Epidural Stimulation Induced Modulation of Spinal Locomotor Networks in Adult Spinal Rats

Abstract

The importance of the in vivo dynamic nature of the circuitries within the spinal cord that generate locomotion is becoming increasingly evident. We examined the characteristics of hindlimb EMG activity evoked in response to epidural stimulation at the S1 spinal cord segment in complete midthoracic spinal cord-transected rats at different stages of postlesion recovery. A progressive and phasedependent modulation of monosynaptic (middle) and long-latency (late) stimulation-evoked EMG responses was observed throughout the step cycle. During the first 3 weeks after injury, the amplitude of the middle response was potentiated during the EMG bursts, whereas after 4 weeks, both the middle and late responses were phase-dependently modulated. The middle-and late-response magnitudes were closely linked to the amplitude and duration of the EMG bursts during locomotion facilitated by epidural stimulation. The optimum stimulation frequency that maintained consistent activity of the long-latency responses ranged from 40 to 60 Hz, whereas the shortlatency responses were consistent from 5 to 130 Hz. These data demonstrate that both middle and late evoked potentials within a motor pool are strictly gated during in vivo bipedal stepping as a function of the general excitability of the motor pool and, thus, as a function of the phase of the step cycle. These data demonstrate that spinal cord epidural stimulation can facilitate locomotion in a time-dependent manner after lesion. The long-latency responses to epidural stimulation are correlated with the recovery of weight-bearing bipedal locomotion and may reflect activation of interneuronal central pattern-generating circuits.

Multisystem Neuroprosthetic Training Improves Bladder Function After Severe Spinal Cord Injury

“…To encourage locomotion via electrical spinal cord stimulation, rectangular pulses were delivered through L2 and S1 electrodes (40 Hz, 0.2 ms duration, 200-400µA) 9 . …”

A review of published reports on neuroprotection in spinal cord injury

“…It may provide a new therapeutic approach to complete SCI, as well as objective, electrophysiological proofs for the autonomous activity of lumbar CPG. Studies on both lab animals 61 and humans (a total of 10 patients) showed that low frequency electrical stimulation (2.2-50 Hz) with epidural electrodes elicited stepping-like movements; although a synergistic activation of kinematic chains (triple flexions alternating with extensions) was observed, it is obvious that a functional gait could not be achieved. 62,63 It should be noted that this technique involves some significant risks for the patient, such as infections, local hemorrhages, etc.…”

Coapplication of noisy patterned electrical stimuli and NMDA plus serotonin facilitates fictive locomotion in the rat spinal cord

“…The lack of effectiveness of electrical stimulation can be attributed to the filtering effect of CPG interneurons receiving synaptic inputs from the spinal rhythm generator to gate the flow of sensory information in the spinal cord (Sillar 1991). Interestingly, a better outcome is observed when stimuli are applied close to the spinal cord region, which putatively contains the CPG (Kiehn and Butt 2003), using epidural (Lavrov et al 2008a(Lavrov et al , 2008b or intraspinal (Gaunt et al 2006) electrodes.…”