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D Viala

Publications and source records attributed to D Viala.

At least 19 recordsLinked to original sources
PubMed2001

Forelimb locomotor generators and quadrupedal locomotion in the neonatal rat.

The spinal localization of the forelimb locomotor generators and their interactions with other spinal segments were investigated on in vitro brainstem-spinal cord preparations of new-born rats. Superfusion of the cervicothoracic cord (C1-T4) with high K+/low Mg2+ artificial cerebrospinal fluid (aCSF) evoked rhythmic motor root activity that was limited to low cervical (C7, C8) and high thoracic (T1) spinal levels. This activity consisted of synchronous, homolateral bursts and a typical alternating bilateral pattern. Rhythmic activity with similar locomotor-like characteristics could be induced with either serotonin (5-HT, 5 microm), N-methyl-d-aspartate (NMDA, 5 microm), kainate (10 microm) or a "cocktail" of 5-HT (5 microm) and NMDA (5 microm). During 5-HT/NMDA perfusion of the cervicothoracic cord, induced bursting was no longer restricted to C7-T1 levels, but also occurred at cervical C3-C5 levels and with C5-C8 homolateral alternation. Spinal transections between C6 and C7 cervical segments did not abolish rhythmic activity in C7-T1, but suppressed locomotor-like rhythmicity at C3-C5 levels. Reduced regions comprising the C7-C8 or C8-T1 segments maintained rhythmicity. Superfusion of the whole cord with 5-HT/NMDA induced ventral root bursting with similar frequencies at all recorded segments (cervical, thoracic and lumbar). After isolation, the T3-T10 cord was unable to sustain any rhythmic activity while cervical and lumbar segmental levels continued to burst, albeit at different frequencies. We also found that the faster caudal and the slower rostral locomotor generators interact to produce coordinated locomotor-like activity in all segments of the intact spinal cord. In conclusion, C7-T1 spinal levels display a strong motor rhythmogenic ability; with the lumbar generators, they contribute to coordinated rhythmic activity along the entire spinal cord of a quadrupedal locomoting mammal.

Action Potentials↗
PubMed2000

Development of lumbar rhythmic networks: from embryonic to neonate locomotor-like patterns in the mouse.

Different aspects of spinal locomotor organization have been studied in the mouse during embryonic and neonatal development using in vitro preparations of isolated lumbosacral cords. The first consideration was the embryonic development of an alternating bilateral pattern. From embryonic day (E) 12, perfusion of serotonin could induce relatively synchronous lumbar bursts across the cord. Bilateral activity became progressively alternate at E15 due to the appearance of glycinergic inhibitory interactions (revealed by strychnine application). Strictly alternating patterns were expressed at E18 and were maintained after birth. In a second step, we investigated cellular properties involved in lumbar rhythmogenesis in postnatal day 0-2 preparations which displayed spontaneous locomotor-like activity. Perfusion of receptor antagonists showed the co-operative involvement of N-methyl-D-aspartate (NMDA)- and non-NMDA-receptors for excitatory amino acids-mediated operation of locomotor networks. In a final step we investigated the localization of locomotor networks within the lumbar cord. Data obtained from preparations exhibiting spontaneous or Mg2+-free induced bursts revealed that the networks are present throughout the lumbar cord and that rhythmogenesis is distributed throughout all segmental levels.

Animals↗
PubMed2000

alpha1-adrenergic receptor-induced slow rhythmicity in nonrespiratory cervical motoneurons of neonatal rat spinal cord.

Previous studies have reported that the alpha1-adrenergic system can activate spinal rhythm generators belonging to the central respiratory network. In order to analyse alpha1-adrenergic effects on both cranial and spinal motoneuronal activity, phenylephrine (1-800 microM) was applied to in vitro preparations of neonatal rat brainstem-spinal cord. High concentration of phenylephrine superfusion exerted multiple effects on spinal cervical outputs (C2-C6), consisting of a lengthening of respiratory period and an increase in inspiratory burst duration. Furthermore, in 55% of cases a slow motor rhythm recorded from the same spinal outputs was superimposed on the inspiratory activity. However, this phenylephrine-induced slow motor rhythm generated at the spinal level was observed neither in inspiratory cranial nerves (glossopharyngeal, vagal and hypoglossal outputs) nor in phrenic nerves. Whole-cell patch-clamp recordings were carried out on cervical motoneurons (C4-C5), to determine first which motoneurons were involved in this slow rhythm, and secondly the cellular events underlying direct phenylephrine effects on motoneurons. In all types of motoneurons (inspiratory and nonrespiratory) phenylephrine induced a prolonged depolarization with an increase in neuronal excitability. However, only nonrespiratory motoneurons showed additional rhythmic membrane depolarizations (with spiking) occurring in phase with the slow motor rhythm recorded from the ventral root. Furthermore the tonic depolarization produced in all motoneurons results from an inward current [which persists in the presence of tetrodotoxin (TTX)] associated with a decrease in neuron input conductance, with a reversal potential varying as a Nernstian function of extracellular K+ concentration. Our results indicate that the alpha1-adrenoceptor activation: (i) affects both the central respiratory command (i.e. respiratory period and inspiratory burst duration) and spinal inspiratory outputs; (ii) induces slow spinal motor rhythmicity, which is unlikely to be related to the respiratory system; and (iii), increases motoneuronal excitability, probably through a decrease in postsynaptic leak K+ conductance.

Adrenergic alpha-Agonists↗
PubMed1998

Genesis of spontaneous rhythmic motor patterns in the lumbosacral spinal cord of neonate mouse.

The isolated spinal cord of the neonatal mouse spontaneously generates two different motor patterns of continuous rhythmic bursting: one in lumbar ventral roots in earliest postnatal preparations (P0-2) and another at the sacral level at later postnatal times (P3-5). Lumbar rhythmic motor discharges clearly alternate on contralateral roots and are in a frequency range (approximately 1 Hz) usually described for locomotor-like activity, while sacral motor sequences include mixed synchrony and irregular bilateral alternation that differ from typical locomotor-like activity. A significant decrease in the frequency and increase in the duration of spontaneous rhythmic bursts occur between lumbar and sacral motor patterns. In quiescent preparations from both postnatal periods, perfusion with Mg(2+)-free medium systematically induces a rhythmic activity at both lumbar and sacral level. Temporal characteristics of motor patterns under Mg(2+)-free medium are similar to spontaneous rhythms. Activating NMDA receptor channels by diminishing their Mg2+ block appears to be an efficient way of decreasing the threshold for genesis of the spinal rhythm in mouse. Bath application of NMDA and non-NMDA receptor antagonists blocks Mg(2+)-free-induced rhythmic activities in an irreversible or reversible manner, respectively. The effects of Mg(2+)-free medium and of glutamate antagonists provide evidence for the excitatory amino acid (EAA) dependence of both rhythmic motor patterns. Finally, the possibility that the recording of two different motor patterns may reflect a rostrocaudal developmental process is discussed.

Animals↗
PubMed1998

Entrainment of the medullary respiratory generators by electrical stimulation in the cervical grey matter on in vitro preparations of newborn rat.

The present study describes how the medullary respiratory generators (mRGs) can be driven by periodic electrical stimulations applied to the ventral part of the spinal grey matter at the C5 level. The general effect of an electrical stimulus (5 pulses at 200 Hz and between 50 and 80 microA) was either to delay or to advance the occurrence of the medullary respiratory burst via a resetting process, depending on its time of application within the corresponding cycle. Compared to the spontaneous medullary periods, the phase-response curves show that the non-spontaneous medullary period increased progressively when the electrical stimulus was applied within the first two-thirds of the corresponding medullary cycle and decreased when it was applied within the last third of the latter one. These curves were constructed in order to predict the limits of a stable 1:1 entrainment. As predicted, the 1:1 entrainment was obtained when we stimulated repetitively at resetting intensity within the frequency limits determined by the phase-response curves. The entrainment became harmonic (2:1, 3:1, 4:1) when the stimulation frequency increased near submultiples of the fundamental mRGs frequency. From these data, we conclude on the presence of ascending connections from the C5 segment of the spinal cord which might be involved in the realisation of the locomotor-respiratory coupling.

Animals↗
PubMed1998

Effects of CO2 and pH on the spinal respiratory rhythm generator in vitro.

In vitro brainstem spinal cord preparations isolated from newborn rats were used to separately test the effects of modifications of FCO2 and pH of artificial cerebrospinal fluid on the frequency and amplitude of spinal respiratory activity recorded from C2-C8 ventral roots. Different substances such as L-glutamic acid (3 x 10[-3] M), N-methyl-D-aspartic acid (5 x 5 x 10[-6] M), amphetamine (6 mg/100 ml), 5-hydroxytryptophane (10[-3] M), or modified K+ (10[-3] M) were tested for their capacity to elicit stable changes in spinal respiratory activity over a long time period (more than 30 min) and with high frequency of occurrence, i.e., in at least 50% of the cases. None of the above drugs were found to be suitable for the investigation of the chemosensitivity of the spinal respiratory generator (sRG) because they were only able to maintain spinal respiratory activity for around 15 min. Given these data, the previously used procedure of activation through initial deep diethyl ether anaesthesia of newborn rats was employed [3] to test the chemosensitivity of the sRG because this treatment resulted in the maintenance of spinal respiratory activity with a regular pattern for 30 min, even if it occurred in only 25% of the preparations. After an increase in FCO2 from 5 to 7% (at constant pH 7.4), a significant (p < 0.05) enhancement of the mean frequency was observed on spinal respiratory bursting in both brainstem spinal cord and isolated spinal cord preparations. The changes in burst amplitude, however, were quite variable from one experiment to the other. At constant FCO2 (5%), a decrease in pH from 7.4 to 7.2 enhanced spinal respiratory frequency on brainstem spinal cord or isolated spinal cord preparations, while an increase in pH from 7.4 to 7.6 decreased it. Under these pH conditions, we did not observe any reproducible variations in spinal burst amplitude. From these results, we conclude that this spinal generator is chemosensitive to both CO2 and [H+], suggesting that it belongs to the respiratory system. Our data provide evidence for the existence of spinal CO2 and/or H+ chemoreceptors.

5-Hydroxytryptophan↗
PubMed1998

Involvement of AMPA receptors in posterior locomotor activity in the rabbit: an in vivo study.

Although AMPA receptors are known to be widely involved in excitatory synaptic neurotransmission at the spinal level, very little is known about their role in modulating motor activity in mammals. In curarized decerebrate or spinalized rabbit preparations, fictive locomotion was monitored on hindlimb nerves after either activation or blockade of AMPA receptors. In decerebrate preparations, the administration of the antagonist, NBQX (3.5 mg/kg i.p.) or the agonist, AMPA (0.5 mg/kg i.v.) produced, in both cases, a depression of locomotor activities induced by stimulation of cutaneous afferents (evoked locomotor activity). This potent effect was transient with AMPA (recovery after 20 min) and followed by the occurrence of spontaneous locomotor sequences, while no recovery was observed with NBQX treatment. In spinal preparations where a continuous 'spontaneous' locomotor activity resulted from the pharmacological activation of noradrenergic descending pathways (nialamide-DOPA pretreatment), the same drugs injected at higher doses (5 mg/kg NBQX i.p. and 1 mg/kg AMPA i.v.) only weakly affected the frequency of 'spontaneous' and evoked locomotor bursts while they exerted inhibitory and facilitatory effects on the burst amplitude respectively. The results suggest that AMPA receptors are involved at spinal level: 1) in direct mediation of cutaneous afferent excitatory effects on the posterior locomotor generators (pLG); 2) in indirect mediation of a supraspinal descending inhibition controlling, likely presynaptically, the cutaneous afferent activation; and 3) in transmission to motoneurons of the output signals from the pLG. Finally, tight spinal interactions between potent descending noradrenergic pathways and spinal AMPA neurotransmission were disclosed.

Animals↗
PubMed1996

Localization of the spinal respiratory rhythm generator by an in vitro electrophysiological approach.

An in vitro electrophysiological approach allowed the localization of the spinal respiratory generator (sRG) within the cervical cord of newborn rats. Rostral and caudal limits were determined through transections of the successive spinal segments. The sRG is mainly located in the C5 segment with a partial extension in the C4 and C6 segments. The presence of two lateralized sRG was found after a split of the brain stem cervical cord from T8 to C1. Spinal respiratory activity could be kept synchronous after this split in the right and left halves of the spinal cord. This spinal activity also displayed a bilateral synchrony on separated spinal cord preparations after a C1 transection with no split. These findings are the first attempt to localize the sRG and are discussed in terms of bilateral segmental coupling and of interactions between the medullary and the spinal respiratory generators.

Animals↗
PubMed1996

Effect of posture on the onset of fictive locomotion in the decerebrate rabbit preparation.

Spontaneous locomotor episodes were recorded from hindlimb muscle nerves of decerebrate curarized rabbit preparations. Changes in the static position of both hindfeet (from extended to flexed) or of the head (from horizontal to bent forward) were shown to elicit a shift of the first locomotor burst from flexion to extension. Interneurones whose activity was recorded in the lumbar spinal cord were active throughout the first locomotor burst only when the latter was an extensor burst. Such data show that proprioceptive inputs are able to determine the onset of central locomotor programmation. Neuronal interactions which, at the spinal level, could account for this effect, are discussed.

Animals↗
PubMed1996

Interactions between medullary and spinal respiratory rhythm generators in the in vitro brainstem spinal cord preparation from newborn rats.

As medullary and spinal respiratory activities coexist in the in vitro brainstem spinal cord preparation from newborn rats previously deeply anaesthetized with diethyl ether, we sought evidence for reciprocal interactions between the medullary and spinal respiratory generators. A descending influence of medullary onto spinal respiratory generators has been characterized by the constant onset latency of the spinal burst within the corresponding medullary respiratory cycle. Non-harmonic (29%) and harmonic (9%) correlations were observed between the two phenomena, but correlations could also be low (27%) or absent (35%). Variations in the pH or FCO2 of the artificial cerebrospinal fluid were able to induce or suppress this medullary control of spinal respiratory activity. An ascending relationship between spinal and medullary respiratory generators has been revealed as a systematic variation of the medullary period due to resetting. Depending on the timing of the spinal respiratory activity, the medullary burst could be either advanced through a shortened medullary period, or delayed through a lengthened one. In conclusion, it was possible to show the existence of reciprocal relationships between the medullary and spinal respiratory generators in the in vitro brainstem spinal cord preparation from newborn rats. These results are interpreted in relation to the central interactions between locomotion and respiration in mammals which occur during rapid propulsion and which could be mediated by the spinal respiratory generator.

Animals↗
PubMed1996

Immunocytochemical distribution of ionotropic glutamate receptor subunits in the spinal cord of the rabbit.

Several histochemical and physiological studies in the literature suggest that ionotropic glutamate receptors are involved in various sensory and motor control mechanisms at the spinal level. The present immunocytochemical study used three specific antibodies to GluR2,4, GluR5,6,7 and to NMDAR1 to differentiate between the regional distribution of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA), kainate and N-methyl-D-aspartate (NMDA) subtypes of glutamate receptors throughout the rabbit spinal cord. All of these immunoreactivities were prominent in the superficial dorsal horn and motor column. Each antibody gave rise to regionally specific immunostaining patterns but which were similar at all spinal levels. Numerous small neurons in superficial laminae were immunostained with GluR2,4 antibody while only neuropilar elements were immunostained with the two other antibodies. Cell bodies of the intermediate zone and fibres in the motor column were particularly densely immunostained with GluR5-7. Such an immunostaining pattern, which was particularly abundant with the GluR5-7 antibody, suggests the presence, at the spinal level, of an extensive population of neurons exhibiting a high density of kainate receptors. Immunostaining with NMDAR1 antibody was less dense in comparison with the two others and especially in the motoneuron area. The present results provide the first immunohistochemical comparison between the respective regional distributions of the three types of ionotropic glutamate receptors in the spinal cord. Their parallel distributions throughout the spinal cord support the concept of a tight functional cooperation between NMDA and non-NMDA receptors which has been extensively described for spinal events.

Animals↗
PubMed1994

Characteristics of slow bursting activities recorded in cervical ventral roots in the in vitro brainstem-spinal cord preparation of the neonatal rat.

The aim of the present work was to disclose, through pharmacological activation of an isolated central nervous system maintained in vitro, spinal locomotor and respiratory-like activities inferred from an in vivo rabbit preparation. In a brainstem-spinal cord preparation in neonatal rats (0-3 days old), medullary respiratory activity occurred spontaneously in the cervical ventral roots. During 5-hydroxytryptophan (5-HTP) superfusion (0.2 mM), a slower rhythm with longer burst duration developed in the same ventral roots, with the pre-existing long-lasting slow bursting (LLSB) activity. At the same time, locomotor bursts were recorded from lumbar ventral roots. The LLSB activity was mainly recorded in cervical ventral roots, but they could also be encountered at the lumbar level, where they were eliminated after thoracic transection. The LLSB activity and the locomotor bursting were maintained after a C1 or C2 spinal transection, whereas medullary activity disappeared. Bilateral recording of the three types of rhythmic activity demonstrated that the LLSB activity and the medullary respiratory bursting typically displayed a synchronous bilateral coupling, whereas at caudal levels an alternate bilateral pattern was the rule for locomotor activity. Lactic acid could reinduce LLSB activity if introduced after it had just disappeared during the washout phase following 5-HTP superfusion. These results strongly suggest that the LLSB activity that originates from cervical generators belongs to the respiratory system, and not to locomotor activity. Finally, similar results in an in vivo rabbit preparation have been obtained through pharmacological activation. This preparation appears to be a suitable model for the analysis of this cervical burst generator and for the study of interactions among the different pattern generators.

Animals↗
PubMed1993

Characterization of hindlimb muscle afferents involved in ventilatory effects observed in decerebrate and spinal preparations.

Neurogenic changes of phrenic activity have previously been observed during periodic passive motions of one hindlimb in decorticate, unanaesthetized and curarized rabbit preparations before and after high spinal transection (Palisses et al. 1988). In decerebrate and spinal preparations, we aimed to determine, through rhythmic electrical stimulation of hindlimb muscle nerves, which muscle afferents are involved in these effects. In decerebrate preparations, these electrical stimulations (trains of shocks at 80 Hz for 300 ms every second for 20 s) produced ventilatory effects when group I + II afferent fibres of either flexor or extensor nerves were stimulated together and more powerful changes as soon as group III fibres were recruited. Stimulation of group I fibres alone induced no such effects. When present, these changes in respiratory activity consisted of a maintained decrease of the respiratory period due to both inspiratory and expiratory time shortening; in addition, the amplitude of the phrenic bursts greatly increased at the onset of electrical stimulation. After spinal transection at C2 level and pharmacological activation by nialamide and DOPA, only short-lasting phrenic bursts developed spontaneously; the electrical stimulation of group II and mainly group III flexor afferent fibres induced large amplitude phrenic activity whereas the stimulation of the same extensor afferents was relatively ineffective. The activation of phrenic motoneurones during group III flexor afferent stimulation was closely linked to each 300 ms period of stimulation. While the phrenic effects obtained in the spinal preparations by natural and by electrical periodic stimulation are quite similar to each other, those produced in decerebrate preparations differ substantially.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Origin of the central entrainment of respiration by locomotion facilitated by MK 801 in the decerebrate rabbit.

In order to establish the origin of the central coupling between locomotion and respiration which operates in freely moving mammals during galloping, we sought experimental conditions that readily lead to such a coupling in decerebrate and curarised rabbit preparations. In such preparations, stimulation of the mesencephalic locomotor region (MLR) evokes locomotor activities, recorded from hindlimb muscle nerves, that are rarely totally coordinated with phrenic inspiratory activity. However, low doses (0.2 mg/kg i.v.) of MK 801, a non-competitive NMDA antagonist which has been shown to increase the activity of the spinal locomotion generators (Fenaux et al. 1991), dramatically enhanced this coupling during MLR stimulation in most experiments: 1/1 coupling was dominant but 2/1 and 3/1 couplings (i.e. two or three locomotor cycles per respiratory cycle) were also obtained. Compared with spontaneous respiratory activity, which was apneustic under these conditions, the respiratory period was drastically decreased during coupling. However, a further transection of the spinal cord at the C6 or C7 level, which isolated the spinal locomotion generators from the supraspinal levels, totally suppressed this reduction of the inspiratory period during MLR stimulation in the presence of MK 801. In experiments where locomotor activity was simultaneously recorded at forelimb and hindlimb levels, the 1/1 evoked locomotor-respiratory coupling remained after the lumbar cord had been isolated by L1 spinal transection. The present data do show that intact spinal mechanisms are required for entrainment to occur. They suggest either tha a common supraspinal drive cannot entrain locomotion and respiration when being depressed, or that respiration is entrained at the locomotor rate by the spinal locomotion generators.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

[Possible existence of spinal inspiratory activity in the in vitro brain stem-spinal cord preparation from newborn rats].

Summing up with classical shortlasting inspirations, periodic longlasting inspirations (approximately 10 s) may be recorded with the normal inspirations through plethysmographic method in the intact newborn rat under deep diethyl ether anaesthesia. When they are present in vivo, the fast brainstem-spinal cord isolation allows to record in vitro periodic longlasting motor bursts (10-25 s) on C2-C8 ventral roots adding to shortlasting respiratory bursts (1-3 s) on C1-T13 ventral roots. Both kinds of rhythmic activities display a synchronous bilateral pattern. The longlasting bursts are maintained after a C2 spinal transection, especially if they have been induced by phenylephrine hydrochloride superfusion (0.4-0.5 mM).

Animals↗
PubMed1991

Localization of the lumbar pools of motoneurones which provide hindlimb muscles in the rabbit.

The localization of the pools of motoneurones (Mns) to the main hindlimb muscles was performed in the rabbit, using the retrograde transport of HRP from motor end plates. After 48 h survival time, the large alpha Mns were labeled. All the pools were met inside L6-S2 limits and a functional organization was observed: the pools to proximal muscles formed a ventral group of Mns and the pools to distal muscles a dorsal group, with flexor and extensor pools apart. The relative disposition of the different pools fits with that described in the cat and rat.

Animals↗
PubMed1991

Effects of an NMDA-receptor antagonist, MK-801, on central locomotor programming in the rabbit.

NMDA has been shown to disclose spinal fictive locomotor activity in various in vitro preparations. In the present work the NMDA-mediated effects of endogenously released excitatory aminoacids (EAA) on fictive locomotion in the adult rabbit preparation were assessed in vivo using systemic injections of a non competitive NMDA-antagonist, MK-801. In acute low spinal and curarized preparations, the amplitude of the "spontaneous" fictive locomotor activities recorded from hindlimb muscle nerves after nialamide-DOPA pretreatment was much decreased in flexor and extensor nerves after MK-801 administration (0.25 mg/kg i.v.) whereas the locomotor period increased slightly. The more potent locomotor bursts, evoked by repetitive sural nerve stimulation at 10 Hz during 10 s, were differently affected after MK-801: the main effect was a lengthening of the locomotor period and a less drastic drop in the burst amplitude. These changes in the burst period were maximal for activities evoked by A fibre group stimulation (+100%) and less when C fibres were recruited (+70%). In decerebrate curarized preparations where the locomotor sequences were evoked either by sural nerve stimulation or by stimulation of the mesencephalic locomotor region, MK-801 (0.25 mg/kg i.v.) caused the same drop in burst amplitude (by at least 50%) as in the spinal preparation but, in contrast, it reinforced rhythmic bursting: this was revealed by a clear shortening (up to -65%) of the locomotor period and by the prolongation of rhythmic bursting after stimulation. All these effects obtained in decerebrate preparations were maximal 20-30 min after MK-801 injection.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids↗