Regenerated Synapses in Lamprey Spinal Cord Are Sparse and Small Even After Functional Recovery From Injury

J. Comp. Neurol., 2010 · DOI: 10.1002/cne.22368 · Published: March 23, 2010

Spinal Cord Injury Regenerative Medicine Neurology

Simple Explanation

This study investigates how nerve cells (neurons) in the spinal cord regenerate connections (synapses) after an injury. Specifically, the researchers examined the structure and function of these regenerated synapses in lampreys, a type of fish known for its ability to recover from spinal cord injuries. The study found that even when lampreys regained their ability to swim after a spinal cord injury, the regenerated synapses were fewer in number and smaller in size compared to normal synapses. This suggests that the recovery of function is not solely dependent on the perfect restoration of synapses. Instead, the researchers propose that other changes in the spinal cord network, such as adjustments in the strength of existing synapses or the involvement of other neurons, may compensate for the deficiencies in the regenerated synapses, allowing the animal to regain functional abilities.

Study Duration

10-12 Weeks

Participants

Late larval stage lampreys (Petromyzon marinus)

Evidence Level

Not specified

Key Findings

1
Regenerated giant RS axons produced very few synapses compared to control axons, particularly within and distal to the lesion scar.
2
Regenerated giant RS synapses were simpler in structure, with fewer complex presynaptic sites and smaller active zones.
3
Despite the reduced number and size, the density of presynaptic sites and docked vesicles in distal regenerated axons was partially restored to control levels.

Research Summary

This study used lampreys to investigate the regeneration of synapses after spinal cord injury, focusing on the giant reticulospinal (RS) neurons. The key finding was that despite robust functional recovery of swimming, the regenerated synapses were sparse and small compared to normal synapses. The authors suggest that functional recovery is likely due to a complex set of compensatory changes throughout the spinal network, rather than a complete restoration of synapse number and structure.

Practical Implications

Understanding Functional Recovery

The study suggests that functional recovery after spinal cord injury may not require perfect synapse regeneration, highlighting the importance of compensatory mechanisms within the nervous system.

Therapeutic Strategies

Future therapeutic strategies for spinal cord injury could focus on enhancing plasticity and compensatory changes in the spinal network, rather than solely aiming to regenerate a normal number of synapses.

Synaptic Plasticity Research

The findings contribute to a broader understanding of synaptic plasticity and the ability of the nervous system to adapt after injury.

Study Limitations

1
The study focused on giant RS neurons in lampreys, which may not fully represent the complexities of synapse regeneration in mammalian spinal cords.
2
The precise functional consequences of the observed structural differences in regenerated synapses were not directly assessed.
3
The study examined synapse regeneration at a single time point (10-12 weeks post-transection), limiting the understanding of the temporal dynamics of synapse formation and maturation.

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