Maladaptive spinal plasticity opposes spinal learning and recovery in spinal cord injury

Frontiers in Physiology, 2012 · DOI: 10.3389/fphys.2012.00399 · Published: October 10, 2012

Simple Explanation

Synaptic plasticity within the spinal cord has great potential to facilitate recovery of function after spinal cord injury (SCI). Spinal plasticity can be induced in an activity-dependent manner even without input from the brain after complete SCI. However, not all spinal plasticity promotes recovery of function. Central sensitization of nociceptive (pain) pathways in the spinal cord may emerge in response to various noxious inputs, demonstrating that plasticity within the spinal cord may contribute to maladaptive pain states. The literature demonstrates that activity-dependent plasticity within the spinal cord must be carefully tuned to promote adaptive spinal training. On the other hand, stimulation that is delivered in an unsynchronized fashion, such as randomized electrical stimulation or peripheral skin injuries, can generate maladaptive spinal plasticity

Study Duration

Not specified

Participants

Rats

Evidence Level

Review Article

Key Findings

1
Spinal synapses can be strengthened or weakened in response to external stimulation, demonstrating the basic properties required for use-dependent learning and memory.
2
Exposure to uncontrollable/unpredictable peripheral stimulation induces a central sensitization-like state that inhibits adaptive spinal learning and undermines recovery of locomotor function after spinal contusion injury.
3
Response-contingent (master), predictable nociceptive stimulation promotes future spinal cord learning whereas unpredictable, intermittent nociceptive stimulation undermines future spinal learning and generates central sensitization.

Research Summary

The present review discusses the features of spinal cord plasticity with a speciﬁc emphasis on protecting against maladaptive plasticity in nociceptive systems and promoting adaptive forms of spinal plasticity for rehabilitation after SCI. The general theme is that uncontrollable/yoked stimulation produces a maladaptive form of spinal metaplasticity that is associated with impaired spinal learning, reduced recovery of function after SCI, and nociceptive hyper-reactivity. While studies of spinal cord plasticity after SCI have uncovered a remarkable degree of plasticity, it must also be remembered that this plasticity is a two-edged sword; adaptive processes can foster recovery and reduce neuropathic pain while maladaptive mechanisms have the opposite effect.

Practical Implications

Rehabilitation Strategies

Effective rehabilitation strategies should integrate approaches to maximize positive elements of spinal cord training while limiting the negative consequences of inappropriate stimulus timing and nociceptive input below the injury.

Pain Management

Understanding the mechanisms of maladaptive spinal plasticity can help in developing better strategies for managing chronic pain after SCI.

Therapeutic Development

Identifying molecular mechanisms that modulate spinal learning can lead to the development of therapeutic approaches to promote rehabilitation and recovery of function after SCI.

Study Limitations

1
The specific stimulus conditions that promote effective spinal cord learning are not fully understood.
2
Conditions that lead to a spinal learning deficit require elucidation.
3
Mechanisms for neuropathic pain after SCI are not fully understood.

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