Novel Evoked Synaptic Activity Potentials (ESAPs) Elicited by Spinal Cord Stimulation
Mahima Sharma1, Vividha Bhaskar2, Lillian Yang3
1Neural Engineering Laboratory, Department of Biomedical Engineering, The City College of the City University of New York, City College Center for Discovery and Innovation, New York, NY 10031 mahima.sharma0@gmail.com.
Eneuro
|May 2, 2023
Summary
Spinal cord stimulation (SCS) evokes fast epidural evoked compound action potentials (ECAPs) and a novel, slower synaptic response termed evoked synaptic activity potentials (ESAPs). This discovery may clarify SCS mechanisms by identifying spinal cord synaptic activity.
Area of Science:
- Neuroscience
- Spinal Cord Injury Research
- Neuromodulation
Background:
- Spinal cord stimulation (SCS) is used therapeutically, but its precise mechanisms remain incompletely understood.
- Fast epidural evoked compound action potentials (ECAPs) reflect dorsal column axon activity, not necessarily spinal circuit responses.
Purpose of the Study:
- To identify and characterize a delayed, slower potential evoked by SCS that reflects synaptic activity within the spinal cord.
- To differentiate this novel potential from ECAPs and determine its origin.
Main Methods:
- Utilized a multimodal approach in anesthetized rats, including epidural SCS, motor cortex stimulation, epidural and intraspinal recordings, and EMG.
- Administered AMPA receptor antagonist CNQX and varied stimulation parameters to analyze evoked potentials.
- Recorded epidural, intraspinal, and EMG responses to SCS and cortical stimulation.
Main Results:
- SCS evoked characteristic ECAPs (<2ms latency) and a distinct, slower wave (S1-wave).
- The S1-wave was verified as non-artifactual, not related to EMG, and demonstrated unique stimulation-intensity and spatial profiles.
- AMPA receptor antagonism (CNQX) significantly diminished the S1-wave but not ECAPs.
- Cortical stimulation evoked CNQX-sensitive epidural responses, confirming epidural recording of synaptic activity.
- High-frequency SCS (50 Hz) dampened the S1-wave but not ECAPs.
Conclusions:
- The S1-wave is synaptic in origin and termed evoked synaptic activity potentials (ESAPs).
- ESAPs represent spinal cord synaptic activity, distinct from ECAPs.
- Characterization of epidurally recorded ESAPs offers new insights into SCS mechanisms.
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