Modulation of forelimb and hindlimb muscle activity during quadrupedal tied-belt and split-belt locomotion in intact cats

In humans, gait adapts to prolonged walking on a split-belt treadmill, where one leg steps faster than the other, by gradually restoring the symmetry of interlimb kinematic variables, such as double support periods and step lengths, and by reducing muscle activity (EMG, electromyography). The adaptation is also characterized by reversing the asymmetry of interlimb variables observed during the early split-belt period when returning to tied-belt locomotion, termed an after-effect. To determine if cats adapt to prolonged split-belt locomotion and to assess if spinal locomotor circuits participate in the adaptation, we measured interlimb variables and EMG in intact and spinal-transected cats before, during and after 10 min of split-belt locomotion. In spinal cats, only the hindlimbs performed stepping with the forelimbs stationary. In intact and spinal cats, step lengths and double support periods were, on average, symmetric, during tied-belt locomotion. They became asymmetric during split-belt locomotion and remained asymmetric throughout the split-belt period. Upon returning to tied-belt locomotion, symmetry was immediately restored. In intact cats, the mean EMG amplitude of hindlimb extensors increased during split-belt locomotion and remained increased throughout the split-belt period, whereas in spinal cats, EMG amplitude did not change. Therefore, the results indicate that the locomotor pattern of cats does not adapt to prolonged split-belt locomotion, suggesting an important physiological difference in the control of locomotion between cats and humans. We propose that restoring left-right symmetry is not required to maintain balance during prolonged asymmetric locomotion in the cat, a quadruped, as opposed to human bipedal locomotion.

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Lack of adaptation during prolonged split‐belt locomotion in the intact and spinal cat

Kuczynski

Telonio

Thibaudier

et al. 2017

“…, ; Frigon et al . ). Before surgery, induction was made with an intramuscular injection of Butorphanol (0.4 mg kg −1 ), Acepromazine (0.1 mg kg −1 ), Glycopyrrolate (0.01 mg kg −1 ) and ketamine/diazepam (0.11 ml kg −1 in a 1:1 ratio).…”

Section: Methodsmentioning

confidence: 97%

Spinal control of muscle synergies for adult mammalian locomotion

Desrochers

Harnie

Doelman

et al. 2018

Key points The control of locomotion is thought to be generated by activating groups of muscles that perform similar actions, which are termed muscle synergies. Here, we investigated if muscle synergies are controlled at the level of the spinal cord. We did this by comparing muscle activity in the legs of cats during stepping on a treadmill before and after a complete spinal transection that abolishes commands from the brain. We show that muscle synergies were maintained following spinal transection, validating the concept that muscle synergies for locomotion are primarily controlled by circuits of neurons within the spinal cord. Abstract Locomotion is thought to involve the sequential activation of functional modules or muscle synergies. Here, we tested the hypothesis that muscle synergies for locomotion are organized within the spinal cord. We recorded bursts of muscle activity in the same cats (n = 7) before and after spinal transection during tied‐belt locomotion at three speeds and split‐belt locomotion at three left–right speed differences. We identified seven muscles synergies before (intact state) and after (spinal state) spinal transection. The muscles comprising the different synergies were the same in the intact and spinal states as well as at different speeds or left–right speed differences. However, there were some significant shifts in the onsets and offsets of certain synergies as a function of state, speed and left–right speed differences. The most notable difference between the intact and spinal states was a change in the timing between the knee flexor and hip flexor muscle synergies. In the intact state, the knee flexor synergy preceded the hip flexor synergy, whereas in the spinal state both synergies occurred concurrently. Afferent inputs also appear important for the expression of some muscle synergies, specifically those involving biphasic patterns of muscle activity. We propose that muscle synergies for locomotion are primarily organized within the spinal cord, although their full expression and proper timing requires inputs from supraspinal structures and/or limb afferents.

“…As part of our effort to maximize the scientific output of each animal, cats were used in other studies to provide answers to other scientific questions (Frigon et al . , , ; D'Angelo et al . ; Dambreville et al .…”

Section: Methodsmentioning

confidence: 99%

Left–right coordination from simple to extreme conditions during split‐belt locomotion in the chronic spinal adult cat

Frigon

Desrochers

Thibaudier

et al. 2016

121

Key pointsr Coordination between the left and right sides is essential for dynamic stability during locomotion.r The immature or neonatal mammalian spinal cord can adjust to differences in speed between the left and right sides during split-belt locomotion by taking more steps on the fast side.r We show that the adult mammalian spinal cord can also adjust its output so that the fast side can take more steps.r During split-belt locomotion, only certain parts of the cycle are modified to adjust left-right coordination, primarily those associated with swing onset.r When the fast limb takes more steps than the slow limb, strong left-right interactions persist. r Therefore, the adult mammalian spinal cord has a remarkable adaptive capacity for left-right coordination, from simple to extreme conditions. Abstract Although left-right coordination is essential for locomotion, its control is poorly understood, particularly in adult mammals. To investigate the spinal control of left-right coordination, a spinal transection was performed in six adult cats that were then trained to recover hindlimb locomotion. Spinal cats performed tied-belt locomotion from 0.1 to 1.0 m s −1 and split-belt locomotion with low to high (1:1.25-10) slow/fast speed ratios. With the left hindlimb stepping at 0.1 m s −1 and the right hindlimb stepping from 0.2 to 1.0 m s −1 , 1:1, 1:2, 1:3, 1:4 and 1:5 left-right step relationships could appear. The appearance of 1:2+ relationships was not linearly dependent on the difference in speed between the slow and fast belts. The last step taken by the fast hindlimb displayed longer cycle, stance and swing durations and increased extensor activity, as the slow limb transitioned to swing. During split-belt locomotion with 1:1, 1:2 and 1:3 relationships, the timing of stance onset of the fast limb relative to the slow limb and placement of both limbs at contact were invariant with increasing slow/fast speed ratios. In contrast, the timing of stance onset of the slow limb relative to the fast limb and the placement of both limbs at swing onset were modulated with slow/fast speed ratios. Thus, left-right coordination is adjusted by modifying specific parts of the cycle. Results highlight the remarkable adaptive capacity of the adult mammalian spinal cord, providing insight into spinal mechanisms and sensory signals regulating left-right coordination.