Furosemide Unmasks Inhibitory Dysfunction after Spinal Cord Injury in Humans: Implications for Spasticity

Area of Science:

• Neuroscience
• Spinal Cord Injury Research
• Pharmacology

Background:

• Spasticity is a major challenge after spinal cord injury, significantly impacting patient quality of life and rehabilitation.
• The potassium chloride co-transporter (KCC2) is crucial for neuronal inhibition, and its downregulation after spinal cord injury in animals shifts GABAergic and glycinergic signaling from inhibitory to excitatory.
• Furosemide, a KCC2 antagonist in animals, has been proposed to reveal KCC2 dysfunction in humans.

Purpose of the Study:

• To investigate the role of KCC2 dysfunction in human spinal cord injury-induced spasticity.
• To determine if furosemide can modulate spinal inhibitory pathways in individuals with spinal cord injury, as observed in animal models.

Main Methods:

• Administration of furosemide to healthy subjects and individuals with spinal cord injury.
• Electrophysiological assessment of pre-synaptic and post-synaptic inhibition in soleus spinal motor neurons.
• Evaluation of furosemide's effect on excitatory and inhibitory synaptic transmission.

Main Results:

• In healthy subjects, furosemide reduced both pre- and post-synaptic inhibition, confirming its action on KCC2.
• In individuals with spinal cord injury, furosemide failed to modulate pre- and post-synaptic inhibitions in soleus motor neurons.
• This lack of effect suggests impaired KCC2 function in the human spinal cord post-injury.

Conclusions:

• KCC2 dysfunction is implicated in the reduced inhibitory synaptic transmission observed in the human spinal cord after injury.
• This dysfunction may be a key etiological factor in the development of hyperreflexia and spasticity.
• These findings open avenues for developing new therapies targeting chloride homeostasis for spasticity management.