Behavioral recovery after a spinal deafferentation injury in monkeys does not correlate with extent of corticospinal sprouting

Behav Brain Res, 2022 · DOI: 10.1016/j.bbr.2021.113533 · Published: January 7, 2022

Spinal Cord Injury Neurology Rehabilitation

Simple Explanation

This study examines the relationship between nerve fiber growth (sprouting) in the spinal cord and recovery of hand function in monkeys after a specific type of spinal injury. The injuries cut similar afferent pools supplying the thumb, index and middle fingers of one hand but each resulted in a very different corticospinal tract (CST) sprouting response. Two different types of injuries were created, one causing less sprouting and the other causing more. Researchers then compared how well the monkeys recovered hand function after each injury to see if more sprouting led to better recovery. The study found that the amount of nerve fiber growth did not predict how well the monkeys recovered. This suggests that simply having more nerve fiber growth doesn't necessarily mean better functional recovery after this type of spinal injury.

Study Duration

3-5 months

Participants

7 male monkeys (Macaca cynomolgus)

Evidence Level

Not specified

Key Findings

1
The extent of corticospinal tract (CST) sprouting does not correlate with the degree of behavioral recovery in monkeys after a spinal deafferentation injury.
2
Monkeys with a dorsal root lesion (DRL) and those with a combined DRL and dorsal column lesion (DRL/DCL) showed similar recovery of hand/digit function, despite having different CST sprouting responses.
3
More extensive axonal sprouting does not necessarily predict greater functional recovery after spinal cord injury.

Research Summary

This study investigated the relationship between corticospinal tract (CST) sprouting and behavioral recovery in monkeys after two different spinal deafferentation injury models: dorsal root lesion (DRL) and combined DRL/dorsal column lesion (DCL). The researchers found that despite the DRL/DCL group exhibiting more extensive CST sprouting compared to the DRL group, both groups showed similar behavioral recovery in a reach-grasp-retrieval task. The study concludes that the extent of CST sprouting is not a reliable biomarker for predicting behavioral recovery after spinal deafferentation injury, suggesting that other factors beyond sprouting extent play a significant role in functional recovery.

Practical Implications

Rethinking Biomarkers

CST sprouting alone should not be the sole focus as a biomarker for recovery after spinal cord injury.

Complex Mechanisms

Functional recovery likely depends on a combination of factors, including the specific type and location of the injury, the plasticity of other neural circuits, and the effectiveness of compensatory strategies.

Targeted Therapies

Future research should focus on identifying the specific mechanisms that drive functional recovery after spinal cord injury, in order to develop more targeted and effective therapies.

Study Limitations

1
The lesions were purely sensory and not typical of clinical spinal injuries.
2
The descending CST fibers were not themselves directly cut by either of the deafferentation lesions examined.
3
Little is currently known about what happens to terminal sprouts over an extended time period

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