Segmental reflex pathways in spinal shock and spinal spasticity in man.

Area of Science:

• Neuroscience
• Motor Control
• Spinal Cord Injury Research

Background:

• Understanding neural pathway activity is crucial for managing spinal cord conditions.
• Spinal shock and spasticity represent distinct phases of neurological dysfunction following spinal cord injury.

Purpose of the Study:

• To compare activity in three segmental neural pathways in normal subjects, patients with spinal shock, and patients with established spinal spasticity.
• To elucidate the roles of presynaptic inhibition and transmission efficiency in these conditions.

Main Methods:

• Utilized the Achilles tendon reflex (ATR) to assess Ia monosynaptic pathway transmission.
• Employed the tonic vibration reflex (TVR) to evaluate Ia polysynaptic pathway transmission.
• Measured motoneuron pool activation (M-response) and H reflex ratios to quantify transmission and presynaptic inhibition.

Main Results:

• Spinal shock demonstrated increased presynaptic inhibition and reduced Ia monosynaptic pathway transmission, with Ia polysynaptic pathways nearly abolished.
• Established spasticity showed impaired presynaptic inhibition, increased Ia monosynaptic pathway transmission, and a failure of Ia polysynaptic pathway recovery.
• The decline in presynaptic inhibition in spasticity was observed as a progressive process.

Conclusions:

• Spinal shock and spasticity differentially affect spinal cord segmental pathways.
• Presynaptic inhibition plays a critical role in modulating pathway activity during spinal cord injury recovery.
• The findings suggest a gradual failure of presynaptic inhibition contributes to the pathophysiology of spinal spasticity.