The functional properties of synapses made by regenerated axons across spinal cord lesion sites in lamprey

Neural Regeneration Research, 2022 · DOI: https://doi.org/10.4103/1673-5374.335828 · Published: February 28, 2022

Simple Explanation

This study compares synapses made by regenerated axons after spinal cord injury with those in uninjured lampreys. The lamprey is a good model for spinal injury because it can recover locomotor function after spinal cord lesions due to axonal regeneration. The study found that regenerated synapses below the lesion site function similarly to synapses in uninjured animals in terms of the strength and duration of their signals. However, these regenerated synapses had a greater number of synaptic vesicles and increased postsynaptic quantal amplitude. Above the lesion site, the amplitude and duration of synaptic inputs were also similar to uninjured animals. However, these synapses showed a reduction in release probability and facilitated rather than depressed over spike trains, potentially increasing activity across the lesion.

Study Duration

8–10 weeks

Participants

84 juvenile male and female adult lampreys

Evidence Level

Not specified

Key Findings

1
Regenerated synapses below the lesion site exhibit similar amplitude and duration of single excitatory postsynaptic potentials (EPSPs) compared to unlesioned synapses, along with similar activity-dependent depression over spike trains.
2
Regenerated synapses below the lesion site show a greater estimated number of synaptic vesicles and evidence for increased postsynaptic quantal amplitude compared to unlesioned synapses.
3
Axons above the lesion site exhibit a reduction in release probability and show facilitation rather than depression over spike trains compared to unlesioned axons.

Research Summary

This study investigates the functional properties of synapses made by regenerated axons in lampreys after spinal cord injury, comparing them to synapses in unlesioned animals. The findings indicate that while the amplitude and activity-dependent plasticity of regenerated synapses below the lesion site are similar to unlesioned synapses, they exhibit different release properties, including a greater number of synaptic vesicles. Synapses above the lesion site show facilitation and reduced release probability, suggesting a functional strengthening that may compensate for reduced descending input.

Practical Implications

Understanding Compensation Mechanisms

The study highlights how the nervous system compensates for spinal cord injury by altering synaptic properties to maintain function.

Targeting Synaptic Properties for Therapy

Identifying specific changes in release properties after injury can inform the development of targeted therapies to enhance recovery.

Importance of Supraspinal Plasticity

The altered synaptic properties above the lesion site underscore the importance of considering plasticity in regions beyond the immediate injury site for effective rehabilitation strategies.

Study Limitations

1
The analysis of release properties is difficult to determine, and the measures used here are subject to several caveats.
2
The analysis only considers properties at one-time point after the lesion.
3
The small sample size of paired recordings in poorly recovered animals limits the conclusions that can be drawn about synaptic properties in this group.

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