Biomedical subjects

Gregoire Courtine

Publications and source records attributed to Gregoire Courtine.

4 recordsLinked to original sources

PubMed2006

Plasticity of spinal cord reflexes after a complete transection in adult rats: relationship to stepping ability.

Changes in epidurally induced (S1) spinal cord reflexes were studied as a function of the level of restoration of stepping ability after spinal cord transection (ST). Three types of responses were observed. The early response (ER) had a latency of 2.5 to 3 ms and resulted from direct stimulation of motor fibers or motoneurons. The middle response (MR) had a latency of 5 to 7 ms and was monosynaptic. The late response (LR) had a latency of 9 to 11 ms and was polysynaptic. After a complete midthoracic ST, the LR was abolished, whereas the MR was facilitated and progressively increased. The LR reappeared about 3 wk after ST and increased during the following weeks. Restoration of stepping induced by epidural stimulation at 40 Hz coincided with changes in the LR. During the first 2 wk post-ST, rats were unable to step and electrophysiological assessment failed to show any LR. Three weeks post-ST, epidural stimulation resulted in a few steps and these coincided with reappearance of the LR. The ability of rats to step progressively improved from wk 3 to wk 6 post-ST. There was a continuously improved modulation of rhythmic EMG bursts that was correlated with restoration of the LR. These results suggest that restoration of polysynaptic spinal cord reflexes after complete ST coincides with restoration of stepping function when facilitated by epidural stimulation. Combined, these findings support the view that restoration of polysynaptic spinal cord reflexes induced epidurally may provide a measure of functional restoration of spinal cord locomotor networks after ST.

Animals↗

PubMed2006

Spinal cord reflexes induced by epidural spinal cord stimulation in normal awake rats.

Motor responses in hindlimb muscles to epidural spinal cord stimulation in normal awake rats during bipedal standing were studied. Stimulation at L2 or S1 induced simultaneous and bilateral responses in the vastus lateralis, semitendinosus, tibialis anterior, and medial gastrocnemius muscles. Stimulation at S1 evoked an early (ER), middle (MR) and late (LR) response: stimulation at L2 elicited only a MR and LR. Vibration and double epidural stimulation testing suggests that the ER is a direct motor response, whereas the MR and LR are mediated synaptically. MR has properties of a monosynaptic reflex, i.e., inhibited during vibration and depressed during the second pulse of a double stimulation. Some components of the LR seem to be mediated by afferents associated with the flexor reflex and probably involve group II afferents. During bipedal treadmill stepping, the MR was modulated in extensors, whereas the LR was modulated in flexors. These results show differential modulation of monosynaptic and polysynaptic reflexes in flexor and extensor motor pools during locomotion. Monosynaptic responses to stimulation at either L2 or S1 generally were amplified in extensors during the stance phase and in flexors during the swing phase of the step cycle. No correlation was found between the ER and the EMG background during stepping, whereas both the MR and LR were closely correlated with the changes in the EMG activity level of the corresponding muscle. These data demonstrate the feasibility of using epidural stimulation for examining monosynaptic and polysynaptic pathways to motor pools associated with multiple muscles during movement and over a prolonged period.

Afferent Pathways↗

PubMed2002

Neck muscle vibration and spatial orientation during stepping in place in humans.

Unilateral long-lasting vibration was applied to the sternomastoid muscle to assess the influence of asymmetric neck proprioceptive input on body orientation during stepping-in-place. Blindfolded subjects performed 3 sequences of 3 trials, each lasting 60 s: control, vibration applied during stepping (VDS), and vibration applied before stepping (VBS). VDS caused clear-cut whole body rotation toward the side opposite to vibration. The body rotated around a vertical axis placed at about arm's length from the body. The rotation did not begin immediately on switching on the vibrator. The delay varied from subject to subject from a few seconds to about 10 s. Once initiated, the angular velocity of rotation was remarkably constant (about 1 degrees /s). In VBS, at the beginning of stepping, subjects rotated for a while as if their neck were still vibrated. At a variable delay, the direction of rotation reversed, and the effects were opposite to those observed during VDS. Under no condition did head rotation, head roll, or lateral body tilt accompany rotation. The results confirm and extend the notion that the neck proprioceptive input plays a major role in body orientation during locomotion. The body rotation does not seem to depend on the same mechanisms that modify the erect posture; rather, the asymmetric neck input would seem to modify the egocentric body-centered coordinate system.

Adult↗

PubMed2002

Head position during various locomotor executions after prolonged microgravity exposure.

Head orientation in the sagittal plane was assessed before and the second and sixth days after a prolonged microgravity exposure (6 months) in 7 astronauts, which were instructed to execute various locomotor movements (stair ascent, jump down and level walk). Crewmembers systematically flexed down the head when they executed the locomotion the second day post-flight compared to the pre-flight walk. Cephalic orientation was normally positioned when movements was performed the sixth day after Earth re-entry. This head flexion may reflect a strategy used by cosmonauts to increase the vestibular sensibility, and then improve the control of the dynamic equilibrium during locomotor movements. The high rate of re-adaptation indicated that cosmonauts rapidly recovered their normal walking capacities despite the prolonged microgravity exposure.

Journal Article↗