Compensatory adaptation of parallel motor pathways promotes skilled forelimb recovery after spinal cord injury

iScience, 2024 · DOI: https://doi.org/10.1016/j.isci.2024.111371 · Published: December 20, 2024

Simple Explanation

This study investigates how the brain and spinal cord adapt after a spinal cord injury to help recover skilled hand movements. It focuses on two pathways: cervical propriospinal interneurons (PNs) and rubrospinal neurons (RNs). The research involved creating lesions in the spinal cords of rats to mimic injury, followed by rehabilitative training. The scientists then temporarily silenced the activity of PNs and RNs to see how this affected recovery. The study found that both PNs and RNs play a role in regaining hand function after injury. When both pathways were silenced, the rats experienced a greater loss of function, suggesting these pathways work in parallel to support recovery.

Study Duration

4 weeks

Participants

Sprague-Dawley rats

Evidence Level

Not specified

Key Findings

1
Rehabilitation after dorsal funicular lesions promotes recovery of skilled reaching.
2
Partial recovery is mediated by either rubrospinal or C3/C4 propriospinal tracts.
3
Rehabilitation induces CST sprouting into the red nucleus and C3/C4 spinal cord.

Research Summary

This study examines the roles of cervical propriospinal interneurons (PNs) and rubrospinal neurons (RNs) in the recovery of reaching and grasping behaviors in rats with spinal cord injury. The lesions resulted in a 50% decrease in pellet retrieval, which normalized over four weeks of training. Silencing PNs or RNs after recovery resulted in reduced retrieval success. Silencing both pathways corresponded to greater functional loss, underscoring their parallel contributions to recovery, alongside evidence of CST ﬁber sprouting in the spinal cord and red nucleus.

Practical Implications

Therapeutic targets

The study suggests that therapeutic interventions aimed at enhancing the function of both the rubrospinal and propriospinal pathways could be more effective in promoting recovery after spinal cord injury.

Rehabilitation Strategies

Rehabilitation strategies should focus on promoting plasticity and reorganization of spared supraspinal-propriospinal circuits to maximize functional recovery.

Understanding Compensatory Mechanisms

A deeper understanding of how the brain compensates for CST damage can inform the development of more targeted and effective treatments for spinal cord injuries.

Study Limitations

1
This study is limited to lesions affecting the CST in the cervical spinal cord, since a dorsal funiculus lesion was used in the study.
2
Other forms of spinal injury such as moderate or severe contusion would injure more or different pathways and circuits, possibly the ones contributing to recovery in this model.
3
CST lesions primarily cause deﬁcits in skilled forelimb reaching and grasping and digit dexterity, but not locomotion.

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