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Quantifying Changes in Pain Sensitivity Using Reproducible Transcutaneous Optogenetic Stimulation in Behaving Mice
Yu-Feng Xie1, Christopher Dedek1,2,3, Steven A Prescott4,2,5,3,6
1Neurosciences and Mental Health, The Hospital for Sick Children, Toronto, Ontario M5G 0A4, Canada.
Summary
This study introduces a robot-assisted optogenetic method for precise pain testing in mice. Ramp-based photostimulation is more effective than pulse-based methods for measuring inflammation and analgesia.
Area of Science:
- Neuroscience
- Pain Research
- Optogenetics
Background:
- Optogenetics enables selective activation of somatosensory afferents to study pain.
- Previous optogenetic pain studies were limited by imprecise photostimulation.
- Quantitative behavioral testing requires reproducible and precise stimulation methods.
Purpose of the Study:
- To develop and validate a robot-assisted transcutaneous optogenetic stimulation system for quantitative pain behavior testing in mice.
- To compare the efficacy of different photostimulus waveforms (pulses vs. ramps) and response metrics (threshold vs. latency) in assessing pain states.
- To investigate the role of specific sodium channels (NaV1.7, NaV1.8) in nociception and analgesia.
Main Methods:
- Utilized a robotic system for reproducible transcutaneous optogenetic stimulation of mouse hind paws.
- Employed channelrhodopsin-2 (ChR2) expressed in Advillin-ChR2 and NaV1.8-ChR2 mice.
- Compared withdrawal responses to pulsed and ramped photostimuli under baseline, inflammatory (CFA), and analgesic conditions.
- Performed electrophysiological recordings to correlate afferent excitability with behavioral outcomes.
Main Results:
- Ramped photostimuli effectively detected inflammation-induced hypersensitivity (faster withdrawal latency) and analgesia.
- Pulsed photostimuli showed a modest increase in withdrawal threshold during inflammation.
- Electrophysiology indicated that inflammation increases nociceptor excitability, affecting withdrawal latency.
- Nav1.8 channel blockade reduced withdrawal, while NaV1.7 upregulation was observed after CFA, impacting analgesia.
Conclusions:
- Robot-assisted optogenetic stimulation with strategically designed ramped photostimuli provides a quantitative and efficient method for pain testing.
- Ramp-based latency measurements are superior to pulse-based threshold measurements for detecting inflammatory pain and analgesia.
- Findings on sodium channel involvement in nociception have significant clinical implications for developing targeted analgesics.
