Resveratrol prevents the wasting disorders of mechanical unloading by acting as a physical exercise mimetic in the rat.

Long-term spaceflight induces hypokinesia and hypodynamia, which, along microgravity per se, result in a number of significant physiological alterations, such as muscle atrophy, force reduction, insulin resistance, substrate use shift from fats to carbohydrates, and bone loss. Each of these adaptations could turn to serious health deterioration during the long-term spaceflight needed for planetary exploration. We hypothesized that resveratrol (RES), a natural polyphenol, could be used as a nutritional countermeasure to prevent muscle metabolic and bone adaptations to 15 d of rat hindlimb unloading.

ERK is involved in the reorganization of somatosensory cortical maps in adult rats submitted to hindlimb unloading.

Sensorimotor restriction by a 14-day period of hindlimb unloading (HU) in the adult rat induces a reorganization of topographic maps and receptive fields. However, the underlying mechanisms are still unclear. Interest was turned towards a possible implication of intracellular MAPK signaling pathway since Extracellular-signal-Regulated Kinase 1/2 (ERK1/2) is known to play a significant role in the control of synaptic plasticity.

Activity-dependent changes in the electrophysiological properties of regular spiking neurons in the sensorimotor cortex of the rat in vitro.

Sensorimotor performance is highly dependent on the level of physical activity. For instance, a period of disuse induces an impairment of motor performance, which is the result of combined muscular, spinal and supraspinal mechanisms. Concerning this latter origin, our hypothesis was that intrinsic properties and input/output coupling of cells within the sensorimotor cortex might participate to the alteration in cortical motor control.

A 3D analysis of fore- and hindlimb motion during locomotion: comparison of overground and ladder walking in rats.

The locomotor pattern, generated by the central pattern generator, is under the dependence of descending and peripheral pathways. The afferent feedback from peripheral receptors allows the animal to correct for disturbances that occur during walking, while supraspinal structures are important for locomotion in demanding situations such as ladder walking. Such walking, by regards to the control needed for accuracy of movements, is now widely used for description of consequences of nervous system dysfunction on motor performance.

Effect of hindlimb unloading on motor activity in adult rats: impact of prenatal stress.

Environmental changes that occur in daily life or, in particular, in situations like actual or simulated microgravity require neuronal adaptation of sensory and motor functions. Such conditions can exert long-lasting disturbances on an individual's adaptive ability. Additionally, prenatal stress also leads to behavioral and physiological abnormalities in adulthood.

Effect of hindlimb suspension on activation and MHC content of triceps brachii and on the representation of forepaw on the sensorimotor cortex.

The aims of this work were to analyze the effects of a chronic (14 days) increase in the functional demand imposed on the triceps brachii and to evaluate the changes of the cortical representation of forelimb to this increased activity. The activation of triceps brachii was obtained by the hindlimb unloading (HU) model. Electromyographic activity changed from a phasic to a tonic pattern.

Soleus motoneuron excitability after rat hindlimb unloading using histology and a new electrophysiological approach to record a neurographic analogue of the H-reflex.

Hindlimb unloading (HU) induces neuromuscular disturbances in slow postural muscles such as the soleus. Among these perturbations, a reorganization of soleus motor units and decreases in peripheral afferent feedback have been reported and could change the alpha-motoneuron excitability. The purpose of this study was, therefore, to examine the distribution of soleus motoneuron soma sizes and the neurographic analogue of the H-reflex (NAH) induced by the soleus afferent excitation after 14 HU days.

Variations in amino acid neurotransmitters in the rat ventral spinal cord after hindlimb unloading.

We have measured by HPLC the neurotransmitter content in L(4) and L(5) spinal segmental levels in CONT rats, after 7 (HU7) and after 14 days (HU14) of hindlimb unloading. These segments are known to contain the hindlimb muscle motoneurons. The main result is the increase of two neuroexcitators (glutamate and aspartate) and two neuroinhibitors (glycine and GABA) at the L(5) spinal segmental level in HU7 group.

Concentration of amino acid neurotransmitters in the somatosensory cortex of the rat after surgical or functional deafferentation.

Hindlimb unloading is considered as a model of functional deafferentation, since in this situation the tactile information from the paw and the proprioceptive input from the limb are dramatically reduced. Unloading induces a shrinkage of the cortical representation of the affected body part associated to a reorganization of topographic maps and to an expansion of receptive fields. Previous studies have suggested that cortical plasticity was the result of a change in the balance of excitation and inhibition in the cortex.

Physiologically adaptive changes of the L5 afferent neurogram and of the rat soleus EMG activity during 14 days of hindlimb unloading and recovery.

The hindlimb unloading rat model (HU, Morey's model) is usually used to mimic and study neuromuscular changes that develop during spaceflights. This Earth-based model of microgravity induces a muscular atrophy of the slow postural muscle of hindlimbs, such as the soleus, a loss of strength, modifications of contraction kinetics, changes in histochemical and electrophoretical profiles and modifications of the tonic EMG activity. It has been suggested in the literature that some of these neuromuscular effects were due to a reduction of afferent feedback during HU.

The structure and response properties of Golgi tendon organs in control and hypodynamia-hypokinesia rats.

The Golgi tendon organs (GTOs) are encapsulated mechano-receptors that, in normal conditions, monitor via Ib afferent fibers the contractile force. A 14-day period of hypodynamia, absence of weight bearing and hypokinesia, and reduction of motor activity (HH) is known to induce changes in postural muscles such as the soleus. At present, there is no data available regarding the Ib afferent feedback in normal rats (CONT group) and in rats after a hypodynamia-hypokinesia (HH group) period.

Electromyographic activity in the Rhesus monkey forelimb muscles during a goal directed movement and locomotion before, during and after spaceflight.

The aim of the present study was to analyse the effects of microgravity on i) the achievement of goal-directed arm movements and ii) the quadrupedal non-human primate locomotion. A reaching movement in weightlessness would require less muscle contraction since there is no need to oppose gravity. Consequently the electromyographic (EMG) activity of the monkey forelimb muscles should be changed during or after spaceflight.

Dual effect of deafferentation on contractile characteristics and sarcoplasmic reticulum properties in rat soleus fibers.

The neural message is known to play a key role in muscle development and function. We analyzed the specific role of the afferent message on the functional regulation of two subcellular muscle components involved in the contractile mechanism: the contractile proteins and the sarcoplasmic reticulum (SR). Rats were submitted to bilateral deafferentation (DEAF group) by section of the dorsal roots L(3) to L(5) after laminectomy.

Changes in rat soleus muscle phenotype consecutive to a growth in hypergravity followed by normogravity.

It has been demonstrated that a long-term stay in hypergravity (HG: 2G) modified the phenotype and the contractile properties of rat soleus muscle. The ability of this muscle to contract was drastically reduced, which is a sign of anticipated aging. Consequently, our aim was to determine whether rats conceived, born, and reared in hypergravity showed adaptative capacities in normogravity (NG: 1G).

Effects of a 14-day period of hindpaw sensory restriction on mRNA and protein levels of NGF and BDNF in the hindpaw primary somatosensory cortex.

Neurotrophins have been reported to play an important role in neuronal plasticity and to be regulated by neuronal activity and/or neurotransmitters. Recently, we have shown that hindpaw sensory restriction induces a cortical reorganisation in the hindpaw primary somatosensory cortex, and that acetylcholine plays a significant role in this process. Sensory restriction was obtained by hindlimb suspension for 14 days.

A 3D analysis of hindlimb motion during treadmill locomotion in rats after a 14-day episode of simulated microgravity.

This study describes the effect of simulated microgravity in rat on kinematics and electromyographic activity during treadmill locomotion. The analysis was performed in rats submitted to 14 days of hindlimb unloading (HU), in rats submitted to hindlimb unloading and then authorized to recover for 7 days (REC), and in aged-matched control rats (CON). Movements of the right hindlimb were measured with a 3D-optical analyzer (SAGA3 system) and five small infrared-reflective disks positioned on the skin, recorded by three CCD cameras.

Hypergravity from conception to adult stage: effects on contractile properties and skeletal muscle phenotype.

This study examined the effects of an elevation of the gravity factor (hypergravity--2 g) on the molecular and functional characteristics of rat soleus and plantaris muscles. Long Evans rats were conceived, born and reared (CBR) continuously in hypergravity conditions until the age of 100 days. Whole muscle morphological parameters, Ca2+ activation characteristics from single skinned fibers, troponin (Tn) subunit and myosin heavy (MHC) and light (MLC) chains isoform compositions were examined in CBR and control muscles from age-paired terrestrial rats.

Enhancement of hybrid-fiber types in rat soleus muscle after clenbuterol administration during hindlimb unloading.

Our objective was to determine the effects of a clenbuterol (CB) treatment orally administered (2 mg per kg) to rats submitted to 14 days of hindlimb unloading (HU). The morphological and the contractile properties as well as the myosin heavy chain isoforms contained in each fiber type were determined in whole soleus muscles. As classically described after HU, a decrease in muscle wet weight and in body mass associated with a loss of muscular force, an evolution of the contractile parameters towards those of a fast muscle type, and the emergence of fast myosin heavy chain isoforms were observed.

Effects of unilateral and bilateral labyrinthectomy on rat postural muscle properties: the soleus.

The aim of our study was to determine whether the suppression of the vestibular inputs could have effects on the soleus muscle properties similar to the modifications observed after an episode of microgravity. The inner ear lesion was performed by surgical labyrinthectomy. Twenty-nine male Wistar rats were used for this study and were divided into three experimental groups: control (CONT, n=7), unilateral labyrinthectomized (UL, n=14) and bilateral labyrinthectomized (BL, n=8).

Expression of Myosin heavy chain isoforms in rat soleus muscle spindles after 19 days of hypergravity.

The aim of this study was to determine whether a period of 19 days in hypergravity was long enough to induce changes in the expression of myosin heavy chain (MyHC) isoforms in the muscle spindles. The soleus muscle of 10 male Wistar rats (control: CONT, n=5; hypergravity: HG, n=5) was frozen, cut into serial sections, and labeled with antibodies against MyHCs: I, IIA, IIA + IIX + IIB, slow-tonic, and alpha-cardiac. Forty CONT and 45 HG spindles were analyzed.

A 14-day period of hindpaw sensory deprivation enhances the responsiveness of rat cortical neurons.

Hypodynamia-hypokinesia (HH) is a model of hindpaw sensory deprivation. It is obtained by unloading of the hindquarters during 14 days. In this situation, the feet are not in contact with the ground and as a consequence, the cutaneous receptors are not activated; the sensory input to the primary somatosensory cortex (SmI) is thus reduced.

Effects of hypodynamia-hypokinesia on somatosensory evoked potentials in the rat.

The aim of this study was to determine if a prolonged period (7 or 14 days) of hypodynamia-hypokinesia (HH) affects the conduction of afferent input and the cortical and spinal responsiveness. Acute recordings of cortical and spinal somatosensory evoked potentials (SEPs) were performed after stimulation of the sciatic nerve in control rats and in rats submitted to 7 or 14 days of HH. HH was obtained by unloading the hindquarter.

Compared effects of hindlimb unloading versus terrestrial deafferentation on muscular properties of the rat soleus.

Hindlimb unloading is known to induce some neuromuscular changes especially in postural muscles such as the soleus. Our goal was to determine the role of proprioceptive inputs on these modifications by comparing soleus muscle properties of rats being either hindlimb unloaded or terrestrial deafferented. Under deep anesthesia, a first group of rats were submitted to a bilateral deafferentation (DEAF group, n = 6) performed by section of the dorsal roots L(3) to L(5) after laminectomy.

p53 inactivation leads to impaired motor synchronization in mice.

We have combined genetic and pharmacological approaches to investigate the behavioural consequences of inactivation of the murine p53 protein. Our behavioural analysis revealed that p53-null mice (p53KO) exhibit a very specific and significant motor deficit in rapid walking synchronization. This deficit, observed using the rotarod test, was the only behavioural defect of p53KO mice.

Effects of hypodynamia-hypokinesia on the muscle spindle discharges of rat soleus muscle.

The aim of this study was to determine whether Ia and II fiber discharges of soleus muscle spindles were modified after a 14-day period of hypodynamia (absence of weight bearing) and hypokinesia (reduction of motor activity). Fifty-one and 38 afferent fibers were studied, respectively, in control and hypodynamia-hypokinesia (HH) groups. Under deep anesthesia (pentobarbital, 30 mg/kg), a L3-L6 laminectomy was performed.