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M Lenoir

Publications and source records attributed to M Lenoir.

At least 19 recordsLinked to original sources
PubMed2006

Kinematics of the transition between walking and running when gradually changing speed.

The purpose of this study was to examine kinematics of the walk-to-run transition (WRT) and run-to-walk transition (RWT) when speed is altered with a constant acceleration of 0.1 m s(-2), respectively -0.1 m s(-2). Thirteen women (height: 168.9+/-3.36 cm) performed gait transitions on a motor-driven treadmill. WRT-speed was 2.16+/-0.12 m s(-1), RWT-speed 2.19+/-0.12 m s(-1). Kinematics were examined in the range from eight steps before to eight steps after transition in order to identify the possible occurrence of a transition process to facilitate the actual realization of transition. A transition step in which the main changes from one gait to another are realized is present in WRT and RWT. Despite this clear discontinuity, a transition process also appeared in both transitions. In the WRT, transition was prepared and kinematic adaptations were found in the last swing before transition leading to altered landing conditions. During RWT posttransition changes were observed and RWT was only completed after reorientation of the trunk in the first walking stride after transition. A noteworthy finding was that spatiotemporal (presence of a flight phase), kinematic (knee flexion) and energetic (kinetic and gravitational potential energy fluctuating in-phase versus out-of-phase) criteria to define transition stride correspond to each other. Furthermore, a functional interlimb asymmetry was recognized as a unique characteristic of the transition stride, offering a fourth way of identifying the transition stride.

Acceleration↗
PubMed2006

Influence of M. tibialis anterior fatigue on the walk-to-run and run-to-walk transition in non-steady state locomotion.

The purpose of this study was to examine the influence of muscular fatigue of tibialis anterior (TA) on the walk-to-run transition (WRT) and run-to-walk transition (RWT) when speed is altered at different constant accelerations (a=0.01, 0.07 and 0.05 ms(-2)). Twenty women (height: 168.9+/-3.36 cm) performed WRTs and RWTs on a motor-driven treadmill, before and after a protocol inducing muscular fatigue of the TA. WRT-speed decreased after TA fatigue whereas RWT-speed did not change except during the intermediate deceleration. Integrated EMG (iEMG) of the activity burst of TA around heel contact was examined in the last steps before transition, the transition step and the first steps after transition. iEMG increased before WRT, then decreased after transition to running. In the RWT the opposite was observed: iEMG increased after RWT, then decreased with decreasing walking speed. After inducing fatigue in the TA, there was a decrease in iEMG in the WRT whereas no influence of fatigue was found on iEMG in the RWT. As a result of TA fatigue, WRT occurred at a lower speed, probably to avoid over-exertion of the TA. This indicates that the TA is a likely determinant of WRT as previously reported. The RWT, on the other hand, was not altered following TA fatigue, which would indicate that WRT and RWT are determined by different factors.

Acceleration↗
PubMed2006

Visual contribution to walking in children with Developmental Coordination Disorder.

BACKGROUND: The motor co-ordination problems of children with Developmental Coordination Disorder (DCD) have been frequently associated with poor visuospatial processing. In order to extend these findings mainly based on fine motor experiments, the present study investigates the contribution of vision to the control of walking in children with DCD. METHODS: Children with DCD (n = 12) walked at their preferred speed on a straight, firm and uncluttered walkway in a condition with normal lighting and in a dark condition. Spatiotemporal gait variables were assessed by means of a three-dimensional ProReflex camera system and compared with the gait pattern of matched, typically developing (TD) children (n = 12). RESULTS: In normal lighting, the gait pattern of both groups was similar, with the exception of subtle differences in the temporal phasing, showing a slightly longer support phase in the children with DCD. In the dark, step frequency and step length were decreased in the children with DCD, resulting in a significantly slower walking velocity. In addition, the medio-lateral excursion of the centre of mass tended to increase in this group. In the TD children, adaptations to the spatiotemporal pattern remained absent. CONCLUSIONS: These results suggest that children with DCD are more dependent on global visual flow information than TD children for the maintenance of balance and the control of velocity during walking. This increased dependency on visual control might be associated with a poorly developed internal sensorimotor model.

Child↗
PubMed2005

Spatiotemporal characteristics of the walk-to-run and run-to-walk transition when gradually changing speed.

The purpose of this study was to examine spatiotemporal parameters of the walk-to-run transition (WRT) and run-to-walk transition (RWT) when speed is altered with different constant accelerations. Twenty women (height: 168.9+/-3.36cm) performed three accelerations (0.05, 0.07 and 0.1ms(-2)) and three decelerations (-0.05, -0.07 and -0.1ms(-2)) on a motor-driven treadmill. The transition step in the WRT (first step with a flight phase) and RWT (first step with a double stance phase) occurred at the same speed for all accelerations but these did not occur in the same way. The most striking difference was the presence of a transition step with specific spatiotemporal characteristics in the WRT, whereas this was not observed in the RWT. The transition is not a sudden one-step-event. WRT occurred before transition and consisted of a "pre-transition period" and the transition step whereas RWT occurred after transition and consisted of the transition step and a "post-transition period". Both transition periods were characterized by an exponential evolution of step frequency and step length. Step frequency and step length showed a linear evolution before and after transition. The flight phase of the transition step in the WRT reached a minimum with comparable duration of the last flight phase in the RWT. The flight phase could be considered as an intrinsic dynamical factor of transition. Further research in kinematics, the trajectory of the body centre of mass and energy fluctuations will give more insight in these transitions.

Acceleration↗
PubMed2002

Riluzole rescues cochlear sensory cells from acoustic trauma in the guinea-pig.

Acoustic trauma is the major cause of hearing loss in industrialised nations. We show in guinea-pigs that sound exposure (6 kHz, 120 dB sound pressure level for 30 min) leads to sensory cell death and subsequent permanent hearing loss. Ultrastructural analysis reveals that degeneration of the noise-damaged hair cells involved different mechanisms, including typical apoptosis, autolysis and, to a lesser extent, necrosis. Whatever the mechanisms, a common feature of noise damage to hair cells was mitochondrial alteration. Riluzole (2-amino-6-trifluoromethoxy benzothiazole) is a neuroprotective agent that prevents apoptosis- and necrosis-induced cell death. Perfusion of riluzole into the cochlea via an osmotic minipump prevents mitochondrial damage and subsequent translocation of cytochrome c, DNA fragmentation, and hair cell degeneration. This was confirmed by functional tests showing a clear dose-dependent reduction (ED(50)=16.8 microM) of permanent hearing loss and complete protection at 100 microM. Although less efficient than intracochlear perfusion, intraperitoneal injection of riluzole rescues the cochlea within a therapeutic window of 24 h after acoustic trauma.These results show that riluzole is able to prevent and rescue the cochlea from acoustic trauma. It may thus be an interesting molecule for the treatment of inner ear injuries.

Acoustic Stimulation↗
PubMed2000

Sodium stibogluconate (Pentostam) potentiates oxidant production in murine visceral leishmaniasis and in human blood.

Sodium stibogluconate (Sbb), a leishmanicidal drug, was studied for its in vivo effect on the formation of reactive oxygen species (ROS), assessed by chemiluminescence (CL) in the whole blood of mice infected with Leishmania infantum. Stimulation of ROS formation induced ex vivo by zymosan particles or the protein kinase C activator phorbol myristate acetate (PMA) was reduced by approximately 25% (P < 0.05) after infection of mice. Treatment of infected mice with Sbb (50 to 400 mg/kg of body weight) enhanced the blood CL induced by zymosan and PMA (47 to 96%, P < 0.01). The drug potentiation effect also occurred in uninfected mice. In vitro treatment of normal human blood with Sbb (1, 10, or 100 microg/ml) for 1 h primed the CL response to PMA (29 to 54%). The priming effect of Sbb was also observed on the production of superoxide by isolated polymorphonuclear leukocytes stimulated either by PMA and zymosan or by the chemoattractants N-formyl-Met-Leu-Phe and platelet-activating factor. These data provide the first evidence of priming of the phagocyte respiratory burst by Sbb. This novel property of Sbb may contribute to the drug's leishmanicidal effect.

Animals↗
PubMed2000

Are better eye movements an advantage in ball games? A study of prosaccadic and antisaccadic eye movements.

The aim of this study was to compare prosaccadic and antisaccadic eye movements of experts in ball sports and controls. In the prosaccadic and antisaccadic task, subjects made saccades respectively towards and away from a suddenly appearing stimulus. By means of infrared-oculography, we compared horizontal eye movements of experts (n=18) and controls (n=20). Experts had shorter overall saccadic latencies, but significantly shorter latencies occurred only on the antisaccade task, not on the prosaccade task. Our findings seem to support the concept that prosaccades and antisaccades have different underlying mechanisms and that expertise in ball games mainly improves antisaccadic performance in terms of latency and variability.

Adult↗
PubMed2000

[Regenerative potential in the organ of Corti after otic intoxication].

The auditory sensory cells are sensitive to a variety of influences such as noise, ototoxic drugs and aging. In the cochlea of mammals, the destroyed sensory cells are not replaced by new sensory cells. That leads to cochlear deafness, a frequent disease in human. Unfortunately, such auditory impairment is out of reach of treatment. The development of new therapeutic strategies in this field requires a precise knowledge of the mechanisms involved in auditory sensory cells disappearance and in organ of Corti's degeneration. The aim of our study was to characterize cellular and molecular changes in the cochlea of rats which had been intoxicated with the ototoxic antibiotic amikacin. The animals were sacrificed at different survival times during and after the antibiotic treatment and their cochleas were investigated using transmission and scanning electron microscopy and using confocal microscopy after tissue labellings with different fluorescent probes. The results revealed the existence of three periods. The first one corresponds to the disappearance of the sensory cells which die by apoptosis. During the second period, the organ of Corti undergoes a scarring process; concomitantly, a contingent of nonsensory supporting cells attempts to transdifferentiate directly into sensory cells. This process however fails, and the supporting cells never reach the status of hair cells. A general process of dedifferentiation of all the epithelial cells of the organ of Corti followed by a massive apoptosis of numerous epithelial cells and of most ganglion cells occurs during the third period. After that, the organ of Corti is definitely reduced to a simple monolayered epithelium. On the basis of these data, experimental strategies aimed i) to protect the sensory cells against apoptosis and ii) to promote sensory cell regeneration are now under study. They might have important implications in human therapy.

Amikacin↗
PubMed1999

Contribution of mitogen-activated protein kinase to stimulation of phospholipase D by the chemotactic peptide fMet-Leu-Phe in human neutrophils.

Phospholipase D (PLD) plays an important role in signaling through phosphatidylcholine (PC) and in the production of superoxide (respiratory burst) by polymorphonuclear leukocytes (PMN) stimulated by the chemoattractant fMet-Leu-Phe (fMLP). However, the regulation of PLD activity by protein kinases is not fully understood. In the present study, we have used a mitogen-activated protein (MAP) kinase inhibitor (PD 98059) to investigate a possible connection between extracellular signal-regulated kinase (ERK) and PLD activity and respiratory burst. Using a range of concentrations (3-20 microM) which inhibit ERK activity, PD 98059 inhibited PLD activity induced by fMLP in cytochalasin B-primed PMN, as assessed by production-tritiated phosphatidylethanol (PEt), phosphatidic acid (PA), and hydrolysis of PC. However, the inhibition was partial (approximately 50%), while inhibition of PC hydrolysis was almost complete, suggesting a concomitant inhibition of PLA2 activity. In addition, PD 98059 reduced fMLP-induced respiratory burst by 50%, an effect which was correlated with PLD inhibition of PLD (r = 0.981, P < 0.01), and neither did PD 98059 inhibit the PLD activity and respiratory burst induced by PKC upon its direct activation by phorbol myristate acetate. These data provide the first evidence for implication of the ERK cascade in the stimulation of PLD through Gi signaling. They further indicate that PLD stimulation by fMLP receptors occurs through two pathways, dependent and independent on MAP kinase, the former pathway being linked to superoxide production.

Enzyme Activation↗
PubMed1999

Sequential changes in anti-GAL-1 staining of the rat organ of Corti following amikacin exposure.

Hair cell loss and a non-functional epithelial reorganization appeared in the organ of Corti after acoustic or toxic damage. Moreover, in the drug damaged organ of Corti, transient atypical cells were recently described with characteristics of both immature hair cells and/or non-sensory epithelial cells. The phenotype of these atypical cells has been now investigated by using the galectine 1 (GAL-1) antibody. In the normal organ of Corti, this antibody recognizes all the epithelial cells except the sensory hair cells and their supporting cells. At PD 21, transient atypical cells were not stained by GAL-1 antibody, suggesting that they were originated from hair cells or their supporting cells. Later, the organ of Corti was substituted by an epithelial scare, GAL-1 stained. This study also emphasizes the particular resistance of the cochlear apex to degeneration after antibiotic intoxication.

Amikacin↗
PubMed1999

Intercepting moving objects during self-motion: effects of environmental changes.

The purpose of this study was to examine the role of background texture on an interception task during self-motion. Twenty-six participants modulated tricycle speed along one arm of a V-shaped track so as to intercept a ball approaching horizontally on the other arm of the V. Either a plain or a textured background (consisting of contrasting vertical stripes) was used. Velocity modulations occurred so as to keep the angle beta between the direction of heading and the line head-ball constant (constant bearing angle, or CBA strategy), indicating that this observer-environment relation might regulate the approach phase. In the textured condition, participants initially drove faster than predicted by the CBA model and compensated by slowing down in the second half. This is in line with the texture-induced overestimation of the ball velocity and implies that absolute velocity information is also used.

Analysis of Variance↗
PubMed1999

Expression pattern of mammalian cochlea outer hair cell (OHC) mRNA: screening of a rat OHC cDNA library.

The aim of this study was to characterize the mRNA content of mammalian cochlear outer hair cells (OHCs) and to search for specific genes possibly involved in their unique properties. Indeed, OHCs, which feature high-frequency electromotility, are responsible for the exquisite sensitivity and frequency selectivity of the cochlea. Damage to these cells, which occurs in various conditions, causes a reduction in the cochlear sensitivity by about 50 dB and the alteration of frequency discrimination. Total RNA was extracted from about 2000 mechanically dissociated OHCs, and a polymerase chain reaction (PCR) amplified cDNA library was constructed. The presence of the alpha-9 acetylcholine receptor subunit, preferentially expressed in OHCs, was found by direct PCR amplification of the library. A systematic sequencing of 218 clones showed 78% known genes, 11% EST-related sequences, and 11% unknown genes. The known-gene group was characterized by two main features: a large proportion (55%) of mitochondrial transcripts and an abundance in calcium-binding proteins, such as calmodulin and calbindin, for which expression has already been demonstrated in OHCs. Another protein, the oncomodulin recently shown to be OHC specific, was also found, and its mRNA expression was confirmed by in situ hybridization. Among the 24 unknown genes, 7 were expressed in a restricted pattern, including one expressed in cochlea and spleen and, to a lesser extent, in lungs.

Animals↗
PubMed1999

Ecological relevance of stereopsis in one-handed ball-catching.

The aim of this study was to compare one-handed catching performance between catchers with high (n = 10) and low (n = 10) binocular depth vision or stereopsis. In two sessions of 90 trials, tennis balls were projected at three different velocities towards the subject's shoulder region. Participants with good stereopsis were more successful, although the difference in number of correct catches fell short of significance. More specifically, catchers with low stereopsis made more temporal errors, but no differences in spatial errors. As the velocity of the ball increased, the initiation of the catch was delayed and catching performance decreased. The finding that stereopsis affected timing of the catch challenges the 'monocular tau hypothesis' in the control of interceptive timing, while the velocity effect shows that the act of catching a ball is not initiated at a constant time-to-contact.

Cues↗
PubMed1999

[Flow cytometry and pathology AFC-089. Fluorescence recovery after photobleaching: principle and applications. An example: research of gap junctions between immature sensory cells of the cochlea].

In image cytometry, fluorescence recovery after photobleaching (FRAP) is wildly used to study molecular displacements at tissular, cellular or infracellular levels. The principle and the main applications of FRAP are presented. An example is given: the investigation of functional communications between cochlea's immature sensory cells.

Cochlea↗
PubMed1999

[Regenerative potential of the sensory epithelium of the mammalian organ of Corti after poisoning with ototoxic antibiotics].

Cochlear sensory hair cells are very sensitive to noxious influences such as ageing, noise and ototoxic drugs. Whereas lost auditory hair cells are replaced by new hair cells in the avian and lower vertebrates, cochlear sensory hair cells do not regenerate in mammals. Recently, we have observed transient atypical cells in the cochlea of amikacin intoxicated rats. We have related their presence to an attempt at sensory hair cell neodifferentiation. The aim of the present study was to i) investigate the mechanisms responsible for sensory hair cell losses during the intoxication and the subsequent appearance of atypical cells, ii) characterise the phenotype of these atypical cells and iii) evaluate the influence of cochlear immaturity in such an attempt at sensory hair cells neo-differentiation.

Amikacin↗
PubMed1998

Attempt at hair cell neodifferentiation in developing and adult amikacin intoxicated rat cochleae.

Recent studies have shown that an attempt at auditory hair cell neodifferentiation occurs in vivo in the rat organ of Corti after amikacin intoxication during the last stages of cochlear maturation. Atypical cells, with morphological characteristics reminiscent of very immature sensory hair cells, were transiently observed after outer hair cell losses. The aim of the present study was to assess (i) if this attempt at hair cell neodifferentiation was related to the degree of maturity of the organ of Corti and (ii) to characterise morphological and molecular changes in the scarring epithelium. We therefore investigated, using electron and confocal microscopy, morphological and molecular changes in cochleae from rats treated with amikacin at two different periods: from post natal day (PND) 1 to PND 8, when the organ of Corti is very immature; and from PND 30 to 37, when the organ of Corti is morphologically and functionally mature. In both groups, transient atypical cells were observed, attesting that the attempt at hair cell neodifferentiation is not strictly related to the immaturity of the cochlea. The results also suggest that Deiters cells are involved in the appearance of atypical cells, possibly through a transdifferentiation process. Finally, it appears that non-sensory epithelial cells from the outer spiral sulcus progressively colonize the region of pre-existing outer hair cells.

Amikacin↗