movements prevent cortical disruption caused by immobilization.

Enforced limb disuse strongly disrupts the cortical networks that are involved in sensorimotor activities. This disruption causes a cortical reorganization that may be functionally maladaptive. In this study, we used functional magnetic resonance imaging (fMRI) to investigate whether it is possible to prevent this reorganization by compensating for the lack of actual kinesthetic perception with illusory movements induced by "neuromimetic" proprio-tactile feedback that is artificially delivered during immobilization. Sixteen healthy volunteers were equipped for five days with full-hand ortheses that prevented them from performing finger and hand movements but allowed for kinesthetic and tactile sensations. Eight participants received a twice-daily proprio-tactile treatment consisting of the perception of kinesthetic sensations resembling those felt during actual movements generated by miniature vibrators set in the ortheses at the finger and wrist levels. Eight untreated participants received no stimulation. The effects of hand immobilization and treatment were assessed by fMRI during a calibrated voluntary hand movement task and hand tactile stimulation before cast placement and immediately after cast removal. We found that the sensorimotor network was preserved in subjects who underwent this treatment during hand immobilization, while the sensorimotor network of untreated subjects was significantly altered. These findings suggest that sensory feedback and associated movement perception may counteract disuse-induced cortical plastic changes through recruitment of a large part of the cortical network used for actual performed movement. The possibility of guiding cortical plasticity with proprioceptive augmented feedback is potentially relevant for rehabilitation efforts.

Proprio-tactile integration for kinesthetic perception: an fMRI study.

This study aims to identify the cerebral networks involved in the integrative processing of somesthetic inputs for kinesthetic purposes. In particular, we investigated how muscle proprioceptive and tactile messages can result in a unified percept of one's own body movements. We stimulated either separately or conjointly these two sensory channels in order to evoke kinesthetic illusions of a clockwise rotation of 10 subjects' right hand in an fMRI environment. Results first show that, whether induced by a tactile or a proprioceptive stimulation, the kinesthetic illusion was accompanied by the activation of a very similar cerebral network including cortical and subcortical sensorimotor areas, which are also classically found in passive or imagined movement tasks. In addition, the strongest kinesthetic illusions occurred under the congruent proprio-tactile co-stimulation condition. They were specifically associated to brain area activations distinct from those evidenced under the unimodal stimulations: the inferior parietal lobule, the superior temporal sulcus, the insula-claustrum region, and the cerebellum. These findings support the hypothesis that heteromodal areas may subserve multisensory integrative mechanisms at cortical and subcortical levels. They also suggest the integrative processing might consist of detection of the spatial coherence between the two kinesthetic messages involving the inferior parietal lobule activity and of a detection of their temporal coincidence via a subcortical relay, the insula structure, usually linked to the relative synchrony of different stimuli. Finally, the involvement of the superior temporal sulcus in the feeling of biological movement and that of the cerebellum in the movement timing control are also discussed.

Vibration-induced post-effects: a means to improve postural asymmetry in lower leg amputees?

Muscle vibration has been shown to induce long-lasting and oriented alteration of standing posture in healthy individuals. The postural alterations can last several minutes following the end of vibration and are called post-effects. The goal of this study was to determine whether persons with lower leg amputation that show persistent postural asymmetry after usual rehabilitation experience these postural post-effects and if this could improve their weight bearing on the prosthesis. Centre of pressure (CP) position during stance was recorded prior to and up to 13 min after a 30s unilateral vibration applied during sitting to lateral neck (trapezius) or hip (gluteus medius) muscles in 14 individuals with unilateral lower leg amputation and 18 controls. The amputees' postural asymmetry was confirmed prior to the vibration intervention. A CP displacement, without an increase in CP velocity, was observed in both groups of participants over the 13 min post-vibration. For both the neck or hip vibration sites, the CP shifts were directed in the medio-lateral plane and were oriented either towards the vibrated side or the opposite side across subjects. This led to a decrease of postural asymmetry in half of the group of amputees. Within subject, the orientation of the post-effect was constant and changed to the opposite direction with vibration of the opposite body side. It is suggested that the post-effects are produced by a change of the postural reference consequent to the sustained proprioceptive message induced during the muscle vibration period. The orientation of the post-effects is discussed in relation to the notion of reference frame preference. All in all, because post-effect orientation is constant within subject and adaptive, future studies should investigate if individuals with lower leg amputation could benefit from postural post-effects induced by muscle vibration to improve function.

Cerebral correlates of the "Kohnstamm phenomenon": an fMRI study.

This paper addresses the issue of the central correlates of the "Kohnstamm phenomenon", i.e. the long-lasting involuntary muscle contraction which develops after a prolonged isometric voluntary contraction. Although this phenomenon was described as early as 1915, the mechanisms underlying these post-effects are not yet understood. It was therefore proposed to investigate whether specific brain areas may be involved in the motor post-effects induced by either wrist muscle contraction or vibration using the fMRI method. For this purpose, experiments were carried out on the right wrist of 11 healthy subjects. Muscle activity (EMG) and regional cerebral blood flow were recorded during isometric voluntary muscle contraction and muscle vibration, as well as during the subsequent involuntary contractions (the post-effects) which occurred under both conditions. Brain activations were found to occur during the post-contraction and post-vibration periods, which were very similar under both conditions. Brain activation involved motor-related areas usually responsible for voluntary motor command (primary sensory and motor cortices, premotor cortex, anterior and posterior cingulate gyrus) and sensorimotor integration structures such as the posterior parietal cortex. Comparisons between the patterns of brain activation associated with the involuntary post-effects and those accompanying voluntary contraction showed that cerebellar vermis was activated during the post-effect periods whereas the supplementary motor area was activated only during the induction periods. Although post-effects originate from asymmetric proprioceptive inputs, they might also involve a central network where the motor and somatosensory areas and the cerebellum play a key role. In functional terms, they might result from the adaptive recalibration of the postural reference frame altered by the sustained proprioceptive inputs elicited by muscle contraction and vibration.

Long-lasting body leanings following neck muscle isometric contractions.

Our objective was to investigate the neural mechanisms and the functional relevance of motor effects that develop involuntarily following the release of a sustained isometric muscle contraction. The few data available in the literature deal only with post-contractions occurring in a body segment. Although these data emphasise the role of proprioceptive input, the question as to whether this phenomenon is of central or peripheral origin remains unclear. Given the leading role of neck muscle proprioceptive input in body orientation and posture regulation, we designed two experiments to test for postural posteffects after voluntary and involuntary neck muscle contraction. The spatiotemporal characteristics of the posteffects were analysed by means of stabilometric recordings following 30-s isometric contraction of splenius, trapezius and levator muscle groups, and 30-s electrically-induced contraction of the levator muscle group. Results show that a postural response occurred after voluntary contraction of each muscle group tested, which was oriented in the plane of action of the muscle, and lasted 14 min at least. In contrast, no clearly oriented body leanings were found after electrical stimulation of the levator muscle, except for a slight increase in natural postural instability. Data are interpreted as a change in the postural reference resulting from an increase in proprioceptive inflow accompanying mainly the voluntary muscle contraction.

Gas chromatography for in situ analysis of a cometary nucleus. IV. Study of capillary column robustness for space application.

As part of the development of the European Space Agency Rosetta space mission to investigate a cometary nucleus, the selection of columns dedicated to the gas chromatographic subsystem of the Cometary Sampling and Composition (COSAC) experiment was achieved. Once the space probe launched, these columns will be exposed to the harsh environmental constraints of space missions: vibrations, radiation (by photons or energetic particles), space vacuum, and large temperature range. In order to test the resistance of the flight columns and their stationary phases, the columns were exposed to these rough conditions reproduced in the laboratory. The comparison of the analytical performances of the columns, evaluated prior and after the environmental tests, demonstrated that all the columns withstand space constraints, and that their analytical properties were preserved. Therefore, all the selected capillary columns, even having porous layer or chiral stationary phases, were qualified for space exploration.

Enantiomer separation of hydrocarbons in preparation for ROSETTA's "chirality-experiment".

Until now the favored method for separating racemic pairs of underivatized alcohols, diols, and phenylsubstituted amines has been gas chromatography on cyclodextrin phases. However, certain enantiomers of saturated chiral hydrocarbons could not be resolved in this way because they lack the functional groups necessary to undergo "intensive" diastereomeric interactions with the cyclodextrins. The present study describes a gas-chromatographic technique for resolution of saturated aliphatic hydrocarbons into their enantiomers and presents a brief discussion of the possible applications. The (enantiomer) separations were performed in preparation for the Cometary Sampling and Composition Experiment on board the cometary lander RoLand, part of ESA's cornerstone mission ROSETTA. This experiment has been designed to investigate the hypotheses that biomolecular asymmetry has an interstellar origin and to separate and identify a wide range of organic enantiomers in situ on the surface of a comet's nucleus.

Foot sole and ankle muscle inputs contribute jointly to human erect posture regulation.

In order to assess the relative contribution and the interactions of the plantar cutaneous and muscle proprioceptive feedback in controlling human erect posture, single or combined vibratory stimuli were applied to the forefoot areas and to the tendons of the tibialis anterior muscles of nine standing subjects using various vibration frequency patterns (ranging from 20 to 80 Hz). The variations in the centre of foot pressure, ankle angle and the EMG activities of the soleus and tibialis anterior muscles of each subject were recorded and analysed. Separate stimulation of the plantar forefoot zones or the tibialis anterior muscles always resulted in whole-body tilts oppositely directed backwards and forwards, respectively, the amplitude of which was proportional to the vibration frequency. EMG activity of ankle muscles also varied according to the direction of the postural responses. However, the same vibration frequency did not elicit equivalent postural responses: in the low frequency range, tactile stimulation induced stronger postural effects than proprioceptive stimulation, and the converse was the case for the higher frequency range. Under sensory conflict conditions, i.e. foot sole-flexor ankle muscle co-stimulation, the direction of the body tilts also varied according to the difference and the absolute levels of the vibration frequencies. In all cases, the resulting postural shifts always corresponded to the theoretical sum of the isolated effects observed upon vibrating each of these two sensory channels. We proposed that tactile and proprioceptive information from the foot soles and flexor ankle muscles might be co-processed following a vector addition mode to subserve the maintenance of erect stance in a complementary way.

Phosphorylated pleckstrin induces cell spreading via an integrin-dependent pathway.

Pleckstrin is a 40-kD phosphoprotein containing NH(2)- and COOH-terminal pleckstrin homology (PH) domains separated by a disheveled-egl 10-pleckstrin (DEP) domain. After platelet activation, pleckstrin is rapidly phosphorylated by protein kinase C. We reported previously that expressed phosphorylated pleckstrin induces cytoskeletal reorganization and localizes in microvilli along with glycoproteins, such as integrins. Given the role of integrins in cytoskeletal organization and cell spreading, we investigated whether signaling from pleckstrin cooperated with signaling pathways involving the platelet integrin, alphaIIbbeta3. Pleckstrin induced cell spreading in both transformed (COS-1 & CHO) and nontransformed (REF52) cell lines, and this spreading was regulated by pleckstrin phosphorylation. In REF52 cells, pleckstrin-induced spreading was matrix dependent, as evidenced by spreading of these cells on fibrinogen but not on fibronectin. Coexpression with alphaIIbbeta3 did not enhance pleckstrin-mediated cell spreading in either REF52 or CHO cells. However, coexpression of the inactive variant alphaIIbbeta3 Ser753Pro, or beta3 Ser753Pro alone, completely blocked pleckstrin-induced spreading. This implies that alphaIIbbeta3 Ser753Pro functions as a competitive inhibitor by blocking the effects of an endogenous receptor that is used in the signaling pathway involved in pleckstrin-induced cell spreading. Expression of a chimeric protein composed of the extracellular and transmembrane portion of Tac fused to the cytoplasmic tail of beta3 completely blocked pleckstrin-mediated spreading, whereas chimeras containing the cytoplasmic tail of beta3 Ser753Pro or alphaIIb had no effect. This suggests that the association of an unknown signaling protein with the cytoplasmic tail of an endogenous integrin beta-chain is also required for pleckstrin-induced spreading. Thus, expressed phosphorylated pleckstrin promotes cell spreading that is both matrix and integrin dependent. To our knowledge, this is the first example of a mutated integrin functioning as a dominant negative inhibitor.

Construction of a new multi-turn time-of-flight mass spectrometer.

A new type of multi-turn time-of-flight mass spectrometer was constructed, consisting of four cylindrical electric sectors and 28 electric quadrupole lenses, the size of the vacuum chamber being 60 x 70 x 20 cm. It was demonstrated that the mass resolution can be increased according to the number of cycles of the ions through the ion optical system.

Agonists cause nuclear translocation of phosphatidylinositol 3-kinase gamma. A Gbetagamma-dependent pathway that requires the p110gamma amino terminus.

In hematopoietic cells, the signals initiated by activation of the phosphoinositide 3-kinase (PI3K) family have been implicated in cell proliferation and survival, membrane and cytoskeletal reorganization, chemotaxis, and the neutrophil respiratory burst. Of the four isoforms of human PI3K that phosphorylate phosphatidylinositol 4, 5-bisphosphate, only p110gamma (or PI3Kgamma) is associated with the regulatory subunit, p101, and is stimulated by G protein betagamma heterodimers. We performed immunolocalization of transfected p110gamma in HepG2 cells and found that, under resting conditions, p110gamma was present in a diffuse cytoplasmic pattern, but translocated to the cell nucleus after serum stimulation. Serum-stimulated p110gamma translocation was inhibited by pertussis toxin and could also be induced by overexpression of Gbetagamma in the absence of serum. In addition, we found that deletion of the amino-terminal 33 residues of p110gamma had no effect on association with p101 or on its agonist-regulated translocation, but truncation of the amino-terminal 82 residues yielded a p110gamma variant that did not associate with p101 and was constitutively localized in the nucleus. This finding implies that the intracellular localization of p110gamma is regulated by p101 as well as Gbetagamma. The effect of PI3Kgamma in the nucleus is an area of active investigation.

Specific whole-body shifts induced by frequency-modulated vibrations of human plantar soles.

This study sought to analyze the postural responses induced by separately or simultaneously vibrating with different frequencies the forefoot and rear foot zones of both soles in standing subjects. Stimulating each zone separately resulted in spatially oriented body tilts; their amplitude and velocity varied linearly according to the frequency, and their direction was always opposite to the plantar site vibrated. When the two zones were each co-stimulated at different frequencies, the parameters of the postural responses depended on the frequency difference. When this frequency difference was zero, no clearly oriented body tilts occurred. We concluded that the change in the relative pressures evoked by differently co-vibrating these zones gave rise to regulative postural adjustments able to cancel the simulated body deviation.

[Errors in targeted movements of the hand under the conditions of orbital space flight]. / Oshibki tselevykh dvizhenii ruki v usloviiakh orbila'nogo poleta.

Three crew members of the Russian-French MIR mission were tested to determine errors in pointing to memorized visual targets. In the laboratory, all test-subjects consistently used to point to the spot below the actual target presentation. The mean Y-error (the vertical error) made up -31.6 +/- 21.8 mm. In microgravity, the Y-error moved "upward" so that the mean Y-error was -16.8 +/- 37.0 mm. The data demonstrate adaptation of the central program of aiming arm movement to the microgravity conditions.

Pleckstrin 2, a widely expressed paralog of pleckstrin involved in actin rearrangement.

We have identified a cDNA for pleckstrin 2 that is 39% identical and 65% homologous to the original pleckstrin. Like the original pleckstrin 1, this protein contains a pleckstrin homology (PH) domain at each end of the molecule as well as a DEP (Dishevelled, Egl-10, and pleckstrin) domain in the intervening sequence. A Northern blot probed with the full-length cDNA reveals that this homolog is ubiquitously expressed and is most abundant in the thymus, large bowel, small bowel, stomach, and prostate. Unlike pleckstrin 1, this newly discovered protein does not contain obvious sites of PKC phosphorylation, and in transfected Cos-7 cells, it is a poor substrate for phosphorylation, even after PMA stimulation. Cells expressing pleckstrin 2 undergo a dramatic shape change associated with actin rearrangement, including a loss of central F-actin and a redistribution of actin toward the cell cortex. Overexpression of pleckstrin 2 causes large lamellipodia and peripheral ruffle formation. A variant of pleckstrin 2 lacking both PH domains still had some membrane binding but did not efficiently induce lamellipodia, suggesting that the PH domains of pleckstrin 2 contribute to lamellipodia formation. This work describes a novel, widely expressed, membrane-associating protein and suggests that pleckstrin 2 may help orchestrate cytoskeletal arrangement.

From balance regulation to body orientation: two goals for muscle proprioceptive information processing?

This study was based on the assumption that the central processing of proprioceptive inputs that arise from numerous muscles contributes to both awareness and control of body posture. The muscle-spindle inputs form a "proprioceptive chain" which functionally links the eye muscles to the foot muscles. Here, we focused on the specific contribution of two links in the control of human erect posture by investigating how proprioceptive messages arising from ankle and neck muscles may be integrated by the central nervous system. Single or combined mechanical vibrations were applied to different muscle tendons at either one (ankle or neck) or both (ankle plus neck) body levels. The amplitude and the specific direction of the resulting oriented body tilts were analyzed by recording the center of foot pressure (CoP) through a force platform with four strain gauges. The results can be summarized as follows: (1) the vibration-induced whole-body tilts were oriented according to the muscles stimulated; furthermore, the tilts were in opposite directions when neck or ankle muscles on the same side of the body were stimulated; (2) except for the ankle antagonist muscles, co-vibrating adjacent or antagonist muscles at the same body level (ankle or neck) resulted in body sways, whose orientation was a combination of those obtained by stimulating these muscles separately; and (3) likewise, co-vibrating ankle and neck muscles induced whole-body postural responses, whose direction and amplitude were a combination of those obtained by separate vibration. We conclude that the multiple proprioceptive inputs originating from either one or both body levels may be co-processed in terms of vector-addition laws. Moreover, we propose that proprioceptive information from ankle and neck muscles may be used for two tasks: balance control and body orientation, with central integration of both tasks.

Proprioceptive information processing in weightlessness.

The "illusions" experiment carried out on five astronauts during the last two French-Russian flights (Antarès in 1992 and Altaïr in 1993) and in the Russian Post-Antarès mission (1993) was designed to investigate the adaptive changes in human proprioceptive functions occurring in weightlessness at both the sensorimotor and cognitive levels, focusing on two kinds of responses: (1) whole-body postural reflexes, and (2) whole-body movement perception. These kinesthetic and motor responses were induced using the tendon-vibration method, which is known to selectively activate the proprioceptive muscular sensory channel and to elicit either motor reactions or illusory movement sensations. Vibration (70 Hz) was therefore applied to ankle (soleus or tibialis) and neck (splenii) muscles. The subject's whole-body motor responses were analyzed from EMG and goniometric recordings. The perceived vibration-induced kinesthetic sensations were mimicked by the subjects with a joystick. The main results show that a parallel in-flight attenuation of the vibration-induced postural responses and kinesthetic illusions occurred, which seems to indicate that the proprioceptive system adapts to the microgravity context, where standing posture and conscious coding of anteroposterior body movements are no longer relevant. The same sensory messages are used at the same time in different sensory motor loops and in the coding of newly developed behavioral movements under microgravity. These results suggest that the human proprioceptive system has a high degree of adaptive functional plasticity, at least as far as the perceptual and motor aspects are concerned.

The plantar sole is a 'dynamometric map' for human balance control.

This study investigated the role of the plantar cutaneous information in controlling human balance. We hypothesized that the cutaneous afferent messages from the main supporting zones of the feet have sufficient spatial relevance to inform the CNS about the body position with respect to the vertical reference and consequently to induce adapted regulative postural responses. Skin mechanoreceptors of anterior and/or posterior areas of one or both soles of 10 standing subjects were activated by superficial mechanical vibration with high frequency and low amplitude. Variations of the subject's center of pressure (CoP) were recorded. Spatially oriented whole-body tilts were observed for every subject. Their direction depended on the foot areas stimulated and was always opposite to the vibration-simulated pressure increase. These responses are found to subserve a postural regulative function and we suggest that co-processing of the various cutaneous messages followed a vector addition mode.

A chicken c-Rel-estrogen receptor chimeric protein shows conditional nuclear localization, DNA binding, transformation and transcriptional activation.

In this report, we characterize the biological and biochemical properties of a conditional protein containing chicken c-Rel fused to the hormone-binding domain of the human estrogen receptor. This chimeric c-RelER protein causes estrogen-dependent, but otherwise c-Rel-specific, transformation of avian fibroblasts in vitro. Our results demonstrate that c-RelER heterodimerizes with wild-type c-Rel and forms specific complexes with IkappaB-alpha. Estrogen causes translocation of c-RelER to the nucleus and stabilizes its binding to DNA. Hormone-activated c-RelER induces transcription of at least four cellular genes that are constitutively active in wild-type c-Rel-transformed fibroblasts. Two distinct cell populations were examined that differed with respect to their growth phenotypes. The growth of fibroblasts with moderate expression levels of c-RelER was stimulated by estrogen. In contrast, the addition of estrogen to cells with high cRelER expression levels resulted in inhibition of cytokinesis and the arrest of growth. The carboxy terminal transactivation domain of c-Rel was required for the induction of these effects since neither v-Rel nor c-Rel deletion mutants were able to induce similar changes. Taken together, our results demonstrate that high levels of c-Rel expression can affect cell cycle control and/or cytokinesis. Furthermore, they also indicate that the biological properties of c-Rel in cell growth and differentiation will potentially differ depending on the level of expression.

Phospholipase D2, a distinct phospholipase D isoform with novel regulatory properties that provokes cytoskeletal reorganization.

BACKGROUND: Activation of phospholipase D (PLD) is an important but poorly understood component of receptor-mediated signal transduction responses and regulated secretion. We recently reported the cloning of the human gene encoding PLD1; this enzyme has low basal activity and is activated by protein kinase C and the small GTP-binding proteins, ADP-ribosylation factor (ARF), Rho, Rac and Cdc42. Biochemical and cell biological studies suggest, however, that additional and distinct PLD activities exist in cells, so a search was carried out for novel mammalian genes related to PLD1. RESULTS: We have cloned the gene for a second PLD family member and characterized the protein product, which appears to be regulated differently from PLD1: PLD2 is constitutively active and may be modulated in vivo by inhibition. Unexpectedly, PLD2 localizes primarily to the plasma membrane, in contrast to PLD1 which localizes solely to peri-nuclear regions (the endoplasmic reticulum, Golgi apparatus and late endosomes), where PLD activity has been shown to promote ARF-mediated coated-vesicle formation. PLD2 provokes cortical reorganization and undergoes redistribution in serum-stimulated cells, suggesting that it may have a role in signal-induced cytoskeletal regulation and/or endocytosis. CONCLUSIONS: PLD2 is a newly identified mammalian PLD isoform with novel regulatory properties. Our findings suggest that regulated secretion and morphological reorganization, the two most frequently proposed biological roles for PLD, are likely to be effected separately by PLD1 and PLD2.