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Biomedical subjects

S Rossignol

Publications and source records attributed to S Rossignol.

86 records · Page 5Linked to original sources
PubMed1981

Stimulus--response relationships during locomotion.

Crossed hind limb responses to high intensity stimulation of the superficial peroneal nerve in the cat were studied under various conditions. In precollicularly decerebrate cats walking on a treadmill, the same stimulus train evokes a crossed extension response during the contralateral stance phase and a crossed flexion response during the contralateral swing phase. In acute spinal cats (Th 13) injected with clonidine, a similar stimulus train can evoke a crossed extension response when the limb is manually placed in flexion and a crossed flexion response when the limb is positioned in extension. During "fictive" locomotion, induced in spinal paralyzed cats by nialamide an L-DOPA, the same stimulus may increase the amplitude and (or) the duration of crossed flexor or crossed extensor activity (in-phase responses). In some instances in these preparations, the crossed responses may be out-of-phase with the central rhythm. It is concluded that crossed hind limb responses during locomotion are selected by both central and peripheral mechanisms.

Animals↗
PubMed1981

Interactions between the jaw-opening reflex and mastication.

Electrical stimulation of the anterior hard palate or upper lip was used to evoke the jaw-opening reflex in rabbits lightly anesthetized with urethane. The amplitude of each excitatory response recorded in the digastric electromyogram during mastication was compared with the mean amplitude of 10 prior control responses. When weak stimuli were used, the mean amplitude of the reflex dropped markedly during mastication and was smallest when the digastric muscle was inactive (closing and occlusal phases of the masticatory cycle). As the stimulus strength was increased, the size of the response during closing rose progressively until it exceeded values obtained during the control period or the jaw-opening phase. In addition, strong stimuli altered the total cycle length and the duration and amplitude of muscle activity in a phase-dependent manner. Stimuli given during closing were particularly effective in causing inhibition of jaw-closing muscle activity and in reducing the velocity and amplitude of closure. It is concluded that the cyclical gain changes of the reflex response to noxious stimuli are controlled to a large extent by premotoneuronal mechanisms and that the overall effect on the masticatory cycle structure is phase dependent.

Animals↗
PubMed1980

An analysis of mechanisms controlling the reversal of crossed spinal reflexes.

In acute spinal cats injected with clonidine, a noxious stimulation applied to a hindlimb may evoke in the other hindlimb an extension or a flexion response depending on whether it is respectively flexed or extended passively at the time of stimulation. The contribution of various afferents in the control of such reflex reversal was investigated. After denervation of joints, reflex reversal could still be found. Reflex reversal could be obtained in a pair of antagonist muscles whose distal tendons were cut to prevent length changes during manipulations of the whole limb. This suggests that the response in either the flexor of the extensor of one muscle pair can appear without stretch signals originating from the pair itself and can be determined by the state of stretch of other muscles acting at the same or other joints. When the whole limb was practically denervated except for one muscle pair responses were found only in the extensor muscle indicating that stretch signals from that pair alone were not sufficient to reverse the reflex pattern. After complete rhizotomy, strong responses were also observed only in extensor muscles. These results indicate that crossed extensor responses are not evoked because of interactions with afferent impulses related to the position of the limb. On the other hand, when afferents are intact and the limb extended, crossed extension can be blocked and replaced by crossed flexion. Evidence has been obtained suggesting that the stretch of flexor muscles might indeed change the pattern of crossed extension to a pattern of crossed flexion. These findings are discussed in the context of a purposeful role in posture and locomotion.

Afferent Pathways↗
PubMed1980

The locomotion of the low spinal cat. II. Interlimb coordination.

The interaction of the two hindlimbs were investigated by an analysis of the muscular activity and the movements in 14 chronic spinal kittens during treadmill locomotion (i.e. in kittens subjected to a transection of the spinal cord (Th10--12)) one or two weeks after birth). At low speed the limbs were alternating (walk or trot). At higher they were activated more simultaneous, as during gallop. The two limbs could walk at different velocities, as during walking in a circle, when the two belts of the treadmill were driven at different speeds. The duration of the support phases was mainly influenced by the speed of the belt on which the limb was walking. The limbs could still maintain a common rhythm up to a two or three fold speed difference, as the flexion or the first extension phase of the limb walking on the "fast" belt was prolonged and the flexion phase of "slow limb" was shortened. At extreme speed differences the limb on the "fast belt" performed 2, 3 and even 4 steps during one stepcycle of the "slow limb". The placement of the feet was found to maintain the most stable relationship during alternating gaits at different speed differences. It is concluded that all phases of the step cycle are modifiable and that there are several mechanisms coordinating the limbs within the spinal cord.

Animals↗
PubMed1978

On the initiation of the swing phase of locomotion in chronic spinal cats.

In chronic spinal cats walking with the hind legs on a treadmill, one limb can be stopped by holding the paw while the other limb continues to walk. If the held limb is slowly brought backwards at one point the limb flexes and continues walking. It was found that the hip position at which the leg lifts off during such reaction is very close to the hip angle at the initiation of swing during locomotion. Similar findings were obtained by extending only the femur. The hand-held limb tends to initiate lift-off during the midstance or the midswing of the contralateral limb step cycle. It is concluded that hip position and the contralateral step cycle phase are two important factors determining the initiation of swing in one leg.

Action Potentials↗
PubMed1977

The adaptation of a reflex response to the ongoing phase of locomotion in fish.

The reflex response to stimulation of the tail fin has been studied in the swimming fish, by bilateral electromyographical (EMG) recordings in several segments along the body. The response varies with the phase of swimming. When the muscles on one side (segment) are active, a large response will occur on this side but no response on the contralateral side at the same level. When the other side becomes active an identical stimulus will cause an activation of this side but no response on the previously active side. When the movements were filmed a powerful mechanical effect was demonstrated with an augmentation of the ongoing movement, that would result in an instantaneous increase in speed. The stimulus causes in addition a shortening of the duration of the swimming cycle and its components. Most of the results were obtained on spinal dogfish, which also exhibits spontaneous locomotion after a spinal transection. Mainly electrical bipolar stimulation of the tail fin was used. Identical stimuli applied in different phases on an ongoing movement, thus give a reflex response that changes dramatically with the phase of the movement. This phase dependent reflex reversal is functionally meaningful; it is fast and due to spinal mechanisms.

Adaptation, Physiological↗
PubMed1977

Phasic gain control of reflexes from the dorsum of the paw during spinal locomotion.

In chronic spinal cats walking with their hindlimbs on a treadmill belt, tactile stimuli were applied to the dorsum of the paw during various phases of the step cycle. A stimulation during the swing phase evoked a flexion response with a concomitant crossed extension, whereas in stance it induced an increased ipsilateral extension. EMG-recordings show short latency reflex responses in flexors and extensors, respectively. The responses are organized such that latencies of knee muscles are shorter than those of ankle and hip muscles. The movements induced by the stimulations appear to be very meaningful during normal conditions in compensating for any unpredicted obstacle disturbing the movement of the paw during locomotion. Responses during forward flexion and during the support phase are well adapted to the ongoing locomotor activity and do not influence the interlimb coordination whereas a stimulation when the foot approaches the ground after the end of flexion disturbs the regular alternating pattern. Different possible mechanisms underlying this phase-dependent reflex reversal are discussed.

Animals↗
PubMed1976

Audio-spinal influence in man studied by the H-reflex and its possible role on rhythmic movements synchronized to sound.

An investigation was made of the time course of audio-spinal influences in man using the H-reflex technique and non-startling sounds. It was found that in all subjects the sound potentiated the H-reflex at a central latency of 80 msec, the peak facilitation (185%) being attained at 110--130 msec. The mean duration of this facilitation was 200 msec ranging from 120 to 460 msec. No inhibition was seen to follow the excitatory period. An habituation study showed a significant drop in peak facilitation after exposure to ten conditioning stimuli but a constant increase of the H-reflex above control level even after 60 presentations. The time course of this audiospinal facilitation was superposed over the EMG events during hopping to a simplified musical stimulus. In this situation, landing occurred some 50 msec prior to the ON beat or strong beat of the music. With this mode of synchronization, the timing of the ON and OFF beats of the musical stimulus would be suitable to potentiate the EMG events related respectively to the peak upwards acceleration determining the take-off and to the landing. It is inferred that during synchronized stereotyped movements to repetitive auditory stimuli, the motor events are timed to make best use of a potential audio-spinal facilitation.

Adolescent↗
PubMed1975

Startle responses recorded in the leg of man.

The EMG pattern of startle reactions in the leg was studied in man using a 100 msec, 1 kc/sec squre wave tone burst of 114 dB as the auitory stimulus. At rest, 74 responses were recorded in the ankle flexor tibialis anterior (TA) and 23 in the ankle extensor gastrocnemius (G) with a significantly different mean latency of 151 and 123 msecrespectively. During tonic extension or flexion of the ankle, the EMG response in TA or G consisted in a burst of activity superimposed on the voluntary EMG at a latency of approximately 150 msec after the onset of the tone burst and followed, at 200 msec, by a period of EMG silence lasting close to 100 msec. Similar periods of silence also occurred as the sole EMG modulation in response to sound. Although predominant in flexors, startle reactions are significant in extensors during or after tonic ankle extension suggesting that audiospinal influences may be channelled to one or the other group depending on their functional state. The silent period of EMG following an excitatory startle or appearing on its own suggests an important inhibitory component in audiospinal mechanisms particularly related to startle since it had not been disclosed in a previous study of the modulation of the H-reflex by non-startling auditory stimulus. From the distribution and EMG pattern of startle, it is inferred that audiospinal influences may be meaningfully integrated through the reticulospinal system in sound guided behaviour.

Acoustic Stimulation↗
PubMedDate not supplied

Adaptive changes of locomotion after central and peripheral lesions.

This paper reviews findings on the adaptive changes of locomotion in cats after spinal cord or peripheral nerve lesions. From the results obtained after lesions of the ventral/ventrolateral pathways or the dorsal/dorsolateral pathways, we conclude that with extensive but partial spinal lesions, cats can regain voluntary quadrupedal locomotion on a treadmill. Although tract-specific deficits remain after such lesions, intact descending tracts can compensate for the lesioned tracts and access the spinal network to generate voluntary locomotion. Such neuroplasticity of locomotor control mechanisms is also demonstrated after peripheral nerve lesions in cats with intact or lesioned spinal cords. Some models have shown that recovery from such peripheral nerve lesions probably involves changes at the supra spinal and spinal levels. In the case of somesthesic denervation of the hindpaws, we demonstrated that cats with a complete spinal section need some cutaneous inputs to walk with a plantigrade locomotion, and that even in this spinal state, cats can adapt their locomotion to partial cutaneous denervation. Altogether, these results suggest that there is significant plasticity in spinal and supraspinal locomotor controls to justify the beneficial effects of early proactive and sustained locomotor training after central (Rossignol and Barbeau 1995; Barbeau et al. 1998) or peripheral lesions.

Adaptation, Physiological↗