Glycine: an important potential component of spinal shock

Area of Science:

• Neuroscience
• Neuropharmacology
• Spinal Cord Injury Research

Background:

• Amino acid neurotransmitters (AANTs) are crucial for maintaining muscle tone.
• Abnormal AANT concentrations are linked to hyper- or hypotonic muscle states.
• Spinal shock, characterized by flaccidity, frequently follows spinal cord injury (SCI) and may involve altered AANT levels.

Purpose of the Study:

• To investigate the relationship between AANT concentrations and muscle tone abnormalities (spasticity vs. flaccidity) following ischemic SCI.
• To determine if specific AANTs are associated with flaccid paralysis or spasticity post-SCI.

Main Methods:

• Ischemic spinal cord injuries (SCIs) were induced in rabbits using intraaortic balloon occlusion.
• Microdialysis was employed to sample AANT concentrations from injured spinal cord segments 3 days post-SCI.
• Evoked potentials were utilized to assess spinal cord stability.

Main Results:

• No significant changes in overall AANT levels were observed during the 4-hour sampling period in either spastic or flaccid injury groups.
• Baseline glycine levels were significantly higher (2-3 times) in animals with flaccid injuries compared to spastic animals and controls (p < 0.001).
• Elevated glycine concentrations were specifically associated with flaccidity, not spasticity, post-SCI.

Conclusions:

• High concentrations of the inhibitory amino acid neurotransmitter glycine are associated with flaccidity following spinal cord injury (spinal shock).
• Glycine's role in flaccidity suggests that glycinergic compounds could be a potential therapeutic strategy for suppressing excess muscle tone.
• Further research into glycinergic compounds is warranted for managing muscle tone disorders post-SCI.