Rostrocaudal Distribution of the C-Fos-Immunopositive Spinal Network Defined by Muscle Activity during Locomotion

Case report: Potential physiological sources of the late response in epidural spinal recordings induced by spinal cord stimulation during intraoperative neuromonitoring

Objective

This study aims to investigate the sources of later response in epidural spinal recordings (ESRs) obtained from implanted leads during spinal cord stimulation, a topic has not been widely studied in previous research.

Methods

Two patients with lower back and lower extremity pain underwent SCS implantation with intraoperative neuromonitoring (IONM). The timing of extracted peaks in ESRs and intramuscular electromyography (EMG) recordings were analyzed and compared to a Monte Carlo simulation for synchronization analysis.

Results

Our data show that, when using two most caudal electrodes for stimulation, late response in ESRs collected from SCS leads was not synchronized with EMG recordings from lower extremity muscles. However, parts of the late responses were synchronized with EMG recordings from abdominal muscle groups.

Conclusions

Late response in ESRs is believed to result from muscle contractions, although the exact sources have not been fully identified. They are likely to originate from muscles near the implanted leads.

Significance

This research indicates that components of the late response may originate beyond the abdominal region, potentially offering additional information for current IONM practice. Additionally, understanding the sources of the late response may be useful for emerging clinical applications in neurorehabilitation.

Acute effects of L-DOPA/carbidopa/buspirone (Spinalon™) on rhythmic electrical activity of the lumbosacral spinal cord in cats

Discovered by Guertin and colleagues in 2004, Spinalon™ is a fixed-drug combination (L-DOPA, carbidopa, and buspirone) that can acutely induce temporary episodes of rhythmic locomotor-like activity in complete or near-complete spinal cord-injured (SCI) subjects. However, little is known about the mechanisms of action or the direct effects of Spinalon™ on neural elements of the central pattern generators (CPGs). Our study aims at characterizing the effects of Spinalon™ on electrical activity of the spinal cord in segmental areas known to contain key rhythmogenic elements of the CPGs (i.e., lumbosacral) for scratching and locomotion. We recorded spinal cord dorsum signals from decerebrate cats using a multielectrode array placed over the lumbosacral region. We found that a single intravenous injection of 100/25/7.5 mg/kg L-DOPA/carbidopa/buspirone (Spinalon™) specifically reduced the amplitude of electrical sinusoidal waves associated with fictive scratching and promoted the appearance of electrical sinusoidal-like waves occurring at frequencies compatible with fictive locomotion. These observations suggest a profound impact of Spinalon™ on the lumbosacral CPGs.

Forward Stepping Evoked by Transvertebral Stimulation in the Decerebrate Cat

OBJECTIVES

Implantation of stimulating electrodes into the basement of the vertebral spinous process allows the electrodes to be quickly and stably fixed relative to the spinal cord. Using this approach, we have previously shown the selectivity of rat muscle activation during transvertebral stimulation (TS). In this work, we investigated the TS to induce forward stepping of the cat's hindlimbs in comparison with epidural stimulation (ES).

MATERIALS AND METHODS

TS was performed with an electrode placed in the VL3-VL6 vertebrae in five decerebrated cats. ES was performed on the same cats in L5-L7 segments. Kinematic parameters of stepping were recorded in addition to electromyographic activity of musculus (m.) iliopsoas (IP), m. tibialis anterior (TA), and m. gastrocnemius lateralis (GL) of both hindlimbs.

RESULTS

With VL3-VL4 TS, all five animals were capable of bipedal forward stepping, whereas VL5 and VL6 TS led to the forward stepping in 3 of 5 and 1 of 5 animals, respectively. Well-coordinated muscle activity led to a high level of intra- and interlimb coordination. Kinematic parameters of TS-induced stepping were similar to those obtained with ES. The TS of the VL3 vertebra causes the frequency lock with the integer multiple of the stimulation frequency. Similarly to the rat model, TS-evoked muscle responses were site specific. They were minimal during VL3 TS and were maximal during VL4-VL5 TS (IP) and VL5-VL6 TS (TA, GL).

CONCLUSIONS

The obtained results support hypotheses about the location of the central pattern generators in the upper lumbar spinal segments. The proposed approach of electrode placement is surgically easier to perform than is ES. This approach is useful for studying site-specific neuromodulation of the spinal sensorimotor networks and for investigating new strategies of locomotor recovery in animal models.

Differences in backward and forward treadmill locomotion in decerebrated cats

Locomotion in different directions is vital for animal life and requires fine-adjusted neural activity of spinal networks. To compare the levels of recruitability of the locomotor circuitry responsible for forward and backward stepping, several electromyographic and kinematic characteristics of the two locomotor modes were analysed in decerebrated cats. Electrical epidural spinal cord stimulation was used to evoke forward and backward locomotion on a treadmill belt. The functional state of the bilateral spinal networks was tuned by symmetrical and asymmetrical epidural stimulation. A significant deficit in the backward but not forward stepping was observed when laterally shifted epidural stimulation was used but was not observed with central stimulation: only half of the cats were able to perform bilateral stepping, but all the cats performed forward stepping. This difference was in accordance with the features of stepping during central epidural stimulation. Both the recruitability and stability of the EMG signals as well as inter-limb coordination during backward stepping were significantly decreased compared with those during forward stepping. The possible underlying neural mechanisms of the obtained functional differences of backward and forward locomotion (spinal network organisation, commissural communication and supraspinal influence) are discussed.