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Biomedical subjects

M Falempin

Publications and source records attributed to M Falempin.

At least 37 records · Page 2Linked to original sources
PubMed1999

Short-term plasticity in primary somatosensory cortex of the rat after hindlimb suspension.

Since the last 25 years, the cortex is considered as a dynamic entity, susceptible of changes. Various types of modifications in stimuli may lead to the plasticity of the target neurons. These include immobilisation, denervation, amputation, deafferentation... In the somatosensory system, the most important changes are a substantial reorganisation of the cortical somatotopic representation, and an enlargement of the receptive fields (RF) of cortical neurons. Hindlimb suspension (HS) is characterized by the absence of weight-bearing and a reduced motor activity. In these conditions, the cutaneous receptors located on the foot sole are deactivated. Our hypothesis is that this condition of HS can produce a reorganisation of the somatosensory cortex (SmI) and a modification in the size of the cutaneous RF.

Animals↗
PubMed1998

Effect of hindlimb unloading on interlimb coordination during treadmill locomotion in the rat.

Effects of hindlimb unloading on interlimb coordination were examined in adult rats walking on a treadmill at moderate speed. In the first group of animals, the electromyographic activity (EMG) of soleus muscle of both hindlimbs was recorded after 7 and 14 days of unloading. In the second group, the EMG was recorded daily until the 14th day of unloading. The general organization of locomotion was preserved in the two groups whatever the duration of the unloading. The step cycles of the two hindlimbs were always strictly alternating. However, the locomotor pattern was very irregular. A lateral instability was observed. It was accompanied by an abduction of the hindlimbs, and frequent hyperextensions of the ankle when walking. The EMG analysis showed an increase in step cycle duration and in coactivation duration of the soleus muscles (i.e. in the double stance duration). In the rats recorded daily, mean EMG was dramatically reduced the 1st day of unloading, suggesting a decrease in the neural drive. Taken together, these data indicate that 14 days of hindlimb unloading can alter the neuromuscular pattern during locomotion. It is proposed that these changes are related to changes in the peripheral sensory information.

Animals↗
PubMed1998

EMG activity of three rat hindlimb muscles during microgravity and hypergravity phase of parabolic flight.

BACKGROUND: In man, quantifications of the motor activity have mainly been performed to study changes in posture and locomotion after space-flight. On the contrary, physiological data relative to the motor activity have never been obtained in animals in real microgravity. HYPOTHESIS: The purpose of this study was to evaluate, in rats, the immediate effect of real microgravity on the neuromuscular activity of three hindlimb muscles. METHODS: Under aseptic conditions, the soleus (SOL), lateral gastrocnemius (LG) and tibialis anterior (TA) muscles of rat hindlimb were implanted each with a pair of electrodes. Their electromyographic (EMG) activity was analyzed before, during, and after parabolas, a parabola being composed of two 2 G episodes separated by one 0 G episode. Each episode lasted about 25 s. RESULTS: Our results showed that, when compared to normal gravity (1G), hypergravity increased the EMG activity in the ankle extensors SOL and LG, whereas microgravity immediately induced a redistribution in the motor activity between the two antagonists, SOL and TA. CONCLUSIONS: An immediate adaptation occurred in the motoneuronal recruitment of rat hindlimb muscles at the onset of changes in gravity level. This could be interpreted in terms of a short-term adaptative process involving peripheral mechanisms initiated by changes in activity of muscle spindles.

Adaptation, Physiological↗
PubMed1997

Functional effects of uridine triphosphate on the atrophied soleus muscle of rat after unloading.

The purposes of the study were to determine the effects of a pyrimidine nucleotide, the uridine triphosphate (UTP), on the contractile and histochemical properties of the soleus (SOL) muscle following disuse atrophy due to hindlimb unloading (HU) hypokinesia. UTP was injected either during the HU period (2 weeks) or later during the recovery period. In this latter condition, contractile and histochemical properties were studied after 5, 8, 11, and 15 days of spontaneous recovery. HU induced decreases in the SOL weight, force output (twitch and tetanic tensions), time to peak tension during the twitch, and the percentage of type I fibers. The injection of UTP during the HU period did not counteract the modification in speed-related properties, but the decrease in force output was partly counteracted and the proportion of type II C fibers was increased. When UTP was injected during the recovery periods, force-related properties recovered more rapidly. These results suggest that UTP may reduce the loss of force induced by atrophy.

Animals↗
PubMed1997

Effect of hindlimb unloading on two hindlimb muscles during treadmill locomotion in rats.

The purpose of the study was to examine the pattern of electromyographic (EMG) activity of the rat soleus (SOL) and tibialis anterior (TA) muscles during treadmill locomotion at various speeds after 7 days of hindlimb unloading (HU). Raw EMG signals were processed to determine cycle duration, burst duration and mean EMG (burst surface divided by its duration). Cycle duration and SOL burst duration increased after HU (+7% and +5%, respectively) while TA burst duration decreased (-16%). After HU, the alternating pattern of activity between extensor and flexor muscles was maintained. Nevertheless, a co-activation of the two muscles was sometimes observed. The EMG pattern revealed no difference in the timing of the coordination between flexor and extensor muscles after HU. The delay between TA offset and SOL onset was increased (+12 ms), but this increase could be explained by the decrease in TA burst duration. Neither TA burst duration nor TA mean EMG were changed with increased treadmill speed, so that the flexor muscle activity was not related to speed of locomotion. These results would suggest that SOL activity is centrally programmed. Moreover, it is proposed that a decline in afferent feedback from SOL in rats which are suspended has an effect upon the locomotor pattern, leading to an hyperexcitability of SOL motoneurons and, via reciprocal inhibition, to a reduction in TA activity.

Animals↗
PubMed1996

Effect of hindlimb unloading on locomotor strategy during treadmill locomotion in the rat.

Electromyographic activity (EMG) was recorded from the soleus muscles of adult rats during treadmill locomotion after 7 and 14 days of hindlimb unloading, and after 7 days of recovery. Observation of the rats indicated that treadmill locomotion was disrupted after unloading since the animals had some difficulty in moving. Soleus muscle EMG analysis was performed. Onset and offset of bursts of activity were determined, and the relationships between step duration and cycle duration were analysed. Our main results were as follows: firstly, mean cycle duration was increased after 14 days of hindlimb unloading when walking at low speed. At high speed, no difference was observed. Secondly, linear regression analysis indicated that the relationships between step duration and cycle duration were altered after 7 days of unloading. Thirdly, adaptation occurred, since the normal slope and correlation coefficient were restored after 14 days of unloading. Fourthly, when speed increased, no variation of mean EMG was demonstrated after hindlimb unloading whereas an increase occurred in normal rats. Fifthly, video analysis showed that the rats presented frequent hyperextension of the hindlimb after unloading. These abnormal steps were more numerous when walking at low speed. These data would indicate that a transitory disruption of the soleus muscle motor pattern occurred after 7 days of unloading. This disruption depended on the treadmill belt speed. Possible origins of these modifications are discussed.

Animals↗
PubMed1996

Contractile properties of rat soleus motor units following 14 days of hindlimb unloading.

The purpose of this study was to compare the isometric contractile properties of rat soleus motor units after 14 days of hindlimb unloading (HU) to those under control conditions. The motor units (MU) were classified using two mechanical criteria: the presence or not of a sag during unfused tetani and the value of the twitch time-to-peak (TTP). Under control conditions, the soleus muscle was composed of 85% of slow-type (sag -, TTP > 20 ms) and 15% of fast-type (sag +, TTP < 20 ms) units. Following HU, these two populations were still present and results showed: (1) large decreases in their maximal tetanic tensions (of -67% and -60% for slow- and fast-type, respectively), and (2) changes in their relative proportions, i.e. a decrease in the percentage of slow-type units and a twofold increase in the percentage of fast-type units were observed. These latter changes might be the consequence of a complete transformation of slow-towards fast-type units. A third population appeared in the HU solei, 26% of the samples, combining the presence of a sag and speed-related properties between those of slow- and fast-type units. These slow-intermediate units might come from slow units partially transformed into a faster type during HU. Thus the present study showed that unloading conditions induced a reorganisation of the soleus motor unit profile. The complete or partial transformation of the motor units could be related to the changes in the electromyographical activity of the unloaded soleus.

Animals↗
PubMed1994

Influence of chronic stretching upon rat soleus muscle during non-weight-bearing conditions.

Morphological, contractile and histochemical properties as well as the myosin heavy chain (MHC) composition of rat soleus muscles were studied after 14 days of non-weight-bearing (NWB) and after immobilization of the foot in dorsiflexion of NWB rats. Significant reductions in soleus mass, fibre sizes and tetanic tension were found after 14 days of NWB. Furthermore, a transformation of the slow-twitch soleus muscle towards a faster type was characterized by a decrease in twitch time parameters, an increase in the fast-twitch type IIA fibre proportion and an increase in fast-twitch type MHC isoforms. Our results showed that the immobilization of the soleus muscle in a lengthened position during NWB not only prevented the loss of muscular mass and force output, but also counteracted the slow to faster shift in contractile and phenotypical parameters normally associated with NWB conditions.

Animals↗
PubMed1994

Compensatory effects of chronic electrostimulation on unweighted rat soleus muscle.

The purpose of this study was to investigate the effects of electrostimulation in counteracting the transformation of the unweighted rat soleus muscle. The stimulation resembled the firing patterns of normal slow motor units and was imposed during hindlimb suspension. For the 10-day hindlimb suspended rats, the transformation of the slow soleus muscle towards a faster type was characterized by a decrease in the time to peak tension and the half-relaxation time of the twitch, a reduction in the P20/P0 index, i.e. the ratio of the subtetanic tension at 20 Hz relative to the tetanic tension, and a decrease in the percentage distributions of type I fibres accompanied by an increase of type IIa and IIc fibres. These changes were prevented by electrostimulation since, for the parameters mentioned above, no significant difference was observed in the soleus of the suspended rats that received electrostimulation when compared with the control rats. Nevertheless, neither the loss of mass nor the decrease in force output in the suspended rats were prevented by electrostimulation. The present results suggest a positive compensation of the suspension-induced alterations in the contractile and histochemical properties of the soleus muscle by means of chronic electrostimulation, which, however, do not prevent atrophy or the loss of contractile force.

Animals↗
PubMed1993

Effects of chronic electrostimulation on rat soleus skinned fibers during hindlimb suspension.

In order to counteract the changes of the contractile properties of the rat soleus occurring during 10 days of hypokinesia-hypodynamia, due to hindlimb suspension (HS), two different patterns of electrostimulation were applied to the tibial nerve. The contractile properties of single chemically skinned muscle fibers were investigated using the tension-pCa relationship characteristics, the similar or different calcium and strontium affinities, and by measuring the P/tmax kinetic parameters. Our results showed that a pattern similar to firing rates of motoneurons innervating slow twitch muscles inhibited the slow to fast fiber changes observed during HS, whereas a pattern similar to firing rates of motoneurons from fast twitch muscles seemed to favor these changes. Since neither pattern maintained the isometric contractile force developed by the soleus fibers, we concluded that the decrease in mechanical strains imposed on the muscle during unloading was the main factor for the development of atrophy, while the kinetic changes might be predominantly modulated by the nervous command.

Animals↗
PubMed1990

Contractile properties of rat soleus muscle after 15 days of hindlimb suspension.

The properties of the contractile elements interacting to develop force in atrophied rat soleus muscle were studied by using single skinned fibers, which permitted direct access to the contractile apparatus. Muscle atrophy was induced by 15 days of hindlimb suspension. Suspension resulted in a decrease of maximal tension relative to an important decline in fiber diameter. Ca affinity of the contractile proteins was not changed insofar as the tension-pCa relationship was not shifted along the pCa axis. However, after hindlimb suspension 1) the value of the Hill coefficient from the tension-pCa curve was found to be higher, 2) a higher Ca threshold for activation was reported, and 3) a significant increase in contraction kinetics was described. All these results suggested that after suspension the mechanical properties of the slow-twitch soleus appeared to resemble more closely those of a fast-twitch muscle. Our results were in complete agreement with published histochemical data.

Animals↗
PubMed1989

Presence of cholinergic neurons in the vagal afferent system: biochemical and immunohistochemical approaches.

The presence of cholinergic fibers in the afferent vagal system of various species was shown using biochemical and immunohistochemical methods. Biochemical activity of choline acetyl transferase, the synthesizing enzyme for acetylcholine, was detected in the nodose ganglion of cat, rabbit, dog and sheep. Immunohistochemistry, using a monoclonal antibody raised against choline acetyl transferase, revealed labelled cell bodies in the nodose ganglion of the rabbit. Acetylcholine endogenous content, measured in nodose ganglia devoid of efferent fibers, was twice as high in the right ganglion as compared to the left. Enzyme transport and choline acetyl transferase activity analysis were each determined on separate peripheral vagus nerves. These results are discussed in terms of functional properties of the vagal afferent neurons, including the modulation of vagal afferent messages at the level of the nodose ganglion and the eventual control of peripheral intrinsic neurons by sensory vagal terminals.

Afferent Pathways↗
PubMed1989

Presence of cholinergic neurons in the vagal afferent system: involvement in a heterogenous reinnervation.

As is now well established, the anastomosis of the central cut end of the vagus with the peripheral stump of the accessory spinal nerve results in a functional reinnervation of the muscular fibers of the sterno-cleido-mastoïd muscle in various species. In chronically anastomosed animals this heterogenous crossed nerve anastomosis allows the electrophysiological characterization of peripheral enteroceptors mainly located in the larynx, oesophagus and stomach. Pharmacological treatments indicate that the reinnervation is supplied by cholinergic afferent fibers of the vagus nerve. 4 months after the anastomosis, when functional responses are recorded in the sterno-cleido-mastoïd muscle, choline acetyl transferase activity is still present in sutured ganglia of rabbit and cat, but is decreased by 88% and 60%, respectively. A decrease of 39% of choline acetyl transferase activity was also observed in the lower brain stem of the rabbit, but no significant change was detected in the nucleus of the solitary tract after 3 months in sutured cats. A kinetic study of the nodose endogenous acetylcholine content of rabbits with vagus-spinal accessory anastomosis shows a decrease of up to 4 months, followed by an increase during the 5th month. On the contrary, a significant decrease of acetylcholine content is observed in the contralateral nodose ganglion after 4 months, suggesting the involvement of central and/or peripheral compensatory mechanisms.

Acetylcholine↗
PubMed1986

Effects of vagal deafferentation on oesophageal motility and transit in the sheep.

Effects of vagal deafferentation on oesophageal motility and transit were studied in conscious sheep by recording the electromyographic activity of different parts of oesophagus during swallowing of saliva, or balloons inflated with 20 ml of air. Surgical isolation and subsequent sectioning of the nodose ganglion, leaving the bundles of motor fibres intact, can be performed in sheep. Division of both ganglia led to immediate death of sheep. However, vagal deafferentation of the thoracic oesophagus could be achieved by sectioning the thoracic vagus nerve in association with sectioning the contralateral nodose ganglion. The sectioning of one vagus nerve did not affect primary oesophageal peristalsis during swallowing of saliva or of a bolus. Balloons inflated in the pharyngeal cavity and left free to move caudally, failed to pass into the stomach within the normal time of 2-2.3 s in only 4-16% of the tests. In these cases, they were always stopped in the thoracic oesophagus. Following total deafferentation of the thoracic oesophagus, balloons were prevented from being propelled into the stomach in each test. They were stopped for several minutes at the beginning of the deafferented part of the oesophagus. Electromyographic activity recorded from the deafferented part was reduced during swallowing of balloons or saliva. Deafferentation was confirmed by the failure of the presumed deafferented segment of oesophagus to respond to distension. These experiments provide direct evidence that the vagus carries information from the oesophagus which influences the central pattern generator during swallowing of a bolus or saliva. In sheep, this feed-back is essential for the effective swallowing of a bolus although not for saliva.

Animals↗
PubMed1985

[Neural control of the motility of the reticulo-rumen].

This paper reviews the nervous mechanisms involved in the control of motility of the forestomach compartments in ruminants. The first part of the review reports the efferent vagal discharge which consists of several distinct and independent types of urinary activity and passes from the gastric centres to the reticulo-rumen. The patterns of each of these activities are temporally related to the contractions of special parts of the forestomach and occur in a sequence which could produce the coordinated series of movements found in the reticulum and rumen. The orderly sequence of motor events that constitutes the gastric cycle is due to this coordination of efferent vagal outputs arising in the gastric centres. The focal point of the second part of the paper is sensory feedback from the complex stomach to the centres. Four types of receptor have been identified according to their location and stimulus; these are tension receptors and epithelial receptors in the reticulo-rumen and tension receptors and mucosal receptors in the abomasum. Mechanical or chemical stimulation of these distinct receptor types leads to either facilitation or inhibition of reticulo-ruminal motility. The third part of the paper deals with the organization of the medullary gastric centres. The gastric vagal motoneurons are controlled by interneurons organized in two functionally distinct networks. The "rate" network for which the periodicity of its activity depends on the cumulative integrated afferent inputs from central and peripheral sources, determines the rhythm of gastric cycles. It is postulated to drive the "amplitude and form" network which adjusts vagal output to instantaneous gastric afferents, enabling the amplitude of gastric contractions to be adapted to peripheral stimulations. The role of the sensory feedback from the complex stomach in the control of the "frequency" network is discussed, taking into account new experiments on vagal deafferentation and the concept of an oscillating generator that would be more or less permanently inhibited by vagal afferents is reviewed. The respective roles of local regulation mechanisms, mediated in the intramural plexus, and of central mechanisms, in the control of forestomach motility, are briefly discussed.

Animals↗
PubMed1984

Activity of lingual, laryngeal and oesophageal receptors in conscious sheep.

Vagal afferent impulse traffic has been studied in conscious sheep by electromyographic recording from the motor units of the sterno-cleido-mastoid (s.c.m.) muscle reinnervated by sensory vagal axons. Units which responded during movements of the tongue and during the pharyngolaryngeal and oesophageal stages of swallowing were chosen for this study. Lingual units showed a phasic discharge bearing a temporal relation to movements of the tongue during licking of the lips or chewing of a bolus before swallowing. Laryngeal units had no spontaneous activity. A discharge occurred with the ascending movement of the larynx during swallowing. Oesophageal units did not exhibit any tonic activity. They fired only at the time of primary or secondary oesophageal peristalsis. The oesophageal units showed a bimodal distribution. The oesophageal receptors are more concentrated at the beginning and the end of the thoracic oesophagus. During primary peristalsis, the afferent discharge was reinforced in only 57% of the cases when sheep swallowed a bolus (pellets or inflated balloons). When the discharge was reinforced, its increase ceased as volumes of the bolus were increased from 20 to 40 ml. During local oesophageal contractions, the afferent discharge was only present when the inflated balloon was located at the site of the receptor. It was enhanced at the time the primary peristaltic wave passed over the balloon. Inflation of a second balloon cranially in the oesophagus led to abolition of the activity of the unit at the caudal site though the distension there was maintained.

Action Potentials↗