State- and Condition-Dependent Modulation of the Hindlimb Locomotor Pattern in Intact and Spinal Cats Across Speeds

Abstract

Locomotion after complete spinal cord injury (spinal transection) in animal models is usually evaluated in a hindlimb-only condition with the forelimbs suspended or placed on a stationary platform and compared with quadrupedal locomotion in the intact state. However, because of the quadrupedal nature of movement in these animals, the forelimbs play an important role in modulating the hindlimb pattern. This raises the question: whether changes in the hindlimb pattern after spinal transection are due to the state of the system (intact versus spinal) or because the locomotion is hindlimb-only. We collected kinematic and electromyographic data during locomotion at seven treadmill speeds before and after spinal transection in nine adult cats during quadrupedal and hindlimb-only locomotion in the intact state and hindlimb-only locomotion in the spinal state. We attribute some changes in the hindlimb pattern to the spinal state, such as convergence in stance and swing durations at high speed, improper coordination of ankle and hip joints, a switch in the timing of knee flexor and hip flexor bursts, modulation of burst durations with speed, and incidence of bi-phasic bursts in some muscles. Alternatively, some changes relate to the hindlimb-only nature of the locomotion, such as paw placement relative to the hip at contact, magnitude of knee and ankle yield, burst durations of some muscles and their timing. Overall, we show greater similarity in spatiotemporal and EMG variables between the two hindlimb-only conditions, suggesting that the more appropriate pre-spinal control is hindlimb-only rather than quadrupedal locomotion.

Sensory Perturbations from Hindlimb Cutaneous Afferents Generate Coordinated Functional Responses in All Four Limbs during Locomotion in Intact Cats

“…For instance, cats participated in experiments where they walked on a split-belt treadmill at different speeds and left-right speed differences with or without stimulating peripheral nerves, such as SP, superficial radial and distal tibial. They also performed quadrupedal and hindlimb-only locomotion in the forward and backward directions (Harnie et al, 2022(Harnie et al, , 2021. Cats also stepped on a walkway where they negotiated obstacles and stepped along a circular path.…”

Decoding Bilateral Hindlimb Kinematics From Cat Spinal Signals Using Three-Dimensional Convolutional Neural Network

“…During each session, the animals could walk on a running treadmill with their hindlimbs only while keeping their forelimbs on the front frame of the treadmill (Figure 2). It should be noted that locomotor pattern resulted during hindlimb-only locomotion with placing forelimbs on a stationary platform is different from that resulted during normal quadrupedal locomotion (Harnie et al, 2022). The walking cadence of cat 1 varied between 0.59 and 0.8 steps per second, while the walking cadence of cat 2 had less variation between 0.9 and 0.99 steps per second.…”

Simultaneous control of forward and backward locomotion by spinal sensorimotor circuits

“…Our study followed ARRIVE guidelines for animal studies (Percie du Sert et al., 2020). To reduce the number of animals used in research, cats participated in other studies to answer different scientific questions, some of which have been published (Audet et al., 2022; Harnie et al., 2022).…”

“…We did not train spinal cats to recover hindlimb locomotion as discussed previously (Harnie et al., 2019). Intact cats performed hindlimb‐only locomotion to facilitate comparisons with after spinal transection (Harnie et al., 2022), but also because most cats only performed hybrid locomotion of their hindlimbs with the forelimbs on a stationary platform. We tested for quadrupedal hybrid locomotion in intact cats and out of the 11, only one cat could do it.…”